Design and function
22 265Gx, 265Ax IM/265Gx/Ax-EN-07
3.1 Principle of operation and construction
The pressure transmitter has a modular structure and consists of the pressure measuring cell
with integrated adjustment electronics, as well as the main electronics plus control unit.
Depending on the measuring range and measured variable, either a ceramic pressure sensor or
a silicon pressure sensor is used.
Ceramic pressure sensor
With ceramic pressure sensors (capacitive measuring system), the applied process pressure
(pe/pabs) is transferred directly to the measuring diaphragm.
Even a very slight deflection of the measuring diaphragm will change the internal output voltage
of the pick-up system.
Silicon pressure sensor
With silicon pressure sensors (piezoresistive measuring system), the pressure is transferred to
the silicon sensor via the isolating diaphragm and the filling liquid.
In accordance with the pressure, four doped piezoresistors in the silicon sensor change their
resistance values and, therefore, the output voltage of the pick-up system.
This output voltage, which is proportionate to pressure, is transformed into an electrical signal
by the adjustment electronics and main electronics.
Depending on the model, the transmitter is connected to the process by means of a G ½ B
spigot (DIN EN 837-1), ½14 NPT male or female thread, front-bonded diaphragm with special
thread G ½" for, e.g., a ball valve, or via various remote seals.
The transmitter operates on the basis of two-wire technology. The same wires are used for the
operating voltage (device-specific, see "Technical data") and the scaled output signal
(4 … 20 mA or digital). The electrical connection is established via a cable entry or plug.
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