Siemens SITRANS P - Manual (Page 31)

SITRANS P measuring instruments for pressure
Transmitters for food, pharmaceuticals and biotechnology
SITRANS P300 for gage and absolute pressure
2/31 Siemens FI 01 · 2009
2
Measuring cell for gage pressure
Measuring cell for gage pressure, function chart
The input pressure (p
e
) is transferred to the gage pressure sen-
sor (6) via the seal diaphragm (4) and the filling liquid (5), dis-
placing 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 pres-
sure.
The transmitters with spans ≤ 63 bar measure the input pressure
against atmosphere, those with spans ≥ 160 bar against
vacuum.
Measuring cell for absolute pressure
Measuring cell for absolute pressure, function chart
The input pressure (p
e
) is transferred to the absolute pressure
sensor (5) via the seal diaphragm (3) and the filling liquid (4),
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 re-
sistance causes a bridge output voltage proportional to the input
pressure.
Measuring cell for gage pressure, front-flush diaphragm
Measuring cell for gage pressure, front-flush diaphragm, function chart
The input pressure (p
e
) is transferred to the gage pressure sen-
sor (6) via the seal diaphragm (4) and the filling liquid (5), dis-
placing 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 pres-
sure.
The transmitters with spans
≤ 63 bar measure the input pressure
against atmosphere, those with spans ≥ 160 bar against
vacuum.
Measuring cell for absolute pressure, front-flush diaphragm
Measuring cell for absolute pressure, front-flush diaphragm, function
chart
1
2
3
4
5
6
1 Reference pressure
2 Measuring cell
3 Process connection
4 Seal diaphragm
5 Filling liquid
6 Relative pressure sensor
p
e
Pressure as input variable
p
e
1
2
3
4
5
1 Measuring cell
2 Process connection
3 Seal diaphragm
4 Filling liquid
5 Absolute pressure sensor
p
e
Pressure as input variable
p
e
1 Reference pressure
2 Measuring cell
3 Seal diaphragm
4 Filling liquid
5 Relative pressure sensor
p
e
Pressure as input variable
5
4
3
2
1
S
H
1 Measuring cell
2 Seal diaphragm
3 Filling liquid
4 Absolute pressure sensor
p
e
Pressure as input variable
4
3
2
1
S
H
© Siemens AG 2008