Aging multimeter - Page 1
Forum section: electronics / general

author: slugrustle
author_rank: Frequent Contributor
timestamp: January 04, 2024, 11:30:26 pm
content: Is there any benefit to intentionally aging a multimeter? That is, leaving it on for a long period of time, say one or two years continuously.Here's my thought process: I have a Rigol DM3068 that was (barely) out of spec on two ranges the last time I had it calibrated. My understanding is that only Rigol will do any adjustment on these meters, so I'd have to send it in to get it adjusted.The meter is still accurate enough for my purposes right now. My plan is to keep the meter plugged in for one year continuously (8,766 hours) to let some of the drift due to aging settle out, then send the meter in for adjustment. Adjustment at that point will bring the meter back into specification, and any subsequent aging drift will be less than the aging drift in the first year of continuous operation.Would this actually help like I'm thinking? Or could the meter keep drifting willy nilly even after 1 year such that it's not worth the bother?EDIT: Spelling and grammar mistakes.

author: aronake
author_rank: Frequent Contributor
timestamp: January 05, 2024, 05:24:41 am
content: Your thinking is typically correct, electronics tend to drift more in the beginning and slow down later in its drifting. What you describe is generally a good thing to do.But it is not sure that will be the case, the meter may just continue to drift at an unpleasant rate or change in direction of drift. Ideally if you have some decent references you could track how your meter measures to see how it measures and drifts over time while its keeps running.Ideally after the first calibration and adjustment after say a year of running. For the next calibration say one or two years later you would not want to do an adjustment even thogh there has been some drift (assuming this drift is well within the multimeter's tolerances), but instead use the data you get from the calibration on the multimeters actual new reading to track how it drifts. Then say another one or two years and a new calibration, you can see how well your estimates on drift based on previous calibration work out and can get more and more certainty on measurements, but at the cost of having to calculate actual real value of DUT based on what multimeter read (which will be wrong, but you have a good estimate for how wrong it is) and adjust for this error.This procedure may be a bit overkill for a DM3068. So the shorter answer, yes, have it running for a year, send it for calibration and adjustment and then be happy. But at that time the upgrade syndrome may well have kicked in and you own a 3458a allready....

author: slugrustle
author_rank: Frequent Contributor
timestamp: January 05, 2024, 05:34:24 am
content: Thanks for that. Sounds like the idea is generally ok, but mileage may vary, hence aging for 1 year, adjusting, waiting 1–2 years, and checking drift.Quote from: aronake on January 05, 2024, 05:24:41 amCan we split the difference and say I get a 34465A?The real truth is I have three DM3068s... you can do a lot of things with simultaneous measurements from three 6.5 digit DMMs.If the meter had stayed within the datasheet specifications for 1 year after calibration, I would be plenty happy. The whole idea in getting a 6.5 digit DMM was that it is better than I actually require.

author: Smokey
author_rank: Super Contributor
timestamp: January 05, 2024, 07:18:33 am
content: What voltage reference is used in the DM3068 ?

author: 2N3055
author_rank: Super Contributor
timestamp: January 05, 2024, 07:58:13 am
content: DM3068 uses LM399. After few years mine settled and is very stable. It took about 3 years, when I could not see large changes anymore.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 05, 2024, 08:41:59 am
content: The DM3068 uses a LM399 ref., but it also uses a SD ADC chip and thus needs a divider to scale down the ref. voltage and the 20 V range also needs some division of the input signal. So it is not only the voltage reference that is drifting. With that less favorable configuration compared to a HP34401 the specs may be a bit optimistic and drive may happen.For the LM399 it is known that some show significant initial drift and may need a few 100 hours to get more stable. Similar resistors may show initial faster drift. A possible component here is stress from the soldering process. The meter is expected to get more stable over time and especially the first month or so can make quite a difference. For this reason there should ideally be a burn in period of something like 1 week before the calibration / final adjustment. For a low cost meter this is likely not done.1 Year of constant on is likely overkill, but repeated use over 1 year and maybe a few months (e.g. the winter) with longer on time could be a good idea.Besides true long term drift there can also be a humidity effect, that can react a bit slow (timescale of days to weeks).

author: iMo
author_rank: Super Contributor
timestamp: January 05, 2024, 11:08:33 am
content: Quote from: slugrustle on January 05, 2024, 05:34:24 amWith three DMMs you may do a comparison. Built yourself a reference (or better do build threeof them) and do periodically check out the readings.. There are methods to identify your worst DMM then..

author: bdunham7
author_rank: Super Contributor
timestamp: January 05, 2024, 03:15:42 pm
content: Quote from: slugrustle on January 04, 2024, 11:30:26 pmYes, it appears that the LM399 is not as carefully selected and aged in the lower cost 6.5-digit meters from Siglent and Rigol as it is in HPAK/Keithley/Fluke models. I suppose that's reflected in the lower cost. Letting it burn in for a year solid and then recalibrating will probably result in a much more stable meter, but after that point I think you're actually better off only turning the meter on when you use it, as long as it is in a warm, dry location. The majority of the drifting seems to occur when powered on. Hopefully the meter would stay in spec for decades at that point, just like it's more expensive competitors.

