# How to calibrate RTD transmitter

## 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.

• Transmitter
• 24VDC supply
• 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:  ### • 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.

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