Title: Calibration
Course: PW-Course-Import-Test > Section: Module 4: Sampling and Calibration

Module 4

In this section we are going to learn all about calibration. Equipment that is used for inspecting parts needs to accurately inspect the features they are intended for. Every piece of equipment has a calibration interval when they are re-calibrated to ensure that it can still inspect the feature correctly.

Depending on the size of the company and the expertise present within the company, the company may choose to adopt a calibration program in-house or outsource the calibration process. Calibration is not just required for equipment used in inspection but also for equipment used in manufacturing like temperatures on a oven, pressure gauges on a compressed air line, etc.

Introduction to Calibration

Calibration is defined a set of operations performed in accordance with a definite documented procedure, that compares the measurements performed by an instrument to those made by a more accurate instrument or standard, for the purpose of detecting and reporting errors in the instrument tested.

Review this video on calibration. The presenter explains the meaning of calibration and how it is done. The presenter emphasizes that the medical and aerospace industries have very demanding requirements around calibration. This is very true. A medical device company will spend significant amount of money to ensure that they have a robust calibration program.

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A common question that may come up is why we calibrate. The video does explain some of the reasons for calibration. Here are a few more:

1. Initial calibration ensures that the test and measurement equipment is in specification
2. Periodic calibration is essential to ensure that the test and measurement equipment remain in the state of calibration
3. Ensures that the test and measurement equipment generates consistent results

When is Calibration not Required?

Calibration is not always required. There are some instances in which calibration of test and measurement equipment may be skipped. When this is done, robust justification is required as to why the equipment is not calibrated. Usually a sticker that states ‘No Calibration Required’ is placed on a prominent location on the equipment.

Here are some of the reasons calibration is not required:

1. When the equipment is not is use
2. When the instrument is fail-safe
3. When the equipment is used as a transfer device whose measurement or output value is not explicitly used
4. When an instrument makes a measurement or provides known outputs which are monitored by another calibrated device or gauge

When to Calibrate?

If calibration intervals are too close then it is a waste of resources. If calibration interval are far apart then wrong decisions can be made and product is wasted. A balance between cost to calibrate and cost of not to calibrate needs to be found. There is no universal best practice established for calibration intervals.

Quality Inspector Responsibility

All measuring equipment that a quality inspector uses has a calibration sticker on it. The sticker usually contains the following information:

- Equipment ID Number
- Calibrated By
- Calibration Date
- Calibration Due Date

A quality inspector needs to verify that the calibration due date is some time in the future. If the calibration date has passed then the equipment is ‘out of calibration’ and should not be used. This equipment should be turned into the calibration department following company policies for re-calibration.

Also if the calibration sticker is missing or tampered with or the measuring equipment shows any form of damage, the equipment should not be used.

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Here is another video about calibration. The chief metrologist of the company describes his role and the importance of calibration.