Another bench DMM preferably with a 10A range - Page 1
Forum section: electronics / testgear

author: Jester
author_rank: Frequent Contributor
timestamp: October 28, 2021, 09:43:13 pm
content: I find that I often need several DMM’s simultaneously when working at the bench. To that end I have 3x 34401A’s a Fluke 45 and I just sold the GWInstek 8251A that I would always use as a last resort. I really trust the first 4 meters and even without annual calibration the drift year to year against my calibrator is negligible. There was nothing wrong with the 8251A, I just preferred the more stable display of the first four meters and I felt I could always trust them 100%.The Fluke 45 has a 100ma and 10A (good for up to 20A for quick measurements) current range, and is often more useful than the 3A limitation of the 34401A.So I’m looking for a “better” replacement for the 8251A. Probably a 6.5 digit, but I would consider a good meter with less resolution. Having a 10 or 20 A current range is desirable but not a necessity as I do have a good current shunt for high current measurements, it would just be handy to not have to use it.I typically purchase used on eBay it will most likely be either Fluke, Agilent (KS) or perhaps a Keithley but would also consider buying new if affordable possibly a Siglent. I paid about $300 for the used 34401’s, but that was a while ago, I think prices might be a bit higher now? I don’t want to spend more than say $450ish tops. I want to trust whatever I get like I trust the Fluke and Agilents I have now, I want that warm and fuzzy feeling when I make a measurement that so far only seems to come from the likes of Fluke and HP I have never had a Keithley but they seem to have a loyal following.I just watched the mjlortan review video of the Siglent SDM3055 and it highlights the slightly unstable display on power up, also the long boot time. Perfect example of what I want to avoid.Recommendations?

author: tautech
author_rank: Super Contributor
timestamp: October 28, 2021, 11:56:04 pm
content: Quote from: Jester on October 28, 2021, 09:43:13 pmDon't base purchase decisions on 6 year old videos.

author: Jester
author_rank: Frequent Contributor
timestamp: October 29, 2021, 12:10:59 am
content: Quote from: tautech on October 28, 2021, 11:56:04 pm

author: tautech
author_rank: Super Contributor
timestamp: October 29, 2021, 01:21:04 am
content: Quote from: Jester on October 29, 2021, 12:10:59 amNo SDM3055 in stock but 3045X boots in 16s.Check the firmware history files for the list of each versions improvements:https://int.siglent.com/download/firmwares/?ProId=26

author: beanflying
author_rank: Super Contributor
timestamp: October 29, 2021, 02:40:07 am
content: I would really ignore or diminish your requirement/priority for 10A. The burden voltages (can be a few Volts) on some of the Bench DMM's or any DMM's for that matter are to high and they lack accuracy.Buy another one or two decent quality external shunts instead, the few below are Murata's with a 0.25% tolerance and the big one is 500A. The testing I have done on these shows them well inside 0.25% btw.Also incase you haven't had a play yet make up a Null modem cable and have a look at the few 'free' options for your 34401A (or 34461A etc) for some more functionality.https://www.eevblog.com/forum/testgear/help-need-keysight-34461a-dmm-data-logging-to-xl/https://www.eevblog.com/forum/testgear/hp-34401a-standalone-software/msg3587032/#msg3587032Totally ignore the boot time of a DMM they take minutes to get stable if you want to use the last couple of digits and if you want a quick measurement then a handheld makes sense.

author: tooki
author_rank: Super Contributor
timestamp: October 29, 2021, 06:48:45 am
content: Quote from: Jester on October 28, 2021, 09:43:13 pmJust to expand on what beanflying said, remember that 6.5+ digit meters typically use an ovenized voltage reference (a voltage reference with a built in heater to stabilize the reference’s temperature at above ambient, ensuring ambient temperature doesn’t affect accuracy). So they need time to warm up. Of course, even in a meter without an ovenized reference, the meter will warm up when on.So in any case, if accuracy matters, you have to let the meter warm up first, making boot time irrelevant. Bench meters are basically intended to be turned on in the morning and left on all day.

