
4.4.3.2
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.
4.4.3.3
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 (mA/HART)
32
Operating Instructions, 06/2018, A5E44852162-AA