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Calibration Laboratory Environment and Instrument Tolerances

V

Verod

#1
Hi, ;)
This is my first time asking for your help so I hope I'm giving you enough information for you to understand my problem. We are presently trying to certifiy to AS9100. Our calibration is mostly done in-house and we do not have specific tolerances for each of our instruments. We are a custom machine and fab shop and have over 3000 instruments of about 50 different types. I was wondering if anyone knows of a standard that could help me figure out what the acceptable tolerance for each instrument is. I am also searching for a standard that can give me the acceptable environmental conditions required for my metrology lab, i.e. temperature, humidy, lighting etc. Thanks,

Veronique
 

BradM

Staff member
Admin
#2
Re: Need help on calibration lab environment and instrument tolerances

Well, hello there! Welcome to the Cove!:bigwave:

Are the instruments currently being calibrated? Hopefully, previous calibration certificates would help identify tolerances. Also, hopefully the departments using the instruments would have some assistance.

As a default, you can start with mfg. specifications. Also, if you have access to industry specifications like GIDEP, they will be of assistance.

A good standard may be ISO17025. Basically, you will want to provide an environmentally controlled facility to perform the calibration work. The temperature, humidity, vibration, etc. should be controlled to the point that it does not create undue influence with the calibration. That is not only the Unit Under Test, but also the standards used.

If you would like, aside from any responses here, the search function may be of assistance. We have some Covers who have provided invaluable input on contructing, building calibration labs, control, establishing tolerances, etc. That may be a good option for you.

How long has your area been doing internal calibration work? Has it been done to any other specification/requirement? That can also gauge how much work your procedures and stuff may need.

Hope this helps.
 
#3
Re: Need help on calibration lab environment and instrument tolerances

Thanks, Brad - nice advice, especially about the GIDEP information. This is a relatively overlooked/unknown source.

The issue of controlling the environment isn't strictly required. It is important to know, through monitoring, what the conditions (temp/humidity in this case) are and their effects on the cal. result. You don't necessarily have to provide env. controls, simply to decide what to do, should the environmental conditions exceed the spec - like suspending any cal. work.
 

BradM

Staff member
Admin
#4
Re: Need help on calibration lab environment and instrument tolerances

The issue of controlling the environment isn't strictly required. It is important to know, through monitoring, what the conditions (temp/humidity in this case) are and their effects on the cal. result. You don't necessarily have to provide env. controls, simply to decide what to do, should the environmental conditions exceed the spec - like suspending any cal. work.
Good point, Andy. :agree1:That probably needed to be clarified.
 

Randy

Super Moderator
#5
Re: Need help on calibration lab environment and instrument tolerances

This sounds like a Hershal issue. He's travelling (and inside good old Arkansas as I type this). Hershal will probably drop in to visit the Cove tonight and will most likely jump in.
 

Hershal

Metrologist-Auditor
Staff member
Super Moderator
#6
Another source to look at is NCSLI.....they have Recommended Practices (RPs) that will provide guidance on environmental conditions, calibration cycle establishment, and other laboratory management and technical issues, even one on preparing for accreditation.....

Also as has been mentioned, GIDEP is a good source for procedures and related.....

Hope this helps.
 
V

Verod

#7
So if I get this right, there is nothing absolutely defined for calibration tolerances and environmental conditions in calibration labs that I have to respect. All I have to do is justify that what we are doing for the moment respects our customers' and manufacturers' specifications. Correct me if I am wrong. Thanks alot for your help guys.

Véronique
:thanks:
 
#8
So if I get this right, there is nothing absolutely defined for calibration tolerances and environmental conditions in calibration labs that I have to respect. All I have to do is justify that what we are doing for the moment respects our customers' and manufacturers' specifications. Correct me if I am wrong. Thanks alot for your help guys.

Véronique
:thanks:
Veronique:
If I read your post correctly, it's not quite like that. There are some well-established principles of tolerances on equipment that you will be calibrating, so you have to show that your calibration methods are capable of meeting those tolerances - this is why, for example, measurement uncertainty is important.

If we misled you on the environmental side, a point of clarification is that you don't have to invest in a complex control of the temperature and humidity, if you can show that you monitor conditions, that you can show what effect it has on the calibration result and, then, that you take action(s) when the conditions begin to have some quantifiable effect - like if the temperature got above a certain limit, based on a standard of 68F, let's say.

C'est tout!

Ca Va?
 

BradM

Staff member
Admin
#10
Spot on, Andy!

Verod, the accuracy of the instruments being checked is important. You are wanting to verify the equipment is operating properly, and work correctly for your needs.

As to the calibration lab, what Andy is saying is you are not mandated to go out and spend a fortune on developing some state-of-the-art lab. What you are required to do is control for environmental factors that may be significant (if there are any). Hence, Andy's point about setting up a recorder.

for example, if you are calibrating micrometers/calipers, then the gauge blocks (and Unit Under Test) will be affected by temperature and humidity. However, depending on the tolerance/classification, you may be OK with your current situation. If you already have a room that is monitored and the fluctuations are within the requirements for that class; you're fine. If it is not, then accomodations are in order to remove undue influences. Make sense? And since there are so many different influences, and so many different tolerances/classifications, it's just not accurate to make blanket statements about requirements.

It's less of a Shou Shalt..., and more of a getting control of your process, and assuring that all significant variables (noise) are controlled (minimized) when performing calibrations.
 
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