Intro to Calibration
In the following articles, we will learn about the calibration procedures for the different kinds of process transmitters.
Before we start looking at the transmitters we must first understand calibration. For example, let’s say we have an Electric Pressure Transmitter with a range of 0 to 100 PSI.
Calibration Procedure
First, we must gather a list of known values. We will do a Five-Point Verification. I will send an Input of 0%,25%,50%,75%, and 100% to the transmitter. I will then write down the corresponding output from the transmitter. Our chart may look like this.
Input in % | Input in PSI | Output in mA |
0 | 0 | 3.92 |
25 | 25 | 7.90 |
50 | 50 | 11.94 |
75 | 75 | 15.92 |
100 | 100 | 20.00 |
Looking at our chart we notice that there is a large deviation from what our output should be. Now we must move to the next step.
Next, set your input pressure to the lower range of the scale(0 PSI). Now, it’s time to adjust the zero adjustment. Adjust the zero until you get an output of 4.00 mA.
Now that we have the lower range of our transmitter calibrated, it is time to move to the upper range value(100 PSI). We will now adjust our span adjustment until we have an output of 20.00 mA.
After calibrating the span you may have to go back and forth adjusting your zero and span a couple of times before your calibration is correct. Once your calibration is complete then it is time to perform another Five-Point Verification.
Input in % | Input in PSI | Output in mA |
0 | 0 | 4.00 |
25 | 25 | 7.99 |
50 | 50 | 12.01 |
75 | 75 | 16.00 |
100 | 100 | 20.00 |
Our deviation has reduced immensely and now our calibration is complete. It is now fine to put the sensor back in service
