Siemens P technical specifications Measuring cell for level, function diagram

© Siemens AG 2008

SITRANS P measuring instruments for pressure

Transmitters for gage, absolute and differential pressure, flow and level

DS III, DS III PA and DS III FF series

Technical description

Measuring cell for absolute pressure from gage pressure series Measuring cell for differential pressure and flow

5

4

3

1

1 Measuring cell

2Process connection

3 Seal diaphragm

4 Filling liquid

5 Silicon absolute pressure sensor

pe Absolute pressure as input variable

2 3 4

1	-	+
	7	6

1	Seal diaphragm	2
2	O-ring

3Overload diaphragm

4Silicon pressure sensor

15 Process flange

56 Body of measuring cell 7 Filling liquid

2

pe

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).

Measuring cell for absolute pressure from the pressure series, function diagram

The absolute pressure pe is transmitted through the seal dia- 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

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

3

4 5 6 7

	2	3	4
			5
1			pe
			6
8	7

1Reference vacuum

2 Overload diaphragm

3 Silicon pressure sensor 4 O-ring

5 Process flange

6 Seal diaphragm

7 Body of measuring cell 8 Filling liquid

pe Absolute pressure as input variable

2

+
1	10

1Flange with tube

2 Seal diaphragm on mounting flange

3 Seal diaphragm

4 Body of measuring cell 5 Overload diaphragm

8

-

9

6Silicon pressure sensor

7O-ring

8Process flange

9 Filling liquid

10 Capillary with filling liquid of mounting flange

Measuring cell for absolute pressure from differential pressure series, function diagram

The input pressure pe is transmitted through the seal diaphragm (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.

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

Siemens FI 01 · 2009

2/67