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.
Equipments needed
- Transmitter
- 24VDC supply
- Decade box(resistance)
- Multimeter
Theory
- 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
Example:
For a pt100 RTD
α = .00385
R0=100
Let’s take the temp= 30 degree Celsius
R=R0 (1+α ΔT)
So R30=111.35Ω
- 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.
Comparison between RTD and Thermocouple
