Siemens SITRANS P - Measuring Cell for Absolute Pressure from the Differential Pressure Series

4.4.2.5 Measuring cell for absolute pressure from the differential pressure series
S
H







① Pressure cap ⑥ Overload diaphragm
② Seal diaphragm on the measuring cell ⑦ Measuring cell filling liquid
③ O-ring ⑧ Reference pressure
④ Measuring cell body p
e
Pressure input variable
⑤ Absolute pressure sensor
Figure 4-11 Function chart of measuring cell for absolute pressure
● Absolute pressure is transmitted to the absolute pressure sensor ⑤ through the seal
diaphragm ② and the filling liquid ⑦.
● When
measuring
limits are exceeded, the overload diaphragm ⑥ is displaced until the seal
diaphragm ② rests on the measuring cell body ④. The seal diaphragm thus protects the
absolute pressure sensor ⑤ from overload.
● The difference between the inlet pressure (p
e
) and the reference pressure ⑧ on the
negative side of the measuring cell displaces the seal diaphragm ②. The displacement
changes the resistance of the four piezoresistors (bridge circuit) of the absolute pressure
sensor.
● The change in the resistance causes a bridge output voltage proportional to the absolute
pressure.
Description
4.4 Functional principle
SITRANS P320/P420 with 4 to 20 mA/HART
36 Operating Instructions, 11/2019, A5E44852162-AC