Can I calibrate Optical Comparators internally?

  • Thread starter Bob Gallinger - 2007
  • Start date

Jim Wynne

Staff member
Admin
#11
Re: Optical Comparators - Can I calibrate Optical Comparators internally?

jane_ackerman said:
Sorry if I am beating a dead horse here... but what would you use to certify your angle (and radius) gages besides an optical comparator?
Two thoughts:

1) Calibration masters, reasonably cared for, won't significantly change. There is generally no need for calibration of masters beyond an initial certification.

2) If, for some reason, someone does want to calibrate masters, it's cheaper than having an outside service calibrate the comparator.
 
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Hershal

Metrologist-Auditor
Staff member
Super Moderator
#12
Re: Optical Comparators - Can I calibrate Optical Comparators internally?

Jim Wynne said:
Two thoughts:

1) Calibration masters, reasonably cared for, won't significantly change. There is generally no need for calibration of masters beyond an initial certification.

2) If, for some reason, someone does want to calibrate masters, it's cheaper than having an outside service calibrate the comparator.
Actually, though the masters may or may not change a lot, they do change. That is why they require calibration. Often - depending on how the item is cared for - the cycle can be extended to perhaps 3 years.....but the master still needs calibration, otherwise how much change there has been, and how much error the master device has will not be known. The error of course is meaurement uncertainty.

Using a master as a check internally I certainly support.....but proper calibration is not cheap.....I support having trained and qualified metrology professionals taking care of this technical function, just as a machinist takes care of CNC machines, or a black belt heads up the six sigma functions.

Hope this helps.

Hershal
 

Hershal

Metrologist-Auditor
Staff member
Super Moderator
#13
Re: Optical Comparators - Can I calibrate Optical Comparators internally?

Oh, one other point.....it may well be cheaper to have an outside service cal the comparator.....

Why? Here is what must be considered.....

Price to acquire the master device to calibrate the comparator.
Price to have the master device calibrated properly.
Time required for the company person to obtain or write a procedure.
Time required to train the person in the procedure.
Cost to assure control of the procedure in the QMS.
Time for company person to actually calibrate the comparator.
If the calibration is also to be traceable, time and effort to calculate measurement uncertainty, plus any costs involved for MU training.

Time is calculated at whatever the overhead rate is for the personnel involved.

Hope this helps.

Hershal
 
R

roland_lu

#14
Re: Optical Comparators - Can I calibrate Optical Comparators internally?

Hershal said:
Often - depending on how the item is cared for - the cycle can be extended to perhaps 3 years.....but the master still needs calibration, otherwise how much change there has been, and how much error the master device has will not be known. The error of course is meaurement uncertainty.

Hershal
How do we know the master will not change significantly during these 3 years? The argument will never end.

For small companies, the cost for calibration is really unbearable. I used to work for a small tier-2 auto supplier, we changed the master blocks and CMM external calibration interval to 4 years, backed-up by the facts that they are well cared for and used not very often (how to define often?). The auditor did not challenge us, I guessed he understood the business is tough.
 
G

Grizz1345

#15
Re: Optical Comparators - Can I calibrate Optical Comparators internally?

The best way I know of to check angle blocks is to use a sine plate (calibrated), gage blocks and height gage with indicator. Radius gages you can use pins. I had my radius gages checked by an outside lab and now just do a visual for damage (nicks and burrs). Hope this all helps.:)
 

Jim Wynne

Staff member
Admin
#16
Re: Optical Comparators - Can I calibrate Optical Comparators internally?

Hershal said:
Actually, though the masters may or may not change a lot, they do change. That is why they require calibration. Often - depending on how the item is cared for - the cycle can be extended to perhaps 3 years.....but the master still needs calibration, otherwise how much change there has been, and how much error the master device has will not be known. The error of course is meaurement uncertainty.
The question is how "change" is defined. Of course it depends on the nature of the standard (master) itself, but it's not unusual to see blocks, radius and angle masters remain unchanged for practical purposes for many years.

Hershal said:
Using a master as a check internally I certainly support.....but proper calibration is not cheap.....I support having trained and qualified metrology professionals taking care of this technical function, just as a machinist takes care of CNC machines, or a black belt heads up the six sigma functions.
Hershal
I agree :agree1:
 
B

Bob Gallinger - 2007

#17
Re: Optical Comparators - Can I calibrate Optical Comparators internally?

I mean certified by a 17025 accredited lab, with NIST tracablity.
I believe I would need a couple of good class (tolerances) of angle blocks. Once I have the certified externally then I should be able to use them for my internal calibration of opticals, along with my certified gauge blocks. What else do I need ????? and what class (tolerance) of angle blocks should I purchase ????
Thanks
 

Hershal

Metrologist-Auditor
Staff member
Super Moderator
#18
Re: Optical Comparators - Can I calibrate Optical Comparators internally?

One question.....why NIST traceability? Since you are in Canada, why not traceability through NRC?

Just curious.....

Hershal
 
B

Bob Gallinger - 2007

#19
Re: Optical Comparators - Can I calibrate Optical Comparators internally?

Good question, NRC is the canadian equivalent to NIST correct ?????
Pretty much all the external Labs up here that we use report NIST tracable equipment/standards used when certifing. This question has never been brought up during our annual audit.
 

Hershal

Metrologist-Auditor
Staff member
Super Moderator
#20
Re: Optical Comparators - Can I calibrate Optical Comparators internally?

NRC is in fact the Canadian NIST, both are signatory to BIPM, and either is equally acceptable in North America for traceability.

Hershal
 
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