RTD transmitter Calibrating
In industries temperature is a major physical quantity that has to be monitored and controlled.In this session we are discussing about calibration of RTD transmitter.
Both RTDs and thermocouples are used for process temperature measurements.
- 24VDC supply
- Decade box(resistance)
- RTD has no polarity
- There are different kinds of RTD (2 wire,3 wire,4 wire)
- Output of RTD will be change in resistance due to change in temperature.
- Commonly used RTD materials are nickel, platinum, and copper.
Formula needed for calibration:
Procedure for calibrating RTD transmitter
- Remove the temperature element (RTD) from transmitter.
- Connect the circuit as shown in figure above.
- Put multimeter in ma.
- By the equation we can find what will be the output resistance of RTD in specific temperature
For a pt100 RTD
α = .00385
Let’s take the temp= 30 degree Celsius
R=R0 (1+α ΔT)
- So by the equation we can find resistance values for 5 point calibration (4ma,8ma,12ma,16ma,20ma)
- By setting these resistance values using decade box we can find the corresponding ma in multimer.
- By changing the zero and span potentiometer in transmitter we can do the 5 point calibration.
- Repeat the process.