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Electronic data acquisition system for the energy balance/Bowen ratio measurement of evaporation Tang, Paul Wing Kay 1976

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ELECTRONIC DATA ACQUISITION SYSTEM FOR THE ENERGY BALANCE/BOWEN RATIO MEASUREMENT OF EVAPORATION by PAUL WING KAY TANG B.A. Sc., Univers ity of B.C., 1973 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE DEGREE OF MASTER OF SCIENCE in the Department of Soi l Science We accept th i s thesis as conforming to the required standard. THE UNIVERSITY OF BRITISH COLUMBIA August 1976 (c) Paul Wing Kay Tang 1976 In presenting th i s thesis in par t i a l fu l f i lment of the requirements for an advanced degree at the Univers ity of B r i t i s h Columbia, I agree that the Library shal l make i t f ree ly avai lable for reference and study. I further agree that permission for extensive copying of th i s thesis for scholar ly purposes may be granted by the Head of my Department or by his representatives. I t i s understood that copying or publ icat ion of th i s thesis for f inanc ia l gain shal l not be allowed without my written permission. PAUL WING KAY TANG Department of Soi l Science The Univers ity of B r i t i s h Columbia Vancouver 8, Canada Date August 1976 ABSTRACT A system for the energy balance/Bowen ra t i o measurement of evaporation was designed and tested. The system produces eight chan-nels of integrated meteorological data for evaporation ca l cu la t ion . The various voltages required to operate the meteorological sensors are produced i n te rna l l y by a bank of regulated power supplies. Control signals are generated by a quartz crysta l -clock. The data in a selected channel and the time of day are displayed on the front panel of the data logger. A l l eight channels of data and the time are printed on a paper tape every 15 or 30 minutes as desired. The output c i r c u i t r y was designed to be compatible with microprocessor components. The data logger i s contained in a 60 cm x 50 cm x 40 cm metal cabinet and i s powered by 110 VAC. The laboratory and f i e l d tests of the system were successful. i v TABLE OF CONTENTS Page ABSTRACT . i i i LIST OF FIGURES v ACKNOWLEDGEMENTS v i i i INTRODUCTION 1 THEORY OF THE ENERGY BALANCE/BOWEN RATIO METHOD 3 DESCRIPTION OF SENSORS 7 DESCRIPTION OF DATA LOGGER CIRCUITRY 16 DATA LOGGER OPERATION . 52 CALIBRATION AND TESTS 57 REFERENCES 60 APPENDIX I Inexpensive Diode Thermometry Using Integrated 62 C i r cu i t Components APPENDIX II Precis ion Electronic Integrator for Environ- 68 mental Measurement APPENDIX III Error Analysis of Reversing Psychrometric 72 Sensors . APPENDIX IV Instructions for Operation of the Energy Balance/ 75 Bowen Ratio Measurement System APPENDIX V L i s t s of Components for C i r cu i t Dirgrams 90 V LIST OF FIGURES Figure Page 1 . Schematic representation of the energy balance of a forest volume with no horizontal energy divergence . . . 5 2 Psychrometric apparatus showing reversing assembly supporting the sensing heads 12 3 Measurement c i r c u i t for meteorological sensors. A l l res i s tors are the low temperature coe f f i c i en t type. The 12.7 Kfi res i s tors are matched to 0.2%. A l l res i s tors are 1%, V4 W metal f i lm type 15 4 Block diagram of the data logging system. The analog input c i r c u i t consists of eight integrators. Output pulses from the integrators are counted by eight coun-ters . The control signals are synchronized to a crysta l clock 18 5 C i r cu i t diagram of the switching integrator. The com-ponent l i s t is given in APPENDIX V 21 6 C i r cu i t diagram of the integrator output interface. The output signals from the integrators are converted from CMOS to TTL l e v e l . The component l i s t i s given in APPENDIX V 23 7 C i r cu i t diagram of the decade counters and 1st level mult iplexer. A c i r c u i t as above i s used with every channel in the system. The component l i s t is given in APPENDIX V 26 8 C i r cu i t diagram of the 2nd level mult iplexer and the output interface. E l e c t r i c a l i so la t ion between the data logger and external equipment is provided by four opt ica l couplers. The component l i s t i s given in APPENDIX V • 2 9 9 C i r cu i t diagram of the overflow reg i s ter . The output signal from the reg i s ter causes the pr inter to pr int in red to indicate overflow status. Channel overflow information is also indicated on the front panel. The component l i s t i s given in APPENDIX V 31 Figure vi Page 10 C i r cu i t diagram of the channel se lector. A 3 b i t BCD thumb wheel is used to se lect a counter for front panel display. The component l i s t i s given in APPENDIX V 34 11 C i r cu i t diagram of the output reg i s ter . This reg i s ter converts se r i a l data to pa ra l l e l and feeds a four decade LED display and a d i g i t a l paper tape pr inter . The component l i s t i s given in APPENDIX V . . 36 12 C i r cu i t diagram of the reset l og i c . The component l i s t is given in APPENDIX V 39 13 C i r cu i t diagram of the scan control l og i c . The timing signals are supplied by the crysta l control led master clock. The component l i s t i s given in APPENDIX V . . . 41 14 C i r cu i t diagram of the pr inter control l og i c . This c i r c u i t generates the pr inter control signals as well as the channel select s ignals. The component l i s t i s given in APPENDIX V 44 15 C i r cu i t diagram of the crystal control led master clock. The c i r c u i t produces various timing and control signals for the whole measurement system. The BCD output signal is connected to the f i r s t four columns of the d i g i t a l pr inter and a LED numerical d isplay. The component l i s t i s given in APPENDIX V . . . 47 16 C i r cu i t diagram of the psychrometric sensor control relay. This relay causes the psychrometric head to reverse upon receiving a control signal from the master clock. The component l i s t i s given in APPENDIX V . . . 49 17 C i r cu i t diagram of the system power supplies. A ± 6 V output i s used to power the analog integrators. The d i g i t a l c i r c u i t s draw the i r power from the 5 V supply. A 24 V and two 12 V power supplies are used to run the meteorological sensors . 18 Front view of the data logger. A time and data display can be seen on the upper panel. A channel selector and various status indicators are on the l e f t hand side of the middle panel. A d i g i t a l paper tape pr inter is mounted on the r ight . Al1 the sensor connectors are mounted on the bottom panel vi i Figure Page 19 Details of the data logger control panel. Blocks of data (eight channels per block) can be seen on the paper tape of the pr inter , . ' 56 v i i i ACKNOWLEDGEMENTS I am greatly indebted to my supervisor, Dr. T.A. Black, for his guidance, assistance and fr iendship throughout th i s project. Without his ins ight and encouragement the success of th i s project would not have been possible. A par t i cu la r debt of gratitude i s owed to Mr. F.G. Berry, from whom I have acquired my s k i l l s in instrumentation. My gratitude also goes to Drs. C A . Rowles and T.R. Oke who served on my committee and provided helpful advice during my master's degree program. I wish to thank Mr. Ron Toth who has given me invaluable ass i s -tance in the fabr icat ion and test ing of the system. I would also l i k e to express my thanks to my fel low graduate students and facu l ty members of the department of Soi l Science who have provided me with a f r i end ly and stimulating atmosphere in which to work. The countless hours of discus-sion with them have given me valuable ins ight in the design of the sys-tem. The required funds for th i s research were made avai lable through a contract from Environment Canada: Inland Waters Directorate (SS01. KL398-3-3971) and a grant from the National Research Council of Canada (67-6123). 1 INTRODUCTION The rate of evaporation plays an important role in the energy and water balance of crops and forests. Numerous methods have been developed by researchers to measure evaporation. These methods can be c l a s s i f i e d as meteorological and non-meteorological. The non-meteorological methods usually require the d i rect measurement of hydrological parameters such as p rec ip i t a t i on , water storage and run-off. In s i tuat ions where loca l surface homogeneity is absent, extensive data sampling programs must be carr ied out in order to determine quantit ies with the required degree of accuracy. With non-meteorological methods i t i s almost impossible to determine evaporation rates over periods less than a day. On the other hand, the meteorological methods have the advantage of producing a spa t i a l l y integrated resu l t which is often less affected by local surface heterogeneity. In add i t ion, meteorological methods allow evaporation to be measured over periods of a half-an-hour or les s . This i s essential when studying the evaporation process. Consequently, the meteorological methods have been widely tested by agr i cu l tu ra l micrometeorologists and more recently by forest micrometeorologists. An excel lent summary of these methods, including the i r advantages and disadvantages has been given by Federer (1970). One of the most d i f f i c u l t problems confronting micrometeorologists is in making precis ion measurements. Since most of the equipment required for evaporation measurement i s not commercially ava i l ab le , the f i r s t task of the micrometeorologist i s to design a suitable piece of instrumentation. One of the most successful meteorological methods uses the energy balance/ 2 Bowen r a t i o t e c h n i q u e . The p r i n c i p a l s e n s o r i s an improved v e r s i o n o f the r e v e r s i n g p s y c h r o m e t e r d e s i g n e d by S a r g e a n t and Tanner (1967) f o r a g r i c u l t u r a l c r o p s . The m o d i f i c a t i o n o f t h i s i n s t r u m e n t f o r f o r e s t s i s d e s c r i b e d i n d e t a i l by B l a c k and McNaughton (1971). The s u c c e s s f u l use o f t h i s i n s t r u m e n t a t v a r i o u s f o r e s t t e s t s i t e s on the west c o a s t o f B r i t i s h Columbia ( B l a c k et_ a l _ . , 1973, 1974) i n d i c a t e s the u s e f u l n e s s o f t h i s i n s t r u m e n t i n e v a p o r a t i o n s t u d i e s on v a r i o u s v e g e t a t i o n t y p e s . In s p i t e o f the s u c c e s s w i t h t h i s energy b a l a n c e system t h e r e i s the s e r i o u s problem o f d a t a h a n d l i n g . S i n c e the time i n t e g r a l o f v a r i o u s m e t e o r o l o g i c a l parameters i s r e q u i r e d f o r a s i n g l e measurement o f e v a p o r a t i o n the time consuming manual i n t e g r a t i o n o f d a t a c h a r t s was r e q u i r e d . A l t h o u g h e l e c t r o n i c i n t e g r a t o r s were a v a i l a b l e c o m m e r c i a l l y , most o f them c o u l d not f u l f i l l t h e s t r i n g e n t r e q u i r e m e n t s o f a f i e l d e nergy b a l a n c e i n t e g r a t o r . The v e r y few e l e c t r o n i c i n t e g r a t o r s which c o u l d handle the s m a l l s i g n a l s were too c o s t l y t o e n a b l e e x t e n s i v e use. One o f the g o a l s o f the B i o m e t e o r o l o g y Group i n the S o i l S c i e n c e D e p a r t -ment a t U.B.C. was, t h e r e f o r e , t o d e v e l o p a low c o s t p r e c i s i o n e l e c t r o n i c i n t e g r a t o r s u i t a b l e f o r f i e l d use. T h i s goal was a c h i e v e d , and t h e i n t e g r a t o r was s u c c e s s f u l l y t e s t e d w i t h an energy balance/Bowen r a t i o measurement system ( B l a c k et_ a l _ . , 1974). D e t a i l s o f t h i s i n t e g r a t o r a r e d e s c r i b e d by Tang e t a l . (1975) (See APPENDIX I I ) . T h i s p r e c i s i o n i n t e g r a t o r has g r e a t l y reduced the time r e q u i r e d t o produce a complete a n a l y s i s o f energy b a l a n c e d a t a . However, a c o n s i d e r a b l e amount o f e f f o r t was s t i l l r e q u i r e d t o o p e r a t e the system and t o p e r f o r m n e c e s s a r y c a l c u l a t i o n s . 