How accurate is a good 40-year-old DMM today? - Page 1
Forum section: electronics / testgear

author: Aldo22
author_rank: Super Contributor
timestamp: August 22, 2025, 03:04:15 pm
content: This question has probably been asked many times before, so I'd appreciate a link.For example, a Solartron Schlumberger 7150 had “Limits of Error” in the 2VDC range of 0.006 + 4 (1 Year +-5°C).What is that worth today if you don't know anything about the calibration history?Or is it impossible to say anything general about this?Would you say that a modern ±(0.05%+3) VDC DMM is more reliable/accurate than this old one today?Thanks.

author: KungFuJosh
author_rank: Super Contributor
timestamp: August 22, 2025, 03:47:53 pm
content: What difference does calibration history make if that calibration is long expired? If you want to know the accuracy of a DMM, be it 40 years or 4 years old, you should have it calibrated. Preferably by a lab that can make adjustments if needed.The other option is to compare it to a meter with as good or better specs that you already trust or is in calibration.

author: joeqsmith
author_rank: Super Contributor
timestamp: August 22, 2025, 04:12:00 pm
content: I bought an HP34401A when it was first released. The last time I had it calibrated (with report) was at least 15 years ago and it was still in spec.The only way I would know if it has changed and by how much is to have it calibrated again. Having the previous and original manufacture's data allows me to see how it has drifted.Would a modern meter with better specs be better than my old HP, maybe. That HP has been a rock star. Outside of a lightning strike causing a major surge in the AC mains which damaged the meter's GPIB port, I have had zero problems with it. The port was easy enough to repair and parts were available, so no harm done.

author: bdunham7
author_rank: Super Contributor
timestamp: August 22, 2025, 04:14:45 pm
content: Quote from: Aldo22 on August 22, 2025, 03:04:15 pmI don't think that general statements would be useful here as it depends on a lot of things including the exact model. Some old DMM models will almost always be spot on unless they are broken or have lost their cal memory. Others may not. And there's always a possibility that even if you check 1 or 2 of the DCV ranges you might have other ranges that are off because of malfunctions, miscalibration or other errors. My Fluke 189 that I restored from wrecked condition was completely accurate except the 5VAC range was way off and, of course, the calibration sticker had been peeled off.I've never worked on that particular model so IDK anything specific about it.

author: coromonadalix
author_rank: Super Contributor
timestamp: August 22, 2025, 04:55:29 pm
content: you will need to put it against a calibrator or compare as written earlier with a known / calibrated dmmthis meter as many others has it's own specs, drifts ppm .... you can not compare it against others, you could to some extents with an identical unit BUT ...https://www.holzleitner.com/el/solartron-7150/index-en.html

author: Simmed
author_rank: Frequent Contributor
timestamp: August 22, 2025, 05:00:00 pm
content: Quote from: Aldo22 on August 22, 2025, 03:04:15 pmold one would likely have a well aged VREF inside

author: Sabbatti
author_rank: Newbie
timestamp: August 22, 2025, 05:03:29 pm
content: My Hung Chang 704 Chineese Multimeter was purchased from Conrad Elektronik when I was a boy with 14 years. Now it is 44 Years later...I can remember that I paid 180 Deusche Mark for it and the money was from my very first job.It failed only one time when I tried to measure the short cut current from a 9V block battery. In fact I did want to measure the voltage. It was my very first measurement with this multimeter and it gladfully was fixed by replacing only the fuse :-)The Hung Chang 704 Multimeter was only calibrated once when I was 18 and did visit a German Technisches Gymnasium and had access to electronic tools where I thought I could never afford theese.NOW LET´S SEE:Hung Chang 704 vs brand new UNI-T UT161EFull Res:https://ibb.co/chPtYwjTI think the result is pretty good ;-)The UNI-T did come with a calibration protocol (I had to pay extra for it; ISO9001 - To order a new Multimeter with a calibration protocol was cheaper then to order a calibration protocol for one of my existing multimeters)

author: coromonadalix
author_rank: Super Contributor
timestamp: August 22, 2025, 05:06:33 pm
content: dont compare handhelds with an 6.5 digit meterThey are based on a 1N829A precision, temperature-compensated Zener diodeSure they don't compare against lm399 or ltz1000 based meter, sure the aging may help a bitbut as @Op suggested he has a limit warning ...

