Updated: Apr 4
In a critical process where accuracy is essential RTD is mostly used. We know that RTD comes in variety like 2 wire, 3 wire and 4 wire. Out of them, 4 wire is most accurate as it cancels lead wire resistance error but is the most expensive.
Now let's dig into calibration of RTD temperature transmitter. Here we will discuss 4 wire RTD.
Do connection as shown in the figure.
Here in our example, we have taken resistance decade box to provide resistance. We can use other sources which can provide resistance.
Follow the below step for the successful calibration. Let assume our temperature range is between 0-100 degree Celcius.
1. Make the connections as shown in the figure.
2. Set resistance in resistance box to the corresponding LRV temperature. In our example, we have used RTD PT100 which has a value of 100 ohms at 0-degree temperature.
3. By adjusting 100-ohm resistance, transmitter output to 4 mA if don't then press zero button on the transmitter.
4. Now Set resistance in resistance box to the corresponding URV temperature in our example, maximum range is 100-degree Celcius.
5. By adjusting span screw of transmitter output to 20 mA.
6. For checking linearity of instrument set resistance source output to 0%, 25%, 50%, 75% and 100% at corresponding temperature and read milliammeter for 4mA, 8mA, 12mA, 16mA and 20mA respectively in both ascending and descending order.
7. If an error is there and a curve is not linear then connect HART in parallel, go to online then select 4 wire RTD. If an error is in the input side then do input trim and if there is an error in 4-20 mA output then trim 4-20 mA.