I have received the below comments in relation to the last post about the differences between calibration, verification, and validation.

These are the comments:

- Can you give an example instrument with a specification that we can determine or differentiate calibration, verification, and validation?
- When is verification, validation or calibration is the most appropriate for the intended M&TE?

I presented here a concrete example to differentiate these three terms in a direct and hopefully clear way.

Also, through these examples, it will show if your intention to use these terms regarding your M&TE (Measurement and Test Equipment) is appropriate.

Let us start!

As an example to, we will perform a calibration, verification, and validation in a Liquide Oxygen (LOX) Tank. The tank has Differential Pressure Level Gauge (**DPLG**) and a pressure gauge to determine its level and actual pressure together with Pressure Safety Valve and Pressure Transmitter.

But in this example, I will focus only on the DPLG and pressure gauge for simplicity.

## CALIBRATION

By definition, calibration is the “comparison” of the unknown reading of a UUC to a known reading of the Reference Standard.

During calibration, our objective is to determine how accurate the Differential Pressure Level Gauge by comparing its output reading and computing the error.

Buy determining the error, we can see how far (or close) the value of the UUC to the value of the reference standard, thus, we can also determine the correction value.

#### Calibration Result:

For DPLG, based on the photo above, the standard reads at 1519 mmWC while the UUC reads 1500 mmWC.

Error = Measured value – true value

Error = 1500-1519 = -19 mmWC

Therefore, the Correction Factor is +19 mmWC

Moreover, based on the measurement uncertainty results, we are 95% confident that the exact value of 1519 is within the interval or boundary of +/- 38.5 (between 1480.5 – 1557.5).

**Take note that during calibration, we follow a standard procedure to determine how accurate or close (or far) the result is to the true value. **

**Now, because of calibration, we have determined the error and correction factor. We can use this to improve the accuracy of our measurement results by performing adjustments to return the UUC to its most accurate reading, or if an adjustment is not possible, add/subtract the correction factor to the final results. **

The same procedure applies to the pressure gauge.

## VERIFICATION

From our simple definition, Verification is a process of “confirming” that a given specification is fulfilled.

How to verify after calibration? After the process of calibration, immediately comes verification to determine if the results are within the set tolerance.

During verification, our objective is to determine if the DPLG has an acceptable output reading based on a specification or user requirement. For simplicity, we will use the manufacturer specs regarding tolerance to determine a pass or a fail status.

We will verify if the UUC is within the limits defined by the manufacturer.

The accuracy of the DPLG based on manufacturer specs is **2.5% of Full Scale (FS)** (see photo)

The full scale =2000 mmWC

Therefore,

the tolerance limit is 2000*0.025 = +/-50 mmWC,

#### Verification Result:

The error of the DPLG based on calibration result at 1500 is 19.

Based on the manufacturer specs, it is within the +/- 50 tolerance limit, therefore it is **PASSED.**

The same process of verification with the pressure gauge is applied.

**Take note that during verification, we follow a specification to determine the acceptance criteria.**

**Because of verification, we confirmed that the DPLG is within manufacturer specification and therefore, re-calibration and/or adjustment is not needed.**

## VALIDATION

As we continue in this stage, we define again validation as “ensuring” the acceptability of the implemented measurement process.

Which is in this example, the suitability of the tank to be used as a storage and monitoring for Liquid Oxygen (L0X)

During validation, we will consider the entire system, where all the instruments installed are functioning to its specification, resulting in an output based on the intended purpose.

Let us assume that the intended purpose is to display the exact level of liquid oxygen with an acceptable pressure range.

.

**The objective of the validation is to determine that:**

- The DPLG will display the exact differential pressure at a determined level based on the tank specifications. See in the photo below.
- The pressure should not exceed 35 bar.
- The transmitter is transmitting the right information (level) for remote monitoring.

#### Validation Result:

The tank displays the exact level of liquid oxygen with an acceptable range of pressure as per calibration and verification results with the Tank Specifications.

Therefore, the whole system (tank) is suitable for storing and monitoring liquid oxygen (LOX).

**Take note, that prior to validation, we performed calibration and verification in order to support our objective above. **

**Through calibration, we have determined the instrument accuracy, while through verification, we have confirmed that it is within manufacturer tolerance/specifications.**

**Validation results will conclude if the use of the LOX tank is fit for its purpose (storing and monitoring) and therefore leads to the approval or rejection decision by the concerned individuals. **

This is just an example, in actual, more test and verification is performed during the actual validation process which includes a leak test, the safety valve, the transmitter, and others.

Final results of validation will be documented through a validation report with signatures of approval for ‘*fit to be used*‘ on its purpose

Check out in this link the whole post about the differences between calibration, verification, and validation.

I hope this makes all clear.

Please comment and subscribe.

Edwin

## 12 Responses

## Alvin

Hi S’Edwin,

Good Day!

Now I understand well their differences. I appreciate you sir. I hope my appreciation will boost your enthusiasm to post more about calibration or other topics and be as expert as you someday. Thanks a lot!

Regards,

Alvin

## edwin

Hi Mr. Alvin,

You are welcome. I am happy to know that you understand it.Your appreciation will truly boost my motivation and enthusiasm to create more post that I believe can benefit us all.

Thank you for your valuable comments. I also appreciate it.

Any more comments or concern with regards to calibration, do not hesitate to message me.

Best Regards,

Edwin

## Siva

Dear Edwin,

I want to know ,,

how to calculate uncertainity value (+or -) from Standard Reading and UUC Reading and Error..

## edsponce

Dear Siva,

Thank you for reading my post.

