Siemens SITRANS P300 Operating Instructions Manual page 22

Description
3.6 Mode of operation
Measuring cell for gauge pressure
Figure 3-6
(1)
(2)
(3)
(4)
(5)
(6)
p
e
The input pressure (p
diaphragm (4) and the fill liquid (5), displacing its measuring diaphragm. The displacement
changes the resistance value of the four piezo resistors in the measuring diaphragm in a
bridge circuit. The change in the resistance causes a bridge output voltage proportional to
the input pressure.
The transmitters with spans ≤ 63 bar measure the input pressure against atmosphere, those
with spans ≥ 160 bar against vacuum.
3-8
Function chart of measuring cell for gauge pressure
Reference pressure
Measuring cell
Process connection
Separating diaphragm
Fill liquid
Gauge pressure sensor
Input pressure
) is transferred to the gauge pressure sensor (6) via the seal
e
SITRANS P300 with HART communication
Operating Instructions, 06/2005, A5E00359579-02