Setra System Model 256 - Manual (Page 4)

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Setra Model 256
Pressure Transducer
1.0 GENERAL INFORMATION
Every Model 256 has been tested and calibrated before shipment. Specific
performance specifications are listed on Page 7 of this Guide.
Setra Systems 256 pressure transducers sense gage pressure and convert this
pressure to a proportional high level analog output. Two output versions are
offered: A voltage output of .1 to 5.1 VDC, and a current output of 4 to 20 mA.
2.0 MECHANICAL INSTALLATION
2.1 Media Compatibility
Model 256 transducers are designed to be used with any gas or liquid compat-
ible with 17-4 PH Stainless Steel. (Hydrogen is not recommended for use with
17-4 PH SS.)
2.2 Environment
The operating temperature limits of the 256 are as follows:
Operating Temperature Range
°F (C°) -40 to +185 (-40 to +85)
Compensated Temperature Range
°F (C°) -4 to +176 (-20 to +80)
2.3 Pressure Fittings
Typically, standard pipe fittings and installation procedures should be used.
However, for very high pressure ranges in excess of 500 psig, we suggest the
use of a sealant such as Loctite Hydraulic Sealant. Excessive high torquing of
metal fittings may cause a slight shift of the output, but this shift can be
trimmed out by the zero adjustment. Torquing does not significantly affect
linearity or sensitivity.
2.4 Moisture Precautions
The Model 256 is provided with two 1/2” NPT female conduit ports for electrical
termination. These tapered pipe threads are tapped deeper than the NPT
standard, in accordance with industry guidelines. These ports must be sealed
according to standard industry practice, in order to prevent moisture ingress
into the Model 256.
2.5 Venting
The Model 256 is a true gage pressure transducer. This means that the
reference side of the pressure sensing diaphragm must be vented to atmo-
sphere. If the reference side of the diaphragm were sealed (as in a sealed gage
transducer), temperature changes would cause the reference pressure to vary.
This may affect the overall accuracy, especially in ranges lower than 500 psig.
The Model 256 provides a vent from the reference side of the sensor to the
inside of the housing and the conduit ports. The user-provided electrical
conduit must be vented to atmosphere in a clean dry location. (It is important
to prevent moisture ingress from the environment into the wiring chamber
or reference side of the transducer.)