Is resistance measurement with a multimeter normally so slow (Extech EX330) - Page 1
Forum section: electronics / beginners

author: sjmurdoch
author_rank: Newbie
timestamp: December 21, 2022, 06:25:35 pm
content: I have an Extech EX330 multimeter and one of the most common things I use it for is continuity testing and resistance measurement. I find that it takes about 15 seconds to get a stable reading. When I start it reads usually around 20 Ohms and the gradually goes down to less than 1 Ohm (which seems plausible). The behaviour is the same regardless of whether I use autoranging or setting the range manually.Is this normal for multimeters? I’m not sure why it’s so slow - is it due to how the A/D converter works or is it the result of capacitance (there’s around 2-3m of cable here).It’s a bit tedious so would a better multimeter be significantly faster? I’m considering the Brymen BM525S but would welcome other suggestions.

author: bdunham7
author_rank: Super Contributor
timestamp: December 21, 2022, 06:33:57 pm
content: Typically most DMMS will settle quite a bit faster than that. However, even the Fluke 289 is pretty slow on it's special 50R Lo-Ohms range (I call it Slo-Ohms), although it will settle to within a few percent pretty rapidly. Depending on the current source used, the test voltages at those low resistances may be pretty low and they may be applying a lot of damping to that to keep the display stable.

author: ledtester
author_rank: Super Contributor
timestamp: December 21, 2022, 06:55:58 pm
content: I have a EX330 and yes, it is slow on autoranging mode. The Aneng 8008 I have is a lot faster as is my Fluke 27/FM.You can, of course, get quicker reading times by selecting the range in advance, but that's inconvenient.I also feel the continuity mode of the EX330 is sub-par.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: December 21, 2022, 08:46:04 pm
content: I take mine out of auto ranging. It's an Extech is slow auto ranging too.

author: BeBuLamar
author_rank: Super Contributor
timestamp: December 22, 2022, 12:26:41 pm
content: Check the Fluke 87V I have it takes less than 1 second going from OL to 0.2 ohms in autoranging. The Fluke 287/289 are significantly slower on autoranging. In manual ranging it's less than 1 sec.

author: argentas
author_rank: Newbie
timestamp: December 22, 2022, 09:12:03 pm
content: There are two different things involved here - there's the time it takes the meter to auto-range, and some meters are indeed significantly quicker than others in this respect, but there is also the time it takes for the reading to settle once a range is locked in.The OP mentioned they were seeing the same behaviour whether in auto or manual ranging, so I suspect it is the latter we are dealing with here, but 20 ohms slowly decaying down to 1 ohm over 15 seconds does seem rather extreme.I don't have any direct experience of that Extech meter, but for comparison if I were to short the leads of my fluke 187, I'd expect maybe a little over a second for it to autorange, then I'm likely to see something like 0.17 -> 0.14 -> 0.12 in very rapid succession (a fraction of a second), then it would decay more slowly before settling at 0.09 after maybe 5 seconds.Measuring a 10 ohm resistor, I might expect to see something like 10.05 -> 10.02 -> 10.01 -> 10.00, but I certainly wouldn't expect to see initial readings 20 ohms higher than the actual value.https://youtu.be/ZoeUgMFLyAw?t=2516includes a resistance test on the extech, and whilst it isn't exactly quick, it certainly isn't exhibiting the issues the OP is experiencing. I would probably check batteries and test leads first though, before writing off the meter.

author: EPAIII
author_rank: Super Contributor
timestamp: December 23, 2022, 02:41:15 am
content: It will all be better when we go analog!Quote from: sjmurdoch on December 21, 2022, 06:25:35 pm

author: BillyO
author_rank: Super Contributor
timestamp: December 23, 2022, 03:02:56 am
content: Quote from: BeBuLamar on December 22, 2022, 12:26:41 pmYou can buy a decent used car for the price of that DMM. It's nice to be well healed and have the money to drop on a fully professional instrument for hobbyist needs, but some folk .. beginners and the young come to mind .. would be just plain stupid to drop $500 on a handheld DMM. Sorry to be so blunt.All that aside ..Autoranging depends a lot on the use cases. If you are working circuitry that is mostly HV (tubes) resistance values will be much higher and your very same meter will seem to just pop right into a meaningful measurement. However, if you deal with mostly small resistances (digital) then manually setting the ranges on your meter will be more effective. Back in the day when autoranging meant your grandma wondered off from time to time, I used to set the ohms range on my DMM (or even VOM) to 20K and adjust from there. I mostly did work with microprocessors and had a Fluke 8050A on my bench. With voltages, the 20V DC was my choice. 200mA for current. Life was good. Rarely had to tweak from those choices.Learn how to get the best out of your instrument for your use cases. Don't rely on the meter to do everything. Unless you are convinced it is more intelligent than you. If that is the case .., then carry on.

author: ttx450
author_rank: Regular Contributor
timestamp: December 23, 2022, 04:00:50 am
content: On some newer dvm you can select how many digits you want displayed and that can speed up response time.

author: 807
author_rank: Frequent Contributor
timestamp: December 23, 2022, 10:54:30 am
content: Quote from: sjmurdoch on December 21, 2022, 06:25:35 pmYou mention 2-3m of cable. Do you get the same delay if you short the probes together?

