4.4.3.6 Measuring cell for differential pressure and flow rate
① Inlet pressure P
+
⑥ Filling liquid
② Pressure cap ⑦ Seal diaphragm
③ O-ring ⑧ Inlet pressure P
-
④ Measuring cell body ⑨ Differential pressure sensor
⑤ Overload diaphragm
Figure 4-12 Function chart of the measuring cell for differential pressure and flow rate
● Differential pressure is transmitted to the differential pressure sensor ⑨ through the seal
diaphragms ⑦ and the filling liquid ⑥.
● When measuring limits are exceeded, the seal diaphragm ⑦ is displaced until the seal
diaphragm rests on the measuring cell body ④. The differential pressure sensor ⑨ is thus
protected against overloading since no further deflection of the overload diaphragm ⑤ is
possible.
● The seal diaphragm ⑦ is displaced by the differential pressure. The displacement changes
the resistance of the four piezoresistors (bridge circuit) of the differential pressure sensor.
● The change in the resistance causes a bridge output voltage proportional to the differential
pressure.
Description
4.4 Functional principle
SITRANS P320/P420 (mA/HART)
Operating Instructions, 06/2018, A5E44852162-AA 35
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