APPENDIX C
RTD DISTANCE LIMITATIONS
WITH THE PMC-1 ELECTRO-PNEUMATIC CONTROLLER
When using the PMC-1 electro-pneumatic controller to control
temperature with an RTD and optional built-in signal
conditioning card, consideration must be given to the distance
of the RTD from the PMC-1 controller.
Since the RTD changes resistance in proportion to
temperature change, the signal received by the signal
conditioning card installed in the PMC-1 is a variable voltage
signal. The signal conditioning card converts the voltage signal
into a 4-20mA signal, which can be used by the PMC-1.
The wire connecting the RTD to the PMC-1 provides additional
resistance, which varies according to the gauge and length of
the wire Although the additional resistance of the wire is
insignificant over short distances, it can affect accuracy over
long distances. The following guideline can be used to insure
that any error induced by wire length will be less than 1%.
12
MAX. LENGTH
WIRE GAUGE
FOR 3-WIRE RTD
AWG mm2 Feet Meters
20 .50 90 27.4
22 .25 55 16.8
24 .22 30 9.1
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