ANALOG TO DIGITAL CONVERSION BY MEASURING THE RATIO OF RC TIME CONSTANTS

摘要

MIL-200 4F7 The present invention is a technique for forming a digital signal representing an environmental condition. The technique consists of measuring the variable time constant of an analog sensing device having a variable resistance dependent upon the environmental condition and a capacitor as well as measuring the reference time constant of a precision fixed resistor and the same capacitor. The time constants are measured by discharging the capacitor, charging the capacitor through the appropriate element and measuring the time for the voltage across the capacitor to reach a predetermined level. Lastly, the digital ratio between the two time constants is formed. This digital ratio is the digital representation of the environmental condition sensed by said analog sensing device.