author: Aldo22
author_rank: Super Contributor
timestamp: August 22, 2025, 05:17:09 pm
content: OK, thanks for all your answers.I conclude that such an old precision multimeter without current calibration is virtually worthless as a reference.

author: Simmed
author_rank: Frequent Contributor
timestamp: August 22, 2025, 05:31:57 pm
content: Quote from: Aldo22 on August 22, 2025, 05:17:09 pmthere are hobby level calibration thingies which dont cost an armso it is not totally a crap situationyou just need to know how to do your own checksyou just need alot of time and patiencelike one of thesehttps://www.eevblog.com/forum/testgear/dmmcheck-plus-multimeter-calibration-reference-experiences/?allhttps://www.eevblog.com/forum/testgear/ready-to-use-voltage-reference/

author: TUMEMBER
author_rank: Regular Contributor
timestamp: August 22, 2025, 05:48:14 pm
content: Quote from: Aldo22 on August 22, 2025, 03:04:15 pmSo as not to be groundlesshttps://www.fotosik.pl/zdjecie/b7cc26173634e73ehttps://www.fotosik.pl/zdjecie/9b87904b42cc8090https://www.fotosik.pl/zdjecie/25bcfc77e6b1adfehttps://www.fotosik.pl/zdjecie/660749d45982a25chttps://www.fotosik.pl/zdjecie/7da71ade95a522b4https://www.fotosik.pl/zdjecie/293191360b4ca4edhttps://www.fotosik.pl/zdjecie/47c20ebef8bf9b7chttps://www.fotosik.pl/zdjecie/5bd9db926e281d2cThe year of this calibration was 2017. The Keithley 2700 used as a reference wasn't perfect, having deviations of several digits. After adding the correction from the Solartron calibration certificate, it passed the test. By then, this meter was over 30 years old. Two years ago, I compared it with the Solartron 7062 – and it passed.If anyone in the EU is seriously interested, it's available for purchase. The only requirement is that you arrange your own courier.

author: J-R
author_rank: Super Contributor
timestamp: August 22, 2025, 09:35:34 pm
content: Quote from: Aldo22 on August 22, 2025, 05:17:09 pmWhen you add the word "reference" to the conversation, then yes, "virtually worthless". Using a single device as your final word by which other equipment is judged and/or adjusted requires a high level of care. Maybe you didn't fully mean it in that strong of terms?You can get pretty far as a hobbyist if you have access to some other DMMs even without official references/standards. Using Ohm's law you can verify measurements from multiple directions and ranges. A possible outcome could be that some functions/ranges you have essentially 100% confidence, but some others you would say that the last 2 digits can't be trusted, for example. From there, you could go on with life or buy more gear, references, standards, send out for calibration, etc.

author: KlausKragelund
author_rank: Regular Contributor
timestamp: August 23, 2025, 12:21:50 am
content: Quote from: joeqsmith on August 22, 2025, 04:12:00 pmI have a HP34401A from 1998. It still measures perfectly (I sometimes bring it to work to calibrate against in-calibration instruments)I also have 4 SDM3055, so once in a while I hook them all up in parallel and do a crude home calibration check

