How to Calibrate a Vernier Caliper - Detailed Procedure

A

abdallah - 2005

Hi
can someone please supply me with a detailed procedure of how to calibrate a vernier caliper.
I need to know how many points to measure and how many points to use to obtain the uncertainty.
How should the results be illustrated in the certificate?
tabular or graphical form and what are the results that should be included in the certificate?

Thank you for the help
 
T

TownDawg

Clean jaws and track of dirt, grease and foreign matter. Verify that gear moves across tracks freely. Bring jaws together and note reading (dial should be reading zero, also if dial is not reading zero, move the dial face to zero set and continue with checks).

On the #1 check (OD jaws) insert a .500-inch (12.7 mm) gauge block between the jaws of the caliper and close so both jaws are touching the gauge block. Record reading.

Repeat steps with a 1-inch (25.4 mm) gauge block and 4-inch (101.6 mm) gauge block. Record reading.

Repeat using appropriate size micrometer standard (150, 200 or 300).

On the #2 check (ID Jaws) set the calipers on 12.7mm and lock into place and measure the jaw width with another pair of calipers that have been calibrated (caliper number must be recorded for traceability). Record reading.

Repeat step for 25.4 mm and 101.6 mm and appropriate length of caliper (150, 200 or 300). Record readings.

On the #3 check (height check) set 12.7 mm gauge block on surface plate, extend the caliper above the block and bring down to touch the block. Record reading.

Repeat step for 25.4 and 101.6mm gauge blocks. Place appropriate size micrometer standard on surface plate and extend the caliper above it and bring the caliper down to touch. Record readings.

Maintain readings on file in the Quality Department.
 
A

abdallah - 2005

Thank you TownDawg

Thank you TownDawg for the post. This is quite helpfull.
1. Can you tell me how many readings are necessary to obtain the imprecission?
2. Is the uncertainty that is recorded in a calibration certificate that of the block gauges used? if so how do i obtain this?

Thank you again
 

Hershal

Metrologist-Auditor
Trusted Information Resource
You will likely need at least three readings to calculate the uncertainty for the calipers. More readings are perferred, but typically three is minimum. That is your Type A uncertainty.

The uncertainty for the calibration of the calipers does include the uncertainty of the gage blocks.....but that is only one part. Gage block uncertainty will be a Type B in your calculations, and should be provided in the calibration certificate for the gage blocks.

Other influences include temperature, the coefficient of thermal expansion for both the calipers and for the gage blocks, and the resolution of the calipers. These are all Type B uncertainties.

Hope this helps.

Hershal
 
A

apatil101

Re: How to Calibrate a Vernier Caliper - Seeking Detailed procedure

Hello Everyone ,

This is Amol Patil , I was working on the calibration procedure for Vernier Caliper I found the above information very useful. I just had few questions regarding the procedure specified by 'TownDawg' in his post.

1) Do I have to use same gauge block size as specified above only ? Or I can use the combination that is available. For example I have a gauge block set of 516-931 which doesn't have a 4 inch gauge block.

2) How do we capture the inaccuracies on the entire range of the caliper. Does this sample procedure apply for a caliper on 0-6" and 0-24" ?

These question arise from the fact the we only use higher range of the caliper for our measurements , my concern here is how will certify the entire range of caliper ?

Any guidance and suggestions most welcome ..........as its great learning opportinuity for me

Thanks,
Amol
 
S

sumanstephen

Re: How to Calibrate a Vernier Caliper - Seeking Detailed procedure

@Wes Bucey, nice idea, thats quite easy,
To add more to check for the internal jaws,
what I have seen outside calibrated vendors use are master 1.000" Ring gages to check the inside of the jaws, and you check it @ 2 spots of the ring.
You can also further check the inside @ a bigger size ring 3 -4" size ring, whichever you can find.
Suman
 
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