Room temperature for calibrations on basic equipment like calipers, micrometers, etc.

beaser3

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Hello all,

I have been searching all of the posts but I can't seem to find a clear answer to my question. My company does internal calibrations on basic equipment like calipers, micrometers, etc. We are an ISO certified company so we have a procedure for calibration. The procedure does not specify calibration to be done in any kind of controlled environment. I cannot find anything in the quality system requirements that spells out what the environmental conditions must be. Could an external auditor write a finding if the temperature in the lab was over 75 degrees? What absolute thing can I use to say "we must keep the lab between.....and....."? Help?!?
 

BradM

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Re: Room temperature for calibrations on basic equipment like calipers, micrometers,

Here's one thread I found:

http://elsmar.com/Forums/showthread.php?t=19781

In general, yes, you will need to take into account environmental considerations. The more accurate your equipment and standards, the tighter it will need to be.

Metrology standards like Z540 and 17025 state that environmental conditions must be considered for undue effect and such....
 

Jen Kirley

Quality and Auditing Expert
Leader
Admin
Re: Room temperature for calibrations on basic equipment like calipers, micrometers,

The specifics spelled out would be found within the industry. Even ISO 17025:2005, 5.3.2 does not get specific: it says the laboratory will monitor, control and record environmental conditions as required by the relevant specifications, methods, and procedures or where they influence the quality of the results.

When I did calibration in a family owned machine shop, the room was a lot warmer than the 72 degrees F, 30% relative humidity that many cal labs would maintain. But the conditions were close to the conditions where the tools were being used, so okay, and besides the error would be based on a metals expansion coefficient of millionths... not tens of thousandths.

To summarize, what's required is that your conditions be suitable to produce the right results. That means you have to know what you need, know that you are meeting the need, and keep record of that. How all that's done is what your calibration process defines.

I hope this helps!
 
J

JAltmann

Re: Room temperature for calibrations on basic equipment like calipers, micrometers,

ISO 9000 and 16949 don't really cover enviroment for calibration work, so if your company procedures don't specify anything their is no non-conformity to write up.

This is not to say that an auditor won't site this as an observation, but unless your a 17025 accredited this isn't really covered. But realistically the calbrations should be done in a controlled environment, stability of temperature is more important than the actual temperature, but one should be careful when straying to far from the temperature the standard being used was calibrated at.
 
M

MIREGMGR

Re: Room temperature for calibrations on basic equipment like calipers, micrometers,

One reason why calibration temperatures sometimes are not standardized is that ultimately the goal is accurate measurements under actual conditions, rather than accurate measurements under theoretical conditions. A standard temperature is theoretical.

Isn't your ultimate goal that the devices are accurate across the temperature range at which they will be used?

If your facility is environmentally controlled, your thermostat setting + an engineering determination of the actuation range of your HVAC system on either side of its setpoint + some engineering observations of actual vs. theoretical would provide you with a temperature range for this requirement. Assuming that that temperature range is relatively narrow, single-temperature calibration at its midpoint usually would be justifiable, supported by an analysis that accuracy is acceptable across the temperature range.

Of course, in a facility that is not environmentally controlled and therefore has a wider (possibly much wider) temperature range, this may not be feasible. In order to achieve a goal of accuracy, the correct action is to either have multiple instruments available and indicated for use in particular temperature ranges, or re-calibrate more often...for instance, as the seasons change.
 

Jim Wynne

Leader
Admin
Re: Room temperature for calibrations on basic equipment like calipers, micrometers,

The specifics spelled out would be found within the industry. Even ISO 17025:2005, 5.3.2 does not get specific: it says the laboratory will monitor, control and record environmental conditions as required by the relevant specifications, methods, and procedures or where they influence the quality of the results.

When I did calibration in a family owned machine shop, the room was a lot warmer than the 72 degrees F, 30% relative humidity that many cal labs would maintain. But the conditions were close to the conditions where the tools were being used, so okay, and besides the error would be based on a metals expansion coefficient of millionths... not tens of thousandths.

To summarize, what's required is that your conditions be suitable to produce the right results. That means you have to know what you need, know that you are meeting the need, and keep record of that. How all that's done is what your calibration process defines.

I hope this helps!