3 Attempts have been made in the past by various researchers to automate th i s operation. One of the most notable systems was described by Mcllroy (1970). This was bas i ca l l y a mechanical system, making exten-sive use of the servo motor. Most of the e a r l i e r evaporation measure-ment systems suffered from high equipment cost, and because they were usually mechanical, they required frequent maintenance. With the a v a i l a b i l i t y and wide spread use of compact high speed e lectron ic log ic components in recent years, i t became apparent that the sensor control and data processing function of the energy balance/Bowen ra t i o measurement system could be best handled by e lectron ic means. It i s the objective of th i s thesis to describe the design of an e lectron ic data acqui s i t ion system which i s compact, operates over long periods with low maintenance needs and i s economical to construct. THEORY OF THE ENERGY BALANCE/BOWEN RATIO METHOD The theory of the energy balance/Bowen ra t i o method i s b r i e f l y described as fol lows. Due to the conservative properties of energy, the ve r t i ca l energy balance of a forest (Fig. 1) can be written as: RN = LE + H + G + MH + M E + M p (1) where R^  i s the net radiat ion f l u x , LE i s the latent heat f l u x , H i s the sensible heat f l u x , G i s the so i l heat f l u x , and M^, M^ and Mp are the sensible, latent and photosynthetic energy storage rates in the trunk and canopy volume. The Bowen ra t i o i s defined as: B = H/LE (2) Figure 1 Schematic representation of the energy balance of a forest volume with no horizontal energy divergence. FIGURE 1 ENERGY BALANCE OF A FOREST RN LE V / M 1 rV RN = H + LE + G + M 6 Making the assumption that the eddy d i f f u s i v i t y for sensible heat i s equal to that for latent heat (the s i m i l a r i t y assumption), i t can be shown that B = (AT + rAz)/[(s w/ Y + 1)ATW - AT] (3) where Az i s the ver t i ca l distance between measurement levels above the canopy, AT and AT are the wet and dry bulb temperatures at the bottom w level minus those at the top l e v e l , s,, i s the slope of saturation vapour w pressure curve at the wet bulb temperature above the canopy, y i s the psychrometric constant (0.66 mb °C~^), and r i s the adiabatic lapse rate (-0.01 °C m" 1). Substitution of (2) in (1) to solve for LE gives: LE = (RN - G - MH - M E - Mp)/(1 + B) (4) The photosynthetic energy storage term i s neglected in most evaporation studies since i t i s usually less than 5% of R^ . Research at the U.B.C. Research Forest at Haney, B.C. (McNaughton and Black, 1973) showed that M^ and M^ could be neglected without serious error. The s o i l heat f l u x , G while usually less than 5% of R^  i s r e l a t i v e l y stra ight forward to measure. To a good approximation,therefore, we can wr i te : LE ='(RN - G)/(l + B) (5) In the energy balance/Bowen ra t i o approach when R ,^ G and B are known, a l l four major'components of the energy balance can be calculated. The evaporation rate, E is obtained by d iv id ing LE by the latent heat of vapourization, L. 7 DESCRIPTION OF SENSORS The parameters e s s e n t i a l f o r the energy b a l a n c e c a l c u l a t i o n a r e net r a d i a t i o n , s o i l heat f l u x and Bowen r a t i o . In a d d i t i o n t o t h e s e b a s i c measurements, the energy b a l a n c e measurement system d i s c u s s e d i n t h i s t h e s i s a l s o p r o v i d e s s e c o n d a r y measurements such as s o l a r r a d i a t i o n . In t h i s s e c t i o n , the s e n s i n g i n s t r u m e n t s and t h e i r o p e r a t i n g p r o c e d u r e s a r e b r i e f l y d e s c r i b e d . 1. Measurement o f Net R a d i a t i o n A S w i s s t e c o t y p e S - l n e t r a d i o m e t e r was chosen f o r n e t r a d i a t i o n (R^) measurement. T h i s i n s t r u m e n t i s an improved v e r s i o n o f the CSIRO ( A u s t r a l i a ) n e t r a d i o m e t e r . The upward and downward r a d i a t i o n streams a r e i n t e r c e p t e d by two b l a c k e n e d s u r f a c e s . The t e m p e r a t u r e d i f f e r e n c e between the s u r f a c e s due t o the d i f f e r e n c e i n r a d i a t i v e exchange i s sensed by a t h e r m o p i l e . Two t h i n p o l y e t h y l e n e h e m i s p h e r i c a l w i n d s h i e l d s p r o t e c t the s u r f a c e . The hemispheres a r e i n f l a t e d by d r y a i r . The s e n s i t i v i t y o f t h i s -? i n s t r u m e n t i s a p p r o x i m a t e l y 45 yV/W.m and remains s t a b l e p r o v i d e d the p o l y e t h y l e n e s h i e l d s a r e kept c l e a n and r e p l a c e d when n e c e s s a r y . The r a d i o m e t e r view f a c t o r ( R e i f s n y d e r and L u l l , 1965) s h o u l d be c o n s i d e r e d when d e c i d i n g on the v e r t i c a l d i s t a n c e between the i n s t r u m e n t and the c r o p o r f o r e s t canopy. I t i s e s s e n t i a l t h a t the i n s t r u m e n t s h o u l d have a downward view o f a broad a r e a o f canopy i n o r d e r t o p r o v i d e a measurement r e p r e s e n t a t i v e o f the v e g e t a t i o n . The i n t e r n a l v e n t i l a t i o n o f the n e t r a d i o m e t e r i s s u p p l i e d by a s m a l l aquarium a i r pump. A 15 t o 20-cm deep water column i s used t o 8 regulate the a i r pressure. S i l i c a gel i s used to dry the a i r . The dry a i r i s delivered to the net radiometer through a piece of 12 gauge e l e c t r i c a l insu lat ion sleeving ( "spaghett i " ) . It i s then returned to a second water column to allow visual monitoring of the flow of a i r by observing the a i r bubbles. Our experience i s that a bubbling rate of approximately one per second i s most su i table. 2. Measurement of Soi l Heat Flux The so i l heat f lux sensor i s a Middleton (Austral ia) heat f lux plate. It has a s en s i t i v i t y of approximately 2.2 yV/W m . The most sat i s factory procedure for measuring so i l heat f lux at the s o i l surface (G) i s to measure the heat f l ux at a depth of 5 cm with the heat f l ux plate (Gp), and to correct ca l o r imet r i ca l l y for the rate of heat storage in the surface 5-cm layer (Tanner, 1963). The rate of heat storage in the surface 5 cm of s o i l i s ca lcu-lated from the heat capacity of the layer and the rate of change of the average temperature of the layer (T g ) . In order to obtain the heat capacity, so i l samples of the 5-cm layer should be taken on each day that energy balance measurements are made and analyzed for water content. The diurnal trend in average temperature of the 5-cm layer i s measured with a s i l i c o n diode s o i l thermometer. The thermometer should be located near the heat f lux plate. The so i l thermometer consists of f i ve Fa i r ch i l d FD-300 s i l i c o n diodes. They are soldered together in series and are positioned 2 cm apart (measured from centre to centre). Sensing wires are soldered at each end of the diode s t r i ng . The diode s t r ing i s then potted with 9 No. 8 Scotchcast (3M) epoxy res in . The thermometer i s driven by a constant current source (Tang et al_., 1974) (See APPENDIX I). Ther-mometer s en s i t i v i t y i s approximately 10 mV ° C ~ \ Sampling locations should be selected such that the so i l heat f lux and the so i l temperature measurement are representative of the so i l beneath the vegetation. Care must be taken to minimize so i l disturbance when i n s t a l l i n g the plates and thermometers. The so i l should be watered af ter i n s t a l l a t i o n and measurement should not be considered r e l i a b l e unt i l the sensors have remained in the so i l for several weeks. 3. Measurement of the Bowen Ratio The theoret ical basis and design deta i l s of a psychrometric apparatus used for Bowen ra t i o determination have been described by Black and McNaughton, 1971. The psychrometric apparatus used in the present system i s a modified version of t he i r design. The apparatus (often referred to as the Bowen ra t i o machine or BRM) consists of a pair of psychrometric sensing heads with s i l i c o n diode sensors, an e lect ron ic measurement c i r c u i t and an aspirat ion system. The apparatus measures wet and dry bulb temperature differences (AT w and AT) over a small ve r t i ca l distance above the plant canopy. Using these temperature differences together with the absolute wet and dry bulb temperatures, the Bowen ra t i o can be calculated e i ther from equation (3) or an a l ternat ive form of the equation given in APPENDIX IV. The use of semiconductor diodes as temperature sensors has been described adequately in many publications (Hinshaw and Fr itschen, 10 1970; Sargeant, 1965; Tang et a]_., 1974). In th i s psychrometric system, two pairs of s i l i c o n diode (Fa i rch i ld FD-300) are used. The diode pairs must be matched c lose ly to eliminate any large of f set voltage between the diodes. Typical temperature s en s i t i v i t y is approximately 2.0 mV °C~^ when the diodes are driven at 0.5 mA. The design of the psychrometric sensing head i s s im i la r to the one described by Black and McNaughton, 1971. The body of the sensing head i s constructed from a 22-cm length of th in-wal l s ta in less steel tubing. S i l i c on diode sensors are mounted along the c y l i nd r i c a l axis of the tubing on a trap door. A reservoir mounted on one side of the tubing provides a water supply to the wet bulb sensor through a wick. The sensing head i s thermally insulated with a layer of polyurethane. Aluminized mylar tape covers the polyurethane layer to serve as a radiat ion sh ie ld . The back end of the sensing head i s connected to an aspirat ion pump. Two sensing heads are separated by a distance of one to three meters v e r t i c a l l y and are supported by two lengths of th in-wal l s ta in less steel tubing (Fig. 2). The two lengths of sta in less steel tubing are coupled together by a machined "T" j o i n t and fastened in pos it ion by two set screws. The out let of the "T" j o i n t is connected to one end of th ick -wall s ta in less steel tubing which i s supported in a sealed ba l l bearing housing. The tubing i s perforated inside the ba l l bearing housing to permit passage of a i r through the aluminum supporting pipe. The other end of the.tubing is mechanically coupled to the shaft of a revers ib le 4 r.p.m. Hurst model GA motor through a f l e x i b l e coupling. The f l e x i b l e coupling which is made of a short length of heavy duty f l e x i b l e p l a s t i c Figure 2 Psychrometric apparatus showing reversing assembly supporting the sensing heads. FIGURE 2 RESERVOIR -SEALED BALL BEARING HOUSING FLEXIBLE COUPLING DIRECTION OF AIR FLOW 13 hose acts as a shock absorber when the motion of the tubing i s terminated abruptly by the rotat ion stop. A i r i s drawn through a side nipple near the base of the aluminum supporting pipe by a Gast model 1022 3/4 h.p. vacuum pump. The optimum aspirat ion ve loc i ty i s approximately 300 cm s ^ within each sensing head. The s i l i c o n diodes are driven by a constant voltage source (Fig. 3) s im i la r to the one described by Tang et_ al_. (1974). Four 12.7 Kn metal f i lm res i s tors are used to supply current to the diodes. The diodes are connected to the measurement c i r c u i t by means of a mu l t i -conductor shielded cable. Current leads and sensing leads are separated to prevent measurement error introduced by cable resistance. A l l the shielding wires are grounded at only one point to avoid ground loop current. In operation, care should be taken to ensure the proper wetting of the wet bulb sensors. A sudden large increase in wet bulb temperature i s normally an ind icat ion of a drying wet bulb. The wicks should be frequently checked and replaced i f necessary. 4. Measurement of Global Radiation Global rad iat ion (R g) i s provided as a secondary measurement in th i s energy balance measurement system. It provides a means of checking whether the net radiat ion measurement i s reasonable. In addit ion, i t allows the micrometeorologist to obtain the re lat ionsh ip between net and solar rad iat ion. The sensor i s a Kipp and Zonen model CM6 solarimeter. The ca l ib ra t ion s t a b i l i t y of th i s instrument i s excel lent. It has a good spectral response at wavelengths between 0.3 to 2.0 ym. The Figure 3 Measurement c i r c u i t for meteorological sensors. A l l res i s tors are the low temperature coe f f i c i en t type. The 12.7 Ko, res i s tors are matched to 0.2%. A l l res i s tors are 1%, 1/4 W metal f i lm type. FIGURE 3 MC78I2 24 V 12V 9, 8| MCI469G 10] 3. Z tr. 0.1 jjf 3.6 V, CA3I30 - O + >l2.7k Sl2.7k >l2.7k >l2.7k <30.2k ?6l.9k <68.Ik <68.lk FD300 SILICON DIODES O <i> <i> 14 13. MC I466L 3| Z IZ_ ^ ,10k ^<200A <50A ^ <50A r*? r f r i r T S I T S T J G I R „ 3.0V £ 540mV< 5mV < 5mV >24.9k <536k S 45.3A > 45.3A - O -0.5 mA FD300 SILICON DIODES « H > K £ H > R > r - f 4 - « --o -Ik 2k 12 V 8 5 9 MCI469G 7 2 I0| 0.1 iif 3.6 V 249A A T 500A 357 k • -0 + -o — 5mV OFFSET 12 V 0.1 pf 3.6 V 249A :<r. AT* 5 mV OFFSET 500A 357 k - O -16 instrument has a s en s i t i v i t y of approximately 15 yV/W m~ . DESCRIPTION OF DATA LOGGER CIRCUITRY This section describes the c i r c u i t r y of the data logging system. The front end of th is system consists of eight switching integrators (Fig. 4). Each one of these integrators performs mathematical integ-ration of the incoming voltage signal and produces an output pulse frequency which is proportional to the input voltage. These input signals include AT, A T , T, T . R.., G . T , and R . The output pulses W W IN p s S from these integrators are coupled to eight counters v ia an interface c i r c u i t . Each one of the counters has a four-decade capacity and the i r output l ines are connected to a data mult iplexer. When triggered by the master clock, the multiplexer c i r c u i t scans the counters and produces a f ou r -b i t pa ra l l e l data stream. From the mult ip lexer, the data stream can be directed to an external device through a set of opto- i so lators , or to a synchronous output reg ister for pa ra l le l output conversion. This output reg i s ter is compatible with most para l le l data equipment such as paper tape pr in ter s , paper tape punches or LED numerical d isplays. Logic functions such as se lect ing data, resett ing counters and generating pr inter command signals are carr ied out by a central log ic unit . The central log ic unit can be divided down further into two components, namely, the scan cont ro l le r and the pr inter cont ro l l e r . The analogue portion of th i s system is powered by a ± 6 V, 1 A power supply, while the d i g i t a l portion i s powered by a 5 V, 6 A unit . The reference timing pulses are produced by a quartz crysta l control led d i g i t a l master clock ava i lable commercially. Figure 4 Block diagram of the data logging system. The analog input c i r c u i t consists of eight integrators. Output pulses from the integrators are counted by eight counters. The control s ignals are synchronized to a crysta l clock. FIGURE 4 MASTER CLOCK C O N T R O L LOGIC T H U M B W H E E L CHANNEL INDICATOR L J INT. 0 INT. INT. 2 L JL JL JL J INT. 3 INT. 4 I INT 5 I INT. 6 INT. 7 COUNTER INPUT GATING 8 CMOS/TTL INTERFACE BUFFER RESET! LOGIC OVERFLOW|_J INDIC. CTR. CTR. CTR. CTR. CTR. CTR. CTR. C T R . 