When it comes to calibration requirements, make sure you get what you need.

Risk management is critical in every business, particularly in today’s volatile economy. Failure to assess potential risks and take action to mitigate them can result in financial loss, harm to people or the environment, and ultimately failure of the business.

Calibration is one area where risk management is needed to reduce liability and expenses, whether you have an internal calibration department or outsource calibration. In either case, one must determine the risks associated with the equipment and its calibration. In some industries this is more critical, such as pharmaceuticals, medical device, aerospace and defense.

Depending on the company, improperly calibrated equipment could impact the quality of the product or service they provide, resulting in potential harm to people or the environment. Product may need to be recalled or services performed again resulting in a financial impact to the company.

Calibration of test, measurement and inspection equipment is critical to manufacturing. Measurement equipment may be embedded in processing equipment and is used to verify that processes are running within acceptable parameters. Calibrated inspection equipment is used to ensure that materials, components and end items are within specifications after a process is completed.

What are the risks associated with calibration and what can be one to mitigate or reduce those risks?

Calibration Risks

Overdue calibration-condition unknown

Failure-out of tolerance (impact to product/process)

Used outside specs/range-unintended purpose

Incorrectly calibrated-wrong calibration standard, procedure, specifications, technician training

Over calibration-calibrated too often, too much

False failure-fails calibration, but is actually in tolerance


Business risk-increased scrap, expenses, reduced productivity and missed schedules

Process risk-defective product produced and enters supply chain and customer impact

Safety risk-potential harm to people or environment

As an auditor with a calibration background, I have found many instances where the business did not understand what they received when their equipment was calibrated. What was performed was different from what they needed, but they did not know it.They had a calibration certificate and assumed that the equipment was properly calibrated-in some cases it wasn’t.

Auditors have a basic motto:

Say what you do (documents).

Do what you say (action).

Prove that you did it (data records).

When it comes to calibration, the motto is:

Say what you need (document requirements).

Ask for it (action).

Prove that you got it (data records).

Sounds rather simplistic, but it is really very important. Most companies ask for what they want-their equipment calibrated. They leave the requirements up to an internal or external calibration provider. Many manufacturers outsource some or all of their calibration activities since this is not one of their core competencies. They receive a calibration certificate and a bill for the services and assume that the calibration and the calibration certificate are what they need. Often this is not the case.

For companies with an internal calibration department, one of the engineering groups may take their process requirements and divide by 4 to obtain a 4:1 test accuracy ratio. If the process control requires ±1.0 psi, they assign a calibration accuracy of ±0.25 psi (wishful thinking specs). This would be fine if the gage were rated by the manufacturer for this accuracy. This leads to false failures and extra work when the gage fails to meet the assigned specification but is within the manufacturer’s specification.

What's Happening?

Few companies have metrology engineers, metrologists or senior calibration technicians on staff. They rely on others to determine the calibration specifications. Who are these others? It depends on the company. In some companies they may be inspectors, technicians or engineers.

Very few engineers are trained in metrology and even less are trained in calibration. The result can be calibration specifications which are unrealistic for the equipment (better than the manufacturer’s specifications). Or they do not take into account all of the measurement components that make up the measurement system. Normally, they are just looking at range and accuracy specifications and not considering the measurement uncertainty of the system.

When outsourcing calibration, a company is relying on the supplier to perform the calibration correctly. But what is correct? The calibration supplier will probably use their own procedure since most calibrations do not have standardized procedures. They may use the same calibration process as the manufacturer, if one is available. Or they may obtain procedures from the Government-Industry Data Exchange Program (GIDEP, www.gidep.org )which are contributed by the government (military services) and commercial industry.

Have you documented your equipment’s calibration specifications and linked them to the product or process? Have you communicated them to the calibration supplier? If not, how does the calibration supplier (internal or external) know what you need?

While there are many risks and risk management processes, we are just going to look at calibration specifications and what can be done to reduce the risk.

Calibration Customer

As a customer of a calibration supplier you need to document your equipment’s calibration specifications and link them to the product or process. At the least, ensure that the manufacturer’s specifications meet your needs and document it.

To determine the calibration requirements, form a team. The roles of the team are engineering (manufacturing, quality, and/or R&D), customer (production or manufacturing) and metrology (calibration).

If all of the equipment is commercial, off-the-shelf, then you should be able to use the manufacturer’s specifications. You still need to verify that the equipment specifications meet your process needs before purchasing it, not after.

If the equipment is custom-built, there is more work to do. Identify the measurement components of the system and their specifications, from the manufacturer. Determine how these devices will be calibrated. Be sure to design calibration capabilities into the equipment before you build it or you will delay implementation when the equipment has to be modified so it can be calibrated.

How to combine the accuracies of the components in the system is more complicated. You’ll need a metrologist or someone with measurement systems assurance experience to help with this.

