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Description
3.5 Functional principle
SITRANS P500 with HART
28
Operating Instructions, 12/2014, A5E02344528-09
3.5.2.2
Measuring cell for level
①
Process flange with pro-
cess connection
⑥
Filling liquid of the measuring cell
②
O-ring
⑦
Seal diaphragm in the measuring cell
③
Silicon pressure sensor
⑧
Capillary tube with the fill fluid of the mounting flange
④
Measuring cell body
⑨
Flange with a tube
⑤
Overload diaphragm
⑩
Seal diaphragm on the mounting flange
Figure 3-7
Function diagram of the measuring cell for level
●
The input pressure (hydrostatic pressure) acts hydraulically on the seal diaphragm at the
mounting flange
⑩
on the measuring cell.
●
The differential pressure existing at the measuring cell is transmitted via the fill fluid
⑥
to
the silicon pressure sensor
③
.
●
If the measuring limits are exceeded, the overload diaphragm
⑤
flexes until the seal
diaphragm
⑦
touches the body of the measuring cell
④
. This protects the silicon
pressure sensor
③
against overload.
●
Differential pressure causes the measuring diaphragm of the silicon pressure sensor to
be displaced. The displacement changes the resistance value of the four doped piezo
resistors arranged in a bridge circuit in the measurement diaphragm.
●
The change in resistance causes the bridge output voltage to vary in proportion to the
differential pressure.
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