BM789, BM867s or BM857s - help needed - Page 1
Forum section: electronics / testgear

author: mac00
author_rank: Newbie
timestamp: September 27, 2021, 04:31:14 pm
content: Hi AllFor several days I have been searching the internet for information about Brymen meters. I am not a great specialist, but I would like to buy a good meter that will serve me for several years. I am considering purchasing one of the BM789, BM867s or BM857s models.The prices of each of them are similar for me, so I have a problem with the choice.The BM789 is a new product, it has some interesting features (Auto-Real-Hold), but I don't know if it is less or more accurate than the other - ex BM867s. The BM789 also has a temperature measurement and non-contact EF field detection. Voltage drop when measuring ultra-low currents 0.2mV / microA versus 0.15mV / microA in BM867s - can it be a problem?One of the factors I care about is measuring currents in the range of about 10-20 µA. Will the brymen BM 789 be a good solution or is it better to choose the BM867s?Can you tell me which one is more accurate / or the same?I usually deal with low voltages and battery devices (ULC), rarely measure high AC voltages.

author: Fungus
author_rank: Super Contributor
timestamp: September 27, 2021, 06:11:41 pm
content: I'm a fan of my BM857s because of the smaller size, square industrial vibe and very simple user interface (almost zero function overload on the range selections).The BM857s and BM867scanmeasure some things slightly better than the BM789 (eg. 500,000 count mode, crest mode has much faster response) but overall the new BM789 is a very compelling meter. If I was buying a meter today it's probably the one I'd go for.The only downside I see is the huge size.

author: Neutrion
author_rank: Frequent Contributor
timestamp: September 27, 2021, 07:50:00 pm
content: Hello bratanki!I had to make the same choice a few months ago, and after a long contemplation period I am still not sure I chose the right oneThough if you end up choosing the 789, there might be some smaller issues that can be corrected in the FW but no one is sure about it. See the topic. Although it might affets the other modells.Fungus: The 789 is actually faster in crest mode with 0,35 ms VS 0,8 ms of the 857.How long the backlight stays on with the 857? (The latest versions I mean, if it was corrected like with the 869s.)Oh and the 859 has the same price as the 789. Which indeed is just slightly cheaper than the 869s.+859 +789-More count in some modes -Bigger display-5V Diode check -Faster crest mode-lower continuity treshold -Auto hold-optical rs232 -16min backlight-slightly more accurate -Conductance mode-higher frequency level on ac+dc current -Low impedance mode-higher frequency on line level+logic level -Joe Tested-Lower power consumption -Low pass filter on AC Volt mode (VFD)-separate rubber holster -60000 countIf the 859, 857 has a backlight turned off after a few seconds, than I could sleep much better tonight.

author: J-R
author_rank: Super Contributor
timestamp: September 27, 2021, 07:52:16 pm
content: All of these can somewhat trade blows back and forth depending on what you're discussing.For accuracy in the uA ranges, those two 1) and 2) footnotes on the BM789 are not present for the BM8xx so I'm curious how that impacts very low uA measurements. I do have the BM789 and the BM869s, so I will do some tests and report back.The BM789 has the advantage of 60,000 counts in all ranges, while the other two are 50,000 count with the 500,000 count ONLY available for the DCV ranges.*UPDATE* BM789 is 65,931 count and BM869s is 530,802 count (at least the highest I could get them to display!)The 500,000 count mode can be hit or miss, depending on what you're measuring. The last couple digits CAN be quite a bit off if you're measuring 5V for example since that is near the top of the range and you're also seeing the most digits. But if you were measuring 12V, then it will probably be spot on and you'd gain an extra digit compared to the BM789.BM867 has the dual display which can be an advantage in certain scenarios, the other two don't.BM789 does not have any computer connectivity options, the other two do.9V vs AAA might matter for some users.

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: September 27, 2021, 08:21:09 pm
content: Quote from: mac00 on September 27, 2021, 04:31:14 pmThat low current measurement is Dave Jones muCurrent territory. If you are trying to measure fluctuating micro-currents you will be up against the low sample rate of handheld meters.

author: Caliaxy
author_rank: Frequent Contributor
timestamp: September 28, 2021, 12:43:54 am
content: Quote from: Fungus on September 27, 2021, 06:11:41 pmI'm quite sure BM789 is a bit smaller than BM859, if that's a concern (WxHxD: 89x193x51mm vs. 97x198x55mm).

author: J-R
author_rank: Super Contributor
timestamp: September 28, 2021, 06:57:20 am
content: I updated my earlier post with the exact counts.Did some testing from down around 0.5uA up through 100uA and both the BM789 and BM869s were basically within 0.02uA of my calibrated Fluke 287 throughout.

