Digitization of Carrier-Excited Transducers using a Programmed Attenuator

A precision analog-to-digital converter has been developed for use in measuring parameters which appear as carrier output voltages from transducers. The analog-to-digital conversion is accomplished by means of a successive-approximation technique in which the unknown output of a transducer is matched to that of a precision relay-operated attenuator. A common a.c. carrier supply source is used for both the transducer and the attenuator so that any change in the excitation voltage does not affect the measurement accuracy. This also eliminates the necessity for a standard voltage source for the attenuator. The time required for digitization in the system described is 30 milliseconds, precision is one part in 3,000, and the sensitivity of the comparator device is such that a 5-microvolt change in the unknown voltage representing the parameter being measured is easily detected.