7 M U L T I P L E X E R O U T P U T REGISTER LED DISPLAY PRINTER 19 1. Integrators This section of the system includes eight switching integrators as described by Tang et al_. (1976) (See APPENDIX I I). Each of these integrators has a s e n s i t i v i t y that allows them to process the various signal levels associated with d i f fe rent sensors e f f ec t i ve l y . Since most of these signals require a d i f f e r e n t i a l input treatment, a d i f -fe ren t i a l preamplif ier such as the one described in the above pub l i -cation i s , therefore, included in a l l the integrators (Fig. 5). These preamplif iers also provide the extra gain needed in Channel 0 and 1 to integrate the small temperature difference s ignals , AT and AT w > Since only pos i t ive input signals can be processed with these integrators, the signals from sensors such as the net radiometer and the so i l heat f lux plate must be kept pos i t ive by using a constant pos i t ive o f f set voltage. A summary of the s e n s i t i v i t i e s and of f set voltages associated with the various integrator channels i s given in APPENDIX IV. The output signals from these integrators are CMOS compatible, 12 V peak-to-peak rectangular waves. Sen s i t i v i t y adjustment i s provided on each of the eight integrators. 2. Integrator Output Interface Since the output signals from the integrators are of CMOS l e v e l , while the rest of the instrument operates at TTL l e ve l s , i t i s necessary to insert an interface c i r c u i t (Fig. 6) between the integrators and the rest of the data logging c i r c u i t . This interface c i r c u i t consists of eight diode r e c t i f i e r s , D-j to Dg, each permitting only the pos i t i ve portion of an integrator output to pass through. These pos i t ive pulses Figure 5 C i r cu i t diagram of the switching integrator. The component l i s t i s given in APPENDIX V. FIGURE 5 Figure 6 C i r cu i t diagram of the integrator output interface. The output signals from the integrators are converted from CMOS to TTL l e v e l . The component l i s t i s given in APPENDIX V. FIGURE 6 7 E A S B (J 9 4 C 3 0 2 I bl COUNT INHIBIT CH.O CU.t CH. 2 C H . J CH. 4 CH.S C H . « C H . 7 ° 7 + °e4 Yui Yuz Y U 3 YU 4 VU5 VU6 Y U 7 Y u * 9* RIO< "a? ^ 4 " I S ? (unj L 3 J {uwj L 3 J {u^ j U y j C H - 0 CH.I CH.2 CH.S CH.4 CH.J CH.6 CK.7 1 24 are transmitted separately to eight buffers, U-| to Ug. A BCD/decimal converter, U g , i s used to suppress the transmission of a signal through the buffer which i s being read by the data scanner. A count i n h i b i t function i s provided for Channels 0 and 1. This consists of two diodes, Dg and D-JQ which stop the transmission of pulses in the above two chan-nels during the f i r s t f i ve minutes a f ter the Bowen ra t i o sensors have been reversed. This i s done to ensure s u f f i c i en t time for the Bowen ra t i o sensors to equ i l i b ra te . Output pulses from each channel are sent to a set of decade counters v ia the integrator output interface. 3. Decade Counters The data logging system contains eight sets of ident ica l decade counters. Each set of these counters includes four BCD decade counters (U-|, U2, U^, U )^ connected in series (Fig. 7). The most s i gn i f i cant b i t (MSB) of the highest decade i s connected to a channel overflow reg i s ter that w i l l be discussed l a te r . A l l the output l ines from the counters, including the MSB, are coupled to an eight channel d i g i t a l mult iplexer. Each set of decade counters can be reset to zero i nd i v idua l l y by a reset l i n e . 4. Mult iplexer The multiplexer is made up of two levels of d i g i t a l signal selectors. On the f i r s t l e v e l , signal l ines from the four decade coun-ters of each channel are connected to the input terminals of four 4-channel data selectors (Ug, Ug, U^, Ug) (Fig. 7). The signal i s selected by the address l ines D and E. The output signals from these Figure 7 C i r cu i t diagram of the decade counters and 1st level mult iplexer. A c i r c u i t as i l l u s t r a t e d is used with every channel in the system. The component l i s t i s given in APPENDIX V. FIGURE 7 TO RESET TO INTEGRATOR INTERFACE h h - d C 0 U £ 4 R9 I ? 9i RO R9 U 2 -?-?- Ci h h -CJCo U 3 9 ) ? ^ R9 h h qc 0 Ro R9 U 4 0 I S 3 Ct DECADE COUNTERS CH. OVERFLOW D •*- 0 12 3 U 5 Z I 2 3 U 6 Z I 2 3 U 7 Z I 2 3 U 8 I st LEVEL MUX t t L S B M S B TO 2nd LEVEL MUX INPUT ro 27 data selectors represent one BCD d i g i t out of a tota l of four that has been accumulated in the decade counters. A signal reduction of 128 to 32 l ines i s rea l ized on th i s l e v e l . These signals then enter the second level mult iplexer (Fig. 8). This part of the c i r c u i t consists of four 8-channel data selectors (U-j, Ug* Ug, U^). The output signal from these selectors i s chosen by the address l ines A, B and C. A further signal reduction of 32 to 4 l i ne s i s rea l ized here. The pos i -t ion of switch S-j determines the output signal configuration. With S-j in the upper pos i t ion, NAND gates Ug, Ug, U-JQ and U-^ are activated resu l t ing in output signals with a pos i t ive log ic configuration. When S-| i s in the lower pos i t ion, Ug, Uy, Ug and are act ivated, thus providing a negative log ic output configuration. In appl icat ions where tota l e l e c t r i c a l i s o l a t i on of the system i s required, op t i ca l - i s o l a to r s ^13' ^14' ^15 a n c ' ^16 a r e P r o v i d e d . 5. Overflow Register The overflow reg i s ter consists of a group of eight J-K f l i p -f lops (U 2 , U 3 , U 4 , . . . ,U g ) (Fig. 9). The MSB l i ne from the highest decade of each set of decade counters (Fig. 7) i s connected to the clock terminals (C) of the f l i p - f l o p s . The 0 and K inputs of each f l i p - f l o p are wired in such a way that they are only permitted to respond to one log ic high (5 V) to low (0 V) t r an s i t i on . After being tr iggered, the output,(Q) of the f l i p - f l o p w i l l latch on a high log ic state unt i l i t i s reset. The status of each of these f l i p - f l o p s i s indicated on the front panel of the data logger by a row of LED i n d i -cators. An 8-channel data selector U-, i s used to sample the log ic Figure 8 C i r cu i t diagram of the 2nd level multiplexer and the output interface. E l e c t r i c a l i s o l a t i on between the data logger and external equipment i s provided by four opt ica l couplers. The component l i s t i s given in APPENDIX V. FIGURE 0 CH.7 CH.O CH.7 CH.O. CH.7 CH.O CH.7 . CH.O ^ MSB ISOLATED OUTPUT KO Figure 9 C i r cu i t diagram of the overflow reg i s ter . The output signal from the reg i s ter causes the pr inter to pr int in red to indicate overflow status. Channel overflow information i s also indicated on the front panel. The component l i s t i s given in APPENDIX V. FIGURE 9 TO CH. SELECT RED SELECT CH.O O.F. CH.I Of. CH.7 O.F. 32 status of the f l i p - f l o p s and i n i t i a t e s the RED TAPE SELECT signal when the data from the channel with overflow i s being printed by the paper tape pr inter . 6. Channel Selector The channel select address or iginates from two sources. When operating in the monitor mode, an octal thumb-wheel switch controls the address l ines A, B and C (Fig. 10). This mode i s activated by a high log ic state signal on the SYSTEM EN l i ne and a low log ic state signal on the SYSTEM EN l i n e . During a scanning operation, the log ic states on these two control l ines are reversed, thus allowing the channel counter (des-cribed la ter ) to take over the control of the address l i ne s . The status of the SYSTEM EN, SYSTEM EN, A, B and C l i nes are displayed on the front panel and label led as SCAN, RANDOM (select) and SCAN INDICATOR respec-t i v e l y . 7. Output Register The output reg i s ter consists of four 4 -b i t s h i f t reg i s ter s , U-j, U^, U^ and U^ (Fig. 11). The input signal i s received from the mult iplexer and goes d i r e c t l y into the J and K terminals of the s h i f t reg i s ter . Data sh i f t i ng i s triggered by the clock pulses on the O.R. LOAD (output reg i s ter load) l i n e . Four clock pulses are needed to s h i f t in a set of data (4 d i g i t s ) for one channel. The output l ines are coupled to a 4-decade LED numerical display and the l a s t four columns of a d i g i t a l paper tape pr inter . Figure 10 C i r cu i t diagram of the channel se lector. A 3 b i t BCD thumb wheel i s used to select a counter for front panel display. The component l i s t i s given in APPENDIX V. FIGURE 10 A U l A U2 A U3 A CH. SELECT 0 0 ( H 0 0 0 SYSTEM EN SYSTEM EN ui3 A ,4 A u,5A Q Q Q T M S B L S B t M S B LS B C B A TO CH COUNTER TO THUMB WHEEL Figure 11 C i r cu i t diagram of the output reg i s ter . This reg i s ter converts se r i a l data to para l le l and feeds a four decade LED display and a d i g i t a l paper tape pr inter . The component l i s t i s given in APPENDIX V. MSB TO 2nd LEVEL MUX LSB 0.R. LOAD FIGURE 11 u I PE MR Q J C * m U 2 0 Pi J C ft R R U 3 9 I ? J C U 4 * MR 0 I 2 PE I it 2nd 3rd 4th CHAR CHAR CHAR CHAR MSB TO DISPLAY AND PRINTER I tt CHAR 2nd CHAR 3rd CHAR 4th CHAR LSB t C C O O 37 8. Reset Logic This section i s responsible for resett ing the counters of each integrator channel at the appropriate time. The channel select ion i s control led by the channel select l ines A, B and C (Fig. 12). The reset action i s triggered by the PRINT COMMAND pulse from the pr inter control c i r c u i t (described l a t e r ) . The above signals are decoded by a BCD-to-decimal decoder and transmitted to the corresponding counters through inverters to Ug. 9. Scan Control Logic The function of th i s c i r c u i t r y (Fig. 13) i s to generate clock pulses needed to s h i f t data into the output reg i s ters . The character address signals D and E are also produced here. The scanning sequence i s started by a START pulse from the master clock. In RANDOM SELECT mode, th i s pulse repeats 100 times per second. In SCAN mode, i t i s reduced to once per second. It turns on a f l i p - f l o p ca l led CHAR. SCAN EN (character scan enable). The output from th is f l i p - f l o p is synchronized with 100 KHz signal in Ug. Once syn-chronized, the pulse then latches on a second f l i p - f l o p ca l led RUN. The RUN f l i p - f l o p releases U g and allows the 100 KHz signal to be gated into a two-bit binary counter Ug. Each one of these 100 KHz pulses advances the character address counter by one count. At the t r a i l i n g edge of each of these pulses, a pair of 100 ns pulses, LOAD and LOAD are triggered at U^. LOAD i s used as the clocking pulse at the output reg i s ter (Fig. 10). The counter Ug overflows a f te r the fourth count. When th i s happens, a CHAR. SCAN RESET (character scan reset) pulse i s generated in UQ and i t Figure 12 C i r cu i t diagram of the reset log ic . The component l i s t i s given in APPENDIX V. FIGURE 12 u I 0 1 2 3 4 5 6 7 A B C PRINT COMMAND U 2 Y us y U4 y us y 06 V U7 Y U 8 Y 0 9 Y R.CH. O. R.CH.I R.CH.2 R. CH.3 R. CH.4 R.CH.5 R. CH.6 R.CH.7 to Figure 13 C i r cu i t diagram of the scan control l og ic . The timing signals are supplied by the crysta l control led master clock. The component l i s t i s given in APPENDIX V. FIGURE 13 C H A R . S C A N E N A B L E U l s c S T A R T c R 100 KHz CLOCK 7 us O.P. REG I STER L O A D RUN T 0 „ U 4 _ I fi Vcc - * - LOAD - * » L O A D " U 3 -OJS Q-R , C H A R . C O U N T E R U 7 ± £ 7 > - 4 > o I c u e 0 f U 9 1 2 T_ C H A R . S C A N R E S E T 42 resets the f l i p - f l o p s Un and Ug. This c i r c u i t then rests un t i l i t i s triggered by another START pulse. 