Calculating measurement uncertainty requires more steps and considerations of other errors. But for simplicity, I will just focus directly on your inquiry.

For standard reading,you need to have the calibration certificate and look there the measurement uncertainty value.That value, you divide it by 2 (normal distribution), example, uncertainty from cal cert = 0.5 therefore, 0.5/2 =

0.25 psiFor UUC reading,compute for the standard deviation of the repetitions you made then divide by Sqrt of 2 = 1.41 (for 2 repetitions)For example,

trial 1 = 2.2andtrial 2= 2.3, using excel to compute for the standard deviation will lead to an answer of 0.07,type in excel, =STDEV(2.2,2.3)then 0.07/1.41=

0.05 psiAnd for the error, we will substitute the error for hysteresis error, for example, equal to 0.2, then 0.2/ sqrt of 3 for a rectangular distribution. Sqrt of 3 = 1.73,therefore, 0.2/1.73 =

0.115. psiNow we will combine all the uncertainties to one result using the Root Sum Square (RSS) method.

It is easy to calculate with the help of an excel sheet. Just type below:

=SQRT(SUMSQ(0.25,0.05,0.115)) = 0.28 psi

Multiply 0.28 by 2 for a 95% confidence level which is equal to 0.56 psi

+/- 0.56>>> the final uncertainty value that you will use.This is just a simple example. Other sources of error are still needed to be determined and include in the calculation.

I believe you have a background about uncertainty calculation in order to understand this.

I hope this helps,

Edwin

## Jagadeesh

Hi Sir,

Good day,

During external audit got one minor NC regarding method verification record not available,

We are not using any Non standard method even our quality manual also address the same, we are using Is standard only…

But auditor told me to verification records need for IS standard also,

So kindly I request you to please clarify how to done method verification record….

## edsponce

Hi Jagadeesh,

Just to let you know that the auditor is correct, all methods used even if it is a standard method should be verified or validated for appropriateness before use.

If you notice, the standard method we use does not recommend or specified a specific reference standard instrument to use, including the exact knowledge and skills necessary to do the job. Therefore, once we adapt this standard method, we need to perform verification using our own reference standard and skilled personnel.

With this in mind, we need a record showing that before we use the standard method, there is an evidence that it has an acceptable results. There is a study performed to verify and show acceptable results in using the method with the instrument we have.

There are no specific rules or guidelines for verification that are required but below are my suggestions.

Perform one calibration of instrument and verify results showing that:

1. It has acceptable results – within specifications

2. It has a good repeatability and reproducibility (precision and bias)

3. Measurement uncertainty is within your CMC

4. Acceptable measurement uncertainty by implementing intra-lab or Inter-lab comparison using the same statistical technique (EN value or Z-score) for acceptance criteria.

Take note that all these should be recorded and approved by an authorized person.

For reference, you may use Eurachem Guide, The Fitness for Purpose of Analytical Methods. This is free to download. Just choose the process that is applicable for you.

I hope this helps,

Edwin

## Uma

Dear Sir,

Good Day!

Now I understand well their differences. Can you please share sample verification record of any one calibration method?

## edsponce

Hi Uma,

Any record where calibration is performed with a remarks of passed or failed based on tolerance is a verification record. You can see more of this when you are performing a quality check or monitoring. One example is the intermediate check performed in the lab or a preventive maintenace report.

See example of the PM report on my other post in this link >> preventive-maintenance-in-calibration

Best regards,

Edwin

## Anna

Hi,

I come from a water/wastewater testing lab. One parameter we test is pH. We were recently audited and got an NC for not having records of verifying our new pH meter & probe before being placed in our lab for use. We also don’t have a procedure for verification of equipment. I’m in the process of developing a procedure.

Can you confirm if the following is sufficient for verifying the equipment before placing it in service (in alignment to ISO/IEC 17025:2017 std);

1. Checks to ensure it meets the Manufacturer’s specifications

-in this case, verifying the proper installation of the probe and meter settings

– successful calibration and acceptable verification of calibration with a reference material

2. Calculation of the equipment MUs

3. Statement is “fit for use” after successful verification

## edsponce

Hi Anna,

The procedure is ok but my suggestion is to separate the calibration part from verification.

These are my suggestions:

1. If not calibrated, perform calibration. The calibration part includes:

a. Determination of the error and MU. Provide a calibration certificate for this. This could be every 6 months or yearly depending on your frequency as per criticality of usage.

b. then perform verification by assessing if the error is within the set tolerance limit and determine if it is fit for use.

2. Now, here comes the requirement of verification before putting it to service. This is a pH meter that needs regular verification.

a. Make a regular schedule, it can be verified before using the pH solution or once every week. Since this is a regular verification, no need to calculate the MU, this is already done in the calibration stage. Your goal for verification is to determine only if it is fit for use or not based on the set tolerance. You only need a verification record.

I hope this helps,

Edwin

## Anna

Thank you for the feedback.

Could you elaborate what is meant by “Determination of the error”. and “perform verification by assessing if the error is within the set tolerance limit and determine if it is fit for use”.

## edsponce

Hi Anna,

‘Determination of error’ means to calculate the error based on the calibration results. Error can be determined or calculated using the formula, Error= UUT value – Standard value.

Once you have determined the error, use this value to assess if it is within the tolerance limit. If it is within the set tolerance limit then you can assess or decide that it is fit for use. The decision made (fit or not fit/pass or fail) is now the verification result.

For example, the error is equal to 0.3, the tolerance limit = +/-0.5. It is clear the 0.3 is within the tolerance limit, therefore it is ‘passed.’

I hope it is clear now.

Edwin