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System for the automatic sensing and recording of a greenhouse environment using moving sensors von Beckmann, Joerg Walter 1972

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A SYSTEM FOR THE AUTOMATIC SENSING AND RECORDING OF A GREENHOUSE ENVIRONMENT USING MOVING SENSORS by JOERG WALTER von BECKMANN B.Sc. Mount. A l l i s o n U n i v e r s i t y , 1971 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of A g r i c u l t u r a l Mechanics We accept t h i s t h e s i s as conforming t o the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA September, 19 7 2. In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission fo r extensive copying of t h i s thesis for scholarly purposes may be granted by the Head of my Department or by h i s representatives. It i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of A g r i c u l t u r a l M e c h a n i c s The University of B r i t i s h Columbia Vancouver 8, Canada Date S e p t e m b e r 2 9 , 1972 ABSTRACT One of the major problems encountered i n c o l l e c t i n g data f o r use i n a n a l y s i n g the i n t e r n a l environment of a greenhouse i s the time r e q u i r e d t o read and re c o r d the many environmental parameters. This problem s e v e r e l y r e s t r i c t s the a n a l y s i s of f a c t o r s a f f e c t i n g the environment by l i m i t i n g the number of l o c a t i o n s t h a t can be conve n i e n t l y sampled and the frequency w i t h which each l o c a t i o n can be sampled. The time and cost f a c t o r s a l s o l i m i t the number of parameters which can be measured at each l o c a t i o n . A sensor module has been developed which w i l l a u t o m a t i c a l l y measure environmental parameters at any number of pre-determined p o i n t s along a f i x e d t r a c k . The module i s capable of sampling 15 v a r i a b l e s at a s i n g l e l o c a t i o n and t r a n s m i t t i n g v i a one cable a l l 15 s i g n a l s f o r i n t e r p r e t a t i o n by a main decoding and r e c o r d i n g s t a t i o n . The module i s capable of a u t o m a t i c a l l y making 10 stops and measuring 15 parameters at each stop i n about 10 minutes; a task which i s very time consuming or expensive by other methods. TABLE OF CONTENTS PAGE ABSTRACT i ACKNOWLEDGEMENTS V-L I S T OF TABLES i i i L I S T OF FIGURES i v t INTRODUCTION I LITERATURE REVIEW 3 DESIGN APPROACH 9 D e s i g n C r i t e r i a 9 C o m p o n e n t . S e l e c t i o n 14 THE MODULE IS O v e r v i e w o f O p e r a t i o n 18 G e n e r a l D e s c r i p t i o n 18 D e t a i l s o f O p e r a t i o n .27 RECORDING STATION RECEIVER 41 O v e r v i e w o f O p e r a t i o n 41 D e t a i l s o f O p e r a t i o n 41 TESTING THE SYSTEM "*8 E x p e r i m e n t A 48 E x p e r i m e n t B 49 DISCUSSION SI RECOMMENDATIONS 55 REFERENCES 58 - i i i -L I S T OF TABLES TABLE DESCRIPTION PAGE I E f f e c t o f O i l L a y e r on M e r c u r y T r o u g h R e s i s t a n c e 50 - i v -L I S T OF FIGURES FIGURE DESCRIPTION 1 A S y s t e m s C o m p a r i s o n 2 The M o d u l e 3 F o r k C o n n e c t o r 4 M a i n P o w e r S u p p l y 5 M e r c u r y T r o u g h s 6 R e c o r d i n g S t a t i o n R e c e i v e r C i r c u i t Box 7 M o d u l e C i r c u i t B l o c k D i a g r a m 8 M i c r o s w i t c h Wedge 9 M o d u l e R e g u l a t o r S u p p l y W i r i n g D i a g r a m 10 S e n s o r E q u i l i b r a t i o n T i m e r a n d V a r i a b l e -S q u a r e Wave G e n e r a t o r 11 M o d u l e W i r i n g . D i a g r a m , I n t e g r a t e d C i r c u i t s o n l y 12 R o t a r y S w i t c h W i r i n g D i a g r a m 13 M o d u l e R e l a y W i r i n g D i a g r a m 14 A u t o m a t i c R e s e t f o r t h e M o d u l e 15 R e c o r d i n g S t a t i o n B l o c k D i a g r a m 16 R e c o r d i n g S t a t i o n R e c e i v e r W i r i n g D i a g r a m , I n t e g r a t e d C i r c u i t s o n l y 17 R e c e i v e r R e l a y s a n d R e l a y D r i v e r s 18 A u t o m a t i c R e s e t f o r R e c o r d i n g S t a t i o n , R e c e i v e r 19 M a i n Power S u p p l y W i r i n g D i a g r a m ACKNOWLEDGEMENTS The author wishes to thank Dr. N.R. Bulley (Department of A g r i c u l t u r a l Engineering, University of B r i t i s h Columbia), the Director of t h i s project, for his encouragement, patience and c r i t i c i s m ; Dr. E.0. Nyborg (Department of A g r i c u l t u r a l Engineering, University of B r i t i s h Columbia), Professor L.M. Staley (Department of A g r i c u l t u r a l Engineering, University of B r i t i s h Columbia), and Dr. P.A. J o l l i f f e (Department of Plant Science, Uni-v e r s i t y of B r i t i s h Columbia) for t h e i r many suggestions in reviewing t h i s thesis. Sincerest gratitude i s extended to the techni-cians of the Department of A g r i c u l t u r a l Engineering, Mr. W. Gleave (deceased May 28, 1972) and Mr. J. Pehlke for t h e i r assistance in the completion of the project. Special thanks are also due to Mrs. E. Stewart for typing the thesis. This research was financed by the National Research Council of Canada. INTRODUCTION T h e r e a r e many v a r i a b l e s i n t h e d e s i g n o f a g r e e n -h o u s e w h i c h a f f e c t p l a n t g r o w t h and d e v e l o p m e n t . I n d i v i d u a l e n v i r o n m e n t a l f a c t o r s s u c h a s t e m p e r a t u r e c a n be r e a d i l y m e a s u r e d a t a s i n g l e l o c a t i o n , a n d s u c h m e a s u r e m e n t s c a n be a p p l i e d t o t h e c o n t r o l o f t h e g r e e n h o u s e e n v i r o n m e n t . w i t h i n p r e s e t l i m i t s . Of c o u r s e , t h e e n v i r o n m e n t a l c o n d i t i o n s a t t h e s i n g l e l o c a t i o n c a n n o t a c c u r a t e l y r e p r e s e n t t h e w i d e v a r i a t i o n s o f e n v i r o n m e n t a l c o n d i t i o n s e x p e r i e n c e d b y t h e p l a n t s i n d i f f e r e n t p a r t s o f a n o r m a l g r e e n h o u s e . T h e s e v a r i a t i o n s i n g r o w t h c o n d i t i o n s a t d i f f e r e n t l o c a t i o n s w i t h i n t h e g r e e n h o u s e a r e due t o s u c h f a c t o r s a s b u i l d i n g o r i e n t a t i o n , b u i l d i n g d e s i g n , a r c h i t e c t u r a l s h a p e , a n d c o n s t r u c t i o n m a t e r i a l s , and t h e y a r e u l t i m a t e l y r e f l e c t e d by a l t e r a t i o n s i n p l a n t g r o w t h r a t e and p r o d u c t i v i t y . I n t e s t i n g a n y new c o n c e p t s i n g r e e n h o u s e d e s i g n , o r s t r u c t u r a l m a t e r i a l , i t i s n e c e s s a r y n o t o n l y t o a n a l y s e t h e p o s s i b l e e f f e c t t h e o r e t i c a l l y b u t i t must a l s o be p o s s i b l e t o s u p p o r t t h e s e c a l c u l a t i o n s w i t h a c t u a l d a t a c o l l e c t e d f r o m p r o t o t y p e g r e e n h o u s e s . , a n d s u b s e q u e n t l y i n t h e f i n i s h e d s t r u c t u r e . The c o l l e c t i o n o f l a r g e amounts o f d a t a i s r e q u i r e d i n o r d e r t o a s s e m b l e a t r u e r e p r e s e n t a t i o n o f t h e b u i l d i n g ' s c l i m a t i c c o n d i t i o n s . The m e t h o d s p r e s e n t l y a v a i l a b l e f o r - 1 -- 2 -t h i s task are eithe r so time consuming that the data obtained i s d i f f i c u l t to i n t e r p r e t , or they require very elaborate and expensive equipment. U n t i l now, few attempts have been made to employ those sensors and measuring devices commonly found i n a g r i c u l t u r a l research stations and u n i v e r s i t i e s i n a r e a l i s t i c analysis of greenhouse environments. Past trends have been to eit h e r ignore c l i m a t i c gradients completely, or to invest heavily i n systems designed s o l e l y f o r data a c q u i s i t i o n . A new system w i l l be introduced which w i l l enable automatic sensing and recording of environmental parameters at many locations throughout a greenhouse using common sensors, amplifiers and recorders. This system d i f f e r s from other environmental data c o l l e c t i o n systems i n that i t contains the l a t e s t d i g i t a l e l e c t r o n i c s combined with the si m p l i c i t y and low cost of a minimum number of sensors. LITERATURE REVIEW T h e o r e t i c a l analyses of greenhouse environments have been used i n e v a l u a t i n g the e f f e c t of new s t r u c t u r a l m a t e r i a l s , b u i l d i n g o r i e n t a t i o n s , and a r c h i t e c t u r a l designs. In a l l of these cases, the methods have r e q u i r e d a c t u a l measured data from sensing and r e c o r d i n g devices t o support c a l c u l a t e d r e s u l t s (4, 9, 10, 11, 13, 15, 17)*. Without such data, a p p l i c a t i o n of the t h e o r e t i c a l r e s u l t s i s not j u s t i f i e d . The a n a l y s i s of t h i s environmental data has a l s o been used t o p r e d i c t or e x p l a i n v a r i a t i o n s i n p l a n t growth r a t e s and p r o d u c t i v i t y ( 1 , 3, 6, 14). The approaches t o the measurement of the e n v i r o n -ment i n s i d e l a r g e enclosures which have been used i n the past and are p r e s e n t l y being used, may be c a t e g o r i z e d i n t o f o u r groups of systems: (a) data a c q u i s i t i o n systems (4, 5, 6, 11, 13) (b) systems using a few sensors t o o b t a i n approximations of the environment ( 1 , 2, 7, 9, 14, 15, 16, 17) (c) telemetry systems (8, 12) (d) non-automated systems ( 3 ) . Examples from each of the groups have been s e l e c t e d and w i l l be c i t e d as being t y p i c a l of t h a t category. The need f o r a system which does not f a l l i n t o one of the above groups should be evident a f t e r the d i s c u s s i o n of each of the * Numbers i n parentheses r e f e r t o appended