Drive circuit for variable resistance transducers - uses linear current amplifier producing current proportional to variable resistance of e.g. resistance thermometer

摘要

A drive circuit for use with a variable resistance transducer, such as a variable resistance platinum wire thermometer, produces a current, typically in the range 4 to 20 mA proportional to the resistance with offset line zero or not as required. - Basically, a transistor constant current source (1) supplies current (J1) to the variable resistance concerned (3) while a linear current amplifier (2) produces a current (J2) proportional to the voltage across that resistance. The two currents, one constant (J1) and one process dependent (J2) are summed in the supply cables (a, b) and monitored (5a, 5b) to give a live zero characteristic. A compensated null zero circuit can be built by incorporating a further constant current generator in the arrangement at the power source (4).