BM235 vs BM786: Which EEVBlog Multimeter Is Better? - Page 1
Forum section: electronics / projects

author: paul_g_787
author_rank: Frequent Contributor
timestamp: January 12, 2022, 04:11:08 pm
content: I have been thinking of treating myself to a decent multi-meter for some time. I have watched Dave's videos about the EEVBlog BM235 and the BM786 but I am torn between the two.What are the pros and cons of these two models, an essentially which one is better? (in the sense of features available and accuracy).I have noted that they are both "True RMS" meters which I have been recommended by a electrician friend to get. What exactly does this mean and why is a "True RMS Meter" better?I also notice that they both boast capacitor testing. Does anyone know the measurement range of this on both these meters?I have been after a decent capacitance meter for some time but every single one I have found only goes up to 100µF which isn't much use to me.I already have an ESR meter (MESR-100) which is fantastic!

author: paul_g_787
author_rank: Frequent Contributor
timestamp: January 13, 2022, 10:34:35 am
content: Quote from: paul_g_787 on January 12, 2022, 04:11:08 pmRather conveniently Dave release a video yesterday which explained what True RMS Meter is.So that answered that one question.

author: Siwastaja
author_rank: Super Contributor
timestamp: January 13, 2022, 11:54:15 am
content: I have developed electronics professionally, and before that for hobby, for two and half decades and never found any use for True RMS functionality.It was a big buzzword in 1990's.Note, the frequency range over which it applies is quite limited; see the manual for details. Frequency content exceeding that, and RMS is again calculated incorrectly, and you don't know when, why and how. TrueRMS feature makes a very poor AC instrument a slightly less but still very poor AC instrument. It only has a few edge use cases, you know if you need it.In electronics, real-world waveforms usually exceed the capability of the true RMS functionality, and often you don't even want RMS, but average for example.Lo and behold,Digital storage oscillosscopeisthedevice which can give you RMS, average, min, max, integral etc., over any arbitrary period you define, plus visual representation of the exact waveform so you never need to guess whether it is calculated correctly or not, and what's actually going on in the circuit. I use scope and its measurement features all the time. Multimeter AC features see almost no use in my lab, they are mostly used for DC voltage, current, resistance, diode and continuity tests.But sure, electricians find use for true RMS multimeters on the field, hence the understandable recommendation. Those who play around in lab - completely meaningless feature if you ask me. Use oscillosscope when dealing with nontrivial AC, it's far more powerful. If you need that power "on the field", I'd recommend even a handheld oscillosscope.

author: rsjsouza
author_rank: Super Contributor
timestamp: January 13, 2022, 12:08:18 pm
content: Quote from: paul_g_787 on January 12, 2022, 04:11:08 pm"Better" is very relative to what you do. As Siwastaja mentioned, the application in the field and in the bench are quite different. What are you planning to do with it and where will you use it? With this information a better assessment can be made.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: January 13, 2022, 01:44:48 pm
content: Mainly I am a hobbyist and I tinker/repair amplifiers, speakers and other devices in my spare time as well as working on arduino projects and also recently modding my PS1 and Sega consoles, fixing my washing machine timer, DVD player etcI am sill very much learning and I love using the EEVBlog as everyone is very helpful here! It is an amazing resource for learning! Hopefully one day soon I will be able to help beginners such as myself and "give back" as it were.I would absolutely love to get lots of good lab equipment one day!! But until I get to that level of knowledge and can afford a good oscilloscope (and other equipment) I think a decent multimeter would be beneficial as a step up for me.I have found my cheap £12 meter is good however it has some limitations which I have come across:* It is not very accurate when I have been making some low voltage DC measurements (mV range).* It has no auto ranging which is slightly annoying and inconvenient.*The AC measurement can be 10-15% off compared to my electrician friend's Fluke True RMS meter which I borrow occasionally when measuring a distorted waveform on a faulty amplifier. (Which because of Dave's video I now understand why this is).Of course, I can still use my cheap meter along side for Average AC measurements etcA few features I am looking for:* I need the ability to measure capacitance. My chinese LCR meter is OK but not very good at times and only does up to 100uF which is very limiting.*The ability to measure inductance would be a bonus.The BM786 is looking quite good but what does it do that the 235 doesn't?Is it worth the extra money?Does it measure above 100uF capacitance?Can it measure inductance?Does anyone here own one or both of these meters?What is your experience?

author: Siwastaja
author_rank: Super Contributor
timestamp: January 13, 2022, 02:45:42 pm
content: Buy a decent digital oscilloscope first if you don't have it. Nowadays you get those Rigol / Siglent etc., 100MHz 4 channels for around $400-500 or so. Used 2-channel DSOs go for maybe $100-200. This is the cost of a "good" multimeter!A $10 multimeter doesn't limit your hobby in any real way. Lack of oscilloscope prevents basically doing anything (both audio and Arduino).If you like to fix things, an ESR meter is a good idea. Multimeter, cheap or expensive, won't do that, either.

