I have received below comments in relation to 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.
By definition, calibration is the “comparison” of the unknown reading of a UUC to a known reading of a 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.
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
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.
Same procedure applies to the pressure gauge.
From our simple definition, Verification is a process of “confirming” that a given specification is fulfilled.
During verification, our objective is to determine if the DPLG has an acceptable output reading based on a specification. 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
the tolerance is 2000*0.025 = +/-50 mmWC,
The error of the DPLG based on calibration result at 1500 is 19.
Based on the manufacturer specs, it is within the +/- 50 tolerance, therefore it is PASSED.
Same process of verification with the pressure gauge is applied.
Take note that during verification, we follow a specification to determine the acceptance criteria.
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 Liquid oxygen storage and monitoring.
During validation, we will consider the whole system, where all the instruments installed are functioning to its specification, resulting to 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 determined level based on the tank specifications. See in the photo below.
- The pressure should not exceed 35 bar at the acceptable level.
- The transmitter is transmitting the right information (level) for remote monitoring.
The tank displays the exact level of liquid oxygen with acceptable range of pressure as per calibration and verification results and the Tank Specifications.
Therefore, the whole system (tank) is suitable for storing and monitoring a liquid oxygen (LOX).
Take note, that prior to validation, we performed calibration and verification in order to support our objective above.
This is just an example, of course more test and verification is performed during the actual validation process which includes a leak test, the safety valve, the transmitter and others.
Check out in this link the whole post about the differences between calibration, verification, and validation.
I hope this makes all clear.
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