-------- In message <[email protected]>, Florian Teply writes:
>Now, as far as I understand, calibration at first sight is merely a >comparison between what the meter actually reads and what it is supposed >to read. As long as the difference between the two is smaller than what >the manufacturer specifies as maximum error, everything is fine, put >a new sticker to the instrument and send it back to the owner. What the sticker really says is that you have credible statistical reasons to think the meter will be inside spec until the date on the sticker. This is why you can go longer between calibrations if you have the calibration history for the instrument. If for instance you instrument over the last five yearly calibrations have been found to show 0.10, 0.15, 0.20, 0.25 and 0.30, then there is every statistical reason to expect it to show 0.35, 0.40, 0.45 and 0.50 at the next four yearly calibrations, barring any unforseen defects or mishaps, and the date for next calibration can be chosen accordingly. If on the other side its calibration history contains something like ... +0.25, -0.35 ... you know it can change 0.6 in one year and you may have to pull up the date on the sticker accordingly. If the instrument has no history and reads 0.35, you will have to consult the manufacturers drift specs and project forward and see what the earliest date the instrument can become out of spec, and write a date conservative to that estimate on the sticker. >Background of my questions is me wondering if it would be feasible to >do the calibration in house instead of sending equipment out for >calibration. The biggest advantage to inhouse calibration, is that you can do it much more often, and therefore don't need to do it as precisely as the cal-lab, because the sticker only needs date some months ahead. The second biggest advantage is that you can perform the calibrations in the target environment, rather than at some artificial enviromental conditions, which don't apply in real life. The third biggest advantage is that the calibration doesn't take the instruments out of commission for several days due to transport and scheduling, and they don't get damaged and lost in transit. The biggest disadvantage is that you need to maintain suitable cal-standards in-house. If it is just DC and AC voltage/current/resitance in the audio range, a HP3458A will handsomely pay itself back. Up to about some hundred MHz you do somethign similar with a good vector network analyzer. In GHz territory it gets nasty. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [email protected] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://lists.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