r e f e r e n c e s . - 3 -- 4 -c a t e g o r i e s . (a) Data a c q u i s i t i o n systems are those systems which employ a sensor f i x e d at every l o c a t i o n where a measurement i s to be taken , and a s i g n a l a m p l i f i e r and r e c o r d i n g device which c o l l e c t s the data. Such a system i s described by Hahn et a l . (5). The system i n c l u d e s a 40 i n p u t channel scanner, each channel capable of being connected to only one sensor, a 40 thermocouple i n p u t , a magnetic and mechanical p r i n t - o u t , and a small computer. The cost of t h i s system i s around $10,000. The cost of the sensors alone i s h i g h , s i n c e f o r every parameter and at each l o c a t i o n where sampling o c c u r s , a sensor i s needed. The main advantages of t h i s system are t h a t the i n f o r m a t i o n at any and a l l sampling p o i n t s may be obtained almost i n s t a n t a n e o u s l y and the frequency of sampling i s n e a r l y u n l i m i t e d . The disadvantages are t w o f o l d . For those researchers who are not s o l e l y i n v o l v e d i n environmental data a c q u i s i t i o n or who are unable or do not wish t o i n v e s t so h e a v i l y , the cost of the data a c q u i s i t i o n system i s too great. The m o b i l i t y of the system i s a l s o l i m i t e d , s ince the w i r i n g of a l l the sensors back to the r e c o r d i n g u n i t o f t e n r e s u l t s i n a huge s p i d e r web, where the 40 channel scanner becomes the f l y ! Such a system works only w i t h sensors designed f o r the a m p l i f y i n g u n i t , and i n s t a l l a t i o n s are almost permanent. Another s i m i l a r type of system contains at every sampling l o c a t i o n , not only a sensor, but a l s o a measuring - 5 -instrument and the recorder outputs of each of the instruments i s fed i n t o m u l t i p o i n t chart r e c o r d e r s . Such work has been i n v e s t i g a t e d by Hand et a l . (6) who measured l i g h t and tempera-tur e i n the f o l l o w i n g way. "So l a r r a d i a t i o n f l u x d e n s i t y on a h o r i z o n t a l surface immediately above the l e a f canopy i s measured by means of nine e l e c t r i c a l l y matched Moll-Gurzinsky type s o l a r i m e t e r s " . On the same t o p i c of l i g h t measurement, "a u n i f o r m i t y t r i a l conducted on a b r i g h t sunny day i n mid-June revealed t h a t at midday there was a s i g n i f i c a n t v a r i a t i o n i n both N-S and E-W d i r e c t i o n s " . Quite l i k e l y nine s o l a r i m e t e r s were not enough t o give a good p i c t u r e of the l i g h t d i s t r i b u t i o n i n the greenhouse. The measurement of temperature was accomplished w i t h thermocouples "...on a m u l t i p o i n t chart r e c o r d e r " . M u l t i p o i n t chart recorders s u f f e r from the same drawbacks as the data a c q u i s i t i o n systems due to the many wires i n v o l v e d i n connecting the thermocouples to them. (b) Systems using a few sensors, to o b t a i n approximations of the environment are t y p i f i e d by a temperature sensor at •the a i r i n t a k e port of the greenhouse, and a second tempera-t u r e sensor at the exhaust p o r t . The d i f f e r e n c e i n tempera-t u r e between these two ports represents the gra d i e n t i n the greenhouse, which because of only two data p o i n t s must be considered l i n e a r . A l i n e a r g r adient i s h i g h l y u n l i k e l y i n any greenhouse. Thompson et_ a l . (14) de s c r i b e s such a system and - 6 -the c o n t r o l obtained through i t s use i n an a r t i c l e e n t i t l e d " P l a s t i c Covered Greenhouses Supply C o n t r o l l e d Atmospheres to C i t r u s Trees". "Temperature r i s e on hot days was 7°F. With outside ambient temperature at 104°F, exhaust a i r was 111°F". Measurement of the greenhouse environment employing t h i s system n e g l e c t s to i n c l u d e the p o s s i b i l i t y that areas i n the enclosure are h o t t e r than 111°F and others c o l d e r than 10U°F. Campbell et a l . (2) des c r i b e s a p o u l t r y b u i l d i n g ' housing an "environmental c o n t r o l system" as f o l l o w s : "The c o n t r o l l e d s t r u c t u r e -- a s t e e l b u i l d i n g 20 f t by 60 f t --the range of c o n t r o l l e d temperatures i s + 2 deg.". How were such small v a r i a t i o n s measured and c o n t r o l l e d through-out such a l a r g e b u i l d i n g ? "The minimum monitor r e c o r d i n g s recommended f o r an environmental c o n t r o l f a c i l i t y are (a) temperature of the c o n t r o l sensor, (b) humidity measured at the p o i n t of temperature c o n t r o l sensor ( a ) . " The i m p l i c a t i o n here i s tha t one temperature c o n t r o l sensor i s s u f f i c i e n t t o enable a + 2 deg temperature v a r i a t i o n at any l o c a t i o n i n the enclosure. The temperature and humidity measured at the c o n t r o l sensor i s assumed to be r e p r e s e n t a t i v e of c o n d i t i o n s throughout the b u i l d i n g . I t i s f e l t t h a t t h i s l i m i t e d i n f o r m a t i o n i s not an acceptable b a s i s f o r an "environmental c o n t r o l system". (c) Telemetry systems i n c l u d e some of the attempts which have been made t o t r a n s m i t temperatures from the bodies of - 7 -animals through the use of r a d i o s i g n a l s . The telemetry-approach i s a very good one, s i n c e i t e l i m i n a t e s a l l wires between the sensors and r e c o r d i n g u n i t (8, 12). These systems are best s u i t e d to temperature measurements using t h e r m i s t o r s , s i n c e the use of more complex sensors i s not p o s s i b l e . Due t o t h e i r s i m p l i c i t y , thermis-t o r s may be used i n small o s c i l l a t o r s or modulators, and a change i n temperature w i l l be r e f l e c t e d as e i t h e r a change i n s i g n a l frequency or amplitude. Any other sensor, which r e q u i r e s reference c u r r e n t s , such as a hot wire anemometer, would not lend i t s e l f e a s i l y to these c i r c u i t s . The measurement of temperatures at s e v e r a l l o c a t i o n s may be accomplished through the use of a d i f f e r e n t r a d i o frequency f o r each of the s i g n a l s t r a n s m i t t e d . This allows easy i d e n t i f i c a t i o n of the sensors. U n f o r t u n a t e l y a t r a n s m i t t e r and r e c e i v e r i s r e q u i r e d f o r every sensor which makes the system c o s t l y . (d) Non-automated systems have probably shown the most promising e f f o r t s i n r e a l i s t i c a l l y measuring the d i f f e r e n t c l i m a t i c g r a d i e n t s which e x i s t i n the greenhouse. Unfortun-a t e l y , t h i s approach r e q u i r e s a great d e a l of l a b o r and time, and because of the temporal element the r e s u l t s are d i f f i c u l t to i n t e r p r e t . The system u s u a l l y c o n s i s t s of at l e a s t two t e c h n i c i a n s , one h o l d i n g the sensor and the other the meter and r e c o r d i n g pad. Both t e c h n i c i a n s walk around the greenhouse sampling one v a r i a b l e a f t e r the other at - 8 -each l o c a t i o n . The use of t h i s technique i s described by Cotton (3) i n the study of the microclimate surrounding tomato plants i n the greenhouse. The r e s u l t s of his experiments show that c l i m a t i c gradients exist throughout the greenhouse and that one l o c a t i o n cannot adequately represent the true conditions. He concludes "the present measurements emphasize the large differences of temperature and humidity between the macroclimate and microclimate i n the presence of plants ...These differences pose a problem on the s i t i n g of instruments f o r the measurement and con-t r o l of the glasshouse climate...". The work involved i n taking multiple measurements i s tedious and indicates a need f o r a simple automated system for measuring and recording these c l i m a t i c gradients. DESIGN APPROACH Design C r i t e r i a As i n the case of most designs, the system described here i s the r e s u l t of many compromises. Before the a c t u a l design was achieved, i t was necessary to model an i d e a l system which would accomplish the task at hand, w i t h the preset r e s t r i c t i o n s on cost and complexity. The i d e a l system would i n c l u d e the f o l l o w i n g c r i t e r i a : a) the a b i l i t y to measure v a r i a b l e s at a l l sampling p o i n t s at about the same time, i n order t o a l l o w d i r e c t comparison of r e s u l t s ; b) the a b i l i t y to measure these v a r i a b l e s as o f t e n as p o s s i b l e , t o a l l o w minute to minute comparisons of r e s u l t s ; c) a minimum amount of w i r i n g w i t h i n the greenhouse (or other enclosure) to l i m i t cost and i n t e r f e r e n c e from equipment; d) a r e l a t i v e l y low c o s t , of approximately $1000 or l e s s . The data a c q u s i t i o n system, as described by Hahn et a l . (5) we 12. s a t i s f i e d a) and b) but has l i m i t a t i o n s due to the extensive w i r i n g requirements and high c o s t . A data a c q u i s i t i o n system i n i t s simplest and l e a s t expensive arrangement i s represented by System A i n Figure,1. I t c o n s i s t s of a number of sensors, corresponding a m p l i f i e r s , and a m u l t i - i n p u t r e c o r d i n g u n i t , having as many inputs as there are sensors (or a m p l i f i e r s ) . The sensors - 9 -FIGURE 1. A Systems Comparison - 10 -SYSTEM A .SAMPL/M3 SITE! RECORDING STATION SENSOR. I SENSOR 2. SENSOR "N" SYSTEM B S£L£C70; SWITCH I C A B L E I L . SELECTOR SW/TCH 2 I AMP. AMP. 2. AMP. "N" SIMPLE INPUT RECORD. SELECTOR SWITCH 3 JL SXNCJJ R_°^ L 2 EJ? J SAMPLING SITE. RECORDING STATION - 11 -are l o c a t e d