Electronics > Metrology
EEVblog on calibration
Wartex:
In this blog Dave mentions that "multimeter calibration" is not "adjustment":
https://www.youtube.com/watch?v=U4JFeU-o2kc#t=7m40s
This is FALSE.
Test equipment calibration is a process that consists of 2 steps (note that this is different from for example resistor calibration or some other passive component):
1. Calibration Verification
2. Calibration Adjustment
Verification allows to see deviation trends compared to previous results and measure deviation and uncertainties compared to the reference.
Calibration adjustment is a process where pots or multipliers/curves/offsets values in EEPROM are modified (provided there is nothing wrong with the meter electrically) to bring the meter into manufacturer spec within it's measurement ranges, this compensates for physical changes in the DMM components due to aging and chemical reactions. Calibration adjustment is NOT a repair process. Expensive DMM do this internally without opening the cover, they have internal references built in. Most still require an external high precision source to do the adjustment.
No respectable lab just sends you deviation report if the meter is out of spec, they actually DO adjust it. I called Fluke Calibration services to confirm this.
EEVblog:
--- Quote from: Wartex on December 10, 2011, 08:11:47 am ---In this blog Dave mentions that "multimeter calibration" is not "adjustment":
https://www.youtube.com/watch?v=U4JFeU-o2kc#t=7m40s
This is FALSE.
--- End quote ---
No, it's not.
--- Quote ---Test equipment calibration is a process that consists of 2 steps (note that this is different from for example resistor calibration or some other passive component):
1. Calibration Verification
2. Calibration Adjustment
--- End quote ---
Correct, but only if you ask for it.
Many customers require and will insist on a Verification report only.
--- Quote ---Verification allows to see deviation trends compared to previous results and measure deviation and uncertainties compared to the reference.
Calibration adjustment is a process where pots or multipliers/curves/offsets values in EEPROM are modified (provided there is nothing wrong with the meter electrically) to bring the meter into manufacturer spec within it's measurement ranges, this compensates for physical changes in the DMM components due to aging and chemical reactions. Calibration adjustment is NOT a repair process. Expensive DMM do this internally without opening the cover, they have internal references built in. Most still require an external high precision source to do the adjustment.
No respectable lab just sends you deviation report if the meter is out of spec, they actually DO adjust it. I called Fluke Calibration services to confirm this.
--- End quote ---
Of course no credible lab will just send you report saying it's out of spec.
If you have asked for a full calibration adjustment, then they will of course adjust it. If you only asked for a verification report then they will contact you ask ask if they should do a calibration adjustment as well to bring it back within spec.
Any credible lab with NEVER touch or adjust your equipment unless you specifically ask for it to adjusted.
At one company I worked at, if a cal lab did that, then they would be black listed, end of story.
It is very common practice for companies to maintain their own logs on equipment to build up a calibration history and confidence in the instrument drift over time. If the cal lab adjusts that gear then you have just ruined any traceable history you had built up.
Most of the time, gear does not drift out of spec and hence require readjustment back into spec, that is why good cal labs don't do that unless you ask them.
Every company has their own calibration needs and requirements, and a calibration lab will do exactly what you want them to do. That means first of all assuming that they should NOT touch or adjust your gear unless you specifically ask for it.
Dave.
FreeThinker:
Very True, I used to visit a company and they had their own Cal lab on site for just this purpose BUT sent all equipment off site annually to be externally verified. Was quite handy as I got to know the manager quite well and he would check my meter or scope whilst I was on site, no certificate but good enough for me Lol.
saturation:
Dave is right. It just a question of definitions. In common usage 'calibration' may really only mean verification. Adjustment often triggers an extra charge. For certain devices where adjustment is fairly easy, if not fully automated, they can do it inclusive with calibration.
http://service.tm.agilent.com/infoline/product-redir.aspx?pn=U1272A&lc=eng&cc=US
http://elsmar.com/Forums/showthread.php?t=22944&highlight=calibration+verification+adjust
In the UK:
http://www.npl.co.uk/reference/faqs/what-is-the-difference-between-calibration-and-adjustment-%28faq-pressure%29
Wartex:
Dave my point was that Calibration and Verification are NOT interchangeable like you use them. Calibration is a process, and verification is a procedure. All you are saying is that by default the lab does verification, and doesn't tune the UUT, which is understandable. I don't disagree with that, but stating that calibration is ONLY verification is false. By definition, calibration is ALSO adjustment:
http://www.merriam-webster.com/dictionary/calibrate
--- Quote ---3: to standardize (as a measuring instrument) by determining the deviation from a standard so as to ascertain the proper correction factors
4: to adjust precisely for a particular function
--- End quote ---
Because of your popularity you have a lot of power to greatly misinform public, remember that.
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