
4.4.2.6
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 with 4 to 20 mA/HART
Operating Instructions, 11/2019, A5E44852162-AC
37