Siemens P technical specifications Measuring cell for gage pressure, 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

Mode of operation of the FOUNDATION Fieldbus electronics

Mode of operation of the measuring cells

8	9
	0 0 0 0 0
M
	0 0

Measuring cell for gage pressure

2 2 3 4 5 7

mC	FF
	interface

EEPROM 6

Electronics

1	6
Sensor	EEPROM

Power supply

10

Power supply unit

Coup-

ler

5
4
3	1

2

pe

1Measuring cell

2Process connection

3 Seal diaphragm

4 Filling liquid

5 Silicon pressure sensor

pe Pressure as input variable

pe Measuring cell

Measuring cell for gage pressure, function diagram

The pressure pe is applied through the process connection (2, Figure "Measuring cell for gage pressure, function diagram) to

1	Measuring cell sensor	8	Three input keys
2	Instrument amplifier		(local operation)
3	Analog-to-digital converter	9	Digital display
4	Microcontroller	10	Power supply
5	Electrical isolation	pe
6	One non-volatile memory		Input variable
	each in the measuring cell

and electronics

7FF interface

the measuring cell (1). This pressure is subsequently transmitted further through the seal diaphragm (3) and the filling liquid (4) to the silicon pressure sensor (5) whose measuring diaphragm is then flexed. This changes the resistance of the four piezo-resis- tors fitted in the diaphragm in a bridge circuit. This change in re- sistance results in a bridge output voltage proportional to the in- put pressure.

Function diagram of the electronics

The bridge output voltage created by the sensor (1, Figure "Function diagram of the electronics") is amplified by the instru- ment amplifier (2) and digitized in the analog-to-digital converter

Measuring cell for gage pressure, with front-flush diaphragm for paper industry

(3). The digital information is evaluated in the microcontroller, its linearity and temperature response corrected, and provided on the FOUNDATION Fieldbus through an electrically isolated FOUNDATION Fieldbus Interface (7).

The data specific to the measuring cell, the electronics data, and the parameter data are stored in the two non-volatile memories

(6). The one memory is coupled to the measuring cell, the other to the electronics. As the result of this modular design, the elec- tronics and the measuring cell can be replaced separately from each other.

Using the three input keys (8) you can parameterize the pressure transmitter directly at the point of measurement. The input keys can also be used to control the view of the results, the error mes- sages and the operating modes on the digital display (9).

5

4

1

2

3 pe

1Measuring cell

2Process connection

3 Seal diaphragm

4 Filling liquid

5 Silicon pressure sensor

pe Pressure as input variable

The results with status values and diagnostic values are trans- ferred by cyclic data transmission on the FOUNDATION Fieldbus. Parameterization data and error messages are trans- ferred by acyclic data transmission. Special software such as National Instruments Configurator is required for this.

Measuring cell for gage pressure, with front-flush diaphragm for paper in- dustry, function diagram

The pressure pe is applied through the process connection (2, Figure "Measuring cell for gage pressure, with front-flush dia- phragm for paper industry, function diagram") to the measuring cell (1). This pressure is subsequently transmitted further through the seal diaphragm (3) and the filling liquid (4) to the sil- icon pressure sensor (5) whose measuring diaphragm is then flexed. This changes the resistance of the four piezo-resistors fit- ted in the diaphragm in a bridge circuit. This change in resis- tance results in a bridge output voltage proportional to the input pressure.

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Siemens FI 01 · 2009