Create a controlled form for recording the equipment calibration specifications whether it is in a database or on paper. Be sure to have a process for change control that includes all the members of the risk assessment team.

Finally, communicate the requirements to your calibration supplier if they were not a part of the team.

Calibration Supplier

As a provider of calibration services, you need to request that your customers provide their requirements for each piece of equipment. If you cannot do this electronically, then use paper. You can request it once and maintain it in your system, or request that the customer provide this information with each request for calibration.

This can be a challenge for a third-party calibration supplier as some customers just want their equipment calibrated. Sometimes all the supplier receives is a box of gages with no purchase request or identification. The supplier calibrates the gages and expects the customer to verify that it meets their needs.

When the services do not meet the customer’s requirements, it can result in rework and loss to the service provider. Having documented requirements may take more effort to obtain, but will save time and money in the long run. It also may improve customer relations and enable you to keep the customer.Too many issues and the customer may find another supplier.


Rules for Calibration Requirements

Rule 1. Gages cannot be calibrated to an accuracy better than that specified by the manufacturer. Over time you may collect sufficient data to show that the gage was consistently within a lesser tolerance than the manufacturer specified. However, it is not good practice to use the gage as if it has a better accuracy (smaller tolerance). Just because the opertaor needs the gage to be ±1% does not mean it will consistently meet that accuracy when the manufacturer gave it a ±5% accuracy.

Rule 2. Precision of the gage is built into the manufacturer’s specifications. Do not try to prove precision. You are really determining the repeatability of the measurement process. Think gage repeatability and reproducibility (gage R&R). This has value for critical measurement systems and for measurement systems analysis if you require that level of detail.

Rule 3. Do not trust the specifications found on the Internet. They may be catalog or marketing specs, not the real specifications. Get the specification sheet from the manufacturer. Call them if you have to. For example, a temperature chart recorder may be advertised as having a 1 C accuracy. It will meet it, if you use signal injection to provide the input instead of a temperature probe. However, the paper chart will usually have an accuracy of 2 C due to the mechanics of the pen and chart. After connecting a temperature probe to the chart recorder the measurement system (probe + chart recorder electronics + paper chart) will have an accuracy greater than 1 C (a combined worse accuracy depending on each component in the system). So, the chart recorder accuracy will never equal 1 degree.

Rule 4. Establish a written agreement with the calibration provider. This may be a purchase agreement, service level agreement or a contract. Put the agreement in writing and make sure that you and the supplier understand your respective responsibilities. Include an out of tolerance notification procedure in the event your equipment or the supplier’s calibration standard is found to be out of tolerance.

Rule 5. Document the equipment’s calibration specifications in a controlled system. Identify the parameter, range, accuracy, etc. Provide this information to your calibration supplier and verify their calibration certificate meets the requirements you provided.

For example, consider an environmental chamber (oven). The customer has an oven and needs to monitor temperature. They use a chart recorder to continuously monitor the temperature. The chart recorder has a digital indicator and a paper chart (circular in this case). The calibration provider gives the customer a calibration certificate with multiple temperatures. What the customer does not know is that the provider disconnected the chamber’s temperature probe and signal injected the chart recorder. Then the recorded the temperature from the digital indicator on the recorder.

What’s missing? The calibration data for the temperature probe and the chart. The customer received a calibration certificate and thought their chamber was calibrated, but it wasn’t.

Rule 6. Verify you received what you asked for. One concern with providing the supplier with your requirements is getting those requirements to the technician that performs the work. Talk to your supplier and find out how those requirements will be communicated to the technician and verified by the supplier’s quality person before returning the gages to you. Compare the calibration certificate to the calibration requirements-they should match. If not, contact your supplier and find out what went wrong. Be sure to keep a document trail of the issue in case it happens again.


Bottom Line

If you do not know what calibration specifications you need, get help figuring it out or your financial bottom line could be adversely affected. It is possible to save money if you find out that you have been calibrating equipment that does not need it.

You may be thinking that if you have not had a problem with calibration before, everything must be great. It is, right up until you find out it isn’t from one of your customers, a regulatory agency, or when a product has to be recalled because of a measurement system error-one that could have been avoided if you had worked with your calibration provider to ensure they know what you need and you make sure that you receive it.


Quality Online

For more information on calibration, visit www.qualitymag.com for the following:

“Calibration Made Simple”

Q-cast Podcast: “Calibration Management Software: Important Factors Manufacturers Need to Know”

“The Importance of Scheduling Calibration”


Tech Tips

Calibration is one area where risk management is needed to reduce liability and expenses, whether you have an internal calibration department or outsource calibration.

As a customer of a calibration supplier, document your equipment’s calibration specifications and link them to the product or process.

As a provider of calibration services, request that your customers provide their requirements for each piece of equipment.