author: Caliaxy
author_rank: Frequent Contributor
timestamp: January 13, 2022, 02:48:04 pm
content: Quote from: paul_g_787 on January 13, 2022, 01:44:48 pmI have BM235 and BM789.BM786 has an extra digit of precision (and resolution), a fast updating bar graph (so you can see variations of signals that would otherwise look stable on the digital display) and can do combined AC+DC RMS voltage measurements. It also implements a (slower) auto-hold function inspired from Fluke (holds automatically the last measured value without you having to press the “hold” button - handy when you measure something that requires attention and can’t look at the meter while placing the probes).Both can measure capacitance over 100uF (just tried 2200uF) and, more impressively, down to tens of pF.None of them measures inductance.BM235 is smaller. It feels a bit faster too. Both are very nice meters.It’s up to you (and your budget) if the extra features of BM786 are worthy. As suggested, you might want to save for an oscilloscope (the nicest and the most useful tool one can have other than a DMM) and other lab equipment.Might need an ESR meter for electrolytic capacitors too (or a better LCR meter). (Edit: missed the part that you already have one.)BM789 has a wider AC bandwidth (up to 100KHz) than 235 and 786, which might be handy for audio.

author: rstofer
author_rank: Super Contributor
timestamp: January 13, 2022, 04:03:18 pm
content: We have to deal with Vavg, Vrms, Vpkand Vpk-pkAll have their use case.The thing about measurements with a scope is the bits of resolution of the ADC and many scopes use an 8 bit ADC. They often spec their voltage accuracy as +-4%. The displayed measurement values may have a lot of digits but, in the end, it's still just an 8 bit ADC. Scopes are for looking at squiggly lines, not precision measurements.https://edadocs.software.keysight.com/kkbopen/understanding-voltage-measurement-accuracy-for-infiniivision-oscilloscopes-584425356.htmlWhen you look at the Keysight calculations, make sure you know which ADC they are talking about. One is 8 bit and the other is 12 bit. There is also a discussion of a Max Resolution setting. This tries to get 12 bits of resolution using just an 8 bit ADC by using averaging.https://www.electronicdesign.com/technologies/test-measurement/article/21801317/why-you-should-care-about-oscilloscope-acquisition-modesThe BM786 has a DC accuracy (at hobby voltage levels) of +- 0.03% and an AC accuracy of 0.5%. The problem with the DMM is knowing what the waveform looks like and realizing that unless it is a perfect sine wave, AC readings are going to be off a bit. Potentially, quite a bit.https://www.keysight.com/us/en/lib/resources/training-materials/tip-1-understand-true-rms-measurements-458364.htmlhttps://www.keysight.com/us/en/assets/7018-01113/application-notes/5988-6916.pdfUnless the signal is known to be a perfect sine wave or perfect DC, what that voltage measures has to be viewed along with the waveform.Just a little light reading to give you more insight into what is meant by 'accuracy' and measurements.In my view, you are going to need 3 DMMs, one of which should have a 'real' CAT rating. The other two would be for bench work only. Don't spend a bunch of money on the 2, I would consider Aneng AN8008s and ignore the fact that it is missing some current scales. I can measure on one hand the number of times I have used a DMM to measure current rather than the voltage drop across a resistor. Or, pick one of the other inexpensive meters. The BM786 has a valid CAT rating and, if you simply must work on mains, it would be the meter to use even though it is too expensive for such things. If you do electrical systems every day, buy one of the Fluke Electrician models. Or don't use a DMM at all but that's a separate, and recent, debate.At your earliest opportunity, get a decent scope. The Rigol DS1054Z is older but can be unlocked to 100 MHz 4 channels and Siglent has similar models in the same price range. In any event, you would be under $500 for a really nice scope. And, yes, you will need one.

