4.4.2.7 Measuring cell for level
① Inlet pressure P
+
⑦ Overload diaphragm
② Seal diaphragm on the measuring cell ⑧ Inlet pressure P
-
③ Pressure cap ⑨ Filling liquid of the measuring cell
④ O-ring ⑩ Capillary tube with the fill fluid of the mounting
flange
⑤ Differential pressure sensor ⑪ Flange with a tube
⑥ Measuring cell body ⑫ Seal diaphragm on the mounting flange
Figure 4-13 Function chart of the measuring cell for level
● The inlet pressure (hydrostatic pressure) ①
works hydraulically on the measuring cell
through the seal diaphragm on the mounting flange ⑫
.
● The differential pressure at the measuring cell is transmitted to the differential pressure
sensor ⑤ through the seal diaphragms ② and the filling liquid ⑨.
● When measuring limits are exceeded, the overload diaphragm ⑦ is displaced until one of
the seal diaphragms ② or ⑫ rests on the measuring cell body ⑥. The seal diaphragms ②
thus protect the differential pressure sensor ⑤ from overload.
● The seal diaphragm ② 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.
4.5 System configuration
Introduction
The pressure transmitter can be used in a number of system configurations:
● As a stand-alone version, supplied with the necessary auxiliary power
● As part of a complex system environment, e.g. SIMATIC S7
Description
4.5 System configuration
SITRANS P320/P420 with 4 to 20 mA/HART
38 Operating Instructions, 11/2019, A5E44852162-AC
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