10. Pr inter Control Logic This part of the c i r c u i t r y (Fig. 14) i s responsible for the generation of pr inter command, channel address, overflow reg i s ter reset and the paper tape advance command pulses. The operation of th i s c i r c u i t i s very s imi la r to the scan control l og i c . It i s triggered by a pulse ca l led SYSTEM START from the master clock. The SYSTEM START pulse i s generated once every 15 or 30 minutes, depending on the status of the Integration Period switch on the front panel. It turns on the SYSTEM ENABLE f l i p - f l o p , therefore permitting a 1 Hz clock signal to pass through gate U^ and tr iggers the SCAN f l i p - f l o p Ug. Once on, U^ allows the 1 Hz signal to enter a 3 b i t binary counter Ug. Each one of these 1 Hz pulses advances the channel advance counter by one count, and i t also tr iggers a DATA PRINT COMMAND pulse with the t r a i l i n g edge at Ug. The channel address counter overflows a f te r the eighth count. The overflow signal tr iggers Ug and causes f l i p - f l o p Un and U^ to reset. At the same time, an OVERFLOW REGISTER RESET signal and a PAPER ADVANCE TRIGGER signal are generated. The c i r c u i t then remains i d l e un t i l i t i s triggered 15 or 30 minutes l a te r . 11. Peripheral Equipment The peripheral equipment in th i s system consists of a real time clock, two sets of numerical displays and a d i g i t a l paper tape pr inter . These devices are responsible for generating the system clock pulse, Figure 14 C i r cu i t diagram of the pr inter control l og ic . This c i r c u i t generates the pr inter control signals as well as the channel select s ignals. The component l i s t i s given in APPENDIX V. SYSTEM ENABLE FIGURE .14 SYSTEM START .U I I HZ CLOCX U 3 SYSTEM ENABLE SYSTEM ENABLE UI2 SCAN U 5 IS Qh PRINT COMMAND T Q j U 2 5 DATA PRINT COMMAND OAT A PfiINT COMMAND Vcc .CH. COUNTER U7 0 I 2 -o{C U 8 IRQ . R9. U U9 T <3 T - » - L S B • * - MSB A B C OVERFLOW REGISTER RESET I OVERFLOW REGISTER RESET 2 t + 5V PAPER ADVANCE TRIGGER 45 providing a visual ind icat ion of data and recording the data on paper tape respect ively. The reference frequency of the real time clock i s generated by a quartz crysta l o s c i l l a t o r at 100 KHz (Fig. 15). A series of counters and decoders are used to generate the various system timing and control pulses. Relay contacts are provided to rotate the Bowen ra t i o machine (Fig. 16). The data display consists of two sets of four d i g i t open c o l -lec tor dr ivers and 1.5-cm character LED displays. The data display boards accept 16 b i t pa ra l le l data and are, therefore, d i r e c t l y compatible with the data logger. Hard-copy data output i s provided by a nine column Anadex d i g i t a l pr inter . This pr inter operates at a pr int ing rate of one l i ne per second. The four most s i gn i f i cant d i g i t s indicate time. The f i f t h d i g i t i s the channel number. The four least s i gn i f i c an t d i g i t s represent the to ta l number of counts accumulated in each of the data counters. 12. Power Supplies The ent i re data logging system i s powered by three groups of power supplies. The power requirement for the analog integrators i s provided by a ± 6 V, 600 mA tracking regulator. A 5 V, 8 A regulator i s used to feed the log ic c i r c u i t s . The sensor system is powered by two 12 V, 100 mA f l oa t i ng .supplies and a 24 V grounded supply. A c i r c u i t diagram of these power supplies i s provided in Fig. 17. Figure 15 C i r cu i t diagram of the crysta l control led master clock. The c i r c u i t produces various timing and control signals for the whole measurement system. The BCD output signal i s connected to the f i r s t four columns of the d i g i t a l pr inter and a LED numerical display. The component l i s t i s given in APPENDIX V. FIGURE 15 .MF I5K 470 ms El 5V E2 E3 III 21 141 re re re 10 12 13 I0M I00K l !4-l50pF f EI2 a 12 I 14 II 6 7 2 3 Sla S2a slow -9 600ns E27 E28 E29 1 T 12 1 14 II e 9 2 L 1 "T 12 1 14 8 II 9 2 3 A B C D LS D 12 I •^14 II 8 9 2 3 A B C D 24 HOUR CLOCK B C D OUTPUT A 8 C D I 30min Figure 16 C i r cu i t diagram of the psychrometric sensor control re lay. This relay causes the psychrometric heads to reverse upon receiving a control signal from the master clock. The component l i s t i s given in APPENDIX V. FIGURE 16 2 K o -V\A BRM HEAD CONTROL -O A.C. I N P U T •° NORM. =p IJIF 200V O REV. KRPIID 6V D.C. MJ E 8 0 0 Figure 17 C i r cu i t diagram of the system power syppl ies. A ± 6 V output i s used to power the analog integrators. The d i g i t a l c i r c u i t s draw the i r power from the 5 V supply. A 24 V and two 12 V power supplies are used to run the meteorological sensors. 51 52 DATA LOGGER OPERATION In discussing the operation of the data logger portion of the system (Figs. 18 and 19), i t w i l l be assumed that there are input signals to a l l 8 channels. When the Channel Select switch i s dialed to any one of the eight integrator channels, the number of the channel selected is ve r i f i ed on the Scan Indicator (Fig. 19). The Counts Display w i l l be advancing at a rate which i s proportional to the m i l l i vo l t age signal that i s being applied to that channel. The Manual Reset switch must be pressed to synchronize the system to the master clock. The scanning mechanism in the logger resets i t s e l f when the master clock advances to the next minute count. When th i s occurs, the pr inter pr ints out the accumulated counts stored in each channel since the l a s t reset operation. Counts more than 9999 are printed in red. Together with the count to ta l the channel number and time are also pr inted. The LED labe l led Inh ib i t i s activated at th i s time. This indicates that channels 0 and 1 are being suppressed. The i n h i b i t period las t s for f i ve minutes. (At the beginning of th i s period, the Bowen ra t i o sensors are reversed and they are allowed to equ i l ibrate during the remainder of the period.) The two channels are reactivated and normal integration resumes at the end of the f i v e minute period. During the reset period, the internal scanning c i r c u i t takes over the channel select funct ion, and the scan ind icator w i l l show the channel.advance operation. After the i n i t i a l manual reset, the system w i l l reset automatically every 15 or 30 minutes as desired. The Normal and Reverse indicator shows the status of th i s switching function. A Fast Set switch and a Slow Set switch are provided in the Figure 18 Front view of the data logger. A time and data display can be seen on the upper panel. A channel selector and various status indicators are on the l e f t hand side of the middle panel. A d i g i t a l paper tape pr inter i s mounted on the r i ght . A l l the sensor connectors are mounted on the bottom panel. FIGURE 18 54 Figure 19 Detai ls of the data logger control panel. Blocks of data (eight channels per block) can be seen on the paper tape of the pr in ter . 57 master clock for time sett ing purposes. The Time ind icator should advance rapid ly or slowly corresponding to the Clock Set switch that i s being pressed. CALIBRATION AND TESTS 1. Integrator Cal ibrat ion and Tests Since the d i g i t a l portion of the system does not require any adjustment, the discussion of ca l i b ra t ion i s therefore re s t r i c ted to the analog portion. This part of the system includes the eight integrators, each one of them having i t s own s en s i t i v i t y and of f set adjustment. To carry out ca l i b ra t i on of these integrators , a DC m i l l i v o l t source and a frequency counter with period measurement option are required. In add i t ion, a precis ion Wheatstone bridge and d i g i t a l voltmeter are needed to ve r i f y the accuracy of the m i l l i v o l t source. To begin, the input terminals of the integrator are shorted and the of f set adjustment (R-JQ in Fig. 5) i s adjusted so that there i s no pulse output from the integ-rator. The short c i r c u i t i s then removed and the m i l l i v o l t source con-nected in i t s place. The potentiometer Ry in Fig. 5 i s adjusted so that the output rectangular wave from the integrator has a period that agrees with the calculated value for the signal from the m i l l i v o l t source. (See APPENDIX IV for the s e n s i t i v i t y of each of the eight integrators.) Measure-ment of the output period should be made at several input voltages so that l i n e a r i t y of the integrators can be ve r i f i e d . Extensive laboratory tests were carr ied out on a s ingle integrator unit as described in APPENDIX II. Within the speci f ied signal range, the l i n e a r i t y was found to be better 58 than 0.2%. The integrators were also tested over a temperature range of -10 °C to 80 °C. The average temperature d r i f t in the s e n s i t i v i t y was less than 0.02%/°C 2. Laboratory Tests on the Data Logging System To test the whole data logging system, a m i l l i v o l t source was connected to the input terminals of each integrator. The pr int out on the paper tape agreed with the 15 or 30 minute integral of the input signal in the case of channels 2 to 7 and with the 10 or 25 minute i n -tegral in the case of channels 0 and 1. Tests over several days showed that any errors were within the integrator spec i f i cat ions . 3. F ie ld Tests on the Energy Balance Measurement System Due to the short time avai lable for f i e l d test ing the energy balance measurement system at U.B.C, the f i e l d test data i s l im i ted . However, an e lectron ic integrator of the same design had been tested extensively in the f i e l d previously (Tang et al_., 1976. See APPENDIX I I ). The results of these tests were excel lent. It was found that a 0.1% accuracy could be maintained with neg l ig ib le ca l i b ra t i on d r i f t during a three month test period. Good agreement was found between the temperature s t a b i l i t y obtained in the laboratory and in the f i e l d . The ent i re system was tested over a grass lawn for a s ix hour day-time period. The output from the system showed good agreement with independent measurements made with other sensors. The system was then operated in the f i e l d near Ottawa over a period of several weeks by the Hydrology Research Divis ion of the Inland Waters Directorate during the a summer of 1975. Since there was no other micrometeorological 59 measurements avai lable for comparison, i t was impossible to draw any conclusion on the overal l accuracy of the system; however, the performance of the e lectronic c i r c u i t r y was found to be well within spec i f i cat ions . Based on our previous experience with the energy balance/Bowen ra t i o approach and the test data obtained with th i s system, i t appears that th i s system works as well as our e a r l i e r models (e.g. Black and McNaughton, 1971). However, only the accumulation of more f i e l d test and comparison data can provide an overal l evaluation of the system. The system should be ideal for both short and long term c l imatolog ica l and hydrological studies on land surfaces. 60 R e f e r e n c e s B l a c k , T.A. and K.D. McNaughton: 1971. ' P s y c h r o m e t r i c A p p a r a t u s f o r Bowen - r a t i o D e t e r m i n a t i o n o v e r F o r e s t s , ' B o u n d a r y - L a y e r M e t e o r o l . 2, 246-254. B l a c k , T.A., K.G. McNaughton and P.A. Tang: 1973. ' S t u d i e s o f F o r e s t E v a p o t r a n s p i r a t i o n and T r e e Stem Diameter Growth,' F i n a l  C o n t r a c t R e s e a r c h R e p o r t t o the Can. F o r . Se r v . (DOE), March, 1973. B l a c k , T.A., K.G. McNaughton and P.A. Tang: 1974. 'Measurement T e c h n i q u e s Used i n F o r e s t H y d r o m e t e o r o l o g y , ' F i n a l C o n t r a c t R e s e a r c h R e p o r t t o the Can. F o r . S e r v . (DOE), March, 1974. F e d e r e r , C.A.: 1970. 'Measuring F o r e s t E v a p o t r a n s p i r a t i o n - Theory and Problems,' U.S.D.A. F o r . Se r v . Res. Paper NE - 165, Hinshaw, R. and L . J . F r i t s c h e n : 1970. 'Diodes f o r Temperature Measurement,' J . A p p l . Met. 9, 530-532. M c l l r o y , I.C.: 1971. 'An Ins t r u m e n t f o r Co n t i n u o u s R e c o r d i n g o f N a t u r a l E v a p o r a t i o n , ' Agr. M e t e o r o l . 9, 93-100. McNaughton, K.G. and T.A. B l a c k : 1973. 'A Study o f E v a p o t r a n s p i r a t i o n from a Douglas F i r F o r e s t U s i n g t h e Energy B a l a n c e Approach,' Water Resour. Res. 9, 1579-1590. R e i f s n y d e r , W.E. and H.W. L u l l : 1965. 'Rad i a n t Energy i n R e l a t i o n t o F o r e s t s , ' U.S.D.A. F o r . Se r v . Tech. B u l l . 1344. S a r g e a n t , D.H.: 1965. 'Note on the Use o f J u n c t i o n Diodes as Temperature S e n s o r s , 1 J . A p p l . Met. 4, 644-646. 61 Sargeant, D.H. and C.B. Tanner: 1967. 'A Simple Psychrometric Apparatus for Bowen Ratio Determinations,' J . Appl. Met. 6, 414-418. Tang, P.A., K.G. McNaughton and T.A. Black: 1974. 'Inexpensive Diode Thermometry Using Integrated C i r cu i t Components,' Can. J . For. Res. 4, 250-254 Tang, P.A., K.G. McNaughton and T.A. Black: 1976. ' P rec i s ion Electronic Integration for Environmental Measurement,' Trans. ASAE. 19, 550-552. Tanner, C.B.: 1963. 'Basic Instrumentation and Measurements for Plant Environment and Micrometeorology,' Soi1s Bui 1. 6. Dept. of Soi l Science, Univ. of Wisconsin, Madison, Wis. APPENDIX I INEXPENSIVE DIODE THERMOMETRY USING INTEGRATED CIRCUIT COMPONENTS PREVIOUSLY COPYRIGHTED MATERIAL, IN APPENDIX I, LEAVES 63-67, NOT MICROFILMED. Tang, P.A., McNaughton, K.G., and Black, T.A. 1974. Inexpensive diode thermometry using integrated c i r -cu i t components. Can. J . For. Res. 4£ 250-254. C A N . J F O R . RFiS. V O L . 