author: Jester
author_rank: Frequent Contributor
timestamp: October 29, 2021, 07:25:10 am
content: Quote from: tooki on October 29, 2021, 06:48:45 amFair enough, however if you watch the video with the meter warm, and simply rebooting, the measured value takes about 20s to stabilize on the Siglent and this is after waiting about 20s for it to boot, on the other hand the Fluke displays the correct value as soon as the display is up ( about a second after turning on). A follow up video explains that the problem is hardware related, with the filter enabled a fairly large capacitor is connected across the signal and the time constant is in the neighbourhood of 20s. So you make a step change in the voltage while observing both your trusted Fluke and the Siglent and the last few digits of the Fluke are stable while the Siglent changes for 30s. When I probe something the thought of counting to 30 before trusting the display is exactly what I want to avoid.I’m not bashing the Siglent, there are several aspects of this meter that are really appealing, for example I like the display, and easy access to stats, both of these appear to be an real improvement to either of my go to meters. Not trusting the displayed value is why I sold the 8251.

author: Jester
author_rank: Frequent Contributor
timestamp: October 29, 2021, 07:39:05 am
content: Quote from: beanflying on October 29, 2021, 02:40:07 amThanks for that, I do have some of the Murata shunts and I agree they are pretty decent and economical for measuring higher currents, that being said the current measurement on my cheap Fluke 45 is surprisingly accurate. I just find the 3A max capability of the 34401A is simply too low too often and I often use the Fluke 45 even though it’s a 4.5 vs 6.5 digit meter for current measurements. The burden voltage for the 10A range is actually fairly low.

author: Fungus
author_rank: Super Contributor
timestamp: October 29, 2021, 10:56:03 am
content: Quote from: Jester on October 28, 2021, 09:43:13 pmGet a nice clamp for those sorts of currents, it's much easier.

author: beanflying
author_rank: Super Contributor
timestamp: October 29, 2021, 11:12:14 am
content: Quote from: Fungus on October 29, 2021, 10:56:03 amAt nothing like the accuracy of a shunt or meters current range. Even a decent Fluke clamp meter won't get much below 2% and no where near what 5 or 6 1/2 digits and some good shunts will get you. As per the recent UNI-T thread they are great for a quick rough and dirty check.Quote from: Jester on October 29, 2021, 07:39:05 amIn particular the 3A range on the 34401A sucks when you get near the limit as it is 2V Burden from memory. The 34461A I have as well in the 10A range is much better than the 3A legacy (34401A) range as far as Burden so over 1A it makes sense to switch to the 10A range/connections.Even with it on the bench the shunts are 50mV compared to about 0.5V on the 1 or 10A ranges so it still makes sense to break out the shunts or do the maths to compensate I guess.

author: GerryR
author_rank: Frequent Contributor
timestamp: October 29, 2021, 12:11:33 pm
content: Not sure if you are aware of this, but the 34401 meters had problems making combined AC+DC readings, which the Fluke did not have. When I contacted HP (Keysight) about the problem, they indicated that it was "a hardware issue in an old design" and suggested that I replace the meter with a 34461, which did not have the problem. Just thought I would mention it for those who might be unaware of the problem and need to make those types of measurements.

author: Jester
author_rank: Frequent Contributor
timestamp: October 29, 2021, 12:25:29 pm
content: Quote from: GerryR on October 29, 2021, 12:11:33 pmThat’s interesting, I have observed that but was unaware that this was a known defect. Can you provide more details or a link that describes the problem in detail?

author: GerryR
author_rank: Frequent Contributor
timestamp: October 29, 2021, 02:42:05 pm
content: All I have is some email communications from 2017, when I discovered the problem during some measurement processes. They were disinterested in the problem because of the age of the 34401's and just told me I should replace the meter with the 34461 or something newer. The techs I dealt with set up to verify the problem and then made the recommendation for replacement. Also, this problem showed up in auto mode, not manual mode. I remember telling them how my inexpensive hand-helds (relatively speaking) could make the measurements and the fact that their expensive bench meter couldn't was rather disappointing. I subsequently sold the meter and just use my Fluke 45, which is good enough for my needs, as I am "mostly" retired.

author: Fungus
author_rank: Super Contributor
timestamp: October 29, 2021, 02:46:11 pm
content: Quote from: beanflying on October 29, 2021, 11:12:14 amAccuracy wasn't specified.Quote from: beanflying on October 29, 2021, 11:12:14 amGiven the burden voltages of multimeters in those ranges they won't be very accurate either.

