8
GENERAL
The upper diaphragm has a strain gage element in the configuration of a Wheatstone Bridge. The
deflection of the upper diaphragm causes a change in the resistance of the strain gage and hence a
change in the balance of the bridge. The amount of imbalance is directly proportional to the applied
pressure. This completes the translation of pressure applied to the lower diaphragm into a usable
electrical signal.
Fig. 1-1Fig. 1-1
Fig. 1-1Fig. 1-1
Fig. 1-1
Functioning Principle of the SPX Filled AssemblyFunctioning Principle of the SPX Filled Assembly
Functioning Principle of the SPX Filled AssemblyFunctioning Principle of the SPX Filled Assembly
Functioning Principle of the SPX Filled Assembly
The low level output signal from the bridge is amplified via an instrumentation amp circuit. The amplified
signal then goes to the input of the analog-to-digital (A/D) converter.
Once the microprocessor has the converted voltage input from the A/D converter, the digital signal is
sent to a digital-to-analog (D/A) converter which modulates the current of the unit’s power supply
between 4 and 20 milliamperes for an output current proportional to the applied pressure.
Filling opening
Strain gage
on the
measuring
diaphragm
Capillary with pressure
transmission fluid (Hg)
Total filling
volume = 7mm
3
Separating
diaphragm
0.15mm thick
Base of electronics housing
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