Who calibrates calibration equipment?

Depends on your system. In a ISO 9000 company in the US the metrology department should be using NIST traceable standards to calibrate measurment equipment.

A NIST traceable standard would then go back to NIST occasionally to be checked as well against the NIST standard, and recertified.

More on the NIST here...

http://www.nist.gov/

Each level of instrumentation is calibrated by a higher level laboratory. If you are calibrating a basic pressure gage with a portable unit and send the portable unit out for calibration they will have standards of higher accuracy than you have. That lab will again be traceable to a level 1 lab and that lab will be traceable to NIST or the national institute of science and technology where our country holds its National standards for units of measure. There is also an international lab in france.

The idea is to have each and every measurement traced to a more accurate system.

Hope this helps.

kgohre

It's interesting that so far all comments talk about "accuracy". There is also another feature that is important and that is "precission".

NIST (U.S.A.), N.A.T.A. (Australia) and the other national measurements authorities all have a handy little book of definition of terms that is often very handy even if you're not a calibration lab.

Having such a reference handy will enable you to define the calibrations you need to have done and also to interpret reports the higher level labs provide.

It's up to a standards group to adopt and publish an acceptable tolerance.

It's up a individual to accept and adopt the standard published by the standards group.

This adherance or lack thereof, to said standard should be such to impress a judge and/or jurry in a liability trial.

Actually its the instrumentation department:

Or a lab substituting for that department. For a while I held a gig in such a lab. We worked with all kinds of standards equipment calibrated by the national standards lab.

We recalibrated just about every electronic/mechanical measuring device. That was being used for calibration/test through the rest of the company.

A pressure gage would be connected to a line with a calibrated gague also on the line. It would be tweaked to match the calibrated guage, or tossed/replaced if that was not possible.

Hope that halped a bit.

DBD

As already said by some other colleagues, any measuring equipment should be calibrated against a higher class (best accuracy, less uncertainty) equipment, and so on.

There must be a traceability to national or international standards, that means NIST traceable in the US or an ENAC accredited laboratory in Spain or the similar in any other country.

National laboratories make sometimes inter-laboratory comparisons to validate their primary masters, that's the upper limit. Primary masters of National organisations can't be calibrated against more accurate devices, as they are by principle the "most" accurate so, the only solution is intercomparison between different laboratories.

Best regards

Oh my god! Now I am all confused. Who calibrates the equipment used to calibrate the equipment used to calibrate the equipment used to calibrate the equipment used to calibrate the equipment used to calibrate the equipment used to calibrate the equipment used to calibrate the equipment used to calibrate the equipment used to calibrate the equipment used to calibrate the equipment used to calibrate the equipment used to calibrate the equipment used to calibrate the equipment used to calibrate the equipment used to calibrate the equipment used to ...

Confusion is one thing traceable standards remove.

But understanding the apparent circular logic generated by bureaucrats seems to introduce generate more confusion that even the best traceable standards remove.

I've worked in a Metrology Lab (the Science of Measurement) for the last 15 years. Some of our equipment goes out to 9 digits (billionth). Each facility has a set of Calibration Standards for whatever discipline you have (length, time, amount of substance, light intensity, current, thermodynamic temperature and mass) or you can send it out to a Calibration Service. The Standards are 2 to 3 times more accurate than what your testing. Those instruments are calibrated yearly, semi annually or quarterly depending on how they fall out of tolerance. Everything has a plus or minus tolerance in a proper functioning instrument. If it can't be readjusted or repaired it is replaced. Your instruments are sent to a Calibration Laboratory, theirs are sent to a Secondary Lab and theirs are sent to the Primary Lab which is the highest level you can go. Everything is referenced to the Seven Base Units. An example would be for Mass. The Unit for Measurement is the Kilogram. It is the only unit defined as a physical artifact, the mass of the artifact cylinder of platinum iridium alloy kept by BIPM in Paris, France and Time is measured by the cycles of radiation corresponding to the transition between the 2 hyperfine levels of the ground state of the Cesium-133 atom. So it's all like a pyramid, the more accurate you need the higher you have to go. As for your pressure gauge, you put it in parallel with the standard, pressurize it at the lowest point, a few throughout the range and close to the maximum. Record the results. Look in the spec sheet for the tolerance values. If it's "out of tolerance" you adjust it if possible. If it's "in tolerance", you fill out a calibration report that includes the values you tested at, date, time, who did it, the standard used and when the standard was last calibrated. Everything has to be documented and traceable all the way up to the National Standard.

Ah, but recent reports suggest that the pltinum iridium cylinder is, in fact, losing mass with time...

But, what is a few neutrons or electron amongst friends?

If we're going technical, I seem to remember 'krypton86' or something similar ( a Superman sounding isotope) was used to ascertain the standard for length using the wavelength of it's spectrum! I think it may have changed over the last few years but to what, I'm a bit unsure!