Siemens SITRANS P DS III - Measuring Cell for Level

Description
3.6 Principle of operation
SITRANS P DS III with PROFIBUS PA
Operating Instructions, 06/2013, A5E00053276-07
31
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.