Calibration Interval based on Usage

normzone said:

An interesting challenge, and cases can be made for differing approaches.

In a previous lifetime, I worked with a process equipment manufacturer whose product line went back the better part of a century.

I inspected new electronic components and parts made from wood ordered against sixty year old drawings.

There was a bank of vernier and digital measurement tools - some were calibrated every year, some never.

There was a concealed vault of hundreds of acme thread gages that were antiques. Some saw use once every decade or three.

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if you use the gage, and expect the results of the gage reading to be usable information, the gage must be verified, even if it is 100 yrs old. If it is not known to be accurate, how can you use the results. Especially if it is 100 yrs old. If the results do not have to be accurate, take the reading with your eyes closed....what kind of reading would not have to be accurate results.

To start with, this is what I am trying to do, an "x-days/y-uses" system.


From what I have seen it's all an "educated guess"! If the calibration is 3-months, and it always passes, about how many uses do you figure it goes through in that time; there's your number to start with. You can always adjust.

Due to the usage and amounts of 'personal' calipers, OD mics, and indicators, I check these annually. There are calibrated gages on the shop floor for pre-use checks, this was required long-before we got ISO-9001.

My set-plug gages are used once per year, and only by me. These have a 5-year calibration and have been around for a few decades.

I have three height gages in calibration that are 'not calibrated until used', I've been in this position for about three years and have calibrated one, once.

Hope this helps.

drgnrider said:

To start with, this is what I am trying to do, an "x-days/y-uses" system.


From what I have seen it's all an "educated guess"! If the calibration is 3-months, and it always passes, about how many uses do you figure it goes through in that time; there's your number to start with. You can always adjust.

Due to the usage and amounts of 'personal' calipers, OD mics, and indicators, I check these annually. There are calibrated gages on the shop floor for pre-use checks, this was required long-before we got ISO-9001.

My set-plug gages are used once per year, and only by me. These have a 5-year calibration and have been around for a few decades.

I have three height gages in calibration that are 'not calibrated until used', I've been in this position for about three years and have calibrated one, once.

Hope this helps.

Click to expand...

The info you are presenting sounds reasonable....

This reminds me of getting your oil changed in your car. 3 months or 3,000 miles whichever comes first. It depends on a lot of things. The only way to know 100% is to start collecting data of days, temp and humidity in storage etc.. and see when they actually are out of cal. Then you can see what factors affect the date range. I would suggest your usage calibration interval but add a not to exceed 1 or 2 years depending on what type of equipment it is. Electronics should be done more frequently, anything with "potentially store energy" should be done more frequency. So torque wrenches and such more often.
Pressure gauges don't wear unless used
torque wrenches springs can loose elasticity so more often
electronics can get corroded and gain/loose resistance
dimensional units can get corroded and gain/loose length
These are just a few factors I can think of. It also depends on how accurate you need your measurements to be.

I faced this problem during planning of calibration intervals of my plant and I applied a simple procedure which helped me to control the calibration intervals based upon some factors.

We cam simplify this procedure as per the attached flowchart and the auditor accepted it and I applied it on my calibration plans for tracking of calibration due date according to the history of the equipment.

Your fruitful suggestions will be appreciated.