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Poll

I am rewriting a document for someone who has indicated that a transfer standard may not always have to be calibrated. My opinion is that it would have to be calibrated. There's is that it wouldn't if the outputs weren't "explicitly used?

Do you agree it could be a Class 2?
2 (66.7%)
Agree it should not be Class 2?
1 (33.3%)

Total Members Voted: 3

Author Topic: Test - transfer standard useage  (Read 7695 times)

Offline OperaDiva1

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Test - transfer standard useage
« on: 01-22-2009 -- 18:42:55 »
Hi Again,
The wording on the original document is defining differing kinds of measurement classes assigned to equipment.  Class 1 being a measurement that is taken "only" on an instrument that has been calibrated to a traceable source.  A Class 2 measurement is one taken on an instrument for indication only, non-reportable data, etc.  This document calls out the following as a Class 2.  I do not agree because of the very nature of what a transfer standard is, but I wanted some input from other pro's.  Here's the wording:

The instrument is used as a transfer device whose measurement or output value is not
explicitly used.

Please let me know what you think.

Thanks a lot,
OperaDiva1

Offline flew-da-coup

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Re: Test - transfer standard useage
« Reply #1 on: 01-23-2009 -- 14:54:43 »
If I am reading you correct you are just asking if a transfer standard needs calibration? If this is what you are asking then NO. There is no reason for calibrating a transfer standard. You will not list it as a standard on you cert.

For example: I have a resistance meter (DUT) and a decade resistor (transfer standard) and a 3458A DMM (STD). I would list the 3458A as the standard.

Is this what you are asking?
You shall do no injustice in judgment, in measurement of length, weight, or volume.Leviticus 19:35

Offline OperaDiva1

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Re: Test - transfer standard useage
« Reply #2 on: 01-23-2009 -- 20:35:19 »
Hi flew-da-coup,
Thanks for taking the time to reply.  To answer your questions, yes, I guess that is what I was asking.  I have been out of the metrology field for about 9 years and am a bit rusty on some stuff.  Where I work at now is asking me to help them with their metrology stuff, which I am thrilled about.  I'm just trying to get back up to speed in a hurry.  I have no other professionals in this area to confirm theory questions with; therefore the question.  I had put in an email to my old supervisor at a cal lab I used to work at.  When I posted the question earlier I hadn't yet heard from him.
I did get an email later from my old supervisor from a calibration lab that neither of us work at any longer. 
This was his response:

If the transfer device is used only in a condition where it gives the exact same reading when transferring between two items and the measurement is repeated at least 3 times to account for repeatability, it could be class two.   However, if the transfer relies on the instrument to give a differential reading between two items, then it would be should be a class one.

Example:  A balance being used as a transfer between an unknown and set of standards.   If the balance is brought to the same point using trim weights of the standard set and the value of the unknown is determined by the combined weight of the standard and trim weights, then that would be class two.   If the two readings of the balance is used and subtracted to determine the unknown, then class one.

Many devices that are called transfer devices such as gage block comparators, null meters, and mass comparators need calibration.   It would be incorrect to state that all transfer devices are class two.

From his response and the definition from the PMEL Measurement and Calibration Handbook:HO E3ABR2POX1-OB1A, Nov 2005
Transfer Method: An accurate method of measuring voltages and currents using a thermocouple meter and the universal potentiometer.  It consists of measuring the input, and then duplicating the input reading with an internal source.  The internal source voltage is then read with, the universal potentiometer.

Sorry for the length, but I wanted to make sure you understood what I was asking.
It was my personal experience to have worked with electronic transfer standards.  That's why I assumed they had to be calibrated.  So, yes what I was asking is it is correct to set a policy that states transfer standards do or don't have to be calibrated.  I'm thinking if it's an electrical, active and not passive, that you would have to have it calibrated.  Do you agree?
Again, sorry for the length.  I'm new at this posting stuff, so please be patient.  Thanks for any input in return.
Opera Diva :-)

 

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