Product description Waterpilot FMX21
10 Endress+Hauser
3 Product description
3.1 Function
The ceramic measuring cell is a dry measuring cell i.e. the pressure acts directly on the
robust, ceramic process isolating diaphragm of the Waterpilot FMX21. Potential changes
in air pressure are guided via a pressure compensation tube through the extension cable to
the rear of the ceramic process isolating diaphragm and are compensated for. A pressure-
dependent change in capacitance, caused by the movement of the process isolating
diaphragm, is measured at the electrodes of the ceramic carrier. The electronics unit then
converts this to a signal that is proportional to the pressure and linear to the level.
h
2
1
p
atm
p
hydr.
p = p + p
atm hydr.
p
atm
p
atm
h ~ p
r • g
h =
p
Rel.: p =
sens
(p + p ) - p
atm hydr. atm
p = p + p
atm hydr.
Abs.: p =
sens
(p + p )
atm hydr.
A0019140
1 Ceramic measuring cell
2 Pressure compensation tube
h Height level
p Total pressure = atmospheric pressure + hydrostatic pressure
ρ Density of the medium
g Acceleration due to gravity
P
hydr.
Hydrostatic pressure
P
atm
Atmospheric pressure
P
sens
Pressure displayed on the sensor
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