author: David Hess
author_rank: Super Contributor
timestamp: December 23, 2022, 02:02:57 pm
content: Ohms measurements should not take that long to settle unless there is a lot of capacitance involved, and a cable would not cause that.Ohms measurement is just a voltage measurement with the ohms converter current source applied. Are the voltage measurements similarly slow?

author: BeBuLamar
author_rank: Super Contributor
timestamp: December 23, 2022, 02:40:12 pm
content: Quote from: BillyO on December 23, 2022, 03:02:56 amUhm I have both the 287 and 289 and both are like new condition. The 289 is a few years old but I rarely ever used it and the 287 is new made in April this year and I only tested it didn't use it. Now I do need a decent used car and I don't think I can get a decent used care out of both of them.

author: BillyO
author_rank: Super Contributor
timestamp: December 23, 2022, 04:00:43 pm
content: Quote from: BeBuLamar on December 23, 2022, 02:40:12 pmWell, here in Canada those two meters would set you back about $2000. I can certainly get a useable used car for that much as long as I'm not looking for a BMW or a Mercedes in pristine condition. But I guess someone that needs both a Fluke 287 and a 289 to measure resistors for his Arduino project would not be caught dead in a 10 year old Honda Civic.Jus a matter of degrees I guess. My neighbor just sold a good running 2013 Toyota Corolla for $800 with 230,000KM on it. It was roadworthy even if it had a big dent in the back, was missing it's wheel covers and needed a good cleaning job on the inside, but it will probably keep gong for another 5 years if properly maintained.

author: BeBuLamar
author_rank: Super Contributor
timestamp: December 23, 2022, 04:21:31 pm
content: I have also a 189 and I actually prefer to use it than the 287 or 289. May be I should put them on Ebay?

author: sjmurdoch
author_rank: Newbie
timestamp: December 24, 2022, 10:14:32 am
content: Thanks for the comments everyone. Those were very helpful in trying to diagnose what is going on. It looks like there were a combination of factors at play. I think a big part was the probes not making good contact but rather than just manifesting as high resistance it was an apparent slowly decreasing resistance (due to capacitance?). I switched to crocodile clips and that made things quite a bit faster, but still slower than a Fluke T6-600. For example here’s a video with auto-ranging off where it takes about 8 seconds to get to the right value:https://youtube.com/shorts/FvHaDFEimVY

author: 807
author_rank: Frequent Contributor
timestamp: December 24, 2022, 11:31:24 am
content: I shorted the leads together on my Iso-tech IDM 305. That was painfully slow to settle. Around 10 seconds on manual setting. As for auto ranging. You could go away & make a cup of tea in the time it takes to measure a low resistance!My Brymen BM869s is amazingly fast in comparison. Less than 3 seconds in manual or auto range.Just for camparison, it may have helped if you shorted your probes together, rather than through the extra length of cable.

author: MrAl
author_rank: Super Contributor
timestamp: December 24, 2022, 01:14:06 pm
content: Quote from: sjmurdoch on December 21, 2022, 06:25:35 pmJust a quick note...Some are slower than others. I have some that are within maybe a second and others that take maybe three seconds to settle on a constant reading.I think it has to do with the resolution too, but that's probably not the whole story. It depends on how many samples they take before they render a reading. When i programmed my own voltage meters using microcontrollers, i was easily able to change the number of samples before a new reading would appear, and also was about to program the averaging algorithm with a different number of samples in the "low pass filter" part of the code.The low pass filter section of the algorithm takes in a new sample and then averages it with several older samples. This gives what is called a "running average" and it acts exactly like a discrete (digital) low pass filter. This means that the first reading will be off, then the second reading is a little better, then the third better, then fourth better, etc., by the time you get to 5 time constants of the low pass filter you have a reading that is within 1 percent of the best, and after that it gets even closer. So you may see the digits ramp up that's usually what happens.For example, say you are averaging over 3 samples. The start is zero 0 so the very first reading (for voltage as example) and with vs=input is:V=(2*V+vs)/3and with say 1v input and since V=0 to start with, the first reading is:V=(2*0+1)/3=1/3=0.333and you can see already that although the voltage is 1v the reading shows 0.333 volts.Now the second reading gets better because now V=0.333 so we see (and we round the reading up):V=(2*0.333+1)/3=1.666/3=0.556so the reading got better.Now the next reading will be:V=(2*0.555+1)/3=0.704so now we are getting closer.The next reading is:V=(2*0.703+1)/3=0.802and the next:V=(2*0.802)/3=0.868Looking at 20 samples we see this:[ 1] 0.333[ 2] 0.556[ 3] 0.704[ 4] 0.802[ 5] 0.868[ 6] 0.912[ 7] 0.941[ 8] 0.961[ 9] 0.974 0.983 0.988 0.992 0.995 0.997 0.998 0.998 0.999 0.999 1.000 1.000From this we can see the time constant is about 2.5 samples and we see the reading get to within about 1 percent after 5 time constants which is 11 or 12 samples. Eventually it gets to the exact reading but it takes time. Also, not all results may be shown maybe just every other one or something like that.In practice we would use a slightly more sophisticated low pass filter but that shows how this works.