at the sampling s i t e and the a m p l i f i e r s and re c o r d i n g u n i t at the r e c o r d i n g s t a t i o n . In System A, there i s a cable connecting each sensor to an a m p l i f i e r . The number of cables and t h e i r lengths become important f a c t o r s as the number of sensors and t h e i r d i s t a n c e from the r e c o r d i n g s t a t i o n i n c r e a s e s . The increased number of inputs to the r e c o r d i n g u n i t adds f u r t h e r c o m p l i c a t i o n s . The major advantage of the system i s that a continuous output from the sensors i s o b t a i n a b l e . System B (Figure 1) operates without a continuous recorder output. I t i s f e l t t h a t a continuous output from a sensor i s not e s s e n t i a l , but r a t h e r t h a t a s e r i e s of measurements over a p e r i o d of time would s u f f i c e i n e s t a b l i s h i n g a p a t t e r n . For example, 24 to 48 temperature measurements taken over a p e r i o d of 24 hours would be an adequate i n d i c a t i o n of the temperature v a r i a t i o n at t h a t p o i n t f o r the day. With t h i s i n mind, even though c r i t e r i a a) and b) are not f u l l y s a t i s f i e d an acceptable system can s t i l l be designed. At f i r s t , System B appears to be more complex than System A, but i t has the f o l l o w i n g advantages. The l i n k between the sampling s i t e and the r e c o r -ding s t a t i o n has been minimized from "n" cables i n System A t o only one cable i n System B. I t i s important t o note th a t t h i s s i n g l e cable does not c o n t a i n the sum of a l l the 'n' ca b l e s . The number of wires i n the cable i s independent - 12 -of the value of "n", and s o l e l y dependent on the number of wires going t o the sensor having the most e l e c t r i c a l connections. As a r e s u l t , whether one or f i f t y sensors are employed i n System B, only one cable i s r e q u i r e d . The s i m p l i f i c a t i o n of the w i r i n g i s accomplished by s y n c h r o n i z i n g the three s e l e c t o r switches, so t h a t only one sensor, one a m p l i f i e r - and the recorder are connected at the same time. A l l other sensors and a m p l i f i e r s are at t h i s time not connected. By advancing a l l s e l e c t o r switches at once, the next sensor, a m p l i f i e r and the recorder are made o p e r a t i o n a l . Another advantage of System B i s the incre a s e d m o b i l i t y of the components of the "sampling s i t e " r e s u l t i n g from the use of a s i n g l e c able. The sensors and S e l e c t o r Switch 1 (Figure 1) could be moved as a u n i t to the f i r s t sampling l o c a t i o n and a f t e r a s u i t a b l e sensor e q u i l i b r a t i o n time could be used t o record at a remote s t a t i o n the temperature and humidity at t h a t p o i n t , before r e p e a t i n g the sequence at the next l o c a t i o n . Consider the s i t u a t i o n of having to measure the temperature and humidity at f i v e l o c a t i o n s i n the green-house. System A would r e q u i r e the f o l l o w i n g : ( i ) f i v e temperature sensors ( i i ) f i v e humidity sensors, and ( i i i ) two cables from each of the f i v e l o c a t i o n s to the r e c o r d i n g s t a t i o n -- a t o t a l of ten cables . System B could be used t o o b t a i n the same data as th a t from System A i f the temperature and humidity sensors were moved from one l o c a t i o n to the other. System B then would r e q u i r e only: ( i ) one temperature sensor ( i i ) one humidity sensor, and ( i i i ) one c a b l e , and t h i s i s the key t o meeting c r i t e r i o n c ) . The movable sensors introduce a temporal e r r o r encountered i n some of the non-automated systems discussed e a r l i e r . The magnitude of the e r r o r can be reduced i f the sampling i s done r a p i d l y . This can be achieved through the use of a f a s t moving automatic t r a n s p o r t mechanism f o r the sensors and simple e l e c t r o n i c c i r c u i t s t o act as the s e l e c t o r switches mentioned i n Figure 1. Undoubtedly, time w i l l s t i l l be a f a c t o r t o consider i n the comparison of r e s u l t s . C r i t e r i o n d) may a l s o be approached by using System B i n Figure 1. Because System B has the p o t e n t i a l t o e l i m i n a t e a l l but the minimum number of sensors i n the a n a l y s i s of the environment, i t saves many d o l l a r s i n the cost of sensors alone. The added cost of e l e c t r o n i c c i r c u i t s used i n the s e l e c t o r switches of System B. i s e q u i v a l e n t to the cost of 8 l i g h t , 8 humidity and 8 temperature sensors. In summary, the system which meets a l l the present c r i t e r i a would c o n s i s t of s i x b a s i c u n i t s : 1, a package of sensors, comprised of one sensor type f o r every parameter to be measured, which i s e a s i l y moved throughout the greenhouse. - 14 -2. an a u t o m a t i c , s e l f - p r o p e l l e d c a r r i e r m e c h a n i s m f o r t h e s e n s o r p a c k a g e , t r a v e l l i n g p r e f e r a b l y i n a c o n -t i n u o u s c i r c u i t , 3. t h r e e s e l e c t o r s w i t c h e s , t h e number o f s w i t c h i n g p o s i t i o n s o f e a c h e q u a l t o t h e t o t a l number o f s e n s o r s t o be u s e d i n 1., 4. s e n s o r a m p l i f i e r s , one p e r s e n s o r t y p e i n 1., 5. one c a b l e c o n n e c t i n g t h e s e n s o r p a c k a g e and t h e m o v i n g c a r r i e r , 1. and 2., t o t h e s e n s o r a m p l i f i e r s , a n d 6. a r e c o r d i n g u n i t . Component S e l e c t i o n A b r i e f d i s c u s s i o n o f t h e f i n a l c h o i c e o f c o m p o n e n t s f o r e a c h o f t h e a b o v e u n i t s f o l l o w s . 1. I t was a s s u m e d t h a t i n o r d e r t o g e t a t h r e e d i m e n s i o n a l p i c t u r e o f t h e d i s t r i b u t i o n o f c l i m a t i c v a r i a b l e s i n t h e g r e e n h o u s e , i t w o u l d be n e c e s s a r y t o move t h e s e n s o r p a c k a g e n o t o n l y o v e r a h o r i z o n t a l p l a n e t h r o u g h o u t t h e e n c l o s u r e b u t a l s o v e r t i c a l l y . F o r e x a m p l e , i f m e a s u r e m e n t s a t t h r e e d i f f e r e n t h o r i z o n t a l p l a n e s a r e d e s i r e d , i t w o u l d r e q u i r e t h e s e n s o r p a c k a g e t o e i t h e r t r a v e l a l o n g t h e same c i r c u i t t h r e e t i m e s , o n c e a t e a c h l e v e l , o r t o t r a v e l t h e c i r c u i t o n c e and a t e a c h s t o p move t h e s e n s o r s t o e a c h o f t h e t h r e e l e v e l s b e f o r e p r o c e e d i n g t o t h e n e x t s t o p . T h i s t y p e o f s y s t e m w o u l d h a v e a v e r y l o w s a m p l i n g f r e q u e n c y , a n d f o r t h a t r e a s o n i t was d e c i d e d t o h a v e one s e n s o r p a c k a g e a t e a c h o f t h e t h r e e l e v e l s ; t h u s t h r e e p a c k a g e s o f s e n s o r s w o u l d move t h r o u g h t h e g r e e n h o u s e o n c e p e r c i r c u i t . - 15 -2. The c a r r i e r mechanism f o r the sensor packages should be a u t o m a t i c a l l y c o n t r o l l e d i n i t s movement from one sampling s i t e to another, so t h a t no human s u p e r v i s i o n i s necessary. I t should t r a v e l throughout the greenhouse av o i d i n g o b s t r u c t i o n s and guided i n such a way as t o c o n s i s -t e n t l y l o c a t e a sampling s i t e . The best guide f o r such a c a r r i e r would be a f i x e d t r a c k on which cues are mounted f o r the h a l t i n g of c a r r i e r movement at the sampling s i t e . I f a f t e r the stopping of the c a r r i e r a device i s a c t i v a t e d t h a t a f t e r a f i x e d time allows the c a r r i e r to move to the next s i t e , then the c a r r i e r becomes s e l f o p e r a t i n g . 3. Mechanical r o t a r y switches were not considered f e a s i b l e as s e l e c t o r switches, s i n c e the s y n c h r o n i z i n g of a l l s e l e c t o r switches i s v i t a l f o r the proper o p e r a t i o n of the sys.tem. To synchronize three mechanical r o t a r y s witches, remote from each other, could be a mechanical engineer's nightmare, and a switch "out of step" could be d i s a s t e r o u s . Contacts on r o t a r y switches are u n r e l i a b l e e l e c t r i c a l l y because of t h e i r dust and c o r r o s i v e s u s c e p t i b i l i t i e s . For these reasons, i t was decided t h a t reed r e l a y s , which have dust f r e e , enclosed c o n t a c t s , would be more a p p r o p r i a t e . Consequently, f o r every sensor used a r e l a y i s r e q u i r e d . The s h a f t r o t a t i o n of a mechanical r o t a r y switch i s r e p l a c e d by an e l e c t r i c a l impulse which c l o s e s the r i g h t r e l a y at the r i g h t time. D i g i t a l e l e c t r o n i c c i r c u i t s have been used f o r years i n s w i t c h i n g c i r c u i t s (a computer i s an example) but only r e c e n t l y have t h e i r p r i c e s dropped enough to make them r e a d i l y a v a i l a b l e . The s e l e c t o r switch c o n s i s t i n g of reed r e l a y s and d i g i t a l i n t e g r a t e d c i r c u i t s would f u n c t i o n as a c l e a n , a u t o m a t i c a l l y advancing r o t a r y s w i t c h . The added advantage of the i n t e g r a t e d c i c r u i t s i s t h a t they al l o w easy e l e c t r i c a l s y n c h r o n i z i n g of s e v e r a l s w i t c h i n g c i r c u i t s . The number of s w i t c h i n g p o s i t i o n s of the " e l e c t r o n i c r o t a r y s w i t c h " was chosen to be f i f t e e n , a number d i v i s i b l e by the three sensor packages mentioned i n 1., which allows f i v e sensors per package. The s e n s o r s , c a r r i e r mechanism, and the f i r s t of the three s e l e c t o r switches w i l l be r e f e r r e d to as a sensor module which i n c l u d e s a l l of the components a s s o c i a t e d w i t h the "sampling s i t e " of. System B (Figure 1). 