Linearised platinum resistance thermometer circuit - uses optical coupler between input and bridge with linearising feedback resistor

摘要

The thermometer circuit comprises a reference voltage source with reference current resistor (R) connected to one input of an operational amplifier. The amplified output is connected via an optical coupler (2) to a measuring bridge comprising a differential amplifier (3) and platinum resistance sensor (RT). The output of the differential amplifier is fed back to the input to the first amplifier and to the photo-transistor of the opto-coupler via a linearising resistor (RO). The relationship between the output voltage variation of the differential amplifier and the resistance variation of the sensor is given by dV = K alpha dR+K (d R/Ro)dV. The circuits deliver an output voltage which varies linearly with temp.