How much will a teardown inflict on a instrumenst calibration? - Page 1
Forum section: electronics / testgear

author: ErikTheNorwegian
author_rank: Frequent Contributor
timestamp: April 07, 2017, 09:06:45 pm
content: How much will a teardown inflict on a instrumenst calibration?Do it need a new calibration after a teardown?

author: coromonadalix
author_rank: Super Contributor
timestamp: April 07, 2017, 09:12:32 pm
content: If your teardown is made with caution, do not touch adjustments, or take really good care when unplugging boards etc ... it will retain its quality or integrity.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 07, 2017, 09:31:31 pm
content: It also depends on the instrument. In a 4.5 Digit DMM I would not worry very much. This can be different with something like an VNA. Some instruments are somewhat sensitive to moving shields around.In many cases there is a kind of legal - calibration void if opened rule. So if you need an official calibration (e.g. for ISO900x stuff) don't open it.

author: james_s
author_rank: Super Contributor
timestamp: April 07, 2017, 11:45:23 pm
content: That was annoying when I worked for a place that was ISO certified. Seemed like more often than not equipment would come back to us calibrated but missing screws or put together wrong. We had a very expensive protocol analyzer that came back with the capture card not screwed into the slot, push a cable in a little too hard and the whole card would pop out. Would have been easy to fix except I couldn't open it without voiding the calibration.

author: DaJMasta
author_rank: Super Contributor
timestamp: April 08, 2017, 01:30:22 am
content: A teardown will usually void your calibration, not necessarily because taking it apart and taking a look at things will change things, but because it can and the point of a calibration is to get rid of that uncertainty.If you want a calibrated instrument, a teardown will generally require recalibration afterwards.If you know what you're doing and you're careful (in taking apart, putting back together, what you touch, how parts are treated when dissasembled, etc), your teardown probably won't effect the performance of the instrument.You're not going to run into many bits of gear you want to tear down that require a clean room or some special facility to ensure no contamination messes with things, but you could definitely run into bits of gear where a little extra stress on a board or some fingerprints on the wrong trace will throw it out of cal. Most of a piece of gear with sections that sensitive will not have that requirement, so knowing what you are doing before you start and having good equipment, precautions, and habits when working through a teardown can get you through it with basically no impact on instrument performance, but you also have to accept the uncertainty. The only way to be certain your instrument is in cal is to check.

author: xrunner
author_rank: Super Contributor
timestamp: April 08, 2017, 01:52:09 am
content: Quote from: ErikTheNorwegian on April 07, 2017, 09:06:45 pmI know you're going to hate this answer, but it depends on the instrument.QuoteSame as above unfortunately. It depends on the instrument and the specific use it will be for. I have an Agilent spectrum analyzer that has a specific torquing sequence to the inside rf shield cover screws. Now, again, for "hobbyist" use torquing the screws in the wrong sequence probably doesn't affect the accuracy a whole lot, if you are talking about certified calibration and guarantees for military use and so on, yea taking the cover off and putting back on will probably make a tiny difference, and there are very bad consequences for using equipment that has it's calibration seal broken (I know I've worked in that sort of lab for many years).But again for "hobby" uses, it more than likely won't make a big difference - but no guarantees can be given.It's a hard question to answer unless more specific details are given as to what you are tearing down and so on.

author: boggis the cat
author_rank: Regular Contributor
timestamp: April 08, 2017, 02:58:38 am
content: Quote from: DaJMasta on April 08, 2017, 01:30:22 amThe most common problem is cable routing. If you really,really, want to open up a piece of equipment then take lots of photos of everything before you unplug and unscrew stuff. Make sure it all looks the same when you reassemble.This will minimise the chances of problems. It is what a cal lab should be doing. (The story of getting gear back from calibration with missing screws is definitelynotacceptable. Change your provider if that happens.)

author: technogeeky
author_rank: Frequent Contributor
timestamp: April 08, 2017, 05:05:44 am
content: This question is, as others have pointed out, difficult to answer. If you instead ask a slightly different question, you can frame the answers more carefully. If you instead ask:What actions during tear-down and reassembly will certainly affect calibration on certain classes of equipment?Feel free to copy and add (or subtract) this list, so we have as good of a copy as possible.In any RF equipment, any of the following will change the calibration:QuoteIn any low-leakage circuits in any kind of equipment:QuoteIn any high precision equipment, and any equipment where the signal path travels through rotary switches or potentiometers:Quote: As has been pointed out to me and by others, in these cases you have fundamentally lost calibration anyway; you have an instrument where normal operation (sweeping of metal contacts on metal contacts) could also destroy the calibration (in addition to cleaning, or disconnect/reconnect). In this case, cleaning and recalibrating is the obvious answer; but it may be desirable to characterize the instrument as fully as possible in this degraded state first before cleaning.

author: retrolefty
author_rank: Super Contributor
timestamp: April 08, 2017, 04:29:01 pm
content: Quote from: ErikTheNorwegian on April 07, 2017, 09:06:45 pmThe answer depends on if you have a volt/time-nut type personality or a more normal slight nerd type personality.

author: guenthert
author_rank: Frequent Contributor
timestamp: April 08, 2017, 05:14:04 pm
content: Many a gear's documentation comes with a description of a performance test routine. Do such a test before and after opening the device. If it meets performance targets afterwards, you get as much out of the instrument as it was designed to yield, regardless of calibration or what you did to it. The challenge here of course is doing the performance test, which usually requires other test gear and standards in calibration.