4. The sensor a m p l i f i e r s r e q u i r e d i n the system would be those compatible w i t h the sensors being used i n the module. Only one a m p l i f i e r would be needed f o r every type of sensor used. Whether one or f i f t e e n temperature sensors are employed, i s not important i n the s e l e c t i o n of the a m p l i f i e r . What i s important i s t h a t temperature has been chosen as a sensor type. In both cases, only one temperature a m p l i f i e r i s needed. The same i s t r u e of a l l other sensors used. 5. The s i n g l e c a b l e , or t r a n s m i s s i o n c a b l e , which - 17 -i s u s e d i n t h i s s y s t e m c o u l d be c o n n e c t e d a t one e n d t o t h e m o d u l e a nd t h e o t h e r end t o t h e s e l e c t o r s w i t c h and a m p l i f i e r s . H o w e v e r , due t o s u p p o r t i n g r o o f s t r u c t u r e s i n most g r e e n h o u s e s , i t w o u l d be n e c e s s a r y t o f i x t h e c a b l e t o t h e t r a c k t o a l l o w t h e m o d u l e t o t r a v e l w i t h o u t r e s t r a i n t . A l l o w a n c e s w o u l d h a v e t o be made t o p e r m i t c o n n e c t i o n o f t h e s e n s o r s t o t h e t r a n s m i s s i o n c a b l e a t e a c h s a m p l i n g s i t e . The number o f w i r e s i n t h e c a b l e w i l l d e p e n d on t h e s e n s o r h a v i n g t h e maximum number o f e l e c t r i c a l c o n n e c -t i o n s . I f t h i s number w e r e "M", t h e n t h e number o f w i r e s i n t h e c a b l e w o u l d be M + 1. The e x t r a w i r e w o u l d be u s e d t o t r a n s m i t t h e s y n c h r o n i z i n g s i g n a l b e t w e e n t h e m o d u l e and t h e r e m a i n i n g s e l e c t o r s w i t c h e s . The t r a n s m i s s i o n c a b l e s h o u l d be e l e c t r i c a l l y s h i e l d e d , i n o r d e r t o m i n i m i z e s t r a y s i g n a l i n t e r f e r e n c e a t t h e s e n s o r a m p l i f i e r s . 6. The r e c o r d i n g u n i t c o u l d s i m p l y be a s i n g l e p e n c h a r t r e c o r d e r ; i t s i n p u t b e i n g c o n n e c t e d t o t h e t h i r d s e l e c t o r s w i t c h o f S y s t e m B ( F i g u r e 1 ) . S e l e c t o r s w i t c h e s 2 and 3 ( F i g u r e 1) w i l l be r e f e r r e d t o as t h e r e c o r d i n g s t a t i o n r e c e i v e r , w h i c h i n c l u d i n g t h e s e n s o r a m p l i f i e r s a n d r e c o r d e r make up t h e r e c o r d i n g s t a t i o n o f S y s t e m B. THE MODULE Overview of Operation The module c o n s i t s of a buggy (Figure 2) which t r a n s p o r t s the sensors from s t a t i o n to s t a t i o n w i t h i n the greenhouse along a f i x e d two r a i l t r a c k . The t r a c k i s 7 cm wide and can be suspended or mounted anywhere p r e f e r -ably to form a cl o s e d loop so th a t the buggy can run con-t i n u o u s l y . The module t r a v e l s along the t r a c k u n t i l i t reaches a sampling s i t e . Upon being stopped by a wedge, the fo r k connector (Figure 3) drops i n t o the mercury troughs mounted i n the t r a c k , and makes the module t o r e c e i v e r connection v i a the t r a n s m i s s i o n cable complete. The sensors e q u i l i -b r ate t o t h e i r new environment f o r the length of time (a v a r i a b l e ) preset i n the module c i r c u i t . A f t e r e q u i l i b r a -t i o n , the sensors are s e q u e n t i a l l y connected t o t h e i r r e s p e c t i v e a m p l i f i e r s , and the data i s recorded. The com-p l e t i o n of the r e c o r d i n g r e s u l t s i n the l i f t i n g of the f o r k from the troughs, and the advancement of the module t o the next sampling s i t e . General D e s c r i p t i o n The module i s b a s i c a l l y a t r o l l e y which besides the equipment needed f o r i t s own locomotion, c a r r i e s a box (Figure 2(E)) c o n t a i n i n g the e l e c t r o n i c c i r c u i t s which are - 18 -FIGURE 2. The M o d u l e A. M i c r o s w i t c h MS"1 B. M o t o r C. M o t o r r e v e r s i n g s w i t c h ( t e s t m o d e l o n l y ) D. S e n s o r c a b l e c o n n e c t o r s t r i p E. E l e c t r o n i c c i r c u i t b o x F. M i c r o s w i t c h MS2 G. T i m e r r e l a y H. R e l a y 16 I . F o r k l i f t e r s o l e n o i d J . S p r i n g s u s p e n s i o n a s s e m b l y 4 - 19 -FIGURE 3. Fork Connector ( i ) Fork connector A about to drop i n t o mercury trough B. ( i i ) Connection completed. ( i i ) - 21 -the heart of the environmental parameter sampling system. The module a l s o c a r r i e s the packages of sensors, which w i l l be used f o r the a n a l y s i s , supported at various e l e v a t i o n s under the t r o l l e y by r i g i d p l a s t i c t u b i n g . The sensor c a b l e s , l o c a t e d i n the t u b i n g , are connected to a connector s t r i p (Figure 2 ( D ) ) , and the sensors can then be p o s i t i o n e d at d i f f e r e n t l e v e l s as d e s i r e d . The t r a c k i s constructed by b o l t i n g two r a i l s of the type used f o r l a r g e suspended s l i d i n g doors t o g e t h e r , side by s i d e , t o o b t a i n a double r a i l e d t r a c k . The double r a i l was chosen over the s i n g l e r a i l because i t was b e l i e v e d that i t would l e s s e n the l a t e r a l wavering of the sensor packages by adding t o the s t a b i l i t y of the module. The t r a c k i s s e c u r e l y suspended from the c e i l i n g or r a f t e r s of the greenhouse. A w i n d s h i e l d wiper motor (Figure 2 ( B ) ) from an automobile i s used t o d r i v e one of the four wheels of the module. With the c h a i n , sprockets and wheels used i n t h i s p r o t o t y p e , a forward v e l o c i t y of approximately one fo o t per second i s obtained. Three of the wheels are i d l e r s , one of which has a s p r i n g suspension assembly (Figure 2 ( J ) ) which assures t h a t the four wheels are always i n contact w i t h the t r a c k . The motor as w e l l as the e l e c t r o n i c c i r c u i t s o b t a i n the power necessary f o r ope r a t i o n from a s m a l l power supply which a l s o r i d e s on the module. This a u x i l i a r y supply - 22 -i s s e r v i c e d by t h e m a i n p o w e r s u p p l y ( F i g u r e 4) w h i c h i s l o c a t e d a t t h e r e m o t e r e c o r d i n g s t a t i o n , w h e r e t h e d a t a i s c o l l e c t e d . T r a n s m i s s i o n o f t h e p o w e r f r o m t h e m a i n t o t h e a u x i l i a r y s u p p l y i s a c h i e v e d t h r o u g h t h e u s e o f t h e t r a c k i t s e l f a s one e l e c t r i c a l c o n d u c t o r , a n d a s e c o n d c o n d u c t i n g s t r i p ( F i g u r e 5 ( A ) ) r u n n i n g p a r a l l e l t o and on t h e i n s i d e o f one o f t h e r a i l s , a s t h e o t h e r . E l e c t r i c m o t o r b r u s h e s a r e u s e d t o p i c k up t h e c u r r e n t f r o m t h e s e t w o c o n d u c t o r s . The f u n c t i o n o f t h e e l e c t r o n i c c i r c u i t s i s t o c o n n e c t t h e f i f t e e n s e n s o r s on t h e m o d u l e one by one t o t h e i r r e s p e c t i v e s i g n a l a m p l i f i e r s w h i c h a r e a l l s i t u a t e d a t t h e r e c o r d i n g s t a t i o n t h r o u g h t h e u s e o f a minimum number o f w i r e s . The f a i r l y r e c e n t d e v e l o p m e n t o f i n e x p e n -s i v e i n t e g r a t e d c i r c u i t s commonly u s e d i n c o m p u t e r s makes an e l e c t r o n i c s w i t c h i n g d e v i c e t o a c c o m p l i s h t h i s t a s k , s i m p l e ' , c h e a p and c o m p a c t . The t r a n s m i s s i o n c a b l e ( F i g u r e 5 ( B ) ) w h i c h c o n t a i n s t h e w i r e s t h a t c a r r y t h e s i g n a l s f r o m t h e s e n s o r s t o t h e i r a m p l i f i e r s i s a t t a c h e d midway b e t w e e n t h e t w o r a i l s , ' and r u n s t h e f u l l l e n g t h o f t h e t r a c k . . I t i s n e c e s s a r y t o t a p i n t o t h i s c a b l e a t e a c h o f t h e s a m p l i n g s t a t i o n s a l o n g t h e t r a c k i n o r d e r t o make t h e c o n n e c t i o n o f s e n s o r s t o a m p l i f i e r s p o s s i b l e . S l i d i n g c o n t a c t s c o u l d be u s e d t o make t h e e l e c t r i c a l c o n n e c t i o n o f t h e s e n s o r s t o t h e t r a n s -m i s s i o n c a b l e b u t t h e v a r i a b i l i t y o f e l e c t r i c a l c o n t a c t 0 FIGURE 4. M a i n P o w e r S u p p l y - 23 -< > FIGURE 5. M e r c u r y T r o u g h s A. Power c o n d u c t i n g s t r i p B. T r a n s m i s s i o n c a b l e - 24 -- . -- 25 -r e s i s t a n c e o f o p e n s l i d i n g c o n t a c t s w h i c h a r e s u s c e p t i b l e t o c o r r o s i o n and d u s t c o l l e c t i o n was c o n s i d e r e d t o o g r e a t . A s o l i d - l i q u i d - s o l i d c o n n e c t o r c o n s i s t i n g o f two m e t a l s j o i n e d b y a m e r c u r y medium r e p l a c e d t h e s l i d i n g c o n t a c t a p p r o a c h . E a c h *of t h e w i r e s o f t h e t r a n s m i s s i o n c a b l e i s c o n n e c t e d t o i t s own s m a l l t r o u g h p a r t l y f i l l e d w i t h m e r c u r y a t t h e s a m p l i n g s i t e ( F i g u r e 5 ) . The t r o u g h s a r e m a c h i n e d i n t o a p i e c e o f p l e x i g l a s s a nd t h e p i e c e i s f a s t e n e d b e t w e e n t h e tw o r a i l s a t t h e s i t e . A c a b l e f r o m t h e m o d u l e ' s c i r c u i t r y i s t e r m i n a t e d a t one e n d by a f o r k c o n n e c t o r — a t e r m i n a l s t r i p h o u s i n g w i r e p r o n g s ( F i g