Temperature Control Programs to Select the Optimal Control Input for a Precision Water Bath

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Programs to control the temperature of a precision water bath for versatile uses are reported in which optimal control inputs were selected. Some popular instruments and hand-made interface circuits were used. The hardware was simplified as possible, and the temperature of the bath water was controlled to be kept within a narrow range of fluctuation in the software. The heat exchange of the bath with the surroundings, nonstationary heat flow from warm stirrer motors, and other thermal factors were considered to be a part of heat sources. Cooling water a little lower than the set temperature was circulated in the water bath. The difference between the observed temperature and the set temperature was acquired to a small microcomputer every second via a thermistor used as a temperature sensor. The thermal behavior of the bath water was simulated by a Newtonian cooling equation. From several data points, the temperature to be acquired at the next point was calculated by the method of least squares, and the control input was given to the heater element after power amplification. The programs were written in BASIC and amounted to about 5kbyte. The temperature was controlled within ±3〜4×10^<-4>K at 25℃ and 37℃, and the range was almost the same as that previously reported, or narrower.
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