
3.6.3.3 Measuring cell for level
① Pressure cap ⑥ Seal diaphragm on the measuring cell
② O-ring ⑦ Filling liquid of the measuring cell
③ Measuring cell body ⑧ Capillary tube with the fill fluid of the mounting
flange
④ Overload diaphragm ⑨ Flange with a tube
⑤ Differential pressure sensor ⑩ Seal diaphragm on the mounting flange
Figure 3-9 Function chart of the measuring cell for level
● The
inlet pressure (hydrostatic pressure) works hydraulically on the measuring cell through
the seal diaphragm ⑩ on the mounting flange ⑩.
● Differential pressure at the measuring cell is transmitted to the differential pressure sensor
⑤ through the seal diaphragms ⑥ and the filling liquid ⑦.
● When measuring limits are exceeded, the overload diaphragm ④ is displaced until one of
the seal diaphragms ⑥ or ⑩ rests on the measuring cell body ③. The seal diaphragms
⑥ thus protect the differential pressure sensor ⑤ from overload.
● The seal diaphragm ⑥ is displaced by the differential pressure. The displacement changes
the resistance of the four doped piezoresistors in the bridge circuit.
● The change in the resistance causes a bridge output voltage proportional to the differential
pressure.
Description
3.6 Functional principle
SITRANS P, DS III series with HART
Operating Instructions, 09/2012, A5E00047092-08 27
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