Digital Caliper Calibration vs. Verification - Full Scale vs. Used Range

J

JSmith

#1
Hello,

I have a question regarding the calibration / verification of Digital Calipers.

If my company uses calipers to measure parts up to 1 1/2 " only, would it be acceptable for me to verify the 6" calipers from 1 - 2 " with my gage blocks over that range and not send them out for calibration to an outside company?

Thanks

Jen
 
Last edited by a moderator:

Hershal

Metrologist-Auditor
Staff member
Super Moderator
#2
Only thing to consider here is: What is the likelihood that the calipers will ever be used outside the 2" range?

If none (or almost none), then calibrating to only the needed range is advisable. Caliper calibration is cheap so ou may not save any mone, but ask.

Of course, I always recommend using an calibration lab accredited to SO/IEC 17025.

Hershal
 
K

Kevin H

#3
Hi Jen, ,my experience is a little dated, as I left when the Mechanical Testing lab I ran was transitioning from ISO Guide 25 to ISO Guide 17025 about 4 years ago. That said, in our case the supervisor (me) was responsible for quarterly calibration of the digital electronic calipers we used. The calipers were used to measure elongation from tensile testing of flat rolled stainless steel. The primary measurement area was between 2" and 3", 2" being the initial measurement before beginning tensile testing and 3" being reached or exceeded only on rare occasions. I used gage blocks to check over the ranges we'd typically use, beginning with verifying the zero location, then checking at 1/2", 1", 2", 3" and 4". If they were off, I had some adjustments I could do to bring them into calibration, or could send them out for work & recalibration by an external source. On a daily basis, they were verified by each turn by checking the zero value and then verifying against a 2" gauge block. At that time the program satisfied our Guide 25 registrar - A2LA.
Of course, we also did round robin testing of tensile specimens that was reported to both us and our registrar. That testing included comparing all results from specimens prepared and tested by the lab including elongation.

Hope the information helps in making your decision.
 
G

gaugefixer

#5
Hi Jen,

Yes, perfectly acceptable. I am wondering if you do any calibrations in house or do you send them all out? Seems like a waste to send out a 6" digital caliper for calibration if you have your own gauge blocks and a few basic tools.
If you have gauge blocks you can do your own calibrations; you would just need to record the results and the procedure you used.

Roger



JSmith said:
Hello,

I have a question regarding the calibration / verification of Digital Calipers.

If my company uses calipers to measure parts up to 1 1/2 " only, would it be acceptable for me to verify the 6" calipers from 1 - 2 " with my gage blocks over that range and not send them out for calibration to an outside company?

Thanks

Jen
 
J

JSmith

#6
Hi Roger,

I have gage blocks to calibrate the od side. Will I need to calibrate (verify) the ID side as well? If so do I have to use a set of ring gages or could I use certified micrometers to calibrate the ID?

Thanks for your help,

Jennifer
 
K

Kevin H

#7
Jen, If you're using both ID & OD sides of the calipers you need to calibrate both. You can end up with a minor, visually undetectable flaw that will invalidate the measurement. I've used micrometers to verify the ID jaws of a digital caliper by first using a gage block to set the micrometer, locking the micrometer, then calibrating the ID jaws of the caliper, then double checking the locked micrometer with the gauge block. This was acceptable to our A2LA auditors for an ISO Guide 25 mechanical testing lab at a steel mill.
 
G

gaugefixer

#8
Hi again,

I agree totally with what Kevin said. You can also use master rings if you have them.

Roger
 
G

Graeme

#9
Special calibration: 0 to 2 inch only

The only thing I have to add to this discussion is --

Consider marking the caliper with the range it is calibrated for. That will greatly reduce the chance of inappropriate use. Many companies that sell calibration labels have "special" or "limited" calibration labels or tags for this purpose.
 

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