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UBC Theses and Dissertations

A polarcardiograph computer Park, William Keith Rae


Vectorcardiograms have proved useful in the diagnosis of heart disorders. However, such information as the variation of the magnitude and angle of the vector with time is not directly obtainable from a vectorcardiogram. An electronic device which would present the magnitude and angle of the vector as continuous functions of time, or "polarcardiograph" as it is named, would be useful in electrocardiographic research. It is shown that such a device, which must compute the polar co-ordinates of points from their respective Cartesian coordinates, can be constructed if analogue multipliers, subtractors and adders are available as well as a two-phase sinusoidal voltage source and a device for generating a voltage proportional to the phase difference of two sinusoidal signals. A search of the literature revealed that a similar de-vice had already been constructed, the major difference between it and the present machine being the manner in which multiplication is achieved. The principal difficulty involved in the design of the computer was the development of a simple and accurate multiplier using a pentagrid tube. A mathematical analysis of the dependence of the plate current on the two control-grid voltages was made to determine the operating conditions under which such a tube has an output voltage proportional to the product of the two input voltages. The polarcardiograph was built using the pentagrid-tube multipliers, and when tested proved to have an overall accuracy-well within that required for normal electrocardiographic purposes.

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