A Logarithmic Response Resistor-Capacitor Telemetry Modulator.
Nelson L. Buck · Defense Technical Information Center (DTIC) · 1975
A unique electronic circuit has been developed for use in a rocket-borne temperature sonde to convert a thermistor resistance to a modulation frequency for telemetry application. The modulator's frequency versus resistance curve drifts less than 4% as the temperature of the electronics varies from +60C to -60C. The drift is easily corrected by including a reference circuit in the sonde. The modulator can be made almost entirely insensitive to power supply voltage changes, and can be made to dissipate less than 0.1-microwatt power in the thermistor without degrading resolution, temperature stability, or voltage stability. Because it passes alternating current through the thermistor, it possesses a nearly logarithmic frequency versus resistance curve with a resistor-capacitor (R-C) network instead of a transistor.