Siemens SITRANS P - Measuring Cell for Gauge Pressure, Front-Flush Membrane; Measuring Cell for Absolute Pressure from the Gauge Pressure Series

4.4.2.2 Measuring cell for gauge pressure, front-flush membrane






S
H
① Reference pressure opening ⑤ Filling liquid
② Measuring cell ⑥ Gauge pressure sensor
③ Process connection p
e
Inlet pressure
④ Seal diaphragm
Figure 4-8 Function chart of the measuring cell for gauge pressure, flush mounted diaphragm
The inlet pressure (p
e
) is
transferred to the gauge pressure sensor ⑥ via the seal diaphragm
④ and the filling liquid ⑤, displacing its measuring diaphragm. The displacement changes the
resistance of the four piezoresistors (bridge circuit) of the gauge pressure sensor. The change
in the resistance causes a bridge output voltage proportional to the inlet pressure.
Pressure transmitters with measuring span ≤ 63 bar measure the inlet pressure against
atmosphere, those with measuring spans ≥ 160 bar the inlet pressure against vacuum.
4.4.2.3 Measuring cell for absolute pressure from the gauge pressure series





S
H
① Measuring cell ④ Filling liquid
② Process connection ⑤ Absolute pressure sensor
③ Seal diaphragm P
e
Inlet pressure
Figure 4-9 Function chart of measuring cell for absolute pressure
Description
4.4 Functional principle
SITRANS P320/P420 with 4 to 20 mA/HART
34 Operating Instructions, 11/2019, A5E44852162-AC