author: nctnico
author_rank: Super Contributor
timestamp: October 29, 2021, 05:05:57 pm
content: Quote from: Jester on October 28, 2021, 09:43:13 pmIf 4.5 digits is enough then I can recommend the Vici 8145A. I bought that for exactly the same reason: I wanted a bench DMM with >10A current handling and a clearly readable display. There are not many bench DMMs out there with >10A capability. Long term stability is also good. I have mine for about 10 years now and it is still in spec (compared to my Keysight 34461A).

author: bdunham7
author_rank: Super Contributor
timestamp: October 29, 2021, 05:15:30 pm
content: Quote from: GerryR on October 29, 2021, 12:11:33 pmWhat, specifically, are you referring to? The 34401A does not have an AC+DC mode, nor a dual display.

author: J-R
author_rank: Super Contributor
timestamp: October 29, 2021, 05:32:55 pm
content: Quote from: Fungus on October 29, 2021, 02:46:11 pmBurden voltage doesn't affect current measuring accuracy.

author: Fungus
author_rank: Super Contributor
timestamp: October 29, 2021, 05:47:21 pm
content: Quote from: J-R on October 29, 2021, 05:32:55 pmIt can reduce the number of electrons flowing through the circuit.

author: Kean
author_rank: Unknown
timestamp: October 29, 2021, 05:50:28 pm
content: Quote from: Fungus on October 29, 2021, 02:46:11 pmThe suggestion was to use an appropriate external shunt, in this case beanflying suggested a 0.25% one with 50mV burden at full rated current

author: TimFox
author_rank: Super Contributor
timestamp: October 29, 2021, 06:03:21 pm
content: Quote from: Fungus on October 29, 2021, 05:47:21 pmBurden voltage should not affect the measurement accuracy (except for self-heating problems), but it may well affect the current in the circuit being measured, especially when above the 100 mV or so range.Shunts with small burdens are probably physically larger than high-burden shunt circuits inside some voltmeters.

author: GerryR
author_rank: Frequent Contributor
timestamp: October 29, 2021, 06:06:44 pm
content: Quote from: bdunham7 on October 29, 2021, 05:15:30 pmThis is like resurecting the dead (from Sept. 2017):The Original Problem:"I have a HP34401A (s/n 3146A13493) multimeter, not Agilent or Keysight, that I bought new, many years ago. The firmware is 03-01-01. Recently, when trying tomeasure the DC offset of 0.500 volts of a 2V p-p, 60 Hz sinewave generated from my arb generator, the meter would not auto-select the range and gave an incorrect reading, only showing some small amount of millivolts. When switching to the manual mode, the reading was correct. My handheld meters auto-selected the correct range and read the correct value. Did a later revision of the firmware address this issue, and if so, is a firmware update available that will work on this meter?"Their answer:"The behavior you describe is "normal" for a 34401A when trying to measure dc in the presence of an ac signal. A firmware update would not fix this; it's inherentin the meter's design. By the way, to "update" the firmware would require a unit exchange, same as if it was broken. The firmware is hard coded into ROM's and a board would have to be changed. Unit Exchange for a 34401A is currently about $735."Manual states the following:The multimeter’s ac voltage and ac current functions measure theac-coupled true RMS value. This is in contrast to the ac+dc true RMSvalue shown above. Only the “heating value” of the ac components of theinput waveform are measured (dc is rejected). For sinewaves, trianglewaves, and square waves, the ac and ac+dc values are equal since thesewaveforms do not contain a dc offset. Non-symmetrical waveforms, suchas pulse trains, contain dc voltages which are rejected by ac-coupledtrue RMS measurements.An ac-coupled true RMS measurement is desirable in situations whereyou are measuring small ac signals in the presence of large dc offsets.For example, this situation is common when measuring ac ripplepresent on dc power supplies. There are situations, however, where youmight want to know the ac+dc true RMS value. You can determine thisvalue by combining results from dc and ac measurements as shownbelow. You should perform the dc measurement using at least 10 powerline cycles of integration (6 digit mode) for best ac rejection.ac + dc = sqrt of ac2 + dc2Hope this helps.