author: Performa01
author_rank: Super Contributor
timestamp: August 23, 2025, 12:47:35 pm
content: Quote from: Aldo22 on August 22, 2025, 03:04:15 pmIncidentally, I have a lot of experience with The Solartron/Schlumberger 7150 plus. Its main advantage is the low cost.Let’s recall what we get here: it’s a 5.5-digit DMM in disguise of a 6.5-digit instrument by means of filtering/averaging. And it shows in practice; its stability is nowhere near a true 6.5-digit DMM. From memory, it cannot even compete with the 5.5-digit Fluke 8840A in terms of stability, neither short-term and even less so long-term. From experience with numerous devices, I would trust an old Fluke 8840A anytime (once I’ve done a plausibility check using some other trustworthy meter, which could well be the usual 20000 counts DMM with 0.05% base accuracy). But I would not expect the Schlumberger 7150 plus to deliver reasonably accurate numbers as long as it doesn’t come with a recent (trustworthy) calibration. It is not difficult to calibrate yourself manually though, if you have the appropriate gear (calibrators, standards).The display backlight is very dim, but can be upgraded when fitting modern high efficiency LEDs. Then it can run much cooler at lower current, while finally having a reasonable brightness.While the poor stability – both short- and long-term – don’t make it a candidate for a reference instrument, it has at least a very high impedance front end that draws less than 10 pA bias current. This is substantially better than a Fluke 8840A/8842A (<50 pA) and vastly better than my Picotest 3500A (=Keithley 2100, <350 pA) and Keythley 2015 THD (<450 pA). Only a Keithley 2001 comes close at <12 pA. Still the 7150A is not very useful for high impedance measurements, because its input is high impedance only up to 2 volts.

author: watchmaker
author_rank: Unknown
timestamp: August 23, 2025, 01:00:16 pm
content: Quote from: Aldo22 on August 22, 2025, 03:04:15 pmI address this via another method; external consistency and inferred external validity.I have a two Fuke 45s, a Phillips PM2525, an HP34401a that replaced a 3478, had a Fluke 8840a, have Shannon Tweezers, Agilent 1252 Fluke 27FM. All bought from different sellers at different points in time. NONE "adjusted" by me.As I acquired them, and sold them, I compared their readings on dcV, dcA, acV,, and if applicable, Freq and Cap. These comparisons were made with at least two other instruments using IET boxes and a current volt source that while not calibrated, provides a stable reference over short (5 minutes) periods of time.For capacitance and, my Shannon Tweezer is my reference.Any prospective purchase that does not fit was returned.All the instruments I have or sold were within one digit of the other two. I have resold a couple parts only instruments which do not apply her.I am an amateur who does not require instruments calibrated to a traceable source. All I need are instruments that provide consistent readings. Yes, I may be miles off. But what are the odds of 3 randomly chosen instruments providing the sameincorrectreadings? And I have not blown anything yet that can be traced to anything but my own clumsiness or carelessness.We had a saying in federal reporting (where each state decides its own methodology), "If you can't be right, be consistent".

author: KlausKragelund
author_rank: Regular Contributor
timestamp: August 23, 2025, 01:45:13 pm
content: Quote from: watchmaker on August 23, 2025, 01:00:16 pmThat's how I do the "in-house" calibration alsoFor conducted emission calibration, I have a power supply that has been tested at a notified body, and once in a while I run a retest on it to check if the setup is good

author: BeBuLamar
author_rank: Super Contributor
timestamp: August 23, 2025, 01:48:56 pm
content: I don't know but my Fluke 8050a gives reading very close to my Fluke 289.

