March 1998/053
SCX - Series
Precision Compensated Pressure Sensors
Aubinger Weg 27, 82178 Puchheim, Germany
Phone 0049 - (0) 89 80 08 30, Fax 0049 - (0) 89 8 00 83 33
http://www.sensortechnics.com
TYPICAL PERFORMANCE CHARACTERISTICS
GENERAL DISCUSSION
The SCX series devices give a voltage output which is directly
proportional 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 physi-cal 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
connection and easy PC board mounting. To mount the device
horizontally 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 P
A
should be used as the low pressure port.
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