My one year review of DMMs for Beginners - Page 1
Forum section: electronics / beginners

author: watchmaker
author_rank: Unknown
timestamp: August 31, 2024, 04:48:05 pm
content: I think 3 DMMs is the minimum for a serious learner or amateur. It is very useful to take simultaneous measurements when doing labs; remembering the errors introduced by the meters themselves.I started with an Analog Discovery, and it is a terrific package. But, like my CRT scopes, I think the money is better used elsewhere.Regarding used equipment off eBay: I have had no issues when buying “parts only” instruments from major sellers who provide return privileges. Many of these bench DMMs require computer programs for adjustment and are beyond my (and most?) reach.The pictures below show the consistency of the readings across 4 DMMs purchased on eBay at different times and from different sellers. You will note they represent Fluke, Instek, and Phillips. As noted, I cannot adjust them.All four I use consistently have the ability to “zero” the meter. The three I like most all have reading hold ability. This gets valuable as you age. The Phillips has relative but no hold, but it has high resolution. Besides that, I like the motor for changing functions (it growls).You will also see I used “known” references for the measurements.Since I have a strong measurement background, when I see agreement among several measurement instruments that have not been intentionally set to agree with one another, I tend to think they represent real values. While the little AliExpress V/I reference is not professional, the meters all agree with the provided "calibration" sheet to within one or two counts in the last digit.Also, the resistance board values agree with my ST42.My point is, do not be afraid of buying vintage instruments on eBay (from large sellers with return privileges). I have not paid over $125 (including shipping) for any of them. The Fluke 45 on top was purchased this week for $50 shipped via “Best Offer”. It was dirty but cleaned up good. McGuire headlight restorer cleaned up the display cover.FWIW, I also verified them against a Keysight u1252 I purchased for $125 last year.Bring a hoarder, I also have purchased an HP 3578 for which I added the backlight. I also have my old Simpson 467 and a Micronta 220 and a Fluke 27/FM. I have a sickness. And I like measurement.Not mention 2 Simpson 260 7s. Watched a Wae2W tutorial on transistors, and he convinced me there is value in an analog display for watching changes. You can buy 260 Series 7 for under $60 shipped in great user condition. Let the collectors pay for "new in box" meters.Bear in mind, there is a phenomenon called trivial precision. This is when a measurement is made to a resolution that adds no additional information. The Phillips may well qualify for that given my level of experience and use.Calibration is simply documenting the calibration error between a specific instrument and a certified reference. This is the issue in dial readings for machines such as precision pointing machines, navigational instruments and meters. It tells you how to compensate the dial reading so that you can report the same results as someone in a different environment.It is a minor nuisance for daily use; does not matter if the error is large so long as it is consistent (small std deviation).Adjustment means bringing the dial reading closer to the calibration std. While a navigator can deal a chronometer having a calibration error of 2 seconds fast per day (as long as it has been proven to be consistent), it is much more convenient if the error is adjusted to 1 second per week. Same with any measurement instrument.My wife keeps telling me I am not that special, so I do not think I simply got lucky regarding the usability of the DMMs. Of course, there have been two or three returns (with no issue). Important to look at the sellers completed auctions to see if the item you are looking at has already been returned.Of course, I use eBay US, so things may be very different in other parts of the world.

author: tooki
author_rank: Super Contributor
timestamp: August 31, 2024, 05:34:17 pm
content: Could you edit the post so the images aren't embedded in the text, but just attached? Just delete the "[attach=n]" tags. That would make it much easier to view the images alongside the text.

author: Sensorcat
author_rank: Regular Contributor
timestamp: August 31, 2024, 10:03:44 pm
content: Unless you are forced to calibrate your DMMs (customer's demand, industry standard, law), you can trust old meters from the good brands. By good brands I mean those that worked for decades to establish trust in the brand by constantly delivering high quality. Fluke belongs in this category, and Philips did. The reports on positive results with old DMMs that have not been calibrated for ages are of course all anecdotic, but there are many, e.g. Dave's video of a Philips he got for $140 and found to be within spec after 25 years:For hobby use, you can just leave it uncalibrated, unadjusted, don't worry, and be happy that the market is good for people who want to buy good old stuff for cheap.

author: J-R
author_rank: Super Contributor
timestamp: September 01, 2024, 03:08:27 am
content: Having purchased and repaired/calibrated/adjusted about a dozen bench DMMs over the last few years, I can tell you that the odds are high that these DMMs will be OK, but it's absolutely not always the case. Having more than one DMM is reasonable way to assume they are OK if they all agree, but if they don't you may have a quandary. There is also the point of how far they may be out and whether that can be detected given your equipment on hand. If your three DMMs are a 5.5 digit, a 6.5 digit and a 7.5 digit, you are going to have a tough time validating the 7.5 digit DMM.My reason for jumping in here is that my most recent acquisition was actually a Fluke 45 in mint condition with the calibration sticker intact and original manual and quick reference card. It had never been calibrated after leaving the factory, from what I can tell.I was on the hunt for this due to a forum member who had issues with their Fluke 45 and sent it off to another forum member for calibration/adjustment. I was curious whether another random unit would have drifted the same. Ultimately, I do think the Fluke 45 has a tendency to drift, but if it's been calibrated in the last 10 years, the odds are probably a lot less.With my sample, essentially, every DCV reading from Table 4-2 of the performance tests was just a count or two right below the Min allowed. So for example, 300mV was 299.89mV while spec is 299.90mv-300.10mV.Amazingly, the resistance readings were 100% perfection to the very last digit for every value listed in the 1.0 decade table.I also have some Fluke 8840A/8842A and one has a pretty significant thermal drift issue with I believe the resistance current source, two others don't. It actually is still just within spec after warmup, but it clearly has a problem that I hope to resolve eventually.