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Electronic measurement system

Image Number 7 for United States Patent #3942123.

An electronic method and apparatus for measuring temperatures by means of a thermistor in one arm of an electrical bridge, bridge output being varied by the on and off duty cycle of a shunting impedance selectively switched into and out of the balancing arm of the bridge in accordance with the relative states of a counting display register and a cyclically scanned counting register, the display register state being altered by gated pulses, under the control of bridge output, to provide a digital indication of measured temperature. Bridges of both the nulling and non-nulling types are disclosed using either a dual ramp integrator or conventional detector acting upon bridge output to provide an impedance measurement subsystem independent of reference supply voltage and also enabling non-linear analog to digital conversion to compensate for a non-linear thermistor temperature vs. thermistor resistance characteristics, without sacrificing measurement sensitivity. Anticipation circuitry is provided for monitoring and correlating the display register pulses with the time vs. temperature response characteristic of the thermistor, to selectively alter bridge balance and display register state so as to provide an advance indication of the anticipated temperature at which the termistor will finally stabilize.

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