Good advice. :agree1: If you're really curious about the effects of temperature and humidity on your calibration results, you can calibrate a few different types of devices in different conditions (shop floor and air-conditioned inspection area, e.g.) and record the results. Just make sure that you give the standards a chance to "normalize" (dwell in the area for a few hours, e.g.) before using them. Chances are you won't see significant differences, and you'll have something to show an auditor if the subject comes up.
 

BradM

Leader
Admin
Re: Room temperature for calibrations on basic equipment like calipers, micrometers,

The environmental condition of your metrology lab I don't think is a "You're getting written up for this" matter. ISO10012 and ANSI Z540 (and 17025) specify this undue influence point.

However, you should be able to provide evidence that the conditions are irrelevant, won't affect calibration, etc. Would you not say that necessitates measurement and control?

If it wasn't necessary, why does every legitimate, global metrology organization monitor and control environmental conditions?

As far as good metrology practices, it's borderline mandatory. You cannot calculate correct uncertainties without taking these into account.

I'm not saying a million dollar cal lab is mandatory. I'm saying you need to control undue influences, measure, and be able to provide evidence environment does not impact calibration.
 
J

Jeff Frost

Re: Room temperature for calibrations on basic equipment like calipers, micrometers,

But remember that ASME/ANSI Y14.5 Fundamental Rule (K) states that measurement temperatures “unless otherwise specified, all dimensions are applicable at 20º C (68º F).” Also MIL-STD-120 paragraph 8.2 states that “temperature should be constantly kept as near to 68º F as possible.

Not having time to research gage specifications you usually find that the specified calibration temperature of gages like calipers, mikes, gage block etc. is 20º C (68º F). When temperatures deviate from this nominal temperature you must factor in thermal expansion of contraction of the calibration standard.
 

Jen Kirley

Quality and Auditing Expert
Leader
Admin
Re: Room temperature for calibrations on basic equipment like calipers, micrometers,

But remember that ASME/ANSI Y14.5 Fundamental Rule (K) states that measurement temperatures “unless otherwise specified, all dimensions are applicable at 20º C (68º F).” Also MIL-STD-120 paragraph 8.2 states that “temperature should be constantly kept as near to 68º F as possible.

Not having time to research gage specifications you usually find that the specified calibration temperature of gages like calipers, mikes, gage block etc. is 20º C (68º F). When temperatures deviate from this nominal temperature you must factor in thermal expansion of contraction of the calibration standard.
Fair enough.

This article, Thermal Effects in the Real World, discusses the expansion coefficient. The author describes a larger effect than I would have expected. But my tolerances were in thousandths anyway. Besides, as I said I calibrated my shop's tools in the same temperatures as they would be used - and the gage blocks were in the same temperature all the time. They were rudimentary tools too; calipers, micrometers and dial indicators mostly.

You could also use ceramic gage blocks, though I recall they are a lower grade.

It's a good idea to write a process that recognizes you have thought of all this. Like Jim said, you could design an experiment out of this and keep the results on file if they convince you no temperature or humidity controls are needed.

I hope this helps! This is a good discussion.
 

AndyN

Moved On
Re: Room temperature for calibrations on basic equipment like calipers, micrometers,

Hello all,

I have been searching all of the posts but I can't seem to find a clear answer to my question. My company does internal calibrations on basic equipment like calipers, micrometers, etc. We are an ISO certified company so we have a procedure for calibration. The procedure does not specify calibration to be done in any kind of controlled environment. I cannot find anything in the quality system requirements that spells out what the environmental conditions must be. Could an external auditor write a finding if the temperature in the lab was over 75 degrees? What absolute thing can I use to say "we must keep the lab between.....and....."? Help?!?

If you are talking about ISO 9001 (not ISO/IEC 17025) then you have a pretty wide interpretation of what's 'suitable equipment'. It's very usual (at least in my experience) for calibrations to be performed at 'standard' conditions of temp and humidity. Normally, 68 deg. F.

The danger comes if you don't know about any termal effects on the measuring equipement and therefore on the measurements made. If you are using these basic measuring items at the edge of their resolution (0.001mm) or product feature tolerances, and the thermal effects from 68 to 75 F exceed this value, then you'll have a problem!!

This might seem like a 'gotcha' audit finding, but hey, the auditor is just using experience - especially if you give the 'deer in the headlights' response to their questions about thermal effects (or MSA studies)
 
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