Answer Posted / rajesh.

RTD is Resistance Temperature Detector. As temperature varies resistance also change. So the output of RTD is Resistance. Which in terms converted into current (4 – 20 ma) by means of Transmitter. Generally RTD is available as Pt100.
Pt100 means 100OHMS at 0’ C for a platinum resistance bulb.
Formula for RTD:
Rt. =Ro (1+α t)
Rt. =Resistance of zero temperature.
α = Co. off of thermal (expansion)
t = temperature to be measured.
Example:
Calculation of Resistance or Pt 100.
Ro. = 100
α for platinum = 0.00385/c.
To calculate Resistance at 100’c
R100 =100(1+(38.5*104*100))
100+ (100*0.385)
R100 =138.5
Resistance at 100’c = 138.5

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