author: kmoonwalker
author_rank: Frequent Contributor
timestamp: August 23, 2025, 06:17:45 pm
content: Cal history does not matter if unit was calibrated long time agomore important factors are if it was used from time to time to make electronics operate and not just laying turned off for years in not good storage conditions etcalso each unit was made by different "hands" and from different "parts" so that adds a lot to evaluation => thus one can perform very nice and other one horribly and you never know till you checked itFrom my experience most of those simple 0,00 indication DMMs is indicating very good even if they are pretty oldwhen stepping up into 0,000 range some are decent and some are not but it does not mean they are crappy and what you need them to be as accurate for?then real differences are starting to show up when you go into 0,0000 rangeThis is a measurement of some old and a bit noisy ATX PSU I use for testing some hunter interface boards without warming upSo top left is my old Sanwa that was never adjusted and last time checked by friend of mine in some lab with his meters in +/-2020 I think and I was told it was very good holding specs (better than some of his meters...). Battery is nto new and no low bat indication.Top right is my new Sanwa with lab test with report made few months ago. Battery is almost new as I did not used it much.Bottom is 34465a. It was manufactured in 2017 and last full cal was made 5 years ago. this is newest addition to my home lab and it replaced my old stationary HP DMM so I am still evaluating it but seems to be measuring pretty good so far.As you can see only difference is is on 0,000x and sanwas can go one digit more but I am not using that typically

author: kmoonwalker
author_rank: Frequent Contributor
timestamp: August 23, 2025, 06:22:04 pm
content: Quote from: watchmaker on August 23, 2025, 01:00:16 pmif you know the amount of how much some meter is deviating from others you can always take it into account without paying for cal but from experience some meters are better for current, some for voltage and some for certain ranges so it is not always good to straight disqualify one for a bit larger deviation. Sometimes the devil is in the details hehe

author: kmoonwalker
author_rank: Frequent Contributor
timestamp: August 23, 2025, 06:37:53 pm
content: so after 45 min @25 Celsiussome meters are faster in stabilizing indications than others(Sanwas on 500000 just to show - after turning on they "jumped" by 5-8 last digits or a bit more and now they change about +/-1)34465a was jumping over 10 and now it is inside 1-2 (but I suspect it registers that PSUs tiny fluctuations more than Sanwas)and true PSU also stabilized more in time but we are still talking about 0,00x and not some top notch ATX PSU that has like 15 years or more so I'd say not bad

author: kmoonwalker
author_rank: Frequent Contributor
timestamp: August 24, 2025, 12:58:32 am
content: I also have HDS2202S (almost a year old, never checked in cal lab only agains my old Sanwa on some ranges)as you can see this is perhaps not some superb accuracy compared but you see:0,8%+5 Owon0,03%+sth Sanwa (comment as below)0,003% Keysight (best case scenario not this particular range no time to check its manual hehe)just after turning on:Since HDS is getting hot after some time we will see how much it drifts? later

author: kmoonwalker
author_rank: Frequent Contributor
timestamp: August 24, 2025, 01:34:36 am
content: so getting warm actually helps HDSit stays now most of the time on 5,044 but started to show 5,045 from time to timeI must say I always considered it not bad but never really made such test like nowpity it needs so long to get here but still we are talking about 3 in 1 meter and 1/2 mV difference only to others is impressive (or my 3 other meters are so bad lolz)EDITrunned ACAL on Keysight but no change for its measurements and for it I used most crappy banana cables I have

author: ivo
author_rank: Regular Contributor
timestamp: August 24, 2025, 01:36:44 pm
content: In all likelyhood, if the meter and electronics are in good condition, to 5.5 digits it's probably still holding better than 0.02% accuracy (general 1yr spec is 0.01%)

author: Grandchuck
author_rank: Super Contributor
timestamp: August 24, 2025, 02:12:04 pm
content: Spot on

author: Aldo22
author_rank: Super Contributor
timestamp: August 24, 2025, 02:51:05 pm
content: Quote from: Grandchuck on August 24, 2025, 02:12:04 pmWow, so many counts!Thank you, but I already have something like that.It cost 9€ many, many years ago.

author: joeqsmith
author_rank: Super Contributor
timestamp: August 24, 2025, 06:15:36 pm
content: Vintage tech at 10V. 8506A is a bit on the cheating side as it was aligned using my HP34401A as a transfer standard.I have no idea what my friend had used to align his Sabtronics kit meter. LCD is a bit hard to read.