author: voltsandjolts
author_rank: Unknown
timestamp: October 29, 2021, 06:10:27 pm
content: The nice thing about external shunts is that you won't blow the $10 HRC fuse in your meter

author: Trader
author_rank: Frequent Contributor
timestamp: October 29, 2021, 06:45:33 pm
content: Quote from: beanflying on October 29, 2021, 02:40:07 amI "solved" the burden voltage problem with a Workaround.I got an Aneng AN870, which is measure amps very accurate, and I removed the fuse, connecting it directly. Of course, is not safe, but is to be used only in the lab under my PSU of max 5A. (since the DMM supports up to 20A, is safe to use only in this environment)The burden voltage (without the fuse) is much below a Fluke and any other DMM.

author: Fungus
author_rank: Super Contributor
timestamp: October 29, 2021, 06:49:59 pm
content: Quote from: TimFox on October 29, 2021, 06:03:21 pmI'm assuming that's one of the reasons why the original poster said (and I quote):"...it would just be handy to not have to use it."Hence my suggestion of a clamp meter - much more convenient to use, no need to open up the circuit, can measurelargecurrents quite accurately.The point being madewas(I think) that by giving up the requirement for over 10A measurement capability, the OP will be free to chooseanymeter. He'll have a lot more options.Quote from: TimFox on October 29, 2021, 06:03:21 pmThe end result is the same.

author: bateau020
author_rank: Frequent Contributor
timestamp: October 29, 2021, 06:54:10 pm
content: If you want to compare the KS 344xxA and the SDM3055:About the burden voltage in the 10A range, full scale:KS 34460A: no 10A rangeKS 34465A (and probably also KS 34461A and KS 34470A): < 0.5V say the specs, in reality it is 0.33VSiglent SDM3055: <0.3V (but over 7A only under 30 secs) say the specs, in reality it is 0.55VAbout dual measurement:Both 34465A and SDM3055 do AC+DC, but only the SDM3055 does V+I (and even DCV+ACI) via the UI. (Both cases: not real time though, it switches back and forth).The KS can do V+I, but only a under lot of conditions, with the help of a shunt, and not really intuitively.About bugs in the SDM3055:Yes, there still are some small bugs in the SDM3055, but it has been rather usable to me. The KS is a step above though (but I do miss V+I).Edit: some of the bugs are in the dual measurement:* when in dual, do not use autorange, as otherwise the values either come out way wrong, or it may simply hang the meter (manual reboot needed).* when switching primary and secondary measurement (press "dual") it goes back to auto. Which may immediately hang the meter.

author: TimFox
author_rank: Super Contributor
timestamp: October 29, 2021, 07:45:19 pm
content: Quote from: Fungus on October 29, 2021, 06:49:59 pmWhen measuring the current drawn by a low voltage circuit through a 10 A or so ammeter, I always connect the voltmeter across the load, with the ammeter between the supply and the load. This means that the current measurement is accurate, since the voltmeter current is negligible compared with the load current, independent of the burden voltage. QED.

author: J-R
author_rank: Super Contributor
timestamp: October 29, 2021, 08:04:58 pm
content: Quote from: Fungus on October 29, 2021, 06:49:59 pmThis is a silly conversation. The current flowing through an external shunt/resistor or DMM is the same current that flows to the circuit. If you are wanting to have a conversation about current AND voltage at the circuit, then just say so. But in that case, it is easy to measure the voltage AT the circuit rather than before the shunt. So either way this is a far more accurate method than using a clamp meter.If you want to dive into the small amount of current flowing through the DMM when making voltage measurements then that is also a different conversation, but it's a really short conversation given the disparate resistances involved.

author: TimFox
author_rank: Super Contributor
timestamp: October 29, 2021, 08:16:59 pm
content: Some beginners may be confused, since ideal ammeters have no burden (zero resistance) and ideal voltmeters draw no current (infinite resistance). In practice, with practical meters, see my last comment above (# 25).

