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Calibrate (trim) the RTD correction factor for the RTD R0 (the resistance at 0.00°
Celsius). A resistor equivalent to R0 with .01% (or better) tolerance must be
connected to the RTD terminals.
Calibrate (trim) the RTD span at a temperature below the 557.68° Celsius point.
A resistor with .01% (or better) tolerance that is equivalent to the resistance at
the calibration temperature must be connected to the RTD terminals.
NOTE: A 100 ohm resistor with .1% tolerance can be off by ± .1 ohm; this is equivalent
to ± .26° Celsius (almost 1/4 degree). A 300 ohm .1% resistor can be off by ± .3
ohm; this is equivalent to .93° Celsius (almost a full degree). Calibration
resistors should be .01% tolerance for best results.
4. Point #6
This list contains the signals PRESSURE.TARGET. and STATIC.TARGET. These signals indicate the target value (applied pressure) for span calibration (trim) purposes.
When the differential pressure span is being calibrated the value of the calibration
pressure being applied is written to PRESSURE.SPAN.CAL but it appears here and
remains here until the actual calibration command is written to EXECUTE.CALIB.
When a successful trim occurs the xx.TARGET signal value is saved in xx.SPAN.CAL
and xx.TARGET is cleared. These signals also serve to verify that the applied pressure
write was received without error.
5. Point #7 - Rev 1.90 and later
This list contains the signal TEMP.OFFSET.CFG; this is an offset value set by the user
to “shift” the RTD Temperature reading up or down (5 degrees maximum) to agree with
an external temperature standard.
6. Point #8 - Rev 1.90 and later
This list contains the signals A.USER.CAL, B.USER.CAL and R0.USER.CAL. These
signals are set at the factory for the DIN standard RTD and are changed by the user
when an RTD assembly other than the DIN standard is connected.
7. Point #9 - Rev 1.90 and later
This list contains the signal TEMP.SPAN.CAL that serves two purposes. When the
TEMP span is being calibrated the value of the calibration temperature being applied is
written to this signal. However, in the 3808 the value written is NOT placed into
TEMP.SPAN.CAL; instead it is written to an internal storage location where it is held
until the actual TEMP span calibration command is written to signal
EXECUTE.CALIB. (see point #5). When a successful trim occurs the new span
calibration factor is saved in TEMP.SPAN.CAL and the internal stored value is cleared.
NOTE: The resistance used to simulate RTD resistance MUST be accurate to ± .01%
(.01 ohm out of 100.000 ohms).
Appendix D
Page 9
3808 BSAP Communications