author: kmoonwalker
author_rank: Frequent Contributor
timestamp: August 24, 2025, 08:35:10 pm
content: it is like my grandpas collection(thou he had a lot of old soviet meters)

author: AVGresponding
author_rank: Super Contributor
timestamp: August 25, 2025, 07:06:17 am
content: Only 40 years old? Practically new!

author: TUMEMBER
author_rank: Regular Contributor
timestamp: August 25, 2025, 08:27:32 am
content: Quote from: AVGresponding on August 25, 2025, 07:06:17 amAnd why didn't you include Solartron/Schlumberger, since it's the main thematic meter?

author: Aldo22
author_rank: Super Contributor
timestamp: August 25, 2025, 08:53:00 am
content: Quote from: TUMEMBER on August 25, 2025, 08:27:32 amExactly!AVGresponding has aSolartron 7065at the bottom of the picture, but it's not turned on. Is it broken?I would also be interested to know how to interpret these specifications.For example, 0.004% + 4 (1 year +-5°C) for the 7065.Is it correct that the worst case scenario for a 40-year-old device is 0.004 * 40? So 0.16%?Or how do you read this?

author: neverendingstudent
author_rank: Regular Contributor
timestamp: August 25, 2025, 09:15:39 am
content: I just put up another HP 3478A 5.5 digit multimeter for sale - it's the 3rd of 3 I bought at an auction in Detroit, and after about 10 minutes of warmup it's dead-on exact to my voltage references (5.0000V from my DMMCheck r8, 16.0000V from my Advantest R6144) - it was manufactured in 1986, so it's 39 years old, with the last calibration done in 2004, so 21 years ago.Old DMMs ********CAN BE****** (but of course are not assured to be) very accurate. Voltage references get more stable with more burn-in hours, or burn-in years as the case may be.I've also had something like... half a dozen? Eight maybe? 34401A multimeters pass through my hands, and they have all been either dead-on, or very, very nearly so.Interestingly, both 34461A units I've bought have been off by quite a bit......

author: coromonadalix
author_rank: Super Contributor
timestamp: August 25, 2025, 11:07:44 am
content: had 1x very old 34401a and 2x more recent 34401a,one was fully recapped (at least 20 years old) and a new cloned vfd, and calibrated, it was still in specs ... it was used to compare with the other 2, they where in specs ...

author: J-R
author_rank: Super Contributor
timestamp: August 25, 2025, 11:41:30 pm
content: Published accuracy specs are not reliable metrics at all, in my experience. Some companies are conservative to begin with, and some of their products can regularly exceed those specs by a factor of 10, while other companies and their products just barely meet spec. This can be one reason the HP 34401A and Fluke 8840A/8842A are maybe considered forum favorites. The HP3478A is also frequently recommended for 5.5 digit accuracy, but I personally don't like it (reasons have been discussed elsewhere).But also another factor to consider is that the odds are good an older DMM has been calibrated/adjusted at least once after it had an opportunity to age significantly. (This was why I selected a freshly calibrated HP34401A as my first bench DMM.)So that can explain why a newer 34461A might not appear as good as a 34401A, although a counterpoint is that my few year old black 34461A is better than my HP34401A. Also, the 34465A is considered the better choice over the 34461A when accuracy & stability matters. It's plausible the 34461A got lower-binned references compared to the 34465A.I don't consider any of my bench DMMs to be of much use to me if they just meet the published specs. 1 year DCV @ 10V on a 34401A is +/- 40 counts, and even 24 hour is +/- 19 counts! Most 34401A owners would expect within less than 5 counts.

