Digital temperature controller

Details Digital temperature controller Digital temperature controller

G - Physics

05

D

341/32.31

G05D 21/02 (2006.01) G05B 11/28 (2006.01) G05D 23/24 (2006.01)

Patent

CA 1047141

DIGITAL TEMPERATURE CONTROLLER ABSTRACT OF THE DISCLOSURE A temperature control assembly for a centrifugal chemical treatment apparatus of the type having a temperature monitoring thermistor and a rotor heater. The heater is energized from a power source through a solid state relay. The thermistor is con- nected in a temperature Wheatstone bridge which delivers a volt- age signal to a digital voltmeter. The digital voltmeter generates a binary output which is compared in a computer with a digital com- mand signal from a keyboard unit. The binary computer is a programmed function of the difference between the keyboard digital temperature command signal and the voltmeter output. This computer output controls a variable duty cycle multivibrator stage which pro- vides a relay-operating signal whose "on" time is in accordance with the difference between the keyboard command temperature and the dig- ital voltmeter output signal. This operating signal is delivered to the relay via an over-temperature and failure detector receiving signals form the digital voltmeter. The relay is held open if forbid- den signals are received, such as signals of incorrect polarity, over-range signals, signals resulting from a meter defect, signals resulting from a shorted or open thermistor, or the like. The same reference voltage is used for the digital voltmeter and the tempera- ture Wheatstone bridge so that changes in reference voltage do not affect the voltmeter reading. The bridge is designed so that the bridge output in volts is equal to 1/100 of the temperature in degress Centigrade to facilitate display, over the specified design temperature range. The voltmeter is of a type providing forbidden signal outputs, including over-range, wrong polarity, overload, etc. -1-

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