
3.6.3.2 Measuring cell for differential pressure and flow rate
① Inlet pressure P
+
⑥ Overload diaphragm
② Pressure cap ⑦ Filling liquid
③ O-ring ⑧ Seal diaphragm
④ Measuring cell body ⑨ Inlet pressure P
-
⑤ Differential pressure sensor
Figure 3-8 Function chart of the measuring cell for differential pressure and flow rate
●
Differential pressure is transmitted to the differential pressure sensor ⑤ through the seal
diaphragms ⑧ and the filling liquid ⑦.
● When measuring limits are exceeded, the seal diaphragm ⑧ is displaced until the seal
diaphragm ② rests on the measuring cell body ④. The differential pressure sensor ⑤ is
thus protected against overloading since no further deflection of the overload diaphragm
⑥ is possible.
● The seal diaphragm ⑧ 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
3.6 Functional principle
SITRANS P, DS III series with HART
26 Operating Instructions, 09/2012, A5E00047092-08
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