author: kmoonwalker
author_rank: Frequent Contributor
timestamp: August 26, 2025, 02:36:37 am
content: I worked on few 34461a and they generally were OK (needed adjustment after like 3 years from new) but if you do some evaluation or job for some big company 5a is one they never discuss about from experience... (it was the same with 34410/1a and L4411A in the past)Going with new times I kinda wish Keysight could make some new version with larger and touch screen in format like Rigol DM858 it could be even smaller no problem but I would like to hang one or two of them on wall mounts under monitor - controlling few of them with single PC is not the same comfort and I usually have either microscope pic full screen or schematic + microscope and last time I wanted all big I went full throttle connected a 49" 4K TV and it was kinda too big to work with - for me best is 27" size.

author: GigaJoe
author_rank: Frequent Contributor
timestamp: August 26, 2025, 03:37:42 am
content: Phillips PM2525 i had PM2535 - absolutely horrible in a view of stability ... replaced all caps , did try to adjust just 30V range ... it drifting away in a day , leaving it ON for a month .. a bit better .. but it extremely sensitive to temp change , can be my unit defective ... but ... who knowsoldest i had are fluke 8800A - made in 75 , was completely trashed, stored somewhere in a barn. with extremely strong smell of cowhouse ... cleaned, dead caps replaced , gang switches cleaned ... it shows 10V ref just 0.2mV off ...

author: AVGresponding
author_rank: Super Contributor
timestamp: August 26, 2025, 05:24:40 am
content: Quote from: Aldo22 on August 25, 2025, 08:53:00 amBecause it's an old picture, taken when I'd just acquired my first 8300A. The only TE still in use in my little corner of a "lab" is the Keithley. All the others are in storage. The Solartron 7065 works fine, and is still within cal spec, I just don't particularly like it.EDIT: In storage or sold, in the case of the Thurlby 1905a, which was also bang on. The Solartorn 7065canbe for sale, if I receive the "right" offer.

author: TUMEMBER
author_rank: Regular Contributor
timestamp: August 26, 2025, 03:04:13 pm
content: Quote from: Aldo22 on August 22, 2025, 03:04:15 pmThis declared error applies to another model, the 7150 plus.The 7150 plus has the additional function of measuring temperature using a Pt100 sensor and the ability to calibrate/adjust using the front panel keys.The 7150 can only be adjusted software-based via HPIB/GPIB. The declared error at DC 5 1/2 digits is 0.01% + 5 digits for 2 years at a temperature of +/- 5 degrees.There is no declared one-year error.The declared 24-hour error is 0.002% + 5 digits for a temperature of +/- 1 degree.In general, there is a lot of confusion about these declared accuracy, each document is different.Once I win this broken Xiaomi Redmi Note 14 smartphone and it allows me to transfer the photo to my computer, I will attach a photo from the "paper" manual for the Solartron/Schlumberger 7150 - without the plus.

author: BillyO
author_rank: Super Contributor
timestamp: August 26, 2025, 06:46:58 pm
content: They can be pretty good!

author: AVGresponding
author_rank: Super Contributor
timestamp: August 27, 2025, 08:22:03 pm
content: One serious problem with the 7150 is the EAROM which holds the cal constants. It will lose its data if not read and rewritten periodically.

author: TUMEMBER
author_rank: Regular Contributor
timestamp: August 28, 2025, 08:18:10 pm
content: Quote from: AVGresponding on August 27, 2025, 08:22:03 pmWell, you've both intrigued and worried me. Is there a "refresh" function in the S7062, but I've never seen it in the S7150? Is there only a CAL mode for refreshing? Can you explain this in more detail? Besides, I didn't see any mention of this in the service manual?

author: AVGresponding
author_rank: Super Contributor
timestamp: August 29, 2025, 05:29:07 am
content: Quote from: TUMEMBER on August 28, 2025, 08:18:10 pmYou can read the cal constants via GPIB and rewrite them, the manual contains the instructions. The limitations of the EAROM NVRAM are not mentioned in the manual, you need to read the datasheet for the Nitron NC7033, which you can find online, I believe I downloaded it from the Vintage Radio Forumhttps://www.vintage-radio.net/forum/index.php?