EEVblog on calibration - Page 1
Forum section: electronics / general

author: Wartex
author_rank: Frequent Contributor
timestamp: December 10, 2011, 08:11:47 am
content: In this blog Dave mentions that "multimeter calibration" is not "adjustment":https://www.youtube.com/watch?v=U4JFeU-o2kc#t=7m40sThis 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. CalibrationVerification2. CalibrationAdjustmentVerification 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.

author: EEVblog
author_rank: Unknown
timestamp: December 10, 2011, 08:23:39 am
content: Quote from: Wartex on December 10, 2011, 08:11:47 amNo, it's not.QuoteCorrect, but only if you ask for it.Many customers require and will insist on a Verification report only.QuoteOf 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.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: December 10, 2011, 01:13:29 pm
content: 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.

author: saturation
author_rank: Super Contributor
timestamp: December 10, 2011, 01:37:58 pm
content: 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=UShttp://elsmar.com/Forums/showthread.php?t=22944&highlight=calibration+verification+adjustIn the UK:http://www.npl.co.uk/reference/faqs/what-is-the-difference-between-calibration-and-adjustment-%28faq-pressure%29

author: Wartex
author_rank: Frequent Contributor
timestamp: December 10, 2011, 11:08:14 pm
content: 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/calibrateQuoteBecause of your popularity you have a lot of power to greatly misinform public, remember that.

author: EEVblog
author_rank: Unknown
timestamp: December 11, 2011, 05:33:45 am
content: Quote from: Wartex on December 10, 2011, 11:08:14 pmI am not going to play semantics with dictionary definitions.The whole point was to clear up the very common misconception that when a meter is sent away for "calibration", and gets the calibration sticker attached to it, it does NOT automatically mean that the unit has been adjusted. The fact is of course, in that in the majority of cases, adjustment is NOT made, only a calibration verification is usually performed unless you request otherwise (or the meter is out of spec). That is contrary to what your original post said.It is very common in the industry to simply say your meter is or was simply "calibrated", and few people care whether that means a full calibration adjustment (less common) or a verification (more common). So the one term "calibration" is used interchangeably in both cases. Nobody goes around saying "my meter was verified" etc.In either case, it still gets the magic "calibration" sticker stuck on it, and a report.I did not misinform anyone, I (hopefully) cleared up a misconception that sending your meter away for "calibration" automatically means it was adjusted.Note my use of the word "usually" in the video to qualify that they "don't usually adjust them meter". Yes, I could have gone into more detail on what that meant, but that was not my aim, my aim was to point out that in the majority of cases they don't adjust your meter unless you tell them too. That's the very common misconception.If you've got something to add, or think I am misleading people, or didn't explain it adequately, please upload a video response.Dave.

author: lowimpedance
author_rank: Super Contributor
timestamp: December 14, 2011, 05:05:11 am
content: When a DVM is sent in by a customer for calibration with adjustment, measurements are done before and after adjustment then aCalibrationreport is issued. If no adjustment is requested then measurements are done and aCalibrationreport is issued.If a resistor or a capacitor or Inductor for sent in, it is measured (considered as an artifact) and aCalibrationreport is issued.

author: iromero
author_rank: Unknown
timestamp: February 18, 2016, 04:16:06 pm
content: Quote from: Wartex on December 10, 2011, 11:08:14 pmSorry for bumping this old thread but i wanted to give my two cents.I used to work in an ISO17025 accredited cal lab, according to our governing standards body we used the following definitions (roughly, see below for the VIM definitions):* Calibration: Establish a relationship between a physical variable and an indication (for meters) or another physical variable (for transducers).* Verification: Use calibration data to determine if the meter or transducer performs within the customer's specifications* Adjustment: Alter the behavior of the meter or transducer, usually with the intention of making it conform to it's original or new specificationsSo, when a customer brought a meter to get calibrated with adjustment we did the following sequence of operations: Calibration, Verification. If the verification failed we did Adjustment, Calibration and Verification again. If the second verification failed again we would contact the customer to decide what to do with the instrument. In some cases the instrument could be repaired, calibrated and verified, in others it would just get junked and replaced.Some instruments and artifacts can not be adjusted, for example RTD transducers. In those cases we would only do Calibration, or Calibration and Verification, if the verification failed it usually meant the device was damaged and was thus replaced. We were legally required to preserve the Calibration history of the instruments since they were used for measuring the flow of natural gas at points of transfer ($$$$$$). If an instrument had been measuring high or low for a period of time between calibrations both gas companies would be extremely interested to know about it.Quote from: Wartex on December 10, 2011, 11:08:14 pmMerriam-Webster is not an authority in metrology last I checked, when talking about metrology you should really use the definitions in the VIM (International Metrology Vocabulary) as published by the BIPM.http://jcgm.bipm.org/vim/en/index.htmlQuoteAs it's usual with standards bodies, the above definitions are wrapped in even more jargon but are very precise, and roughly equivalent to the ones i worded at the beginning of the post.