A simple signal conditioning circuit should allow the output of the amplifier to be independent of the sensor used, providing interchangeability and high-level output at low cost. The laser resistor on the compensation board of the sensor adjusts the gain of the external amplifier to normalize it with the change of pressure sensitivity. The signal conditioning circuit shown in the figure provides a precise constant current source for the excitation of the sensor and an instrument amplifier whose gain is controlled by the feedback resistor R in the sensor. For detailed discussion of compensation circuit and output voltage other than 0-5V, please refer to tn-001 and app-103 to app-105
Signal conditioning circuit
The current source is made up of ± The reference diode with 1% band gap is controlled by VR, and the reference current I0 is defined by the following formula:
Where: E0 diode reference voltage: 1.235V ± 1% (lm385) eo — offset of amplifier A1 R2 — feedback resistance value
The amplifier A1 with offset voltage less than 1mV and tolerance of 0 ± If the resistance R2 is less than 1%, the current I0 = 0.996ma can be produced, and the typical accuracy is ± 1.4%。 The gain adjusting resistor R is adjusted to R3 = R4 = 100k, a 2V differential pressure output. If zero adjustment is required, use op227 instead of lt1013 amplifier and add zero potentiometer P1. When the bias of zero position voltage relative to differential hearing is less than 0.5mv, the input voltage is zero ± 4MV, which is a typical value of sensor offset (less than ± 1 MV) ± The zero position of 3.5mv needs compensation.