4, 1974 Inexpensive Diode Thermometry Using Integrated Circuit Components' V. A. T A N G , K. G. M C N A U G H T O N , A N D T. A. B L A C K Department of Soil Science, Ike University of llriti.\li Coliimbiu, Vancouver, llritisli Columbia R e c e i v e d S e p t e m b e r 25, 1973 A c c e p t e d J a n u a r y 3, 1974 T A N G . I'. A . . M C N A U G H T O N , K. C i . , a n d H I . A C K , T . A . 1 9 7 4 . I n e x p e n s i v e d i o d e t h e r -m o m e t r y u s i n g i n t e g r a t e d c i r c u i t c o m p o n e n t s . C a n . J . F o r . R e s . 4 . 2 5 0 - 2 5 4 . T w o t e m p e r a t u r e s e n s i n g c i r c u i t s u s i n g s i l i c o n d i o d e s a n d i n t e g r a t e d c i r c u i t c o m -p o n e n t s a r c d e s c r i b e d . T h e y a r c i n t e n d e d f o r use w i t h d a t a a c q u i s i t i o n s y s t e m s a n d a r e s u i t a b l e f o r f i e l d o r l a b o r a t o r y a p p l i c a t i o n s . H o i l i c a n be c o n s t r u c t e d b y p e r s o n s w i t h o u t e l e c t r o n i c t r a i n i n g a n d h a v e f e a t u r e s o f s i m p l i c i t y , l o w c o s t , a n d h i g h a c c u r a c y . T A N G , 1\ A . . M C N A U G H T O N , K . C i . et B L A C K . T . A . 1 9 7 4 . I n e x p e n s i v e d i o d e t h e r -m o m e t r y u s i n g i n t e g r a t e d c i r c u i t c o m p o n e n t s . C a n . J . F o r . R e s . 4 . 2 5 0 - 2 5 4 . L ' a r t i c l c d c c r i l d e u x c i r c u i t s d c m c s u r e d c t e m p e r a t u r e u t i l i s a n t de s d i o d e s a u s i l i -c i n m ct d e s c o m p o s a n l c s d e c i r c u i t i n l c g r e e s . D e s t i n e s a s e r v i r d a n s les s y s t c m e s d ' a c q u i -s i t i o n d e d o n n c c s , i ls sc p r c t e n l a u x a p p l i c a t i o n s d c t e r r a i n et d c l a b o r a t o i r e . T o n s d e u x p c u v e n t c t r e c o n s t a n t s p a r de s p e r s o n n e s n o n s p e c i a l i s c e s c n e l c c l r o n i q u e et o f f r c n t i ' a v a n l a g e d ' e t r e f a c i l e s d ' c m p l o i , p e u c o u t e u x ct d ' u n c g r a n d c p r e c i s i o n . [ T r a d u i t p a r le j o u r n a l ] Introduction It frequently occurs in forestry research, both in laboratory and field experiments, that an investigator wishes to monitor temperature. Since a variety of sensors arc available to make temperature measurements, careful considera-tion must lie given to factors such as siz.e, l inearity, compat ib i l i ty with recording instru-ments (e.g. strip chart recorders and data log-gers), avai labi l ity, and cost when selecting a suitable thermometry system for the particular problem. Where an extremely small sensor is not essential, a s i l icon diode temperature sensor seems the best choice on the grounds of su-perior l inearity, lower cost, and better ava i l -abil ity when compared with resistance thermom-eters or thermistors. The typical temperature sensitivity of a si l icon diode, approximately 2 m V / ° C is large compared with that of resist-ance thermometers or thermocouples (and thermopi les) , and is ample for most recording instruments. Diode thermometry has been dis-cussed by several authors (Saigeant 1965; l l i n shaw and Fr itschcn 1970) and diode ther-mometers have been successfully used by re-searchers in forestry (B l ack and McNaugh ton 1971). The purpose of this note is to describe ' T h i s r e s e a r c h w a s s u p p o r t e d b y g r a n t s f r o m t h e C a n a d i a n f o r e s t r y S e r v i c e a n d N a t i o n a l R e s e a r c h C o u n c i l o f C a n a d a . Cua.J. For . Res..050(1974) two sensing circuits using integrated circuit components to give simple, inexpensive, yet accurate field or laboratory measurements of temperature in the range of most interest in forestry. Sensing Circuit Design Considerations T h e temperature (7") versus junction voltage ( (• j ) relationship for a si l icon semiconductor junction diode with a small forward bias cur-rent (/) is l inear over the range 0 - 60 ° C if the current is maintained at a constant value or nearly so. It has been customary to operate diode sensors in quasi-constant current mode by use of a constant voltage source (v ) and a resistor in series with the diode such that the effective resistance of the diode (Cj/i) is at least 10 times smaller than the series resistor. The theoretically ideal mode of operation is to use a true-conslant current source. A n ad-vantage of this type of circuit is thai very hinh supply voltages are not required if many diode sensors are to be operated in series. Th is may be done to increase temperature sensitivity or to give an average reading of a set of sensors. In order to decide on sensing circu.it per-formance requirements, the characteristics of the sensor must be examined. Here, we wi l l discuss only the F D 3 0 0 sil icon diode with / 0.5 m A as recommended by H inshaw and Fr i t schcn ( 1 970 ) . 64 F o r c o n s t a n t c u r r e n t s o u r c e o p e r a t i o n [1] del/di={dei/0i)T s i n c e t l ie j u n c t i o n v o l t a g e is a f u n c t i o n o f c u r -r e n t n i u l t e m p e r a t u r e a l o n e a n d the c u r r e n t is i n d e p e n d e n t o f d i o d e t e m p e r a t u r e . T h e t e r m (ilCj/<)i) is c a l l e d the d y n a m i c r e s i s t a n c e o f the d i o d e . F o r the F D 3 0 0 d i o d e , t h e r e l a t i o n s h i p [2] ( t f < ? j / W ) r ~ 0 - 0 4 5 / / w h e r e (<)ej/(')i) T is i n o h m s a n d / is i n a m p e r e s , is a c c u r a t e to. ± 1 2 % f o r a l l t e m p e r a t u r e s i n the r a n g e 0 - 6 0 ° C a n d c u r r e n t f r o m 0 . 1 - 1 . 0 m A as s h o w n b y the set o f n e a r l y s t r a i g h t a n d p a r a l l e l l i n e s in the p l o t o f l o g / versus ci i n F i g . 1. V a r i a b i l i t y o f d y n a m i c r e s i s t a n c e b e -t w e e n d i o d e s w a s f o u n d t o b e q u i t e s m a l l . F r o m E q s . [1] a n d [2 ] , the u n c e r t a i n t y i n j u n c t i o n v o l t a g e ACj d u e t o a n u n c e r t a i n t y i n c u r r e n t A/ c a n be e s t i m a t e d as [3] A e j ~ 0 . 0 4 5 Ai/i , w h e r e A^j is i n v o l t s . A c u r r e n t u n c e r t a i n t y o f 1 % l e a d s t o a n u n c e r t a i n t y i n j u n c t i o n v o l t a g e DIODE VOLTAGE (VOLTS) \ F l o . 1. Relat ionship between forward current and junction voltage of an I-D300 si l icon diode at different temperatures. o f a b o u t 0 . 4 5 m V o r 1 / 4 ° C f o r a d i o d e s e n s i -t i v i t y , (Oci/i/T), ~ - 2 m V / ° C at 0 . 5 m A . F o r c o n s t a n t v o l t a g e s o u r c e o p e r a t i o n w i t h v<Zei a s i m i l a r r e l a t i o n s h i p o b t a i n s [4] A c j « 0 . 0 4 5 A v / v w h e r e A^ is i n v o l t s . T h i s r e l a t i o n s h i p is the s a m e as g i v e n b y S a r g c a n t ( 1 9 6 5 ) , e x c e p t t h a t t h e c o e f f i c i e n t 0 . 0 4 5 V is n o t the s a m e as the v a l u e o f 0 . 0 2 6 V that w a s f o u n d f o r t h e 1 N 2 3 2 6 g e r m a n i u m d i o d e . A g a i n , a 1 % u n c e r t a i n t y i n s o u r c e v o l t a g e g i v e s a n u n c e r t a i n t y o f 0 . 4 5 m V i n es o r 1 / 4 ° C i n t e m p e r a t u r e m e a s u r e m e n t s . T h i s g i v e s a v o l t -age s u p p l y s t a b i l i t y r e q u i r e m e n t c o n s i d e r a b l y less s t r i n g e n t t h a n that s ta ted b y H i n s h a w a n d F r i t s c h c n . If the c o n s t a n t v o l t a g e c i r c u i t is to be e x t e n d e d to a W h c a t s t o n c b r i d g e c o n f i g u r a -t i o n , t h e n the v o l t a g e s u p p l y m u s t be a l m o s t 10 t i m e s m o r e a c c u r a t e , s i n c e the m e a s u r e m e n t e r r o r w i l l be i a r g c l y d e t e r m i n e d b y the v a r i a -t i o n o f r e f e r e n c e v o l t a g e p r o v i d e d b y the r a t i o a r m o f the b r i d g e . It c a n be seen that the a c c u r a c y r e q u i r e m e n t s f o r b o t h c o n s t a n t c u r r e n t a n d c o n s t a n t v o l t a g e s o u r c e s a r c s i m i l a r a n d c h o i c e o f c i r c u i t c o n -f i g u r a t i o n w i l l d e p e n d o n s u c h p a r a m e t e r s as c o s t a n d a p p l i c a t i o n r a t h e r t h a n a c c u r a c y . C o n s t a n t C u r r e n t C i r c u i t F o r c o n s t a n t c u r r e n t o p e r a t i o n , a M o t o r o l a M C 1 4 6 6 L m o n o l i t h i c v o l t a g e a n d c u r r e n t r e g -u l a t o r c a n be u s e d - - In th is a p p l i c a t i o n , o n l y the i n t e r n a l v o l t a i c r c e u l a l o r a n d r e f e r e n c e c u r -rent s o u r c e s tages o f the r e g u l a t o r a r c u t i l i z e d . O u r c i r c u i t , e x c l u d i n g d i o d e s e n s o r s , c o n s i s t s o f f o u r c o m p o n e n t s a n d a p o w e r s u p p l y at a n o m i n a l 2 4 V as s h o w n in F i g . 2 . T h e c a p a c i t o r C p r o v i d e s i n t e r n a l f r e q u e n c y c o m p e n s a t i o n . O u t p u t o f the c u r r e n t s o u r c e c a n be ( r i m m e d b y a d j u s t i n g the v a r i a b l e r e s i s t o r R.. T h e r e -l a t i o n s h i p b e t w e e n o u t p u t c u r r e n t / a n d the r e s i s t o r s R\ a n d is g i v e n b y the m a n u f a c -t u r e r as [5] / = 8.55/(7?, + R-.) ( / < 1.2 m A ) r r h c use of trade, firm, or corporation names in this publ icat ion is for the in format ion and convenience of readers. Such use docs not constitute endorsement or approval of any product or service lo the exclusion of others that may be suitable. C A N . .1. FOR. RF.S. V O L . 4. IV74 65 I6.5K0. IKO. + 24V | R, R Z| 2 ' 12 14 MC 13 I 4 6 6 L 7 3 FD300 SILICON DIODES TO DATA LOGGER F I G . 2. D i o d e t h e r m o m e t e r c i r c u i t u s i n g a c o n -s t a n t c u r r e n t c o n f i g u r a t i o n . where / is in m A and 7?i and /?•_. arc in kn (Mo to ro la Semiconductor Products Inc. 197In). In order to provide a current output of 0.5 m A , 7?i is a 16.5 kn 1% metal film resistor and Rj is a 1 k<? potentiometer. The temperature stabil i ty of the constant current source depends cr i t ical ly on the temperature stabil i ty of / ? , and consequent ly, low temperature coefficient resistors should be used. The circuit was tested with 50 p.p.m./°C metal film resistors as R\ and R... Al though the overal l manufacturer 's specif i -cations of the M C 1 4 6 6 L arc satisfactory, no specif ic data arc given on the stabil i ty of the in-ternal reference current source. Tests were therefore performed on two of the devices to conf i rm the constancy of this reference current over the range of operat ing condi t ions of inter-est. The results showed that, at room temper-ature, the constant current source consumes approx imate ly 7 m A at ful l load. The output current shows negligible change (less than 0 . 0 2 % ) , prov id ing the voltage between pin 7 and 3 in F ig . 2 does not exceed approximately 8.4 V . Th is typical ly al lows up to 12 diode sensors to be operated in series at temperatures above 0 T . The lower temperature limit may be extended to about —30 °C by reducing the number of diode sensors to 11. T h e change in output current due to variat ion in supply voltage is less than 0.01 % / V from 22 to 30 V , and can be kept negligible by using a simple regulated voltage supply. T h e temperature coefficient of which can be accounted for by the temperature coefficient of our metal film resistor A", alone. The reference current temperature stabil i ty can probably be improved by replacing A , with a resistor of lower temperature coefficient. Es t i -mat ion of circuit accuracy using these results and F q . |3) , indicates that temperature can be measured to ±0.05 °C when the ambient tem-perature of the instrument varies ±20 °C and the voltage supply varies ±2 V at 24 V . O u r field experience with the instrument over sev-eral periods of a week or more shows that cur-rent drift with time is small and adjustment is unnecessary, once the current is set after 10 min of warming up. The component cost of the circuit is approximately $12 ( inc lud ing the M C 1 4 6 6 L ) , with the addi t ion of $2 for every F D 3 0 0 s i l icon d iode. Constant Vol tage C i rcu i t In the past, constant voltage has been pro-vided by cither mercury cells or a costly regu-lated power supply. However , a stable voltage source can be constructed from a Moto ro la M C I 4 6 9 G monol i th ic voltage regulator 3 ( F i g . 3 ) . We have not attempted to exhaustively verify the manufacturer 's specif ications, since the voltage regulator is operated in its sug-gested conf igurat ion. Ou r l imited test results have been consistent with the manufacturer 's c la ims. The relevant specif ications are input regulat ion, 0 . 0 0 3 % / V , and temperature co-efficient of output voltage, 0.002%/°C ( M o -torola Semiconductor Product Inc. I97l/>). Ou r tests show that the M C 1 4 6 9 G can give about 6 m A output current so that 11 or 12 diodes (depending on the indiv idual regulator uni t ) can be operated in paral lel . Temperature coefficients of the voltage d i -v id ing resistors A , and R-j in F ig . 