Siemens SITRANS P Brochure & Specs page 67

Transmitters for gage, absolute and differential pressure, flow and level
Measuring cell for absolute pressure from gage pressure series
p
e
Measuring cell for absolute pressure from the pressure series, function
diagram
The absolute pressure p is transmitted through the seal dia-
e
phragm (3, Figure "Measuring cell for absolute pressure from the
gage pressure series, function diagram") and the filling liquid (4)
to the silicon absolute pressure sensor (5) whose measuring di-
aphragm is then flexed. This changes the resistance of the four
piezo-resistors fitted in the diaphragm in a bridge circuit. This
change in resistance results in a bridge output voltage propor-
tional to the input pressure.
Measuring cell for absolute pressure from differential pressure
series
p
Measuring cell for absolute pressure from differential pressure series,
function diagram
The input pressure p is transmitted through the seal diaphragm
e
(6, Figure "Measuring cell for absolute pressure from differential
pressure series, function diagram") and the filling liquid (8) to the
silicon pressure sensor (3).
The difference in pressure between the input pressure pe and
the reference vacuum (1) on the low-pressure side of the mea-
suring cell flexes the measuring diaphragm. The resistance of
the four piezo-resistors fitted in the diaphragm in a bridge circuit
thus changes. This change in resistance results in a bridge out-
put voltage proportional to the absolute pressure.
An overload diaphragm is installed to provide protection from
overloads. If the measuring limits are exceeded, the overload di-
aphragm (2) is flexed until the seal diaphragm rests on the body
of the measuring cell (7), thus protecting the silicon pressure
sensor from overloads.
© Siemens AG 2008
SITRANS P measuring instruments for pressure
p
e
e
p
e
DS III, DS III PA and DS III FF series
Measuring cell for differential pressure and flow
Measuring cell for differential pressure and flow, function diagram
The differential pressure is transmitted through the seal dia-
phragms (1, Figure "Measuring cell for differential pressure and
flow, function diagram") and the filling liquid (7) to the silicon
pressure sensor (4).
The measuring diaphragm is flexed by the applied differential
pressure. This changes the resistance of the four piezo-resistors
fitted in the diaphragm in a bridge circuit. This change in resis-
tance results in a bridge output voltage proportional to the abso-
lute pressure.
An overload diaphragm is installed to provide protection from
overloads. If the measuring limits are exceeded, the overload di-
aphragm (2) is flexed until the seal diaphragm rests on the body
of the measuring cell (7), thus protecting the silicon pressure
sensor from overloads.
Measuring cell for level
Measuring cell for level, function diagram
The input pressure (hydrostatic pressure) acts hydraulically on
the measuring cell through the seal diaphragm on the mounting
flange (2, Figure "Measuring cell for level, function diagram").
This differential pressure is subsequently transmitted further
through the measuring cell (3) and the filling liquid (9) to the sil-
icon pressure sensor (6) whose measuring diaphragm is then
flexed.
This changes the resistance of the four piezo-resistors fitted in
the diaphragm in a bridge circuit.
This change in resistance results in a bridge output voltage pro-
portional to the differential pressure.
An overload diaphragm is installed to provide protection from
overloads. If the measuring limits are exceeded, the overload di-
aphragm (2) is flexed until the seal diaphragm rests on the body
Technical description
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