A simple pressure sensor signal conditioning circuit

A simple signal conditioning circuit should allow the output of the amplifier to be independent of the sensor used, provide interchangeability and high level output and be low cost. Laser-trimmed resistors on the sensor compensation board adjust the gain of the external amplifier to normalize it to changes in pressure sensitivity. The signal conditioning circuit shown in the figure provides a precision constant current source for sensor excitation and an instrumentation amplifier whose gain is controlled by the feedback resistor R in the sensor. For detailed discussion of compensation circuits and output voltages other than 0-5V, please refer to TN-001 and APP-103 to APP-105

signal conditioning circuit

The current source is controlled by the ±1% bandgap reference diode VR, and the reference current I0 is defined by the following formula:

I0=（E0-e0）/R2

Among them: E0-diode reference voltage: 1.235V±1% (LM385)eo---offset of amplifier A1 R2---feedback resistor value

By selecting amplifier A1 with an offset voltage less than 1mV and resistor R2 with a tolerance of ±1%, a current I0=0.996MA can be generated, with a typical accuracy of ±1.4%. The gain adjustment resistor r is adjusted to R3=R4=100K and a 2V differential output. If zero adjustment is required, use OP227 instead of LT1013 amplifier and add zero potentiometer P1. The zero voltage is ±4mV relative to an input with a differential bias of less than 0.5mV, which leaves about ±3.5mV of zero to compensate for typical sensor offsets (less than ±1mV).