Siemens P technical specifications Remote seals, Measuring setups, 182

© Siemens AG 2008

SITRANS P measuring instruments for pressure

Remote seals

Measuring setups

■Overview

This section shows examples of typical measuring setups for us- ing SITRANS P pressure transmitters with and without remote seals.

2Equations for calculating start of scale and full scale are pro- vided for each example.

Questionnaires are included to help you select the right combi- nation of remote seal and pressure transmitter.

Installation

Remote seals of sandwich design are fitted between the con- nection flange of the measuring point and a dummy flange. Re- mote seals of flange design are fitted directly on the connection flange of the measuring point. The respective pressure rating of the dummy flange or the flanged remote seal must be observed.

The pressure transmitter should be installed below the connec- tion flange (and below the lower connection flange in the case of differential pressure transmitters). This arrangement must be used in the low-pressure range.

When measuring at pressures above atmospheric, the pressure transmitter can also be installed above the connection flange.

The capillaries between the remote seal and the pressure trans- mitter should be as short as possible to obtain a good transmis- sion response.

Offset of measuring range

If there is a difference in height between the two connection flanges when measuring with two remote seals, an additional dif- ferential pressure will result from the oil filling of the remote seal capillaries. This results in a measuring range offset which has to be taken into account when you set the pressure transmitter.

An offset in the measuring range also occurs when combining a remote seal with a transmitter if the remote seal is not installed at the same height as the transmitter.

Pressure transmitter output

If the level, separation layer or density increase in closed ves- sels, the differential pressure and hence the output signal of the pressure transmitter also increase.

For an inverted relationship between the differential pressure and the output signal, the start-of-scale and full-scale values of the SITRANS P must be interchanged.

With open vessels, a rising pressure is usually assigned to an in- creasing level, separation layer or density.

Influence of ambient temperature

Temperature differences between the individual capillaries and between the individual remote seals should be avoided.

Temperature variations in the area of the measuring setup cause a change in volume of the filling liquid and hence measuring er- rors.

Notes

•For the separation layer measurement, the separation layer has to be positioned between the two spigots. Also you must make sure that the level in the container is always above the top spigot.

•When measuring density, make sure that the level of the me- dium remains constant. The level should be above the top spigot.

Possible combinations of pressure transmitters and remote seals

Type of installation	Pressure transmit-	Remote seals
	ters
A/B	7MF4033	7MF4900
	7MF4034	7MF4910
	7MF4035	7MF4920
	7MF8023
	7MF8024
	7MF8025
C1 and C2	7MF4233	7MF4900
	7MF4234	7MF4910
	7MF4235	7MF4920
		(vacuum-proof design
		in each case)
	7MF4333	7MF4901
	7MF4334	7MF4921
	7MF4335
D	7MF4433	7MF4903
	7MF4434	7MF4923
	7MF4435
E	7MF4433	7MF4913
	7MF4434
	7MF4435
G, H and J	7MF4433	7MF4903
	7MF4434	7MF4923
	7MF4435

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Siemens FI 01 · 2009