Where high-temperature measurement is required thermocouple is used. The thermocouple is not as accurate as RTD but very efficient in measuring high temperature.
In this article, we will be discussing calibration of the thermocouple.
Equipment required for calibration :
1. Temperature transmitter
2. Power supply
4. Millivolt source (Documenting process calibrator) or can use temperature bath with 10-time accurate reference.
Establish set up as shown below,
Put ammeter in series to measure milliamps. Here millivolt source is used to source mV then transmitter converts that mV to mA which is then measured by the ammeter.
Let assume our calibration range is between 0-200 degree Celcius
now to feed mV we can calculate mV for k-type thermocouple by using below formula,
mV = °C * 0.0416
If I want mV at 100°C temperature then,
mV = 100 * 0.0416
= 4.16 mV
Like this way, we can calculate for our 5 points 0, 50, 100, 150 and 200.
Now we know the value of mA corresponding to the temperature. If any error exists in reading then connect HART in parallel and trim the input or output or if there is the only error in between zero and span then adjust that screw to match it with mA.