3 must be matched, but not necessarily smal l . The most convenient choice for A , and A_. is two simi lar resistors of 10 ks) each. This gives a sensor c i r -cuit dr iv ing voltage of 7.0 V , when A\, is suit-ably adjusted. Us ing a set of accurately matched 12.7 kt! resistors as A , . R:, R„, this circuit gives diode currents of 0.5 m A at approximately 15 °C. Assuming constancy of these resistors and using the manufacturer 's circuit specif ica-"Scc f o o t n o t e 2. 66 NOTKS + 24V F I G . 3. Diode thermometer circuit using a con-stant voltage configuration. tions, a voltage stability of ± 0 . 0 4 % , which gives a temperature uncertainty of ± 0 . 0 1 °C, can be attained over the range of temperature and voltage used previously. The cal ibrat ion curves of our F D 3 0 0 diodes, using this circuit configuration, are linear to above 80 °C. The temperature error in most applications wi l l be l imited by the sensors (e.g. cal ibrat ion dr i f t ) or data logging equipment (e.g. resolution, no i se ) , rather than the voltage supply. W i t h a bridge circuit configuration, the accuracy is about ±0 . 1 °C. The cost of components, ex-c luding sensing diodes and scries resistors, is approximately $10 ( inc lud ing the M C 1 4 6 9 G ) . The main disadvantage of the constant volt-age circuit is in the need to accurately match the resistors R,, /?.-„ . . ., R„ if the diode sensors arc to be interchangeable. Th i s disadvantage suggests that the constant current circuit wi l l usually be more convenient except when a few diodes or a bridge circuit configuration is to be used. Pract ica l Considerations Perhaps the best way to illustrate the use of these circuits is to describe the construction and operation of a thermometry system built in this laboratory. The system was used in a study of the ellecls of site preparation in a forest clearcut on tree seedling microenv i ron-mcnt. A i r temperature at screen height, soil tem-perature at the 30 cm depth, and the average temperature of the top 5 cm were to be mon i -tored at three locations. Data were to be trans-mitted to a Hewlett Packard 2 070A data logger 1 through 40 m long cables. S i l icon diodes were selected as the most suit-able temperature sensors. Integrating thermom-eters for the average temperature measure-ment were constructed in the fo l lowing manner. Sets of five F D 3 0 0 diode sensors 'werc soldered in scries in strings with 2 cm between the diode centers. C o m m o n plastic dr ink ing straws, 5 mm in diameter, were filled with No. 8 Scotchcast ( 3 - M ) epoxy res in ' and clamped at the bottom end. The epoxy was warmed to lower its vis-cosity and a diode string carefully inserted into each straw. The part of the thermometer which was to protrude f rom the soil was wrapped with 3-M aluminized mylar tape 1 to reduce radiative heating of the thermometer stem. The integrating thermometers were inserted at an angle across the top 5-cm soil layer. Four of the constant current sensing circuits described were constructed on a 3 X 5 cm cir -cuit board and mounted in a small a luminum chassis box. T ime required for the circuit con-struction was less than 5 h. Ou r data logger has an input impedance of 10 M n which is much greater than the 300 kO necessary to achieve a 0.1 °C accuracy. A l u m i n u m foil shielded data cables (Bc lden 8 4 5 1 ) ' were used to prevent electrical noise pickup. Ca l ibrat ion of the diode sensors was carried out by immers ing the sensors in a temperature regulated oi l bath at several temperatures. A t 25 °C, the voltages measured across the F D 3 0 0 diodes were approximately 630 m V . Fo r field operation using long data cables, corrections to the bath cal ibrat ion were made to include the voltage drop due to the cable resistance by using Ohm' s law and measured cable resistances. Th is procedure would not have been necessary if the diode sensors had been cal ibrated to-gether with the data cables. In the field the system was powered by a portable D C to A C converter ami two 12 V truck batteries. Results of the tests dur ing that period were entirely satisfactory. A s imilar system which was constructed under the authors ' supervision is currently being used successfully by researchers at the Pacific Forest Research Centre of the C a n a -dian Forestry Service in a tree nursery pathol -'Scc footnote 2. C A N . J. F OR. RES. VOL. 4, 1974 6 7 ogy study. Sccdbcd temperatures at several depths were monitored with a total of 200 PD300 diodes. The same measurements, using precision thermistors, would have cost many times more than the diode sensors making the experiment impractical. Summary Two temperature sensing circuits have been described that have the features of simplicity, low cost, and high accuracy. Although only application to the silicon diode sensor is dis-cussed, both circuits can also be used with thermistors or resistance thermometers. B L A C K . T . A., and MCNAUGHTON, K. G . 1971. Psy-chrometric apparatus for Bowcn-ratio determination over forests. Houndary-Laycr Mctcoml. 1. 246-254. HlNSUAW, R.. and I 'RITSCIUN, 1.. J . 1970. Diodes for temperature measurement. J . App l . Metcorol. 9. 530-532. SAHCJL.ANT, D. II. 1965. Note on the use of junction diodes as temperature sensors. J . App l . Metcorol. 4 , 644-646. MOTOROLA SLMICONDUCTOK PRODUCTS INC. 197in. Multi-purpose regulators, MC I466L. In Linear Inte-grated Circuits Data Hook. 1971/). A n adjustable zcro-lcmpcraturc-cocfficient voltage reference source. In Linear Integrated Cir-cuits Data book. APPENDIX II PRECISION ELECTRONIC INTEGRATOR FOR ENVIRONMENTAL MEASUREMENT PREVIOUSLY COPYRIGHTED MATERIAL, IN APPENDIX I I, LEAVES 69-71 , NOT MICROFILMED. Tang, P.A., McNaughton, K.G., and Black, T.A. 1974 • Precis ion Electronic Integrator for Environmental Measurement. Reprinted from the TRANSACTIONS of th ASAE (Vol. 19, No. 3, pp. 550, 551, 552. 1976). Published by the American Society of Agr icu l tura l Engineers, St. Joseph, Michigan. 69 Precision Electronic Integrator for Environmental Measurement P. A. Tang, K. G. McNaughton, T. A. Black A B S T R A C T A P R E C I S I O N electronic inte-grator with good temperature stability and low power consumption is described. The integrator uses an input signal switching technique to remove error caused by input voltage and current offset. I N T R O D U C T I O N Environmental data can often be best handled by electronic time integration. A precision electronic integrator suitable for environmental measurement must have good sensi-tivity, small temperature drill, low power consumption, high reliability, and low cost. While many integrator designs have been reported in the literature, none of them can satisfy all of the above requirements. Most of these integrators have the disad-vantages of high cost and heavy power consumption. One of the most promising integrator schemes was described by Thurtell and Tanner (1964). The circuit used a signal polarity switching technique lo mini-mize the input offset voltage and current drift due to changes in ambient temperature. This method is theoretically attractive; however, an electromechanical relay was used to perform signal switching. Conse-quently, most of the undesirable features associated with relays are inherent in the circuit. Since electrical contacts in a relay wear out easily and require frequent replacement, the Article was submitted for publication in July 1975; reviewed'and approved lor publication by the Structures and Environment Division of ASAE in January 197b. The authors are: P. A. TANG. Electronics Engineer, Soil Science Dept.. University of British Columbia, Vancouver, 1JC. Canada; K. G. McNAUGIITON. Research Scientist. Crop Research Division. Scientific and Industrial Research Dept.. Clirislchureh, New Zealand; and T. A. BLACK, Associate Professor. Soil Science Dept.. University of British Columbia, Vancouver, H C . Canada. Acknowledgements: This research was sup-ported by grants from the National Research Council of Canada and the Canadian Forestry Service. long-term rcliabilty of the integrator is poor. The circuit also uses power inefficiently, because substantial current is needed to activate and retain relay contact closure. As a result, their integrator was far from ideal as a portable field instrument. With the advent of complementary metal oxide semiconductor (CMOS) components it has proven feasible to redevelop the basic scheme inherent in the Thurlcll and Tanner circuit, to produce an integrator with greatly improved performance and reliability and much lower power consumption and cost. This integrator is described below. CIRCUIT T H E O R Y The block diagram of the switching integrator is shown in Fig. 1. The front end of the integrator consists of an input signal reversal switch. The switching operation is controlled by the logic state of a flip-Hop (bistable multivibrator). The input signal, after being routed through the signal switch, is integrated by an R-C integrator. The theory of R-C integrators lias been adequately dis-cussed elsewhere (Tobey et al. 1971), and will not be repeated here. The change in the integrator output voltage, AVrjUT o v c r a time interval, T 2 - T , , is given by A V O U T = ; (V|N + e)dt RC T i Ul where V|fs| and t represent the input and error signals respectively. The error signal. £ includes the error introduced by the input offset voltage and current of the operational ampli-fier, A , used in the integrator. A pair of voltage discriminators are used to trigger the flip-flop when the inte-grator output voltage reaches either a positive or negative reference voltage. V R E F + " ' id V R E F . respectively. Assuming the integrator output is initially at V|<j:p . the time taken by the integrator output to change from V R E F + to VK]V [ . - . is given by (VREI--- V R E F + ) R C A T , = . . . |2| V 1 N + e As-soon as the output voltage reaches V R E F - . the voltage discriminator. A j is activated, causing a change ir. the logic state of the flip-flop. Conse-quently, the input signal is inverted by the signal switch. The time taken by this switching operation is determined by the speed of the voltage discrim-inator and the logic components. In order to make this time delay insignificant compared to AT,, last amplifiers and logic components must be used. The integrator'then begins to integrate the inverted signal, and VoUT ramps towards VRf£.K + • The time taken by the integrator output to change from VRjrp. to V R £ F + is given by ^ W I T C H CONTROL SIGNAL + SWITCH CONTROL SIGNAL F IG . 1 Block diagram of switching Integrator. The signal, t represent* error caused by offset volUgc and current In amplifier A , . This article is reprinted from the TRANSACTIONS of the ASAE (Vol. 19 , No. 3, pp. 55(1. 551 . 5 5 2 . 1976 ) Published by the American Society of Agricultural Engineers, St. Joseph, Michigan 70 REVERSAL SWITCH +€ VOLTS - « VOLTS COMMON A S F IG . 2 Circuit diagram of switching integrator. The component list Is given In Tabic 1. T A B L E 1. COMPONENT I.I.ST F O R SWITCHING I N T E G R A T O R . R i 28.7 Kil V.W 1 percent metal l i lm resistor R 2 1 K H multi-turn potentiometer R 3 30 K f l */4W carbon resistor R 4 100 K O V.W carbon resistor R 5 100 K I 2 V.W carbon resistor R ( j 390 SI '/«W carbon resistor R 7 300 ri '4W carbon resistor R B 100 K S l l.'.W carbon resistor R 9 100 K i l WW carbon resistor C^ 0.1 uf polystyrene capacitor C2 30 pF ceramic capacitor U i Motorola 1N821 zener diode Ar National LM.'JOKA operational amplifier A 2 - A 3 Motorola MC1741S, or Fairchild MA741S operational amplifier Polarity switch R C A CD4U1GAE, or Motorola MC14016 Flip-flop R C A C U 4 0 2 7 A K . or Motorola MC14027 ( V R E F + - V R E F . ) R C A T 2 = V , N - e A n o t h e r s w i t c h i n g o p e r a t i o n re su l t s w h e n the i n t e g r a t o r reaches V i ^ r f F - f . A l th i s p o i n t , one i n t e g r a t i o n c y c l e is c o m p l e t e . B y a d d i n g e q u a t i o n s [2) a n d [3), the t i m e fo r a c o m p l e t e i n t e -g r a t i o n c y c l e , A T = A T , + A T 2 , is g i ven by 2(VR E F + - VREF-)RCV, N V I N 2 - C 2 HI F i n a l l y , the o u t p u t f r e q u e n c y o f the i n t e g r a t o r , F = 1/AT, is g i ven by VINC r) •  V I N 2  2 R C ( V R E F + - V R E F _ , |5] a n d the r e l a t i v e f r e q u e n c y e r r o r , E is g i ven by E = V|N 2 |6] as c o m p a r e d w i t h t/V|fs| for a n o n -s w i t c h i n g i n t e g r a t o r . W i t h i n c r e a s i n g Vj,f\|, the f r e q u e n c y e r r o r o f the s w i t c h i n g i n t e g r a t o r decreases m u c h f a s te r t h a n tha t o f the n o n - s w i t c h i n g i n t e g r a t o r . H e n c e , by c h o o s i n g an o p e r a t i o n a l a m p l i f i e r w i t h a s m a l l o f f set v o l t a g e a n d c u r r e n t , the i n t e -g r a t o r c a n be de s i g ned to o p e r a t e w i t h e xce l l en t a c c u r a c y for v a r i o u s ranges o f i n p u t s i g na l s . C I R C U I T D E S C R I P T I O N T h e c i r c u i t d i a g r a m o f o u r s w i t c h -i n g i n t e g r a t o r is s h o w n i n F i g . 