u r e 3 ) . T h e s e p r o n g s when d r o p p e d i n t o t h e m e r c u r y t r o u g h s make t h e e l e c t r i c a l c o n n e c t i o n o f s e n s o r s : , t o a m p l i f i e r s c o m p l e t e . They a r e l i f t e d o u t o f t h e t r o u g h s by an arm a c t i v a t e d by a l i f t e r s o l e n o i d ( F i g u r e 2 ( i ) ) b e f o r e t h e m o d u l e moves t o i t s n e x t s a m p l i n g s i t e . The s w i t c h i n g o f a s e n s o r t o i t s p r o p e r a m p l i f i e r i s c o n t r o l l e d _ b y t h e i n t e g r a t e d c i r c u i t s o f t h e m o d u l e --t h e b r a i n o f t h e s y s t e m . H o w e v e r , o n c e t h e f i f t e e n s e n s o r s i g n a l s h a v e b e e n c o n v e r t e d i n t o one s i g n a l p a t h ( t h e w i r e s o f t h e t r a n s m i s s i o n c a b l e ) , t h e y must be d i v e r t e d a g a i n t o t h e i r R e s p e c t i v e a m p l i f i e r s a t t h e r e c o r d i n g s t a t i o n . F o r t h i s r e a s o n , a s i m i l a r c i r c u i t t o t h e m o d u l e c i r c u i t i s r e q u i r e d a t t h e r e c o r d i n g s t a t i o n a n d t h i s i s t h e r e c o r d i n g s t a t i o n r e c e i v e r ( F i g u r e 6 ) . T h i s u n i t r e c e i v e s f i f t e e n FIGURE 6. R e c o r d i n g S t a t i o n R e c e i v e r C i r c u i t Box - 27 -s i g n a l s one a f t e r t h e o t h e r a n d i t d o e s t h e r o u t i n g o f t h e s i g n a l t o i t s p r o p e r a m p l i f i e r . To s i m p l i f y t h e r e c e i v e r c i r c u i t , i t was a r b i t r a r i l y d e c i d e d t o d i v e r t t h e f i r s t t h r e e s e n s o r s i g n a l s t o one a m p l i f i e r , t h e n e x t t h r e e t o a n o t h e r , a n d s o o n , up t o t h e f i f t e e n t h . I n o r d e r f o r t h e s e n s o r s and a m p l i f i e r s t o be c o n n e c t e d a t t h e r i g h t t i m e , i t i s e s s e n t i a l t h a t t h e m o d u l e ' s s w i t c h i n g c i r c u i t s a r e s y n c h r o n i z e d w i t h t h o s e o f t h e r e c e i v e r ' s . A s y n c h r o n i z i n g s i g n a l w h i c h i s t r a n s m i t t e d v i a i t s own w i r e i n t h e t r a n s m i s s i o n c a b l e f r o m t h e m o d u l e t o t h e r e c e i v e r , a s s u r e s t h a t t h i s w i l l o c c u r . As w e l l as c o n n e c t i n g t h e s e n s o r s a n d a m p l i f i e r s t h e r e c e i v e r c o n n e c t s t h e i n d i v i d u a l a m p l i f i e r s t o t h e r e c o r d i n g u n i t one a t a t i m e . T h i s e l i m i n a t e s t h e i n t e r -f e r e n c e o f t h e o u t p u t o f one a m p l i f i e r w i t h t h a t o f a n o t h e r . I f a p e n r e c o r d e r i s u s e d a s t h e r e c o r d i n g d e v i c e , a s t r a i g h t h o r i z o n t a l l i n e w i l l be o b t a i n e d f o r t h e l e n g t h o f t i m e t h a t a s e n s o r i s c o n n e c t e d t o i t s a m p l i f i e r . T h i s t i m e may be v a r i e d by an a d j u s t m e n t i n t h e m o d u l e c i r c u i t . A d i g i t a l p r i n t - o u t o r m a g n e t i c r e c o r d i n g d e v i c e w h i c h may be t r i g g e r e d t o t a k e a r e a d i n g a t a g i v e n i n s t a n t w o u l d be much more c o n v e n i e n t s i n c e t r a n s f e r r i n g o f d a t a f r o m t h e c h a r t p a p e r w o u l d be u n n e c e s s a r y . D e t a i l s o f O p e r a t i o n The s m a l l r e g u l a t o r p o w e r s u p p l y m o u n t e d on t h e m o d u l e i s a l w a y s o n , s o l o n g a s t h e m a i n p o w e r s u p p l y i s o n . - 28 -The m a i n s u p p l y ( F i g u r e 4) o f f e r s 18 v o l t s t o t h e m o d u l e p o w e r s u p p l y , w h i c h p r o d u c e s a r e g u l a t e d 5 v o l t s , v i a t h e t r a c k o n w h i c h t h e m o d u l e t r a v e l s a n d t h r o u g h a m e t a l c o n -d u c t i n g s t r i p ( F i g u r e 5 ( A ) ) i n s u l a t e d f r o m t h e t r a c k . T h i s s t r i p i s t h e p o s i t i v e p o l e , and t h e t r a c k i s t h e n e g a t i v e as w e l l as a g r o u n d c o n n e c t i o n . The c u r r e n t i s p i c k e d up f r o m t h e t r a c k by c a r b o n b r u s h e s , o f t h e t y p e u s e d i n e l e c t r i c m o t o r s . A l l c i r c u i t s a r e o p e r a t e d on 5 v o l t s , due t o t h e l o w v o l t a g e r e q u i r e m e n t s o f t h e i n t e g r a t e d c i r c u i t s . The m o t o r a s w e l l as t h e l i f t e r s o l e n o i d f o r t h e f o r k c o n n e c t o r o p e r a t e on 5 v o l t s . F i g u r e 7 shows t h e b l o c k d i a g r a m o f t h e m o d u l e ' s c i r c u i t s . W h i l e t h e m o d u l e i s i n m o t i o n , m i c r o s w i t c h MSI ( F i g u r e 2 ( A ) , a n d F i g u r e 7) i s i n t h e n o r m a l l y c l o s e d ( N O p o s i t i o n , a n d r e l a y 16 ( F i g u r e 2 ( H ) , a n d F i g u r e 7) i s o p e n . The f o r k c o n n e c t o r i s i n t h e "UP" p o s i t i o n s i n c e t h e f o r k l i f t e r s o l e n o i d S I i s a c t i v a t e d . Due t o a m e c h a n i c a l c o n n e c t i o n , when t h e f o r k i s u p , MS2 ( F i g u r e 2 ( F ) , a n d F i g u r e 7) i s c l o s e d ; c o n s e q u e n t l y c u r r e n t i s s u p p l i e d t o t h e m o t o r w h i c h i s d r i v i n g t h e m o d u l e . B e c a u s e MSI i s i n t h e NC p o s i t i o n , no c u r r e n t i s b e i n g s u p p l i e d t o any o t h e r c i r c u i t s . When MSI i s t r i p p e d by t h e wedge ( F i g u r e 8 ( A ) ) u n d e r t h e t r a c k , i t assumes i t s n o r m a l l y o p e n (NO) p o s i t i o n . FIGURE 7. M o d u l e C i r c u i t B l o c k D i a g r a m - 29 -CONTACTS W.o. RCVV.A: y 0 / 5 H E * W£X i ; ». i N ' V . iwv. j > y y . , J i i •?£•. A Y ' O F . / - ' 5 ; ft ) T O / 5 A O U T P U T S £ To rb/c.< OUTPUT FIGURE 8. M i c r o s w i t c h Wedge A. Wedge B. Mercury t r o u g h s , bottom view - 31 -As s o o n as t h i s o c c u r s , no more c u r r e n t i s s u p p l i e d t o S I ( F i g u r e 7) o r t o t h e m o t o r , w h i c h r e s u l t s i n t h e s i m u l t a n -e o u s s t o p p i n g o f t h e m o d u l e a n d d r o p p i n g o f t h e c o n n e c t o r i n t o t h e m e r c u r y t r o u g h . A l s o , 5 v o l t s a r e s u p p l i e d t o t h e e q u i l i b r a t i o n t i m e r . A f t e r e q u i l i b r a t i o n , t h e t i m e r r e l a y ( F i g u r e 2 ( G ) , and F i g u r e 7) c l o s e s a n d c u r r e n t i s s u p p l i e d t o t h e r e s t o f t h e c i r c u i t s . The i n s t a n t t h a t c u r r e n t i s a p p l i e d t o t h e a u t o -m a t i c r e s e t c i r c u i t , t h e b i n a r y c o u n t e r i s r e s e t t o a r e f e r e n c e c o u n t , s o t h a t t h e s w i t c h i n g s e q u e n c e w i l l a l w a y s o c c u r i n t h e same o r d e r . R e s e t t i n g i s e s s e n t i a l f o r t h e p r o p e r o p e r a t i o n o f t h e s e q u e n c e . The s q u a r e wave g e n e r a t o r i s t h e p a c e s e t t e r f o r t h e s w i t c h i n g s e q u e n c e , and i t s f r e q u e n c y w i l l d e t e r m i n e t h e l e n g t h o f t i m e t h a t any s e n s o r i s c o n n e c t e d t o i t s a m p l i f i e r . S p e c i f i c a l l y , i t s e t s t h e s p e e d a t w h i c h t h e b i n a r y c o u n t e r c o u n t s . The b i n a r y c o u n t e r c o u n t s i n s e q u e n c e f r o m z e r o t o f i f t e e n ( i n b i n a r y f o r m ) a f t e r r e s e t t i n g , and i t i s t h e h e a r t o f t h e s w i t c h i n g s y s t e m . E a c h c o u n t r e p r e s e n t s a s p e c i f i c f u n c t i o n t o be e x e c u t e d , i n t h i s c a s e t h e c l o s i n g o f a s p e c i f i c r e l a y t o a l l o w a s e n s o r t o be c o n n e c t e d t o t h e t r a n s m i s s i o n c a b l e a n d t h e n t o i t s a m p l i f i e r . T h i s i s a c c o m p l i s h e d t h r o u g h t h e d e c o d e r a nd i n v e r t e r s . R e l a y 16 i s n o t c o n n e c t e d t o a s e n s o r , b u t r a t h e r t o MSI. I n t h e s w i t c h i n g s e q u e n c e , r e l a y 1 c l o s e s f o r t h e - 32 -l e n g t h o f t i m e d e t e r m i n e d by t h e s q u a r e wave g e n e r a t o r , a n d as r e l a y 1 o p e n s , r e l a y 2 c l o s e s f o r t h e same t i m e s p a n , and s o o n , u n t i l r e l a y 16 c l o s e s . The s i g n a l w h i c h t r i g g e r s t h e c l o s i n g o f r e l a y 16 i s a l s o c o n n e c t e d t o t h e b i n a r y c o u n t e r t h r o u g h a s e r i e s o f "OR" g a t e s . T h i s p r e v e n t s t h e c o u n t e r f r o m s t a r t i n g i t s c o u n t a t z e r o a g a i n w i t h t h e n e x t i n c o m i n g p u l s e f r o m t h e s q u a r e wave g e n e r a t o r . I t p u t s t h e c o u n t e r on " h o l d " a n d k e e p s r e l a y 16 c l o s e d . T h e c o n -t a c t s o f r e l a y 16 a r e c o n n e c t e d i n p a r a l l e l w i t h M S I , and t h e i r c l o s i n g s u p p l i e s c u r r e n t t o s o l e n o i d S I . The m o t o r w i l l n o t be a c t i v a t e d u n t i l m i c r o s w i t c h MS2 i s c l o s e d , i . e . when t h e f o r k i s i n t h e UP p o s i t i o n . T h i s p r e v e n t s damage t o t h e p i n s : o f t h e c o n n e c t o r by c o m p l e t e l y r e m o v i n g t h e c o n n e c t o r f r o m t h e m e r c u r y t r o u g h s b e f o r e a d v a n c i n g t h e m o d u l e . The s i g n a l w h i c h s y n c h r o n i z e s t h e s w i t c h i n g s e q u e n c e o f t h e m o d u l e w i t h t h e r e c e i v i n g s t a t i o n s e q u e n c e i s o b t a i n e d f r o m t h e i n p u t t o t h e b i n a r y c o u n t e r , c o n s e q u e n t l y when t h e c o u n t e r i s s t o p p e d by t h e a c t i v a t i o n o f r e l a y 1 6 , t h e s y n c h r o n i z i n g s i g n