SCX Series
Precision compensated pressure sensors
3/10
August 2005 / 053
www.sensortechnics.com
TYPICAL PERFORMANCE CHARACTERISTICS
GENERAL DISCUSSION
The SCX series devices give a voltage output which is directly pro-
portional to applied pressure. The devices will give an increasing
positiv going output when increasing pressure is applied to pressure
port P
B of the device. If the input pressure connections are reversed,
the output will increase with decreases in pressure. The devices
are ratiometric to the supply voltage and changes in the supply
voltage will cause proportional changes in the offset voltage and
full-scale span. Since for absolute devices pressure is applied to
port P
A, output polarity will be reversed.
User calibration
The SCX devices are fully calibrated for offset and span and should
therefore require little if any user adjustment in most applications.
For precise span and offset adjustments, refer to the applications
section herein.
Vacuum reference (absolute device)
Absolute sensors have a hermetically sealed vacuum reference
chamber. The offset voltage on these units is therefore measured
at vacuum, 0 psia. Since all pressure is measured relative to a
vacuum reference,all changes in barometric pressure or changes
in altitude will cause changes in the device output.
Media compatibility
SCX devices are compatible with most non-corrosive gases.
Because the circuit is coated with a protective silicon gel, many
otherwise corrosive environments can be compatible with the
sensors. As shown in the physical construction diagram below, fluids
must generally be compatible with silicon gel, plastic, aluminium,
RTV, silicon, and glass for use with Port B. For questions concerning
media compatibility, contact the factory.
MECHANICAL AND MOUNTING
CONSIDERATIONS
The SCX nylon housing is designed for convenient pressure con-
nection and easy PC board mounting. To mount the device horizon-
tally to a PC board, the leads can be bent downward and the package
attached to the board using either tie wraps or mounting screws.
For pressure attachment, tygon or silicon tubing is recommended.
All versions of the SCX sensors have two (2) tubes available for
pressure connection. For absolute devices, only port P
A is active.
Applying pressure through the other port will result in pressure dead
ending into the backside of the silicon sensor and the device will
not give an output signal with pressure.
For gage applications, pressure should be applied the port P
B. Port
P
A is then the vent port which is left open to the atmosphere. For
differential pressure applications, to get proper output signal polarity,
port P
B should be used as the high pressure port and PA should be
used as the low pressure port.
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