Siemens SITRANS P DS III - Measuring Cell for Differential Pressure and Flow Rate

Description
3.6 Principle of operation
SITRANS P DS III with PROFIBUS PA
30 Operating Instructions, 06/2013, A5E00053276-07
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.