VIASYS Vmax Encore, Техническое справочное руководство

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Technical Reference Manual
Vmax Encore
L2707
2–25
Chapter 2 System Description
BAROMETRIC PRESSURE CIRCUITRY
The barometric pressure transducer is comprised of a silicon chip with an integral sensing
diaphragm and four piezoresistors encased in a plastic housing and mounted on the Mass Flow
Sensor Board. Pressure applied to the diaphragm causing it to flex, changing the resistance, which
results in a low level output voltage proportional to pressure. The sensing resistors are connected
as a four-active-element bridge for linearity and sensitivity.
Figure 2-14 Barometric Pressure Signal Conditioning Circuitry
The barometric pressure transducer is a temperature compensated pressure sensor with a 0 - 15
PSI (0-776 mm Hg) sensing range. The supply voltage for the sensor is +10 V dc supplied by the
reference voltage generator circuitry also on the Mass Flow Sensor Board. The maximum output
voltage is –100 mV and the per-volt sensitivity is –6.67 mV.
The signal conditioning circuitry for the pressure sensor consists of 4 op-amps. The first two
stages, U13-A and U13-B, are used as a null compensator for the sensor offset. The third stage,
U13-C, is the offset amplifier used as an adjustment to match the output voltage to barometric
pressure. The input of this stage is to the op-amp’s negative input, inverting the output voltage. The
forth stage, U13-D, is a gain amplifier. The output voltage at TP1 should be barometric pressure/10.
Example:
If the barometric pressure is 751 mm Hg, then the output voltage at TP1 should be +7.51 V dc.