author: slugrustle
author_rank: Frequent Contributor
timestamp: January 05, 2024, 04:24:27 pm
content: Quote from: Kleinstein on January 05, 2024, 08:41:59 amThe interesting thing here is that the newest meter is the one with the problem. I bought it perhaps a few months before the calibration cycle came up at work. I buy my own equipment so I can use it on personal projects without causing contract or IP issues, and work agreed to calibrate the pieces of equipment that I use in my job, primarily DMMs and scopes.I didn't mention the newness factor in part because work just switched to a new calibration company and the old one wasn't the greatest... so it's hard to say if the new meter is really any different or if the prior company didn't check the older meters properly / carefully.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 05, 2024, 04:57:07 pm
content: The datasheet for the LM399 ref. shows a typical aging drift of 20 ppm for the first 1000 hours. This alone makes it impossible to guarantee the 35 ppm specs for the 2 V range without at least some degree of pre-aging / selection. The example graph shows not much more drift after 3 weeks and around 40 ppm of overall change.It does not need a year of burn in, but more like 1 or 2 weeks and than don't use the wost units and maybe let the more drifty ones age a little more and give them a 2nd chance. 1-2 weeks of burn in are not that bad and even for a lower cost meter this may be feasible. 1-2 weeks may also be reasonable for the inital phase of other parts in the meter.AFAIK the dirft of the LM399 is mainly when it is on, due to the relatively high temperature it runs at. It can be different for the resistor part. These are not expected to run hot and would thus also age (though a bit slower) when powered off and may also react to power cycles / humidity.For the specs they give the 20 V range with likely 1 more divider in the path an extra 5 ppm uncertainty compared to the 2 V range. So they do include a bit for the resistors too. The reference divider may be a bit more stable as it could be closer to a 1:1 resistor ratio that often works better than 1:10.

author: mendip_discovery
author_rank: Super Contributor
timestamp: January 05, 2024, 06:12:43 pm
content: Some of the drift might be down to heat cycles so turning it off and on etc can cause some drift.I personally wouldn't worry, the majority of multimeters do keep within specification, they do drift but are not normally out of specification until they get a lot older. Trying to force it to drift might not be as worthwhile as you think.If you are worried then get a few references you can check against every now and then as a way to confirm it is not going out of spec.As around a few labs if they can calibrate and adjust the meter. Rigol might not be the best.As they say themselves,Quotebut they recommend "Navair Technologies" & "Transcat"Worth keeping this in your file of useful info,DM3068 Performance Verification Guide.pdf(719.86 kB - downloaded 86 times.)

author: bdunham7
author_rank: Super Contributor
timestamp: January 05, 2024, 06:37:33 pm
content: Quote from: slugrustle on January 04, 2024, 11:30:26 pmTranscat in Indianapolis should be able to fully calibrate your DM3068.

author: slugrustle
author_rank: Frequent Contributor
timestamp: February 06, 2024, 12:06:06 am
content: Well, this aging idea won't work for a Rigol DM3068 if adjustment is required. I had a DM3068 purchased July of last year that failed a calibration cycle in December or January. Slightly out of spec on a few ranges.It took four emails to get Rigol to understand what I even meant by asking for adjustment. They said the meter was under warranty and to send it in for repair. I did. I just got it back: They replaced the main board and provided no calibration certficate. I followed up with a strongly worded email asking for them to cover the cost of calibration, since the whole point of sending it in was to bring it back into cal. They're looking into what they can do.The tech support person is nice and helpful, but apparently the main boards are calibrated at the factory in China, and the cal certificates are not sent along with the main boards to the service center in the USA (where I am). The service center also doesn't have a calibrator. And, apparently, I'm the first person to ask for a calibration of their repaired meter. Just wild.

author: bdunham7
author_rank: Super Contributor
timestamp: February 06, 2024, 12:39:09 am
content: Quote from: slugrustle on February 06, 2024, 12:06:06 amI'm not sure what to say to that, other than I would have assumed that if they didn't want the expense of buying and maintaining a calibrator they would have a contract with a cal lab that they could sublet to or refer you to. Did you check with Transcat?Perhaps something like a pair of older meters like the 34401A or similar would be a better option?

author: slugrustle
author_rank: Frequent Contributor
timestamp: February 06, 2024, 01:15:09 am
content: Right now, I'm thinking to save up for a pair of DMM6500s. Not completely sure, but that looks good to me.I've asked Rigol to cover the cost of calibration for this repaired unit, and they're going to get back to me on that.

author: mendip_discovery
author_rank: Super Contributor
timestamp: February 06, 2024, 12:12:52 pm
content: Quote from: slugrustle on February 06, 2024, 12:06:06 amSounds like they dont actually fix things, just swap the board out for a new one. Odd that they don't have any cal equipment. I suspect normally they just send units out and the customer deals with calibration. But still its interesting to know they dont even verify the unit is working after replacing boards etc.

author: ArdWar
author_rank: Frequent Contributor
timestamp: February 06, 2024, 12:29:27 pm
content: A lot of vendors operate like that.Even if they *do* have cal equips they'll only say that "we've tested your equipment and it is within spec" and won't give you anything more than that. They simply don't want to deal with the implication of giving a hard numbers, unless you paid for it of course.