IMPROVED IMSTRUMENTATION SYSTEM

摘要

An instrument system includes a voltage regulator (10) using as a pass element a field effect device (36) connected as an unity voltage gain amplifier and a feedback control amplifier (38) coupled to the pass element which is powered solely from the regulated voltage; a bridge (14) having a first switch (108) for coupling various load impedances to the bridge and a second switch (94) cooperating with the first switch to couple the bridge output to the selected load impedance; a phase shifting network coupled to the bridge (14) for providing a predetermined phase shift which is substantially independent of frequency over a range of frequencies; and/or an instrument system response time controlling circuit having a low pass filter (19) utilizing a variable synthesized capacitance (186) to effect changes in response time. The instrument system provides improved simplicity and reliability of operation, and is particularly useful as a radio frequency admittance responsive system for monitoring the condition of materials, such as the level of materials in a vessel.