Verifying a Standard with a Standard using Micrometers

J

jrose

#1
Greetings everyone :agree:

I have a 6 inch starrett standard that is used to verify a set of micrometers before use. I was wondering if I can verify this with another standard? The other standard is a gagemaker Mictrac. Thanks for any help.
 
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E

erbearica

#2
Re: Verifying a standard with a standard

Hi jrose,

As a calibration technician I personally would say no. If I feel that they are questionable I use my set of certified gage blocks to verify them.
 
J

jrose

#3
Re: Verifying a standard with a standard

Hi erbearica. So Then it will be okay to verify them with another standard?
 

howste

Thaumaturge
Super Moderator
#4
Re: Verifying a standard with a standard

Hi Jrose, welcome to the Cove Forums. :bigwave:


Greetings everyone :agree:

I have a 6 inch starrett standard that is used to verify a set of micrometers before use. I was wondering if I can verify this with another standard? The other standard is a gagemaker Mictrac. Thanks for any help.
I'd say it depends on a number of factors. First, the standard used for verification must be traceable to national or international standards. You also want the standard used to be more accurate than the item being verified. The preference is 10 times more accurate, but 4 times more accurate may be acceptable. So, the 6" standard has to be more accurate than the micrometers, then the Mictrac would need to be more accurate than the 6" standard.

Do you know the accuracy of each one? Does the Mictrac have enough resolution to distinguish the accuracy required?
 
J

jrose

#5
Re: Verifying a standard with a standard

Hello howste, The mictrac is traceable back to nist and is accurate out to 5 decimal places. I do not however know what the accuracy of the starrett standard is supposed to be. Thanks for your time
 

howste

Thaumaturge
Super Moderator
#6
Re: Verifying a standard with a standard

As the user of the instruments you have the ability to specify the accuracy needed for each. Look at what the micrometers are used to measure and determine the accuracy required. The 6" standard should be at least 4 times more accurate, and the Mictrac at least 4 times more accurate than that.

If the best you have is a 4:1 (versus 10:1) ratio, you should also pay close attention to the measurement uncertainties reported (I hope) on the calibration certificate for the Mictrac, as this will also help to decide if a 4:1 ratio is enough. Ideally you should also determine the uncertainty of the verification you do on the 6" block.
 

BradM

Staff member
Admin
#7
Re: Verifying a standard with a standard

The accuracy ratios essentially increase your confidence in the results. If you have a 1 to 1 ratio, then you are almost flipping a coin. :)

http://www.transcat.com/PDF/TUR.pdf

This Transcat document does a pretty decent job of visually showing the value of obtaining high ratios.

I think you should write up a comparison ratio between the stated accuracy of the mictrac, and the required accuracy of the micrometers that you are assessing.

How long have you been using this verification process? Have you noticed any issues? Have your customers reported any failures?

While you do need to assure adequate ratios (gives more confidence in the results), it's more important to establish a measuring system that is valid, and one that will detect when you have a problem. :)
 
J

jrose

#8
Hmmm this is more complicated than I thought :tg:. Perhaps its a better option for us to send those standards out to a third party for calibration.
 
I

Inunez

#9
i believe you are talking about a 6" length rod, correct? in this case, assuming (because you didnt mention anything about a vernier scale) your micrometers measure to a resolution of .001", your length rod should be accurate to .0001". there are plenty of options for measuring length rods, just make sure you adhere to the 10:1 rule if possible. personally i would say you need a surface plate, a vice, and a height gage. hope this is helpful:popcorn:
 
S

step30044

#10
Re: Verifying a standard with a standard

Hello howste, The mictrac is traceable back to nist and is accurate out to 5 decimal places. I do not however know what the accuracy of the starrett standard is supposed to be. Thanks for your time
Is the Mictrac accurate to 5 decimals OR is the resolution 5 decimals places? You have to be careful when stating accuracy.
 
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