a l t o t h e r e c e i v i n g s t a t i o n i s a l s o h e l d . The s w i t c h i n g s e q u e n c e o c c u r s a s d e s c r i b e d a b o v e o n l y when t h e r o t a r y s w i t c h ( F i g u r e 7) i s i n p o s i t i o n 1 6 . The f u n c t i o n o f t h i s s w i t c h i s t o a d d t o t h e v e r s a t i l i t y o f t h e c i r c u i t s b y m a k i n g t h e number o f f u n c t i o n s v a r i a b l e f r o m - 33 -0 t o 15. F o r example, i f we were o n l y i n t e r e s t e d i n t a k i n g t h r e e s e n s o r r e a d i n g s , we would s e t t h e r o t a r y s w i t c h t o p o s i t i o n 4, so t h a t on the f o u r t h c o u n t , t h e module would be advanced t o t h e n e x t s t a t i o n . T h i s speeds up t h e c y c l e by a v o i d i n g u n n e c e s s a r y s w i t c h i n g . The r o t a r y s w i t c h i s n o t e s s e n t i a l , however, and may be o m i t t e d . The d e t a i l w i r i n g diagrams and s c h e m a t i c s o f t h e module a r e shown i n F i g u r e s 9 t h r o u g h 14. The r e l a y s shown i n F i g u r e 13 a r e a l l o f t h e s i n g l e p o l e t y p e . The s e n s o r s i n t h i s case must a l l have two w i r e s g o i n g t o them. T h i s i s t r u e o f s e n s o r s such as t h e r m i s t o r s and some h u m i d i t y s e n s o r s . I f a s e n s o r r e q u i r e d t h r e e w i r e s t o be c o n n e c t e d t o i t ( e . g . h u m i d i t y ) , a d o u b l e p o l e r e l a y would have t o be used i n p l a c e o f a s i n g l e p o l e . F u r t h e r m o r e , one a d d i t i o n a l w i r e would have t o be used i n t h e t r a n s m i s s i o n c a b l e , and one a d d i t i o n a l prong added t o t h e f o r k c o n n e c t o r . However, w i t h p r o p e r f o r e s i g h t t h i s i s no p roblem. By s e t t l i n g on t h e maximum number o f w i r e s one would e x p e c t f o r a s e n s o r ( a hot w i r e anemometer r e q u i r e s s i x ) t h e r e l a y s and t r a n s -m i s s i o n c a b l e can be chosen b e f o r e h a n d . For example, i f a t r a n s m i s s i o n c a b l e o f seven w i r e s , a f o r k c o n n e c t o r o f seven p r o n g s , and f i v e p o l e r e l a y s are u s e d , up t o f i f t e e n h o t - w i r e anemometer s e n s o r s c o u l d be used. ( T h i s added i n i t i a l expense a v o i d s t h e g r e a t i n c o n v e n i e n c e o f c h a n g i n g w i r e s and r e l a y s s h o u l d one d e c i d e t o c o n v e r t from a two - 34 w i r e s e n s o r t o a t h r e e o r more w i r e t y p e ) . W i t h t h e same a r r a n g e m e n t , f i f t e e n t h e r m i s t o r s o r f i f t e e n l i g h t s e n s o r o r h u m i d i t y s e n s o r s , o r any c o m b i n a t i o n o f t h e a b o v e w o u l d be p o s s i b i l i t i e s f o r s a m p l i n g , as l o n g as t h e number o f w i r e s t o e a c h s e n s o r d i d n o t e x c e e d s i x . The a d v a n t a g e o f t h i s s y s t e m i s t h a t t h e c o m p l e x w i r i n g i s l i m i t e d t o t h e m o d u l e a n d t h e r e c e i v i n g s t a t i o n r a t h e r t h a n t h e i n t e r c o n n e c t i o n b e t w e e n t h e t w o . T h i s c o m p l e x w i r i n g c a n be f u r t h e r s i m p l i f i e d t h r o u g h u s e o f p r i n t e d c i r c u i t r y . FIGURE 9. M o d u l e R e g u l a t o r S u p p l y W i r i n g D i a g r a m - 35 --+/8v O — To CourAcr BRUSHES 47. -hSv —O To MS/ I5QOJ2. FIGURE 10. S e n s o r E q u i l i b r a t i o n T i m e r and V a r i a b l e S q u a r e Wave G e n e r a t o r . - 36 -6,6k o . P E i - A Y j TIME*. ' O ? R E L A Y - , A^i- RESHYAUCZii A R E W S P £ . C T ; k D OTHERWISE T I M E R D £ £ - A V . - i.6-7oese. F,<E3. RANSE-'- AO IS,- A O H Z . _ n _ n _ To CoofjTE-R FIGURE 11. M o d u l e W i r i n g D i a g r a m , I n t e g r a t e d C i r c u i t s o n l y / - 37 -© © ® AND +5v © ® <*) ® ® RESET O e-SYMC. o OUTPUT /4 J~T_ O— INPUT F 9 3 9 3 r I I l SI T~I r O TO ROTAgY S W I T C H 2^1 F93II I ) F 9 0 / 6 14 1 FSOI6 ~1 F9QIB © @ © A M D R E L A Y S FIGURE 12. R o t a r y S w i t c h W i r i n g D i a g r a m TO INVERTED OUTPUTS <D <@ o 0 9 0 9 9 0 o Q o o 0 0 9 9 o rt 6 6 o \ o -o o--a — T — W \ A 0 a R E L A Y /6 r o M/CRO-sw jrc r t , MS/ 00 CO O ro P I W /a "OR."<3AT£ FIGURE 13. M o d u l e R e l a y W i r i n g D i a g r a m - 39 -0 © ® SENSOR I SENSOR 2 P rO SENSOR 3 O f ;0 ^ 7 -SENSOR IS » -O SENSOR 0 OUTPUTS 0 a o » ( / 5 Ms FIGURE 14. A u t o m a t i c R e s e t f o r t h e M o d u l e - 40 -+ 5 v -a a NOTE-R E S I S T A N C E S A R E IN O H M S R E S I S T O R S AF?£ \/4 W A T T UNLES5 S P E C I F I E D OTHERWISE. RECORDING STATION RECEIVER O v e r v i e w o f O p e r a t i o n The r e c o r d i n g s t a t i o n r e c e i v e r i s e s s e n t i a l l y t h e s l a v e o f t h e s e n s o r m o d u l e . I t s o p e r a t i o n i s d e t e r m i n e d by t h e s y n c h r o n i z i n g s i g n a l o b t a i n e d f r o m t h e m o d u l e c i r c u i t . B e c a u s e o f t h e p r e s e n t mode o f o p e r a t i o n , w h e r e we assume t o h a v e f i v e d i f f e r e n t t y p e s o f s e n s o r s , t h r e e o f e a c h , we must h a v e f i v e d i f f e r e n t t y p e s o f a m p l i f i e r s . T h r e e s e n s o r s must be c o n n e c t e d i n s e q u e n c e t o one a m p l i f i e r , t h e n t h r e e more t o a n o t h e r a m p l i f i e r , and s o o n . The r e c o r d i n g s t a t i o n d o e s j u s t t h a t , a s w e l l a s c o n n e c t i n g t h e a m p l i f i e r t o t h e r e c o r -d i n g d e v i c e , s o t h a t a t any t i m e o n l y one s e n s o r i s h o o k e d t o i t s a m p l i f i e r , a n d o n l y t h a t a m p l i f i e r i s c o n n e c t e d t o t h e r e c o r d i n g d e v i c e . The r e c o r d i n g o f t h e s e n s o r s i g n a l o c c u r s a s s o o n as t h e s e n s o r and a m p l i f i e r a r e c o n n e c t e d . D e t a i l s o f O p e r a t i o n The b l o c k d i a g r a m f o r t h e r e c o r d i n g s t a t i o n i s shown i n F i g u r e 15. W i t h no s i g n a l a t t h e " s y n c h . " i n p u t , t h e a u t o m a t i c r e s e t c i r c u i t k e e p s t h e d i v i d e by 3 and d i v i d e b y 5 c i r c u i t s i n t h e i r r e f e r e n c e p o s i t i o n s , i . e . w h i l e t h e m o d u l e . i s m o v i n g f r o m one s a m p l i n g l o c a t i o n t o a n o t h e r . W i t h t h e f i r s t i n c o m i n g s y n c h , s i g n a l t h e d i v i d e b y 3 and d i v i d e by 5 c i r c u i t s b e g i n f u n c t i o n i n g . The d i v i d e b y 3 c i r c u i t a d v a n c e s t h e d i v i d e by 5 c i r c u i t ( b a s i c a l l y a b i n a r y c o u n t e r s i m i l a r t o t h e one i n t h e m o d u l e ) b y one c o u n t o n l y - 41 -FIGURE 15. R e c o r d i n g S t a t i o n B l o c k D i a g r a m - 42 -A B SENSOR IMPUTS AMP F74 DIV/I ©Y *2-3 F9390 DIVIDE BYS F9301 I OF lO DEC-OOSR FOo 16 RE££> AMR3 AUTO. RESET RECOPblNG DEVICE - 43 -a t e v e r y t h i r d s y n c h , s i g n a l t h a t comes i n . I n o t h e r w o r d s , t h e s w i t c h i n g a t t h e r e c e i v e r o c c u r s o n l y one t h i r d as f a s t as i t d o e s i n t h e m o d u l e . Thus i t a l l o w s t h r e e s i m i l a r s e n s o r s s e q u e n t i a l l y t o be h o o k e d t o one a m p l i f i e r , a nd o n l y t h e n w i l l t h e n e x t g r o u p o f s e n s o r s be c o n n e c t e d t o t h e i r a m p l i f i e r . D e t a i l e d w i r i n g d i a g r a m s and s c h e m a t i c s f o r t h e r e c e i v e r a r e shown i n F i g u r e s 16 t h r o u g h 18. The m a i n p o w e r s u p p l y s c h e m a t i c i s shown i n F i g u r e 1 9 . The i n t e g r a t e d c i r c u i t s i n F i g u r e 16 c a n n o t meet t h e p o w e r r e q u i r e m e n t s t o o p e r a t e two r e l a y s , s o t r a n s i s t o r r e l a y d r i v e r s ( F i g u r e 17) a r e u s e d . One r e l a y c o n n e c t s t h e s e n s o r t o t h e a m p l i f i e r , w h i l e t h e o t h e r c o n n e c t s t h e a m p l i f i e r t o t h e r e c o r d i n g d e v i c e . FIGURE 16. R e c o r d i n g S t a t i o n R e c e i v e r W i r i n g D i a g r a m , I n t e g r a t e d C i r c u i t s o n l y - 44 -TO RELAY I ' DRlVflP IKIPUT5 FIGURE 17. R e c e i v e r R e l a y s and R e l a y D r i v e r s - 45 -2 o FIGURE 18. A u t o m a t i c R e s e t f o r R e c o r d i n g S t a t i o n R e c e i v e r - 46 -NOTE: RE1SISTA/VCE S A R E |N O H M S R E S I S T O R S A R E 1/4 W A T T UNLESS SPECIF \ E D OTHERWISE. •fSv -© 2.2K O RE5ET OUT FIGURE 19. M a i n Power S u p p l y W i r i n g D i a g r a m //Ov AC / AMP SLOW/- Blow To TRACK To RECEIVE.]