author: Fungus
author_rank: Super Contributor
timestamp: October 29, 2021, 08:52:11 pm
content: Quote from: TimFox on October 29, 2021, 07:45:19 pmThat doesn't tell you how much current the circuit will draw when you take the ammeter away.If you use an adjustable bench supply you can raise the voltage to compensate, yes, but it isn't always possible and a clamp is justso much easier.If you're working in the 10A+ range then usually a ballpark figure is enough.Quote from: J-R on October 29, 2021, 08:04:58 pm

author: nctnico
author_rank: Super Contributor
timestamp: October 29, 2021, 08:59:09 pm
content: Quote from: Fungus on October 29, 2021, 08:52:11 pmUsing a bench power supply is a better option IF it has an accurate current meter built in. The burden voltage will be compensated and the voltage is accurate across the load if you use the sense wires. All high current power supplies I have come across have sense wires.

author: TimFox
author_rank: Super Contributor
timestamp: October 29, 2021, 09:11:30 pm
content: A clamp meter is certainly good enough for a ballpark figure. Reasonably priced Fluke ac/dc clamp meters have a (lowest) full scale of 40 A at 2% accuracy on DC. At lower current values, the accuracy suffers normally with the high full-scale.For accurate results, I prefer my approach, using my older Fluke A90 shunt (switchable, max 10 A with 100 mV output, quoted accuracy 0.2% at 10 A range).

author: Jester
author_rank: Frequent Contributor
timestamp: October 29, 2021, 11:47:12 pm
content: Thanks for all the comments. To clarify I have a decent clamp on, that’s a non starter accuracy wise, I sort of implied that when I stated 6.5 digit, but would consider less ie. a 5.5 digit.I have a few options when measuring higher dc currents because I have 3 dc loads that operate up to 30-40A and they seem quite accurate relative to my Murata shunt and (Fluke 45 at lower currents).Ac current it’s either the shunt or Fluke 45.I’m going to read a bit more before deciding on the replacement.

author: nctnico
author_rank: Super Contributor
timestamp: October 29, 2021, 11:55:43 pm
content: Quote from: Jester on October 29, 2021, 11:47:12 pmIMHO that is a rather futile exercise. The specs of my 34461A says that it has an accuracy of .1% for the 10A range (the 3A range is much worse for some reason). The VC8145 sits at 0.5% in the 20A range. It seems current shunts just aren't very accurate.

author: beanflying
author_rank: Super Contributor
timestamp: October 30, 2021, 12:32:40 am
content: Quote from: Fungus on October 29, 2021, 02:46:11 pmSeriously discussing 5 and 6 1/2 digit meters a 2% clamp meter is an order of magnitude WORSE than any of them.Given the burden voltages at higher currents we have clearly being discussing good quality shunts rather than using the internal meter ones.

author: beanflying
author_rank: Super Contributor
timestamp: October 30, 2021, 12:42:15 am
content: The issue with burden voltage becomes much more of an issue as the current gets up but the voltages stay low (say 12v and down) to a point where that burden might effect the DUT doing what it is supposed to. The 50mV of a shunt and corresponding lower resistance makes it 'closer' to the ideal as mentioned a few posts back by TimFox.Quote from: nctnico on October 29, 2021, 11:55:43 pmThe reason for the 3A being worse was to keep reverse compatibility with the 34401A. I skip the 3A range on mine and use the 10A range.Current shunts are as accurate as your $ and or some time allows (break out the file if they are over or open the clamps and shorten them if under). The Murata ones I got as they are 'decent' for $ at 0.25% you can get them off the shelf much better or have them custom made and calibrated if you have a need.

author: Fungus
author_rank: Super Contributor
timestamp: October 30, 2021, 04:51:19 am
content: Quote from: Jester on October 29, 2021, 11:47:12 pmAround here you have tosayit.6.5 digit current accuracy above 10A for $450? Good luck!

author: Fungus
author_rank: Super Contributor
timestamp: October 30, 2021, 04:57:16 am
content: Quote from: beanflying on October 30, 2021, 12:42:15 amDon't forget to build a temperature-controlled box to keep it in and wait for the temperature to stabilize for every single reading.

author: beanflying
author_rank: Super Contributor
timestamp: October 30, 2021, 05:15:17 am
content: Quote from: Fungus on October 30, 2021, 04:57:16 amIf you still insist on being abecause you didn't follow the discussion and what was written then stay out of the topic as you clearly have nothing constructive to add! Further before mouthing off you might do some further reading on what the actual items being discussed are specced at.$30-35 USD gets you a 50A shunt at 0.25% with15PPM/C Manganinelementshttps://www.farnell.com/datasheets/2237929.pdfand as Jester has a nice stack of existing DMM's no real need for a spend apart from some more functionality. For added information the 34401A has a much higher temperature coefficient than this in spite of still being one of the most stable Bench DMM's out there (better than my modern 34461A).

