Description
4.4 Functional principle
4.4.2.5
Measuring cell for absolute pressure from the differential pressure series
①
②
③
④
⑤
Figure 4-11
● Absolute pressure is transmitted to the absolute pressure sensor
diaphragm
● When measuring limits are exceeded, the overload diaphragm
diaphragm
absolute pressure sensor
● The difference between the inlet pressure (p
negative side of the measuring cell displaces the seal diaphragm
changes the resistance of the four piezoresistors (bridge circuit) of the absolute pressure
sensor.
● The change in the resistance causes a bridge output voltage proportional to the absolute
pressure.
36
Pressure cap
Seal diaphragm on the measuring cell
O-ring
Measuring cell body
Absolute pressure sensor
Function chart of measuring cell for absolute pressure
②
and the filling liquid
②
rests on the measuring cell body
⑤
⑥
Overload diaphragm
⑦
Measuring cell filling liquid
⑧
Reference pressure
p
Pressure input variable
e
⑦
.
④
. The seal diaphragm thus protects the
from overload.
) and the reference pressure
e
Operating Instructions, 11/2019, A5E44852162-AC
⑤
through the seal
⑥
is displaced until the seal
⑧
②
. The displacement
SITRANS P320/P420 with 4 to 20 mA/HART
on the