*. -P TESTING THE SYSTEM • E x p e r i m e n t A The o n l y e r r o r s w h i c h m i g h t be e n c o u n t e r e d i n t h e o u t p u t d a t a o f t h i s s y s t e m w h i c h ' c a n n o t be c o r r e c t e d by c a l i b r a t i o n o f t h e s e n s o r s a r e t h o s e w h i c h m i g h t o c c u r a s a r e s u l t o f a b a d c o n n e c t i o n b e t w e e n t h e s e n s o r and i t s a m p l i f i e r . S i n c e t h e m e r c u r y c o n n e c t o r i s t h e o n l y p l a c e w h ere a v a r i a t i o n o f c o n t a c t r e s i s t a n c e s h o u l d be f o u n d , a t e s t was made on t h e r e p r o d u c i b i l i t y o f t h e r e s i s t a n c e o f a s e n s o r - t o - a m p l i f i e r c o n n e c t i o n . A d i g i t a l ohm m e t e r ( W e s t o n 1240) was c o n n e c t e d a t t h e r e c e i v e r s t a t i o n w h e r e n o r m a l l y t h e s e n s o r ' s a m p l i f i e r w o u l d b e . The m o d u l e was a l l o w e d t o go t h r o u g h i t s n o r m a l p r o c e d u r e by a p p r o a c h i n g t h e m e r c u r y c o n n e c t o r a n d d r o p p i n g t h e p r o n g s i n t o t h e t r o u g h s , t h e n s w i t c h i n g i n t h e s e n s o r s and a d v a n c i n g . The r e s i s t a n c e o f a dummy s e n s o r was m e a s u r e d t h r o u g h t h e s w i t c h i n g s y s t e m e v e r y t i m e t h e m o d u l e s t o p p e d a t t h e s a m p l i n g s t a t i o n . The t e s t was r e p e a t e d f i f t e e n t i m e s . The r e s i s -t a n c e v a r i e d + 0.5 ohms o v e r t h e f i f t e e n r e a d i n g s . T h i s d o e s n o t i m p l y t h a t t h e v a r i a t i o n o b t a i n e d f r o m s t a t i o n t o s t a t i o n w i l l be a s s m a l l as t h e v a r i a t i o n a t a s i n g l e s t a t i o n . B u t , any v a r i a t i o n i n r e a d i n g s due t o c h a n g e i n t r a n s m i s s i o n c a b l e l e n g t h f r o m s t a t i o n t o s t a t i o n c a n be r e a d i l y c o r r e c t e d m a t h e m a t i c a l l y . S e n s o r s c o n n e c t e d t o t h e - 48 -- 49 -m o d u l e , a nd s u s p e n d e d u n d e r i t , showed t h a t r e s u l t s f r o m a g i v e n s a m p l i n g s t a t i o n w e r e o b t a i n a b l e i n t h e i r p r o p e r s e q u e n c e and were r e p r o d u c i b l e . C a l i b r a t i o n o f t h e s e n s o r s was o m i t t e d i n t h e t r i a l and c o n s e q u e n t l y t h e r e s u l t s a r e n o t r e p o r t e d . E x p e r i m e n t B Due t o t h e t o x i c e f f e c t t h a t m e r c u r y v a p o r s h a v e o n some p l a n t s , i t was p r o p o s e d t h a t a l a y e r o f t h i n l u b r i c a t i o n o i l c o v e r i n g e a c h m e r c u r y t r o u g h w o u l d s u b s t a n -t i a l l y r e d u c e e v a p o r a t i o n o f m e r c u r y . I t was n e c e s s a r y , t h e n , t o s t u d y t h e e f f e c t o f t h e o i l l a y e r a d d i t i o n on t h e m e r c u r y t r o u g h r e s i s t a n c e r e p r o d u c i b i l i t y . A dummy s e n s o r h a v i n g a 105.5 ohm r e s i s t a n c e o u t o f c i r c u i t , was p l a c e d o n t h e m o d u l e as i n E x p e r i m e n t A. Ten t r i a l s w e r e p e r f o r m e d u s i n g no o i l and t h e n t e n more w i t h t h e o i l c o v e r i n g t h e t r o u g h s . The l a c k o f r e p r o d u c i b i l i t y o f t h e r e s i s t a n c e s , due t o t h e a d d e d o i l , i s e v i d e n t by c o m p a r i n g t h e r e s u l t s l i s t e d i n T a b l e I . The r e s u l t s o f t h i s e x p e r i m e n t i n d i c a t e t h a t t h e a d d i t i o n o f o i l t o t h e m e r c u r y p r o d u c e s r a n d o m i n c r e a s e s i n t h e c o n d u c t o r r e s i s t a n c e , a n d s h o u l d n o t be u s e d f o r t h a t r e a s o n . - 50 -TABLE 1. E f f e c t o f O i l L a y e r on M e r c u r y T r o u g h R e s i s t a n c e R e s i s t a n c e (ohms) o f T r i a l Dummy S e n s o r i n C i r c u i t no o i l l u b . o i l 1 105.8 106.3 2 105.6 117.4 3 105.7 107.5 4 105.6 111.1 5 105.6 127.1 6 105.6 105.9 7 105.6 106.8 8 105.8 106.0 9 105.6 108.9 10 105.6 110.7 Mean = 105.6 Mean = 110.8 S t d . D e v i a t i o n = 0.0 850 S t d . D e v i a t i o n = 6.726 S t d . E r r o r o f S t d . E r r o r o f Mean = 0.0269 Mean = 2.127 DISCUSSION The s e n s i n g m o d u l e was d e s i g n e d t o p r o v i d e a s y s t e m f o r t r a n s p o r t i n g f i f t e e n e n v i r o n m e n t a l s e n s o r s f r o m l o c a t i o n t o l o c a t i o n i n a g r e e n h o u s e . A t e a c h l o c a t i o n , a f t e r a s u i t a b l e e q u i l i b r a t i o n t i m e , t h e m o d u l e c o n n e c t s t h e s e n s o r s t o t h e i r a p p r o p r i a t e a m p l i f i e r s l o c a t e d a t a r e m o t e r e c o r d i n g s t a t i o n . The m o d u l e w i l l f u n c t i o n w i t h a w i d e v a r i e t y o f s e n s o r s many o f w h i c h a r e n o r m a l l y a v a i l a b l e i n e n v i r o n m e n t a l l a b o r a t o r i e s . The mo d u l e h a s b e e n k e p t as f l e x i b l e as p o s s i b l e w i t h a d j u s t m e n t s b e i n g e a s i l y made i n t h e number and t y p e o f s e n s o r s , t i m e a l l o t t e d f o r e q u i l i b r a t i o n a n d t h e t i m e e a c h s e n s o r i s c o n n e c t e d t o i t s a m p l i f i e r . O r i g i n a l l y t h e d e s i g n was i n t e n d e d f o r u s e i n g r e e n h o u s e s , b u t i t s v e r s a t i l i t y s h o u l d e n a b l e i t s u s e i n o t h e r a g r i c u l t u r a l b u i l d i n g s s u c h as p o u l t r y b a r n s , w h e r e e n v i r o n m e n t a l g r a d i e n t s e x i s t a n d c o u l d be m o n i t o r e d . The t o t a l c o s t o f a c o m p l e t e s y s t e m c a n n o t be e s t i m a t e d , s i n c e i t w i l l v a r y w i t h t h e s e n s o r s , a m p l i f i e r s , r e c o r d i n g d e v i c e s and l e n g t h o f t r a c k u s e d . H o w e v e r , t h e m a t e r i a l c o s t o f t h e t r a n s m i t t e r , r e c e i v e r a n d c a r r i e r i s a p p r o x i m a t e l y $ 5 0 0 . The c o s t o f t h e two r a i l e d t r a c k i s a b o u t one d o l l a r p e r f o o t , n o t i n c l u d i n g t h e t r a n s m i s s i o n c a b l e . The l a r g e s t p e r c e n t a g e o f t h e c o s t o f t h e - 51 -- 52 -t r a n s m i t t e r and r e c e i v e r i s b o r n e by t h e m u l t i p l e r e e d r e l a y s . A l t h o u g h t h e s u r f a c e a r e a o f t h e m e r c u r y t r o u g h s i s o n l y 1/8 s q i n c h , i t i s f e l t t h a t due t o e v a p o r a t i v e l o s s o f m e r c u r y t o t h e g r e e n h o u s e a t m o s p h e r e , t h e s y s t e m s h o u l d n o t be u s e d i n b u i l d i n g s c o n t a i n i n g p l a n t s w h i c h a r e v e r y s e n s i -t i v e t o m e r c u r y v a p o u r s , s u c h as r o s e s . A d e q u a t e v e n t i l a t i o n i s p r e s e n t l y t h e b e s t m e t h o d o f p r e v e n t i n g t h e a c c u m u l a t i o n o f m e r c u r y v a p o u r s . The t e m p o r a l e r r o r s i n t r o d u c e d as t h e r e s u l t o f s e q u e n t i a l s a m p l i n g o f l o c a t i o n s t h r o u g h o u t t h e g r e e n h o u s e c o u l d p o s s i b l y be e l i m i n a t e d . I f one w e r e t o u s e a r e f e r e n c e s e t o f s e n s o r s and c ompare a l l o t h e r r e s u l t s w i t h t h i s r e f e r e n c e , one c o u l d e l i m i n a t e t h e i n h e r e n t e r r o r r e s u l t i n g f r o m t h e e l a p s e d t i m e b e t w e e n s a m p l e s . F o r e x a m p l e , a l i g h t s e n s o r l o c a t e d o u t s i d e t h e g r e e n h o u s e c o u l d be u s e d as a r e f e r e n c e s e n s o r , w h i c h w o u l d r e c o r d t h e p r e s e n c e o f a c l o u d r a p i d l y p a s s i n g o v e r t h e s u n . T h u s , a d a r k e n e d a r e a i n t h e g r e e n h o u s e c o u l d be i d e n t i f i e d a s s u c h due t o t h e p a s s i n g c l o u d , r a t h e r t h a n an a r e a w h i c h i s a l w a y s d a r k e r t h a n i t s s u r r o u n d i n g s . I t i s a l s o p o s s i b l e t o a v e r a g e t h e r e s u l t s a t a g i v e n s a m p l i n g p o i n t o v e r p a r t o f , o r an e n t i r e d a y , and c o m p a r i n g t h i s a v e r a g e w i t h t h e a v e r a g e a t a n o t h e r s a m p l i n g p o i n t , t h u s s h o w i n g a n y t r e n d s a t t h e l o c a t i o n s . The s a m p l i n g f r e q u e n c y o f t h e s y s t e m i s p r i m a r i l y - 53 -d e p e n d e n t on t h e s e n s o r s a n d a m p l i f i e r s u s e d . The s e n s o r -t o - c l i m a t e e q u i l i b r a t i o n t i m e i s s o l e l y d e p e n d e n t on t h e s e n s o r w i t h t h e g r e a t e s t t i m e c o n s t a n t , a n d t h e s w i t c h i n g t i m e f r o m one s e n s o r t o a n o t h e r w i l l d e p e n d on t h e a m p l i f i e r r e q u i r i n g t h e l o n g e s t s e n s o r - t o - a m p l i f i e r e q u i l i b r a t i o n t i m e . The s e n s o r - t o - a m p l i f i e r e q u i l i b r a t i o n t i m e i s t h e p e r i o d m e a s u r e d f r o m t h e i n s t a n t t h e s e n s o r i s c o n n e c t e d t o t h e p o i n t w h e r e t h e a m p l i f i e r o u t p u t h a s r e a c h e d 99% o f i t s f i n a l v a l u e . I t i s c o n c e i v a b l e t h a t i f a l l s e n s o r s u s e d h a d a one s e c o n d t i m e c o n s t a n t o r l e s s and a one s e c o n d s e n s o r - t o - a m p l i f i e r e q u i l i b r a t i o n t i m e , 20 s e c o n d s w o u l d be ample f o r t h e s e n s o r s t o e q u i l i b r a t e and 15 m e a s u r e m e n t s t o be made a t t h e s a m p l i n g s i t e . I f t h e t r a v e l l i n g d i s t a n c e i s a p p r o x i m a t e l y 10 f e e t b e t w e e n s i t e s , t h e n a t a v e l o c i t y o f one f o o t p e r s e c o n d , 15 s a m p l i n g s o f t h e e n v i r o n m e n t c o u l d be o b t a i n e d e v e r y 30 s e c o n d s a t a new l o c a t i o n i n t h e g r e e n h o u s e . I n a s m a l l g r e e n h o u s e , t h i s c o u l d mean 150 m e a s u r e m e n t s p e r t r a v e l l i n g c i r c u i t , e a c h c i r c u i t r e q u i r i n g 5 m i n u t e s . The r e s u l t s c o u l d a l m o s t be i n t e r p r e t e d as a c o n t i n u o u s o u t p u t f r o m f i x e d s e n s o r s . More r e a l i s t i c a l l y one s h o u l d e x p e c t a p p r o x i m a t e l y 30 s e c o n d s e q u i l i b r a t i o n t i m e a n d 10 s e c o n d s s w i t c h i n g t i m e and 20 s e c o n d s t r a v e l l i n g t i m e p e r s i t e . Thus w i t h 10 s i t e s , m e a s u r e m e n t s a t a g i v e n s i t e a r e r e p e a t e d e v e r y 10 m i n u t e s . The t o t a l d i s t a n c e c o v e r e d i n t h a t t i m e w o u l d - 54 -be 200 f e e t . The c o m b i n a t i o n s are u n l i m i t e d ; t h e t i m e v a l u e s s t a t e d h e r e are o n l y