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Calibration of steel rulers - Why do I need to calibrate it again?


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Related Topic Tags
calibration (general topics), rulers (as measurement devices), steel rulers & tape measures, tape measure
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  Post Number #1  
Old 4th April 2006, 10:32 AM
amanbhai

 
 
Total Posts: 846
Question Calibration of steel rulers - Why do I need to calibrate it again?

calibration of the steel rulers robe alot of money sometime more than its original cost, other thing that concerns me is that when we have calibrated it once (sometime maintain it as a Master) why do I need to calibrate it again? when it does not wear out, its state does not change. etc etc.

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  Post Number #2  
Old 4th April 2006, 10:40 AM
AndyN's Avatar
AndyN

 
 
Total Posts: 8,459
Let Me Help You What are they being used for.........

that would require calibration??

You have the option to 'verify' they are capable of the measurement they are being used for. That would mean checking legibility, damage and end wear, for example. Not trying to maintain measurement against a 'master'.......but like I said it depends what they're being used for..........

Andy
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  Post Number #3  
Old 4th April 2006, 10:42 AM
Dave.C's Avatar
Dave.C

 
 
Total Posts: 43
Apple calibration of the steel rulers

Quote:
In Reply to Parent Post by amanbhai

calibration of the steel rulers robe alot of money sometime more than its original cost, other thing that concerns me is that when we have calibrated it once (sometime maintain it as a Master) why do I need to calibrate it again? when it does not wear out, its state does not change. etc etc.
Are you talking about small 6" engineers rules, or larger ones?

Their state does change - a simple visual appraisal of its condition will show if it has been damaged, bent, or has markings that are no longer legible. I would also verify indicated sizes using a set of calibrated slip blocks. It doesn't take long and doesn't cost much either. (When I worked in an extrusion company I had to calibrate rules up to 4 metres long.)
  Post Number #4  
Old 4th April 2006, 01:04 PM
little__cee's Avatar
little__cee

 
 
Total Posts: 297
Calibrate vs. validate

I was told by our auditor that many companies confuse the need to validate with the need to calibrate -- I'm pretty sure that steel rules need validation, not calibration -- but don't take my word for it because his comments were directed at me! I'm one of the people who confuse what needs calibrated with what can be validated...
  Post Number #5  
Old 4th April 2006, 01:53 PM
Kevin H's Avatar
Kevin H

 
 
Total Posts: 489
My first question, is do you really need to calibrate the rules?
Secondly, I'll provide an example of what I helped set up in a prior position as a Mechanical Lab supervisor in a steel mill. We addressed calibration/verification of rules/rulers as follows: steel tape measures would be compared against a good quality stainless steel master rule with deep etched markings (I believe we purchased the master rules from Starrett.) that was permanently fastened to a steel lab table at the beginning of the turn & the info recorded. If the tape wasn't within +/- 1/16" they were discarded. (I suspect I supplied most of my employees with more tape measures than they needed, but it was a livable expense so I didn't realy push to eliminate it.) Quarterly, my "master rule" was compared to a master held by the inspection department (there were several other master rules throughout the overall department, & all were compared quarterly). Every 2 years, they sent their master out to verify it's accuracy and calibration. We had no issues with our auditors regarding this practice.
  Post Number #6  
Old 4th April 2006, 09:41 PM
Helmut Jilling

 
 
Total Posts: 4,343
Quote:
In Reply to Parent Post by little__cee

I was told by our auditor that many companies confuse the need to validate with the need to calibrate -- I'm pretty sure that steel rules need validation, not calibration -- but don't take my word for it because his comments were directed at me! I'm one of the people who confuse what needs calibrated with what can be validated...

This is an age-old debate. Metrollogy professionals will correctly argue if you don't adjust, then you are merely "verifying." The quality standards were not intending to be so precise. In fact the new standards now say:

"a) be calibrated or verified at specified intervals," (cl 7.6).

The point is, you have determined that the readings were accurate, and/or adjusted if required. It is the accurate reading they are looking for, not the terminology.
  Post Number #7  
Old 4th April 2006, 09:47 PM
Helmut Jilling

 
 
Total Posts: 4,343
Quote:
In Reply to Parent Post by amanbhai

calibration of the steel rulers robe alot of money sometime more than its original cost, other thing that concerns me is that when we have calibrated it once (sometime maintain it as a Master) why do I need to calibrate it again? when it does not wear out, its state does not change. etc etc.

As others have stated already, once you have verified that the marked increments are accurate, the neat thing about steel rules is the marks don't move around or all slide down to one end if you carry it in your shirt pocket too long. A simple verification of condition can establish that the readings are still reliable. That can still be a recordable inspection/verification event in your calibration database.

By the way, in some cases, the same concept can be applied to gage pins, blocks, and other solid blocks of metal where the actual tolerances used are not unusually precise. Why verify/calibrate a drawer full of pins every year if they don't get much use, and if there is no sign of any damage or markings that would have moved metal?
  Post Number #8  
Old 4th April 2006, 09:52 PM
AndyN's Avatar
AndyN

 
 
Total Posts: 8,459
Bomb! A rose by any other name..........

Quote:
In Reply to Parent Post by hjilling

This is an age-old debate. Metrollogy professionals will correctly argue if you don't adjust, then you are merely "verifying." The quality standards were not intending to be so precise. In fact the new standards now say:

"a) be calibrated or verified at specified intervals," (cl 7.6).

The point is, you have determined that the readings were accurate, and/or adjusted if required. It is the accurate reading they are looking for, not the terminology.
Not true - calibration has nothing to do with adjustment. It is simply knowing the amount an item of equipment is 'off' the standard.

Some cal. professionals might explain that and so might a few consultants. The terminology is important, to those people who understand the concepts........

Happily, that's why accreditation auditors are competent in their tasks (well, they're supposed to be......... )

Andy
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