author: Fungus
author_rank: Super Contributor
timestamp: October 30, 2021, 07:43:23 am
content: Quote from: beanflying on October 30, 2021, 05:15:17 amWhat was written was:"I do have a good current shunt for high current measurements, it would just be handy to not have to use it."Why all the discussion of shunts? Beats me.

author: Jester
author_rank: Frequent Contributor
timestamp: October 30, 2021, 11:32:29 pm
content: Quote from: Fungus on October 30, 2021, 07:43:23 amFungus, what I actually said was“So I’m looking for a “better” replacement for the 8251A. Probably a 6.5 digit, but I would consider a good meter with less resolution. Having a 10 or 20 A current rangeis desirable but not a necessityas I do have a good current shunt for high current measurements, it would just be handy to not have to use it.”The essence of my query is what DMM’s would people recommend. I mentioned the 10-20A current range as a nice to have but not a necessity ( I find it handy on the Fluke 45). There have been a few suggestions to use a shunt and this is a good suggestion as fairly accurate shunts are affordable and relaxing that “nice to have“ opens the door to more viable meters.I did not enquire about clamp-on meters or ball park measurements.Most likely I will get an older Fluke and forgo the high current range, I will use either the shunt for really high currents and ac or one of my dc loads set to 0 ohms for dc under 40A.

author: rsjsouza
author_rank: Super Contributor
timestamp: October 31, 2021, 10:26:12 am
content: Quote from: nctnico on October 29, 2021, 11:55:43 pmWell, even on a 4-1/2 digit meter (which I would expect much worse specs) such as the handheld U1282A it gives 0.3% at 10A and 0.6% at 20A (for 30 seconds only).

author: beanflying
author_rank: Super Contributor
timestamp: October 31, 2021, 10:45:14 am
content: Part of the issues with just reading the basic accuracy for DMM's is it doesn't tell you the full story in the case of current measurement. So just for interest the U1281/2 full current spec and internal shunt details is below. The 10A shunt gets a bit ugly for burden voltage as you get up in current and might cause a problem depending on the DUT and how you wire it.

author: Fungus
author_rank: Super Contributor
timestamp: October 31, 2021, 11:02:10 am
content: Quote from: Jester on October 30, 2021, 11:32:29 pm

author: rsjsouza
author_rank: Super Contributor
timestamp: October 31, 2021, 11:25:28 am
content: Quote from: beanflying on October 31, 2021, 10:45:14 amNo problem with my reading of the specifications; that only proves the point that shunts can vary wildly and depend on other surrounding conditions.As the specifications also say, the shunt is 0.01Ω but the burden voltage is somehow 0.4V @ 10A which could be caused by either heat (shunt is too small and its resistance increases, although I believe Keysight would have mentioned that) or other compounding conditions such as the fuses, jacks, PCB tracks, etc.At any rate, this was just another example as the OP mentioned bench meters.

author: 2N3055
author_rank: Super Contributor
timestamp: October 31, 2021, 11:38:24 am
content: Quote from: rsjsouza on October 31, 2021, 11:25:28 amYeah, mainly fuses...

author: beanflying
author_rank: Super Contributor
timestamp: October 31, 2021, 11:40:44 am
content: Quote from: rsjsouza on October 31, 2021, 11:25:28 amNo issue with your reading of the spec at all just that consideration needs to be given to the total spec and how it will interact with the DUT. The voltage drop and power absorbed by a meter becomes relevant to the measurement (for most meters) if it is to high so a 50mV external shunt makes a lot of sense to minimize these.As to Keysights spec as you point out it is a bit rubbery based on the internal shunts resistance so what it includes is a mystery without some actual testing on one.Fluke exampleQuote

author: rsjsouza
author_rank: Super Contributor
timestamp: October 31, 2021, 05:57:14 pm
content: Cool and thanks for the clarification. Indeed the Fluke is much clearer on its boundary conditions.