2 a n d the c o m p o n e n t l i st is g i v en i n ' f a b l e 1. A C M O S b i l a t e r a l s w i t c h ( R C A C D 4 0 1 6 A E ) a n d f l i p - f l o p ( R C A C D 4 0 2 7 A E ) a r e u s e d to s w i t c h t he i n p u t s i g n a l . O u t p u t v o l t a ge f r o m the i n t e g r a t o r is sensed by a p a i r o f h i g h s p e e d o p e r a t i o n a l a m p l i f i e r s ( F a i r c h i l d ^ tA741S) . T h i s c o m b i n a t i o n o f h i g h speed a m p l i f i e r s a n d l o g i c a l l o w s t he c i r c u i t to o p e r a t e at a n o u t p u t f r e q u e n c y o f at least 100 H z w i t h l e s s t h a n 0.1 p e r c e n t n o n -l i n e a r i t y . T h e (wo r e f e r ence vo l tages . V R E F + a " d V R g p . , a r c g e n e r a t e d by t w o re s i s t o r s , R 6 a n d R 7 . a n d a t e m p e r a t u r e c o m p e n s a t e d 6.2 V z e n e r d i o d e , D , ( M o t o r o l a IN821 ) o p e r a t e d at i t s r e c o m m e n d e d c u r r e n t o f 7.5 m A . T h e i n t e g r a t o r c i r c u i t c on s i s t s o f a h i g h p r e c i s i o n o p e r a t i o n a l a m p l i f i e r ( N a t i o n a l L M 3 0 8 A ) w i t h a t y p i c a l i n p u t o f f set vo l t age o f 0.3 m V a n d a t e m p e r a t u r e d r i f t o f 1.0 p tV/deg C , a c a p a c i t o r . C , , a n d two r e s i s t ance s , R, a n d R 2 . F r o m [5], a s s u m i n g e r r o r s a re n e g l i g i b l e , a n d r e p l a c i n g R w i t h R , + R 2 a n d C w i t h C , , t he f r e q u e n c y o f o u r i n t e g r a t o r c i r c u i t is g i v en by V|N 2(R, + U 2 ) C i ( V R E F + - V R E R .) |7| In the p r o t o t y p e c i r c u i t , a 28.7 K Q m e t a l f i l m r e s i s t o r w i t h a t e m p e r a t u r e c o e f f i c i e n t o f + 5 0 p p m / d c g C a n d a 0.1 f j F p o l y s t y r e n e c a p a c i t o r w i t h a c o e f f i c i e n t o f -50 p p m / d c g C a r c R, a n d C , r e spec t i ve l y . T h e r e s i s t o r , R, mus t be c h o s e n s u c h tha t it is b i g g e r t h a n 2 0 K Q to m i n i m i z e the t h e r m a l r e s i s t a n c e d r i f t i n t h e b i l a t e r a l s w i t c h , a n d s m a l l e r t h a n 100 K Q so t h a t t h e i n p u t s i g n a l c u r r e n t i s s u f f i c i e n t to m a s k the e f fect o f the o f f s e t c u r r e n t i n t h e o p e r a t i o n a l a m p l i f i e r . U s i n g the va lues o f R, a n d C i s ugge s ted a b o v e , the c i r c u i t has a s en s i t i v i t y o f a p p r o x i m a t e l y 100 c o u n t n i V " 1 h " 1 . S i n c e the i n t e r n a l r e s i s t ance o f the b i l a t e r a l s w i t c h , w h i c h is t y p i c a l l y 300 Q, is not i n c l u d e d i n [7], a m i n i a t u r e m u l t i t u r n 1 K Q p o t e n t i -o m e t e r . R 2 is n e e d e d to ad jus t the s en s i t i v i t y o f the c i r c u i t to e x a c t l y 100 c o u n t m V " 1 h " 1 . T h e c o m b i n e d t e m p e r a t u r e c o e f f i c i e n t o f the i n t e r n a l r e s i s t ance o f t he b i l a t e r a l s w i t c h a n d R 2 c o n t r i b u t e s less t h a n a 3 p p m / d c g C c h a n g e i n t h e o v e r a l l t i m e c o n s t a n t o f the c i r c u i t . T h e c u r r e n t d r a w n by the c i r c u i t is a p p r o x i m a t e l y 12 m A . A p o w e r s u p p l y r e g u l a t e d t o ± 1 p e r c e n t s h o u l d be u sed i n o r d e r to m a i n t a i n an o v e r a l l a c c u r a c y o f 0.1 p e r c e n t . T o r e d u c e t h e c i r c u i t c u r r e n t c o n s u m p t i o n f o r p o r t a b l e f i e l d o p e r a t i o n , it is p o s s i b l e to p r o v i d e the r e f e r e n c e v o l t a g e s b y u s i n g t w o m i n i a t u r e r e f e r e n c e m e r c u r y ce l l s , a n d the d i s c r i m i n a t o r s c a n be r e p l a c e d by t w o l o w p o w e r o p e r a t i o n a l a m p l i f i e r s s u c h as the L M 3 0 8 type . In th i s case, the r e s i s t an ce ( R , + R 2 ) m u s t be r e c a l c u l a t e d u s i n g e q u a t i o n |7j a n d the new r e f e r e n c e vo l tages . S i n c e the i n p u t t e r m i n a l s o f the L M 3 0 8 are s h u n t e d w i t h b a c k - t o - b a c k d i ode s for o v c r v o l t a g e p r o t e c t i o n , a 100 K Q r e s i s t o r is, t h e r e f o r e , needed i n ser ies w i t h e a c h o f the m e r c u r y ce l l s to l i m i t the c u r r e n t . U s i n g th i s c i r c u i t c o n -f i g u r a t i o n , the t o t a l c u r r e n t c o n -s u m p t i o n c a n be as low as 2 m A . T h e c u r r e n t d r a i n f r o m the m e r c u r y ce l l s does not e x ceed 10 f iA; t he re f o re , no r e p l a c e m e n t o f these ce l l s is necessary for as l o n g as 2 y r . T h e c i r c u i t is s u i t a b l e f o r p o r t a b l e b a t t e r y use. It s h o u l d be no ted tha t i n the s w i t c h i n g o p e r a t i o n o f the i n t e g r a t o r the c o m m o n p o i n t C is s w i t c h e d 71 between the two input terminals (Fig. 2). T h i s presents no problem when the circuit is powered by batteries. W h e n the circuit is connected to a power s u p p l y where the c o m m o n is g r o u n d e d , nei ther i n p u t t e r m i n a l should be grounded. T h e output from the integrator is a 12 V pcak-to-peak square wave. It can be connected directly to a C M O S digital counter without adding any external component. T h e output can also trigger a simple driver circuit for an electromechanical counter. C A L I B R A T I O N A N D T E S T S T h e most convenient way to cali-brate the integrator is to use an electronic counter and a precision D C m V source set at 10 m V output. T h e variable resistor, R 2 in the integrator is adjusted so that the integrator produces pulses with a 3.6(3 sec i n t e r v a l . W h e n this p r o c e d u r e is completed, the integrator has been calibrated to 100 count m V " 1 h " 1 . Linearity of the integrator circuit was tested using the same instru-ments. Signals ranging from 0.5 m V to 50 m V were a p p l i e d to the integrator. A m a x i m u m deviation of 0.3 percent from the calibration was observed, when the input signal was small . W h e n the integrator circuit was tested with a preamplifier (Fairchild HA725 differential amplifier) inserted between the polarity reversal switch ( C D 4 0 1 6 A E ) a n d the i n t e g r a t o r ( L M 3 0 8 A ) , the circuit performance was greatly improved. W i t h the pre-amplifier set at a gain of 10. the circuit's m a x i m u m deviation from calibration was less than 0.1 percent over the same signal range. W i t h a 0.2 m V input, the integrator alone showed a 5 percent deviation, while the integrator with preamplifier was still within 0.1 percent of the calibration. In small signal applications, there-f o r e , it is r e c o m m e n d e d that a preamplifier be used in the circuit. A l t h o u g h the operating tempera-tures for some of the components i n the circuit v/ere rated from 0 C to 75 C , our circuit tests covered a tem-perature range extending from -10 C to 80 C . A n input signal of 10 m V was again used. T h e change in output frequency over the entire temperature range was very s m a l l , a n d o u r calculations showed that this tem-perature drift amounted to approxi-mately 0.02 p e r c e n t / C . O u r field tests over the last 2 yr have demonstrated the excellent accuracy and stability of the circuit. A P P L I C A T I O N S T h i s i n t e g r a t o r was o r i g i n a l l y d e s i g n e d f o r r a d i a n t energy f lux measurement. T h e output voltages from a thermopile type pyranometer or net radiometer is typically 0 to 30 n i V . Signals of this magnitude can be measured directly using this inte-grator. W h e n the circuit is used with a1 net radiometer, a millivoltage source is often placed in series with the radiometer to maintain a positive signal under negative net radiation conditions. T h i s arrangement has the added advantage of providing the integrator with 1 or 2 m V at the input at all times, thus minimizing the error due to the circuit's non-linearity at the low signal end . W e have s u c c e s s f u l l y used the integrator with the preamplifier in the field to measure small differential t e m p e r a t u r e s with s i l i c o n d i o d e s (Tang et al . 1974). W i t h suitable a m p l i f i c a t i o n or a t t e n u a t i o n , the integrator can also be used to measure s ignals f r o m t h e r m i s t o r ther-mometers, thermopile soil heat flux plates, and numerous other environ-mental sensors with voltage outputs. References 1 Tang, P. A.. K. G . McNaughton and T . A. Black. 1974. Inexpensive diode ther-mometry using integrated circuit components. Can. J. of For. Res. 4:250-254. 2 Thurtcl l . G . W. and C. B. Tanner. 1964. Electronic integrator for micrometcorological data. J. Appl . Meteorol. 3:198-202. 3 Tobcy, G . E.. J. G . Graeme and L. P. Huclsman. 1971. Operational amplifier design and application. Burr-Brown. 213-218. APPENDIX III ERROR ANALYSIS OF REVERSING PSYCHOMETRIC SENSORS 73 ERROR ANALYSIS OF REVERSING PSYCHROMETRIC SENSORS Let us assume that i n i t i a l l y sensing head 1 i s in posit ion 1 where the temperature is T'^  and that sensing head 2 i s in posit ion 2 where the temperature i s J^- Let us assume these temperatures remain i i constant. Let V -|-| and V 2 2 represent the voltage across the diodes in head 1 (at T n ) and head 2 (at 1^) respectively at th i s time. Then, v'n = vio " si Ti (D V ' 2 2 = V 2 Q - S 2 T 2 (2) where V-jQ and V 2g are respective diode voltages at T = 0. Subtracting (1 ) from (2) , we have , V ' 2 2 - V n = (V 2 Q - V 1 Q ) + ( S l T l - S 2 T 2 ) (3) Let the psychrometric heads reverse a short time la te r and equ i l ib rate in the i r new pos it ions, then (v"2] - v"12) = (V 2 Q - V 1 Q ) + (S-,T2 - S ^ ) (4) where V -|2 and V 2-| are the voltages across the diodes a f ter reversing. The change in the voltage difference as a resu l t of reversa l , represen-ted by A, is obtained by subtracting (3) from ( 4 ) , A = (V " 2 1 - v"12) - (v' 2 2 - V ' n ) = (S 1 + S 2 ) (T 2 - T-,) (5) 74 Let be the mean temperature s en s i t i v i t y of the two diode thermometers, and 6S-| and SS2 be the deviations of the s en s i t i v i t y of the respective diodes from the mean. We have S-, = S + <5S1 (6) S 2 = S" + 6S 2 (7) Subst itut ing (6) and (7) in (5), we have A = (T 2 - T 1 ) (2S" + 6S1 + 6S 2) = 2S(T 2 - + (6S 1 + 6S 2 ) (T 2 - T-,) (8) Therefore, the error of measurement, e, i s e = (6S1 + 6S 2 ) (T 2 - T ^ (9) or A = 2S(T 2 - T n ) + e (10) The instrument er ror , e, can be minimized by ca re fu l l y matching the diode thermometers. Note that e i s independent of the diode of f set voltage (V-jQ and V 2Q). Consequently, the mismatch in diode offset voltages does not a f fect the instrument's accuracy. However, the difference should be kept to a minimum to minimize the problem of signal detection. APPENDIX IV INSTRUCTIONS FOR OPERATION OF THE ENERGY BALANCE/BOWEN RATIO MEASUREMENT SYSTEM INSTRUCTIONS FOR OPERATION OF THE ENERGY BALANCE/BOWEN RATIO MEASUREMENT SYSTEM A. INTEGRATING DATA LOGGER UNIT Back Panel a. Plug label led "Hurst power i n " i s to be connected to the 110 V. A.C. l i n e . This i s the power that goes through a relay which switches the d i rect ion of the Hurst motor which i s mounted on the Bowen ra t i o assembly. b. Plug labe l led "Hurst power out" i s to be connected to the cable attached to the Hurst motor. c. "BRM power" i s 110 V.A.C. and i s the main power input to the complete unit other than the A.C. to the Hurst motor. The reason for 2 power cables i s to keep noise and surges caused by the Hurst out of supply c i r c u i t (even though no problems may resu l t with only one, i t i s wise to use two). d. Cables marked "Chart Recorder" are to be connected to the Fisher Recordall s t r i p chart recorder (Red i s +ve and Black i s -ve). One cable i s AT and the other i s AT . Recorder i s w used only to monitor these s ignals. Front Panel a. Top level ( i ) On the l e f t side i s the 4 d i g i t Readout l abe l led "TIME" which can be set to the correct time using the switches 77 ca l led "Fast" and "Slow". Fast i s a fast forward and slow i s a f ine adjust (1 min per sec). The switch ca l led "Lamp Test", when actuated, should show a l l " 8 ' s " on both the "Time" display and the "Data" display. ( If any of the segments are not on then that segment could be burned out.) (Do not worry i f nonsense read-outs occur upon start-up. Speed-up clock and th i s should be f ixed. ) The 2 f lashing "LEDs" in the middle-of the 4 time d i g i t s are 1 second pulses. The clock only shows hours (2 l e f t d i g i t s ) and minutes (2 r ight d i g i t s ) , ( i i ) Data Readout "COUNTS" i s on the r ight and displays a 4 d i g i t number which i s the integrated counts for what ever channel i s being monitored (more about th i s l a t e r ) . b. Middle level ( i ) The "LEDs" marked "NOR + REV" are ca l led Normal + Reverse which just indicates that the heads have been reversed. ( It should alternate between "NOR" and "REV" every 15 min.) ( i i ) The "LED" ca l led "INH" i s the l i g h t that shows the i n -h ib i t i ng of integration of AT and ATW channels. It i s "on" for the f i r s t f i v e minutes on an integrat ion period while the temperature of the sensors i s s t a b i l i z i n g , ( i i i ) The 8 "LEDs" ca l led "Chan. Overflow (numbered 0 - 7 ) w i l l come on when any channel has counted more than 9999 counts. 