The term validation is used by engineers to know the status of any equipment or instrument after the test on the equipment or the instrument is conducted.

If we talk about Instrumentation & Control engineering, then we apply value to any instrument like a transmitter, and check the response of the transmitter.

If the transmitter is producing appropriate output or responding properly to the values applied to it, then we say that the transmitter has passed validation.

If the transmitter does not produce appropriate output or respond properly, then we say that the transmitter has failed validation.

Then there is a need to take action on the transmitter. The action that we can take is called calibration. We will now see what calibration is.

What is Calibration?

The calibration is generally done after the validation of the transmitter.

Suppose we give input to the transmitter and expect some output from that transmitter, but the transmitter produces some other output or produces output with some deviation, then we need to take corrective action for it.

So, we calibrate the transmitter. We generally do zero calibration and span calibration. After doing the calibration, we check the transmitter again.

This is done to ensure that the transmitter is producing appropriate output as per the input given to it.

Now let us see the example of transmitter validation and calibration to make the concept clearer.

We will take the example of a temperature transmitter. We will give the resistance as input to the temperature transmitter and see the output generated by the temperature transmitter.

The temperature transmitter has a range of 0 degrees Centigrade to 200 degrees Centigrade. The acceptable error limit as per the process requirement is within +/- 1 %. We will consider 2 cases.

Case 1 :

Input	Desired Output	Actual Output	Error %	Validation Status	Calibration Needed
0	0	0.5	0.25	Pass	No
50	50	50.2	0.1	Pass	No
100	100	100.3	0.15	Pass	No
150	150	150.3	0.15	Pass	No
200	200	200.2	0.1	Pass	No
150	150	150.2	0.1	Pass	No
100	100	100.5	0.25	Pass	No
50	50	50.4	0.2	Pass	No
0	0	0.5	0.25	Pass	No

Calibration and Validation Table 1

In case 1, the temperature transmitter has produced the output which has acceptable error as per the process requirement. So, we will not calibrate the temperature transmitter.

Case 2 :

Input	Desired Output	Actual Output	Error %	Validation Status	Calibration Needed
0	0	2.3	1.15	Fail	Yes
50	50	52.2	1.1	Fail	Yes
100	100	102.5	1.25	Fail	Yes
150	150	152	1	Fail	Yes
200	200	201.5	0.75	Pass	No
150	150	152.4	1.2	Fail	Yes
100	100	102.6	1.3	Fail	Yes
50	50	52.1	1.05	Fail	Yes
0	0	1.2	0.6	Pass	No

Calibration and Validation Table 2

In case 2, the temperature transmitter has produced the output which is not acceptable because the error is more than the process requirement error.

So, a calibration of the temperature transmitter is required. Generally, we do zero trim after applying the lower range value which is 0 degrees Centigrade in our example.

Also, we do span trim after applying the upper range value which is 200 degrees Centigrade in our case.

After calibration, we will again validate the same temperature transmitter and see the response.

So, what did we learn new here?

Now, after this discussion, you say what is new in this. We all do calibration in this way only. s

First, we check the response of the transmitter or the instrument under calibration and then do the calibration of the transmitter or the instrument if the response of the transmitter or the instrument is not satisfactory.

Now read the below words very carefully.

We generally say that we did calibration of the temperature transmitter, pressure transmitter, flow transmitter, level transmitter, pressure switch, level switch, temperature switch, RTD, vibration probe, and many more.

Do you agree with the above statement?

If you do not agree with the above statement then you are correct. Almost 90 % of you will agree with the above incorrect statement.

Answer me, how will you calibrate an RTD and a vibration probe?

Yes, now you are correct. We can only validate RTD and a vibration probe. Many other instruments are there in which we can only do validation and not calibration.

This instrument either passes the validation or fails the validation. If they pass the validation, then we can use them. If they fail the validation, then we cannot use them.

EndNote

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Difference between Validation and Calibration

Introduction