some examples r a t h e r t h a n f i x e d v a l u e s . The system has approached t h e i d e a l e n v i r o n m e n t a l parameter s a m p l i n g system w i t h r e s p e c t t o c o s t , c o m p l e x i t y and v e r s a t i l i t y more c l o s e l y t h a n any o t h e r s mentioned i n p r e v i o u s p u b l i c a t i o n s . I t i s b e l i e v e d t h a t t h e compromises r e a c h e d a r e w e l l w o r t h t h e s a v i n g s i n c o s t o f more complex d a t a a c q u i s i t i o n s ystems, and t h a t t h i s system w i l l a l l o w more r e s e a r c h e r s t o c a r e f u l l y examine t h e i r greenhouse e n v i r o n m e n t s t h r o u g h t h e use o f i n s t r u m e n t s w h i c h a r e a l r e a d y a t t h e i r d i s p o s a l . R E C O M M E N D A T I O N S T h e r e a r e some i m p r o v e m e n t s i n t h e d e s i g n o f t h i s s y s t e m w h i c h may be i n c o r p o r a t e d i n t o a w o r k i n g s y s t e m . T h e s e p r o p o s e d c h a n g e s h a v e come f r o m t h e c o n s t r u c t i o n and t e s t i n g o f t h e p r o t o t y p e . The m e r c u r y t r o u g h c o n n e c t o r i s p r o b a b l y t h e most c o n t r o v e r s i a l d e s i g n a s p e c t o f t h e s y s t e m . The r e s u l t s o f E x p e r i m e n t A i n d i c a t e t h a t s e n s o r s s h o u l d be c h o s e n whose c a l i b r a t i o n i s n o t s i g n i f i c a n t l y a l t e r e d by a + 0.5 ohm l e a d w i r e r e s i s t a n c e c h a n g e . A s p e c i f i c e x a m p l e i s t h e c h o i c e o f a t h e r m i s t o r w h i c h h a s a 50 ohm c h a n g e i n r e s i s -t a n c e p e r d e g r e e a t 2 5°C. The e r r o r i n t r o d u c e d due t o t h e m e r c u r y t r o u g h c o n n e c t i o n w o u l d be + 0.01°C. T h i s t y p e o f t h e r m i s t o r i s common, an d i d e a l . W i t h t h e same t h e r m i s t o r , and a t r a n s m i s s i o n c a b l e c o n t a i n i n g 2 2 gauge (Awg) c o p p e r w i r e s , h a v i n g a r e s i s t a n c e o f 16.46 ohms p e r 1000 f e e t , w o u l d p r o d u c e o n l y a 0.33°C i n c r e a s e o v e r t h e e n t i r e 1000 f e e t . T h i s means t h a t f o r t h i s t y p e o f s e n s o r and c a b l e , c o r r e c t i o n f o r a c h a n g e i n t r a n s m i s s i o n c a b l e l e n g t h i s p r o b a b l y n o t n e c e s s a r y . The u s e o f o i l t o d e c r e a s e e v a p o r a t i v e l o s s o f m e r c u r y , i n s p i t e o f t h e r e s u l t s o f E x p e r i m e n t B, s h o u l d be s t u d i e d . I t i s p o s s i b l e t h a t w i t h a c h a n g e o f m a t e r i a l u s e d f o r t h e p r o n g s , s u c h a s a h i g h l y p o l i s h e d s t a i n l e s s s t e e l , t h e amount o f o i l a d h e r i n g t o t h e p r o n g s w o u l d - 55 -- 56 -l e s s e n . A l s o , d e e p e n i n g t h e t r o u g h s and i n c r e a s i n g t h e m e r c u r y t o o i l r a t i o m i g h t h e l p i n s t r i p p i n g o f f t h e o i l as t h e p r o n g s e n t e r t h e m e r c u r y . A l s o , t h e t r o u g h s u r f a c e a r e a o f 1/8 s q i n c h i f d e c r e a s e d by a r e f i n e m e n t i n t h e c o n n e c t i n g p r o c e d u r e o r d e s i g n w o u l d c e r t a i n l y l e s s e n e v a p o r a t i o n . I t i s a l s o p o s s i b l e t o t r y a d i f f e r e n t l i q u i d as t h e medium o r t o t r y a c o m p l e t e l y d i f f e r e n t c o n n e c t o r . The p r o t o t y p e m o d u l e i s q u i t e h e a v y b e i n g c o n -s t r u c t e d p r i m a r i l y o f s t e e l . S i n c e t h e m o d u l e must c a r r y o n l y t h e t r a n s m i t t e r a n d i t s own p r o p u l s i o n e q u i p m e n t , r i g i d p l a s t i c w o u l d p r o b a b l y s u f f i c e as t h e c o n s t r u c t i o n m a t e r i a l . I f a r r a n g e m e n t o f m o t o r , t r a n s m i t t e r , c o n n e c t o r a nd c a b l e c o u l d be a c c o m p l i s h e d t o a l l o w t h e m o d u l e t o be s u p p o r t e d by a m o n o r a i l , and l a t e r a l w a i v e r i n g c o u l d be e l i m i n a t e d , t h i s w o u l d s i m p l i f y t h e c o n s t r u c t i o n o f t h e t r a c k , e s p e c i a l l y t h e c u r v e s , a n d w o u l d r e d u c e t h e c o s t o f t h e t r a c k by a h a l f . A m a j o r t e c h n i c a l i m p r o v e m e n t i n t h e module w o u l d be t o o p e r a t e t h e m o t o r and l i f t e r s o l e n o i d by t h e m a i n p o w e r s u p p l y ( i . e . u s e 18 v o l t s as o p p o s e d t o t h e i r o p e r a t i n g f r o m t h e r e g u l a t e d 5 v o l t s u p p l y i n t h e m o d u l e c i r c u i t ) . S i n c e t h e maximum c u r r e n t d r a i n i s p r o d u c e d by t h e s e t w o e l e c t r i c a l d e v i c e s , t h e p o w e r t r a n s i s t o r i n t h e r e g u l a t e d - 57 -module power s u p p l y c o u l d be made s m a l l e r and i t would o p e r a t e a t a lo w e r t e m p e r a t u r e r e q u i r i n g a s m a l l e r heat d i s s i p a t i o n a r e a f o r t h e t r a n s i s t o r . The proposed a l t e r a t i o n has a second advantage. The cue f o r the i n t e g r a t e d c i r c u i t s i n t h e module t o r e s e t t h e m s e l v e s i s the t u r n i n g o f f and t u r n i n g on o f t h e power s u p p l i e d t o them. A s u p p l y v o l t a g e drop below a t h r e s h o l d w i l l be i n t e r p r e t e d by the i n t e g r a t e d c i r c u i t s as the r e s e t s i g n a l . Such a v o l t a g e drop o c c u r s f o r a f r a c t i o n o f a second when t h e motor and s o l e n o i d a re t u r n e d on. I f t h e s e two d e v i c e s are c o n n e c t e d t o t h e same power s u p p l y as t h e i n t e g r a t e d c i r c u i t s , once i n a w h i l e , t h e module w i l l send i t s i n f o r m a t i o n t o t h e r e c o r d i n g s t a t i o n , advance a f r a c t i o n o f an i n c h ( j u s t f a r enough so t h a t t h e f o r k s have passed the mercury t r o u g h s ) and t h e n s t o p and drop the f o r k . The module w i l l " m e n t a l l y " go t h r o u g h i t s c o u n t s one more t i m e and th e n advance t o t h e n e x t s t a t i o n . S i n c e t h e o c c u r r e n c e o f such a c c i d e n t a l s t o p s i s low and the r e s u l t i s o n l y a few e x t r a seconds added t o t h e t r a v e l l i n g t i m e from one s t a t i o n t o t h e o t h e r , the problem i s not con-s i d e r e d c r i t i c a l . I t may be e l i m i n a t e d by e i t h e r c o n n e c t i n g t h e motor and s o l e n o i d t o t h e i r own 5 v o l t s u p p l y , o r choose t h e s e two d e v i c e s so t h a t t h e y a re c o m p a t i b l e w i t h t h e main power s u p p l y v o l t a g e . I n e i t h e r c a s e , t h e v o l t a g e drop which o c c u r s when t h e d e v i c e s a r e t u r n e d on w i l l n o t a f f e c t t h e s e n s i t i v e i n t e g r a t e d c i r c u i t s . REFERENCES 1. A l d r i c h , R.A. and J.W. White (1969). S o l a r r a d i a t i o n and p l a n t growth i n greenhouses. Trans. Amer. Soc. Agr. Eng. 12(1): 90-93. 2. Campbell, L.C. and L.M. Lucas (1968). An environmental c o n t r o l system f o r p o u l t r y research f a c i l i t i e s . Trans. Amer. Soc. Agr. Eng. 11(3): 376-379. 3. Cotton, R.F. (1969). Some measurements of micro-climate i n a glasshouse with a tomato crop. J . Agr. Eng. Res. 14(2): 154-164. 4. Germing, G.H. and D. Bokhorst (1968). Methodology of comparison of greenhouse types. T e c h n i c a l Communications ISHS ( 7 ) : 24-3 5. 5. Hahn, L. , W.D. C l a r k , and T.E-. Bond (1970). Data a c q u i s i t i o n i n environmental research. J . Amer. Soc. Agr. Eng. Si(3) : 137. 6. Hand, D.W. and G.E. Bowman (19 69). Carbon d i o x i d e a s s i m i l a t i o n measurement i n a c o n t r o l l e d environment glasshouse. J . Agr. Eng. Res. 14(1): 92-99. 7. Hoffman, G.J. and S.L. Rawlins (1970). 'Design and performance of s u n l i t c l i m a t e chambers. Trans. Amer. Soc. Agr. Eng. 13(5): 656-660. 8. Kato, D.S., W.L. R o l l e r and H.S. Teague (1970). Temperature telemetry from swine. J . Amer. Soc. Agr. Eng. 51(11): 652. 9. M a c N e i l l , M.M. (1969). A glasshouse having a number of compartments v/ith i n d i v i d u a l c o n t r o l of the environment. J . Agr. Eng. Res. 14(1): 74-77. 10. Manbeck, H.B. and R.A. A l d r i c h (1967). A n a l y t i c a l determination of d i r e c t s o l a r energy t r a n s m i t t e d by r i g i d p l a s t i c greenhouses. Trans. Amer. Soc. Agr. Eng. 10(4): 564-567. 11. Reece, F.N. and J.W. Deaton (1969). Low cost r a d i o t r a n s m i t t e r s f o r t e l e m e t e r i n g chicken body temperatures. Trans. Amer. Soc. Agr. Eng. 12(3): 326-328. - 58 -- 59 -12. Selcuk, M.K. (1969). A n a l y s i s design and performance e v a l u a t i o n of c o n t r o l l e d environment greenhouses. Environmental Research Lab., U n i v e r s i t y of Arizon a . 13. Takakura, T., K.A. Jordan and L.L. Boyd (1969). Dynamic s i m u l a t i o n of pla n t growth and environment i n the greenhouse. Amer. Soc. Agr. Eng. Winter Meeting, Paper No. 69-942. 2 4 Thompson, CR. and P.C. Taylor (1966). P l a s t i c covered greenhouses supply c o n t r o l l e d atmospheres t o c i t r u s t r e e s . Trans. Amer. Soc. Agr. Eng. 9(3): 338-339. 15. Walker, J.M. (1965). P r e d i c t i n g temperature i n v e n t i l a t e d greenhouses. Trans. Amer. Soc. Agr. Eng. 8(3): 445-448. 16. Walker, J.M. and D.J. Co t t e r (1968). Condensation and r e s u l t i n g humidity i n greenhouses c u r i n g c o l d weather. Trans. Amer. Soc. Agr. Eng. 11(2): 263-266. 17. Walker, J.N. and L.R. Walton (1971). E f f e c t of condensa-t i o n on greenhouse heat requirement. Trans. Amer. Soc. Agr. Eng. 14(2): 282-284. 

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