78 The printout from the Pr inter w i l l be printed in Red for the par t i cu la r channel when more than 7999 counts have occurred. The thumbwheel switch ca l led "Chan. Select" goes from 0 to 7 and i s also indicated by 3 "LEDs" ca l led "Chan. Ind." in 4-2-1 binary code. In normal operation the "LED" ca l led "RAND" i s on and i s the random mode indicator (shows that scan i s not occurring). "Scan" l i g h t w i l l come on when the integration period i s over and printout and reset are taking place, then w i l l go out. When using "Chan Select" the channel shown on the switch (and "LEDs" ca l led "Chan Ind") i s the Channel that i s displayed on the "COUNTS" readout (showing tota l counts for that channel to that time). The use of the "Chan Select" switch, i . e . random mode, w i l l not ef fect the operation of scanning (printout) or integrat ion. During the scan cycle the unit w i l l scan from 0 to 7 and indicate the counts at time of pr int ing on the "COUNTS" readout, each in succession. After the scan cycle the "COUNTS" readout w i l l return to the channel you had randomly selected previously. Switch ca l led "INT. PER." i s the integration time period with 15 minutes or 30 minutes (always with 5 minutes of i n h i b i t for AT and AT,,) selectable. w' Switch ca l led "Reset" has an "LED" to indicate when i t i s act ivated. When tr iggered, i t w i l l reset the unit a f te r the f i r s t 1 minute pulse activates i t (e.g. i f you push 79 "Reset" at 16:59 then at 17:00 the unit w i l l reset, no matter when i t was supposed to read in normal machine operation). For i n i t i a l startup, set clock to real time, then 1 minute before desired s tar t time, push "Reset", ( v i i ) Switch ca l led "power" i s the main power switch. It does not control pr inter and Hurst motor. I t also has an i n -dicator l i g h t to show power is on. ( v i i i ) P r inter - the p r i n te r ' s power is turned on separately from the main un i t ' s power. "Manual p r i n t " causes pr int out of current integration t o t a l . "Feed" is the paper feed of the pr inter , c. Bottom level ( i ) The cables to the Bowen ra t i o assembly, net radiometer, heat f lux p late, integrating thermometer and solarimeter are connected to the indicated sockets on the case. The correspondence of channel number, parameter measured and instrument is as fo l lows: Parameter Channel § 0 AT = difference in a i r temperature 1 AT = difference in a i r wet bulb w temperature 2 T* = absolute a i r temperature 3 T * = absolute a i r wet bulb temperature w 4 net radiat ion (R ,^) 5 s o i l heat f l ux (6 ) 80 6 average so i l temperature above heat f lux plate (T s ) 7 solar radiat ion (R g) *head #1 of Bowen ra t i o apparatus Instrument Channel # 0 Bowen ra t i o apparatus 1 Bowen ra t i o apparatus 2 Bowen ra t i o apparatus 3 Bowen ra t i o apparatus 4 Swissteco net radiometer 5 Middleton so i l heat f lux plate 6 Integrating thermometer 7 Kipp solarimeter 3. S en s i t i v i t i e s and Offsets of Integrators period o c u ^ u - . v , ^ Q f f s e t Channel # Signal (min) (counts mV hr" ) (mV) 0 AT 10 or 25 1000 5 1 A T W 10 " 11 1000 5 2 T 15 " 30 100 520 3 T w 15 " " 100 520 4 • RN 15 " " 100 5 5 G 15 " " 100 5 6 V 15 " " 50 3000 7 R s 15 " " 100 0 81 B. CALCULATIONS Obtaining Values of Energy Balance Parameters (for 15 min Reversal Mode Channel 0 AT j Compute- C o u n t s ( 1 s t 15 min per.) - Counts (2nd 15 min per.) Convert to mV using s en s i t i v i t y above for 10 min integrat ion period. Use 1.992 mV °C"1 to get AT and 1.998 mV oc-1 to get ATW. See c a l i -bration sheet for B.R. apparatus. The 5 mV of f set is subtracted out in the above equation. 2 T 2 j } Compute mV using s en s i t i v i t y above for 15 min integrat ion w period. Add 520 mV, the o f f set . Apply the appropriate ca l ib ra t ion equation for the B.R. apparatus. 4 R|\|, Compute mV using the s en s i t i v i t y . Subtract 5 mV, the 5 G of f set . Apply ca l i b ra t ion (Wm-2 mV-I) for net radiometer P and so i l heat f lux plate. 6 T Compute mV using the s e n s i t i v i t y . Add 3000 mV, the o f f set . Apply ca l i b ra t ion equation for integrating thermometer. 7 R Compute mV using the s e n s i t i v i t y . Apply ca l i b ra t ion (Wm_2 mV-"l) for solarimeter. Calculat ion of Bowen Ratio The psychrometric constant ( y 1 ) for the wet bulb sensor is 0.69 mb °C ^ The vapour pressure (mb) i s given by: e = e w * - * ' < T - T W ) where e^* i s the saturation vapour pressure at T w . T - T w i s the depression (°C). , Table IV-1 attached gives saturation vapour pressure as a function of temperature. The vapour pressure difference i s : Ae = s AT - Y'(A-T - AT ) w w ' x w ; where s w i s the slope of the saturation vapour pressure curve (see Table IV-1). The Bowen ra t i o i s : 82 0 AT + T A Z bs = Y ; ' Ae where y i s the "normal" psychrometric constant (see Table IV-2), r i s the adiabatic lapse rate -0.01 °C nH , and A Z i s the distance between sensors (m). NOTE 1: Equation (3) in the main text assumes y' = y. 2 : A T = T bot . " T t o p ' A T w = Tw bot. " Tw top -3. Calculat ion of the Evaporation Rate Use the energy balance/Bowen ra t i o equation E = RN - 6 L( l + B) where L i s the latent heat of vapourization (see Table IV-2), and G i s the surface so i l heat f l u x , the so i l heat plate value (Gp) corrected for heat storage (M) in the so i l above i t using the i n -tegrating thermometer. M = zC AT S/At where z is the depth of the p late, C is the heat capacity of the so i l (roughly 0.5 cal cm~3 ofj-1) and AT S/At is the time rate of change of the integrating thermometer temperature. For a f i r s t approximation G can be neglected or assumed to be 5-10% of RM for moist s o i l . C. INSTRUMENTS 1. Bowen Ratio Apparatus Set Gast pump to 10 p . s . i . with tap near gauge for a 70-90 foot vacuum l i n e . Set stops for correct pos i t ioning. Add water to reservoirs da i ly ( d i s t i l l e d ) . Wet wicks before turning on pump i f wicks have been dry for an extended period. Keep wicks clean. Change as necessary. Check with s l i ng psychrometer occasional ly. Remember the d i f fe rent psychrometric constant. This means the depression for the B.R. apparatus is 0.2 - 0.3 °C less than in the conventional Hg in glass psychrometer. 2. Net Radiometer Obtain s i l i c a ge l . Keep flow rate of dry a i r low to conserve Si ge l . Keep bubbler pressure at 20-25 cm of H2O. Make sure net radiometer is l e v e l . If dew i s a problem external vent i l a t ion w i l l help. Make sure th i s pump i s o i l less. 83 3. Soi l Heat Flux Plate Should be positioned 1 week before taking readings. Watering in is recommended. 4. Integrating Thermometer The stem is b r i t t l e . Be careful when insert ing in s o i l . 5. Solarimeter Level and keep dome dry. This serves as a check on the net radiometer readings. RN - 2/3 R . D. CALIBRATION EQUATIONS 1. Bowen Ratio Apparatus Channel 0 AT 1 ATW 2 T 3 T w FD300 S i l i con diodes (2 matched pairs) T * * > dtte #,1 Head II Tw ' diet "°A *2 Cal ibrat ion equation for #13* and #11: j = 679.0826 - V T 0R 1.9920 V T = 679.0826 - 1.9920 T * For T and T,, measurement w OR Cal ibrat ion equation for #10* and #4: j = 677.9413 - V T  W 1.9978 V T = 677.9413 - 1.9978 T I w * For T and T measurement w 2. Net Radiometer Channel 4 RADIATION INSTRUMENT CALIBRATION CERTIFICATE NO. 136 84 Instrument Type Instrument No.: Sens i t i v i t y at 20° C: Internal Resistance: Balance i f appl icable: Accuracy of ca l i b ra t i on : Date: Net Radiometer Type S-l 7078 Short wave rad iat ion: 0.327 mV/mW cm" Long wave rad iat ion: 0.331 mV/mW cm" 205 Ohms Front to back within 1%% ± 2h% Melbourne, July 24, 1974 Swissteco Pty. Limited 85 3. Soi l Heat Flux Plate Channel 5 SOIL HEAT FLUX PLATE CALIBRATION CERTIFICATE REF. 4/10 Instrument No.: Maker: Sen s i t i v i t y : Temperature coe f f i c i en t : Accuracy of ca l i b ra t i on : Internal resistance: Date: F570 Middleton Instruments Heat out of numbered face 219. uV/mW cm -2 Heat into numbered face 217. uV/mW cnf^ 0.2 % per deg Cels 5 % 24.7 Ohms March 1975 Commonwealth S c i e n t i f i c and Industr ial Research Organization Divis ion of Atmospheric Physics Station Street - Aspendale 3195 4. Integrating Thermometer Channel 6 5 diodes (FD300) in series j = 3383.59 - V T c L 9.85 A T s = 9785 AV T s o r A T s >C ; V T = AVn 86 5. Solarimeter  Channel 7 CALIBRATION CERTIFICATE Cal ibrat ion effected according to International Pyreheliometer Scale 1956 Solarimeter for outdoor i n s t a l l a t i o n type CM 5 - Ser ia l No. 731929 -2 -1 A radiat ion of 1 gcal cm min produces an E M F of 7.2 mV _ ? A radiat ion of 1 Won produces an E M F of 103 mV Resistance of thermopile 8.4 Ohms. Date:. November 28th, 1973 KIPP & ZONEN, Del f t . 87 TABLE IV-1 Saturation vapour pressure (e*) and de*/dT(=s) versus temperature (T). T (°C) T (K) e* (mbar) S -1 mbar °C 1 -5 268.2 4.21 0.32 -4 269.2 4.55 0.34 -3 270.2 4.90 0.37 -2 271.2 5.28 0.39 -1 272.2 5.68 0.42 0 273.2 6.11 0.45 1 274.2 6.57 0.48 2 275.2 7.05 0.51 3 276.2 7.58 0.54 4 277.2 8.13 0.57 5 278.2 8.72 0.61 6 279.2 9.35 0.65 7 280.2 10.01 0.69 8 281.2 10.72 0.73 9 282.2 11.47 0.78 lo- 283.2 12.27 0.83 ll 284.2 13.12 0.88 12 285.2 14.02 0.93 13 286.2 14.97 0.98 14 287.2 15.98 1.04 15 288.2 17.04 1.10 16 289.2 18.17 1.17 17 290.2 19.37 1.23 18 291.2 20.63 1.30 19 292.2 21.96 1.37 20 293.2 23.37 1.45 21 294.2 24.86 1.53 22 295.2- 26.43 1.62 23 296.2 28.09 1.70 24 297.2 29.83 1.79 . 88 TABLE IV-1 (cont.) Saturation vapour pressure (e*) and de*/dT(s) versus temperature (T). T T e* s (°C) (K) (mbar) mbar °C 25 298.2 31.67 1.89 26 299.2 33.61 1.99 27 300.2 . 35.65 2.10 28 301.2 37.80 2.21 29 302.2 40.06 2.32 30 303.2 42.43 2.44 31 304.2 44.93 2.57 32 305.2 47.55 2.69 33 306.2 50.31 2.83 34 307.2 53.20 2.97 35 308.2 56.24 .3.12 36 309.2 59.42 3.27 37 310.2 62.76 3.43 38 311.2 66.26 3.57 39 312.2 69.93 3.76 40 313.2 73.78 3.94 41 314.2 77.80 4.13 42 315.2 82.02 4.32 43 316.2 86.42 4.52 44 , 317.2 91.03 4.73 45 318.2 95.86 4.94 89 TABLE IV-2 Latent heat of vapourization of water (L) and the psychrometer constant (y) versus temperature (T) T T L Y °C K J g mbar °C"1 -5 268.2 2513 0.643 0 273.2 2501 0.646 5 278.2 2489 0.649 10 283.2 2477 0.652 15 288.2 2465 0.655 20 293.2 2454 0.658 25 298.2 2442 0.662 30 303.2 2430 0.665 35 308.2 2418 0.668 40 313.2 2406 0.671 45 318.2 2394 0.675 APPENDIX V LIST OF COMPONENTS FOR CIRCUIT DIAGRAMS 91 FIGURE 3 MC 7812 Motorola MC 1466 L Motorola MC 1469 G Motorola CA 3130 RCA 0.1 yF ceramic capacitor 1 K, 1%, 1/4 W metal f i lm res i s to r 2 K mult i - turn tr im pot 249 fi, 1% 1/4 metal f i lm re s i s to r 500 tt mult i - turn tr im pot 357 to, 1%, 1/4 W metal f i lm res i s to r 12.7 to, 1% 1/4 W metal f i lm res i s to r 30.2 to, 1%, 1/4 W metal f i lm res i s to r 61.9 to, Mo V4 W metal f i lm res i s to r 68.1 to, Mo, 1/4 W metal f i l m re s i s to r 10 to mult i -turn tr im pot 200 Q mult i - turn trim pot » 50 Q mult i - turn trim pot FD-300 diodes Fa i r ch i l d Five FD-300 diodes in series FIGURE 5 Ul CD 4016 AE U2 LM 725 CH U3 LM 308 N U4, U5 MC 1741 CP U6 CD 4027 AE DI IN 4733 zener diode (selected) 92 CI .0015 yF ceramic capacitor C2 .05 yF ceramic capacitor C3 1 yF polystyrene capacitor C4 30 pF ceramic capacitor R l , R2 1 Mn, ± Mo, 1/4 W metal f i lm res i s to r R3, R9 4.7 Mn, ± 1%, V4 W metal f i lm re s i s to r R4 30 n, ± 5% 1/4 W carbon res i s to r R5 270 n, ± 5%, 1/4 W carbon res i s to r R6, R8 ± 1%, 1/4 W metal f i lm re s i s to r . See table below. R7 Trim pot. See table below. R10 100 Kn tr im pot R l l 35.7 Kn, ±1%, 1/4 W metal f i lm re s i s to r R12 33 Kn, ± 5% 1/4 W carbon re s i s to r R13, R14, R17, R18 10 Kn, ± 5% 1/4 Wcarbon re s i s to r R15, Rl6 360 n, ± 5% 1/4 W carbon res i s to r R19, R20 100 Kn, ± 5% 1/4 W carbon res i s to r Channel No. Preamplif ier Gain R6 R7 R8 C o u n t / m V hr 0, 1 100 10 Kn 1 Kn 1 Kn 1000 2, 3, 4, 5, 7 10 1 Kn 200 n 1 Kn 100 6 5 _ 200 n 1 Kn 50 FIGURE 6 Ul - U8 . ] /6 CD 4049 each RCA U9 IMC 7445 Motorola Ul0 - Ul7 1/4 MC 7401 each Motorola DI - D10 IN 4148 Motorola Rl - Rl6 2 K 1/4 W res i s tors FIGURE 7 Ul - U4 U5 - U8 1 MC 7490 each 1/2 MC 8309 each Motorola Motorola Ul - U4 U5 - U12 U13 - U16 R l , R2 R3 - R6 R7 - RIO FIGURE 8 1 MC 8312 each 1/4 MC 7401 each 1 4N28 each 1 K 1/4 W res i s tor s 4.7 K 1/4 W res i s tors 360 n 1/4 W res i s tors Motorola Motorola Motorola Ul U2 Rl U9 R8 FIGURE 9 1 MC 8312 1/4 SN 74279 1 K 1/4 W res i s tors Motorola Signetics Ul U4 U3 U 12 FIGURE 10 1/6 MC 7404 each 1/4 MC 7400 each Motorola Motorola Ul - U4 FIGURE 11 1 9300 each Fa i r ch i l d Ul U2 U9 FIGURE 12 1 MC 7442 1/6 MC 7404 each Motorola Motorola FIGURE 13 U l , U3 U2, U6 U5, U7 U8 1/4 74279 each ] /4 MC 7400 each !/6 MC 7404 each 1 MC 7493 Signetics Motorola Motorola Motorola FIGURE 13 cont. U4, U9 1/2 8602 Fa i r ch i l d *U4, U9 time constant: U4 .001 yf 5.1 K = 1.5 y s U9 50 pf 5.1 K - 80 ns FIGURE 14 U l , U5 1/4 U2, U9 1/2 U3, U7, U12 1/6 U4, U6, U10, U l l 1/4 U8 1 *U2, U9 time constant: U2 1 K 0.05 yf 74279 each 8602 each MC 7404 each MC 7400 each MC 7493 U9 50 K 22 yf (10V) 15 ys 0.3 s. Signetics Fairchi Id Motorola Motorola Motorola FIGURE 15 El - E3 1/3 CD 4007 AE RCA E4 - E7 1/2 8602 Fa i r ch i l d E8 - E l l , E21 - E26, E35 - E37 1/4 MC 7400 CP Motorola El2 - E20, E27 - 30 1 MC 7490 CP Motorola E31 - E34 1/2 MC 7476 CP Motorola 

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