Derivative Measurands to CMC

Jerry Eldred

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#1
Don't you love the big words.... Okay, Lets say I am accredited to generate and measure (for example) 1000 VDC and to measure current to as low as 1 pA (picoamp). But, for example, I am accredited on my CMC to measure up to 2 Giga Ohms.

Even though I am accredited to 2 Giga Ohms, I can put 1000 ACCREDITED Volts across an unknown resistance, and measure the ACCREDITED current to as low as 1 picoamp. This combination theoretically results in 10E15 Ohms (1 Peta Ohm = 1,000 Tera Ohms = 1 Million Giga Ohms). There are of course all of the contributors of repeatability, drift, resolution, uncertainties of calibrations, etc...

So although the cumulative uncertainty of a given established resistance would have lots of contributions, would it nevertheless be accreditable? This, as a derivative measurement to my CMC? Or even if I am able to make the measurement and subsequent derived (possibly) accredited resistance value, would I be limited to CMC, even though my CMC allows me to directly accredit the input parameters (i.e.: voltage source and current measurement).

I could then (if this is accreditable) accredit these values, and make accredited measurements with them which would not exceed my CMC. Or is this the sort of question I should ask my accrediting body?
 
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dgriffith

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#2
Don't you love the big words.... Okay, Lets say I am accredited to generate and measure (for example) 1000 VDC and to measure current to as low as 1 pA (picoamp). But, for example, I am accredited on my CMC to measure up to 2 Giga Ohms.
I just read this, and perhaps you already have it: https://www.ilac.org/documents/ILAC_G18_04_2010.pdf
What is your measurement method for the 2G accreditation (resistor std?), and why so low if you can derive greater?
I could then (if this is accreditable) accredit these values, and make accredited measurements with them which would not exceed my CMC. Or is this the sort of question I should ask my accrediting body?
Hopefully by now you have done so. Even with the wealth of knowledge others here have, this looks like a stickler.

I might add that according to the document, flexible scopes are not allowed for calibration labs, only testing, if I read that right. Perhaps you cannot derive greater than your scope or use methods other than described in your scope?
 
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