author: EPAIII
author_rank: Super Contributor
timestamp: January 14, 2022, 11:07:12 am
content: I have maintained, repaired, and even designed professional video and audio electronics in TV stations for over 45 years. This has included both analog and digital based equipment. In this I made extensive use of ANALOG scopes which, unlike the popular and inexpensive digital scopes of today, would allow accuracy approaching 1%; 2% was easily doable if you took the trouble to check the calibration first. Make no mistake, digital is great, but an analog scope will show you things that you can only wonder about on a digital one.As for meters, VOMs, my favorite was and still is the Simpson 260. Yes, it is analog. Sure, there were a few times when I really needed to measure or set a Voltage to 1% or better and, at in at least the last part of that 45+ year career, there were digital meters around to do so on those very rare occasions. But those were DC Voltages and the need for such precision was very, very rare. Most such measurements that I made were just fine at a +/- 3% or even a +/- 5% level. For AC measurements and waveforms it usually was a lot more important to match two or more levels to 1 or 2% rather than have them at some exact value. By using one analog scope over the entire system that level of matching was easily possible.True RMS? In my whole professional career I only worked at two places which had true RMS meters and I never needed that feature. NEVER!For amateur and around the home shop use as you describe, I can't even imagine where it would really be needed. Or even be useful. As far as I am concerned, true RMS is a feature that is in search of a purpose. I can think of far more uses for four, five, or more places of accuracy and even those are going to be quite rare.Please do not take my remarks as being against digital scopes, meters, and other equipment. I have both types in my shop and use both.You mention wanting a way to check capacitors. There have been a variety of capacitance meters and VOMs with this capability. I have examples of both. But in today's world, I would suggest one of those nifty component testers which are available on the web. I bought one and found it so useful that I immediately purchased a second one for my second electronic bench so I wouldn't have to carry the one back and forth.They are all over the internet, this is just the first one my quick search found:https://smile.amazon.com/Mega328-Digital-Transistor-Resistance-Capacitance/dp/B07WT9VVZB/ref=sr_1_3?keywords=electronic+component+tester&qid=1642157822&sr=8-3They will test inductors, capacitors , diodes, dual diodes, transistors, SCRs, and other components. You just plug a two or three wire part component in and push the button. They not only test them, they will even tell you just what the component is. They are remarkable and one of the best bargains on the web. Play with one of these for a while and then decide if you really need a meter that checks capacitors.PS: I am thinking about getting one of those EEVBolg meters myself, but it is on hold until I can pay off some bills. Probably next year at the earliest.PS2: Probably a more useful feature in a VOM would be a continuity beeper. That is a simple feature I have used a number of times. It allows some quick checks without pausing each time to look at the meter.Quote from: Siwastaja on January 13, 2022, 11:54:15 am

author: rsjsouza
author_rank: Super Contributor
timestamp: January 14, 2022, 02:02:48 pm
content: Ok, I was going to reply but others gave quite good inputs already.One detail: although I think True RMS has its purposes, it is indeed necessary only on very limited cases.On the other hand, averaging meters (the opposite of True RMS) do not have the True RMS IC that has a noise floor above the one inherent to the multimeter's acquisition system (this is true for a great number of meters, not only the cheaper ones).Also, yesterday I received aGreenlee DM-200A(a rebrand of aBrymen BM251S) that I got on a bargain from eBay and was immensely impressed with how sturdy it feels, including the rotary switch (it also feels much sturdier than my other Brymen, a BM857). Given Brymen's BM25x and BM23x series share the same mechanical housing, I can tell this is an excellent quality product from my own experience.I also echo others' suggestions to save for a decent oscilloscope - even if you are in a very tight budget, you could even start with a ultra-low costFnirsi 1014Dfor not much more money than the BM786 (which is better than having no oscilloscope)Good luck in your decision!

author: paul_g_787
author_rank: Frequent Contributor
timestamp: January 14, 2022, 02:44:12 pm
content: @EPAIIIInteresting you mention those component testers. I have heard about these and thought about getting one a few times.Am I correct in assuming it is an open source project that created these? I am sure I read this before somewhere. I see it uses the ATMega 328 so it must be Arduino based?It would be great if I could find the source code and schematic for one as I have always wondered how they do it.

author: rsjsouza
author_rank: Super Contributor
timestamp: January 14, 2022, 03:47:47 pm
content: I just got one of these component testers as well. It is indeed a great helper, especially for repair or identify parts.As for schematics, models, etc. There is a very long thread here in EEV about this:https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/I suggest looking at the last page and making your way back page by page to find some interesting resources and discussions.

author: bdunham7
author_rank: Super Contributor
timestamp: January 14, 2022, 04:11:55 pm
content: Quote from: Siwastaja on January 13, 2022, 11:54:15 amSometimes (not often) you need TRMS, sometimes you specifically want averaging, most of the time if a meter reading is good enough, either will do. However the big drawback with TRMS is residual counts--even good TRMS meters don't read to zero and the aren't accurate at all until at least 2-5% of FS. As a result, I have at least 4 average-responding meters still hanging around and although they're old, they aren't cheapies.

author: arcitech
author_rank: Regular Contributor
timestamp: July 08, 2022, 10:20:20 pm
content: Tossing this in the mix for what shouldn't be interpreted as (purely) tongue-in-cheek... one "killer feature" of the BM235 is the banana slots (or at least whatever these grooves are that can be used as such).Also, when the banana adapters are in use, the probe tip sleeves (don't crucify me if there's a better name!) can sit in the back of the rubber baby buggy bumper probe slots quite securely.As a person who tends to misplace the little bits 'n bobs, I appreciate this feature.I'm guessing OP's already made their decision, but figured for those searching in the future, this could be worth pointing out.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: July 09, 2022, 02:21:51 pm
content: Quote from: arcitech on July 08, 2022, 10:20:20 pmQuite a neat feature. Not sure how well they would stay put mind you but a neat idea!I went for the BM786 in the end and I am very happy with it.I bought the Brymen 78X case for it too and the BAC3 crocodile clip adapters are useful for high voltage measurements.I just store the accessories in the pouch in the case.Shame Dave doesn't sell the cases with the EEVBlog Logo on it hahaI would definitely have bought one when I got the meter if he did.