Siemens SITRANS P Manual de usuario descargar pdf (Pagina 182)

SITRANS P measuring instruments for pressure

Remote seals

Measuring setups

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Siemens FI 01 · 2009

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Overview

This section shows examples of typical measuring setups for us-

ing SITRANS P pressure transmitters with and without remote

seals.

Equations 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 r

espective 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

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 pr

essure 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 dif

ferential pr

essure 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 r

emote seals should be avoided.

Temperatur

e 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 sur

e that the level in the container is always above the

top spigot.

• W

hen 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-

ters

Remote seals

A/B 7MF4033

7MF4034

7MF4035

7MF8023

7MF8024

7MF8025

7MF4900

7MF4910

7MF4920

and C

7MF4233

7MF4234

7MF4235

7MF4900

7MF4910

7MF4920

(vacuum-proof design

in each case)

7MF4333

7MF4334

7MF4335

7MF4901

7MF4921

D 7MF4433

7MF4434

7MF4435

7MF4903

7MF4923

E 7MF4433

7MF4434

7MF4435

7MF4913

G, H and J 7MF4433

7MF4434

7MF4435

7MF4903

7MF4923

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