author: mac00
author_rank: Newbie
timestamp: September 28, 2021, 09:12:57 am
content: Thank you for the tests.I am closer to the DM789 meter compared to the DM867s. On the other hand, I like the dual display and the usb connection. This one has no temperature measurement, which is a downside for me.I guess I'll never be sure if I made the right decision.A lot of people are satisfied with the BM869s - it's a bit more than enough for me, but maybe it's worth paying a few extra dollars.

author: J-R
author_rank: Super Contributor
timestamp: September 28, 2021, 10:58:41 pm
content: There are plenty of happy customers with all of these. I think the performance is going to be similar, so then it becomes a feature comparison question.Just buy another DMM when the first one doesn't have all the things you want.Speaking of the uCurrent Gold, it's sold out from what I see but the CurrentRanger might be an option for you:https://lowpowerlab.com/guide/currentranger/https://lowpowerlab.com/shop/product/152https://www.welectron.com/LowPowerLab-CurrentRanger-R3-Current-Sense-Amplifier

author: Fungus
author_rank: Super Contributor
timestamp: September 29, 2021, 04:33:25 am
content: Quote from: J-R on September 28, 2021, 10:58:41 pmThe only deal breaker for BM867s or BM857s might be temperature but that's why you have more than one meter.(and also for measuring volts/amps simultaneously, etc.)

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: September 29, 2021, 07:58:35 am
content: I have an anecdote that somehow is fitting in this thread, although I don't think it will help the original poster decide.3 weeks ago the battery in my parents car died. They are elderly, in their 90's and I worry about them all the time. I knew the existing battery in their 18 year old car was at least 9 years old and due for exchange so I went ahead and bought a new one and installed it. I have a Brymen 857a and a 869 (non s). I like both my meters as general purpose meters and would buy the 869 again if I needed to. I like the temp function on the 869 and use it fairly often.I take the 857a on service trips, the 869 lives in the lab. After putting in the new car battery I checked to see if there were any vampire loads draining the battery with the ignition off. It was reading 700 mA! What the hell. No wonder mom's car was dead. Standing back from the car I noticed the running lights were on. Not the headlights, just the side lights. It is hard to see if those are on in the bright sunlight.I turn those off and I measure again. Now the 857a display is jumping around 3mA for one reading then micro-amps, just jumping around. That is to be expected, after turning off the big vampire lights, all the little background vampires dominate as microcontroller(s) wake up and go to sleep.What is the moral of the story. Well the Brymen did its job from the repair perspective. But also showed that if you are designing low power battery operated circuits and want to measure small variable current draw the handheld isn't the right tool. This is a measurement problem where the designer is not well served by the usual lab instruments. Dave did a teardown/review video of the Joulescope at the 38:00 minute mark of this mailbag monday which handles the dynamic range problem but is fairly expensive.

author: HKJ
author_rank: Super Contributor
timestamp: September 29, 2021, 08:08:12 am
content: What is the moral of the story. Well the Brymen did its job from the repair perspective. But also showed that if you are designing low power battery operated circuits and want to measure small variable current draw the handheld isn't the right tool. This is a measurement problem where the designer is not well served by the usual lab instruments.If the meter has a min/max/avg (REC on Brymen) it can do a fairly decent job of it.

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: September 29, 2021, 06:30:21 pm
content: Quote from: HKJ on September 29, 2021, 08:08:12 amI did not think of using averaging as I was not particularly interested in the result beyond determining there was no major current draw. However if I was a designer of battery powered products I would question the usefulness and accuracy of averaging mode. When you have a microcontroller using nano-amps in sleep, then waking up and using a few milliamps for perhaps 10-30 micro-seconds and then sleeping again on irregular intervals the slow sample rate is going to give misleading results unless you are averaging over days. Even then you require coulomb counting.

author: HKJ
author_rank: Super Contributor
timestamp: September 29, 2021, 06:43:13 pm
content: Quote from: chickenHeadKnob on September 29, 2021, 06:30:21 pmAs long as you put the meter in a high enough range, that it do not need to change range, the result will be fairly good if the high current pulses is the main energy consumption (DMM's will average pulses in the DC ranges, this means the max may be wrong, but the average will be fairly good).

author: xbb
author_rank: Newbie
timestamp: October 02, 2021, 01:50:02 am
content: I had to make the same choice and went with the BM869s in the end.I was kinda afraid that the BM789 being a "new" product is still not "mature" and I may regret it in future... also the USB connection is a big plus for me.

author: Neutrion
author_rank: Frequent Contributor
timestamp: October 02, 2021, 10:21:20 am
content: The only two problems with the 789 which has been found so far are also there with the 869s as well. (About the AC+DC current measuring I am not comletely sure but thats not a huge issue, see in the topic.) But it is not a major thing, except if someone regularly wants to measure mV ripple on DC power supplies. However, no one was sure whether that could be solved in FW so I might would wait whether a new FW version comes out.