more than 200 KHz BW portable DMMs - do they exist? - Page 1
Forum section: electronics / testgear

author: Bobson
author_rank: Regular Contributor
timestamp: November 04, 2021, 06:21:31 pm
content: I routinely measure voltages around 1mv in 50-300 KHz range. The signal varies both in voltage (not much, about 20%) and frequency (100-200KHz mostly, but wider sometimes), non-harmonic.Are there any portable DMMs with at least 200 KHz TRMS bandwidth?I need at least 2% precision on AC (no DC component).Some my DMMs can show 200 KHz signal, but since sensitivity is not constant over 100 KHz, they could not be used for the task, and I use Velleman HPS-140i pocket scope, which unfortunately is at the limit of its sensitivity (5mv/div). I tried pocket FNIRSI scopes, but they do not have sensitivity.I hope some Mustool combined DMM/scopes could have single ADC path for both DMM and scope, and have high BW, but I'm not sure.Or maybe I should seek for MHz range TRMS probes? This is an amature project, and probes I see start around $500, too high for me.Thanks.

author: bdunham7
author_rank: Super Contributor
timestamp: November 04, 2021, 06:44:23 pm
content: Not likely with any digital TRMS meter I know of. Even the $2K Fluke 8846A bench meter is only good for 4% accuracy plus the residual counts at 300kHz--and on its lowest 100mV range, your 1mV will be lost in the noise and offset. The $3500 Keysight 34470A with TrueVolt will be better at 1%, but again the 0.1% of range (100mV) is 10% of your reading. I doubt any handheld is going to be better than TOTL 6.5 and 7.5 digit meters....You're going to need a specialty instrument. The cheapest, simplest thing I can think of is something like an old HP 403B analog AC voltmeter. It has a 1mV range, 2M input impedance, a 2MHz bandwidth and a 2% accuracy rating to 1MHz. It also has NiCd batteries so it is portable, and they aren't all that big, perhaps an 8 inch cube sort of thing.

author: RoGeorge
author_rank: Super Contributor
timestamp: November 04, 2021, 07:05:03 pm
content: My old MetrixMTX-3283https://ie.rs-online.com/web/p/multimeters/5124959/has 200kHz bandwidth and 100 000 count, 0.02% accuracy. Good overall quality, and with some goodies like selectable 1 GOhm / 10 MOhm impedance, simultaneous voltage and current recording/logging (good to measure batteries charge/discharge), etc. but slow if you wait for the numbers to settle.There are more recent models with similar parameters.Never tested it's response in frequency until today. With a Rigol DG4102 DDS generator (no idea about the generator's accuracy) set on 10 mV RMS, my mtx3283 measures something like this:9.818 mV / 10 Hz9.875 mV / 100 Hz10.050 mV / 1 kHz10.060 mV / 10 kHz9.360 mV / 100 kHz9.497 mV / 200 kHz9.733 mV / 250 kHz9.600 mV / 300 kHz8.768 mV / 350 kHz7.279 mV / 400 kHz5.312 mV / 450 kHz3.386 mV / 500 kHz

author: Bobson
author_rank: Regular Contributor
timestamp: November 04, 2021, 07:09:00 pm
content: Quote from: bdunham7 on November 04, 2021, 06:44:23 pmI have 8846A at work, and it is adequate for my task, maybe accuracy I requested is too high, and 5% would be enough. But I need my own and portable.QuoteI already have 5 MHz Russian analog TRMS microvoltmeter B3-57, it is very good, but too heavy. Also, I'm afraid needle system of analog meters would not survive my city walk.Ok, i'll rather try to get used MHz TRMS DMM probe.I 've never used active oscilloscope probes, I understand they are used too boost GHz range signals, but maybe they can boost 1 MHz range signals also?

author: Bobson
author_rank: Regular Contributor
timestamp: November 04, 2021, 07:15:06 pm
content: Quote from: RoGeorge on November 04, 2021, 07:05:03 pmWow! Definitely would fit my needs, if I'll get it at good price. Thanks a lot!Always loved Chauvin meters, have some at work, but they are pricey for personal usage.

author: bdunham7
author_rank: Super Contributor
timestamp: November 04, 2021, 07:16:34 pm
content: Quote from: Bobson on November 04, 2021, 07:09:00 pmI don't know what that is. Do you mean an RF probe? Is there a reason you need TRMS vs average (or even peak) responding?

author: 2N3055
author_rank: Super Contributor
timestamp: November 04, 2021, 07:18:02 pm
content: Quote from: RoGeorge on November 04, 2021, 07:05:03 pmMTX3293 is very similar specified to 200KHz but pretty much good to 300KHz..There are many handhelds that will do 100KHz nicely, but more than that is rare..

author: Bobson
author_rank: Regular Contributor
timestamp: November 04, 2021, 07:27:06 pm
content: Quote from: Fungus on November 04, 2021, 07:18:39 pmHow is it connected with my problem?

author: bdunham7
author_rank: Super Contributor
timestamp: November 04, 2021, 07:28:25 pm
content: Quote from: Fungus on November 04, 2021, 07:18:39 pmYou're off by a factor of 1000 on the frequency, let alone the amplitude....

author: bdunham7
author_rank: Super Contributor
timestamp: November 04, 2021, 07:30:42 pm
content: Quote from: RoGeorge on November 04, 2021, 07:05:03 pmWhat scale is that on and can you get similar results down at 1mV? That seems quite a bit better than either my F189 or F289, but those are only specced to 100kHz and they roll off too much by 300kHz.

author: Bobson
author_rank: Regular Contributor
timestamp: November 04, 2021, 07:35:35 pm
content: Quote from: bdunham7 on November 04, 2021, 07:16:34 pmI mean something like this:https://www.aemc.com/store/products/current-probes/current-probe-miniflex-hfYes, there IS a reason for TRMS.

author: bdunham7
author_rank: Super Contributor
timestamp: November 04, 2021, 07:41:44 pm
content: Quote from: Bobson on November 04, 2021, 07:35:35 pmThat's a current probe and it doesn't TRMS anything....

author: Kleinstein
author_rank: Super Contributor
timestamp: November 04, 2021, 07:43:57 pm
content: One could consider a portable DSO. 1 mV with 1 MHz BW is already somewhat demanding on the noise.With the DMMs 1 mV is a bit on the low side. With most analog True RMS chips the BW goes down when the amplitude is at the low end. So 200 kHz BW at 1 mV is quite demanding. This would be more something for a special RF mV meter or maybe a portable spectrum analyzer.

author: RoGeorge
author_rank: Super Contributor
timestamp: November 04, 2021, 07:50:47 pm
content: OK, I'm curious, too, let's try again with 1mV RMS, though this is at the lower limit of the generator, minimum possible is 0.4mV RMS, so not very trusty:DMM on 100.00 mV RMS (max scale), 10 Mohm input impedance, filter on, DDS with coax cable terminated in a 50 ohms resistor (with very low quality connectors and DIY terminator and cable, 5-10 minutes of instruments heating):10 Hz / 00.938 mV RMS100 Hz / 00.950 mV1 kHz / 00.959 mV10 kHz / 00.952 mV100 kHz / 00.743 mV150 kHz / 00.644 mV200 kHz / 00.558 mV250 kHz / 00.494 mV300 kHz / 00.409 mV350 kHz / 00.280 mV400 kHz / 00.177 mV

author: Fungus
author_rank: Super Contributor
timestamp: November 04, 2021, 07:57:52 pm
content: Quote from: Bobson on November 04, 2021, 07:27:06 pmBrain fart. I read it as 200Mhz for some reason. Message removed.

author: TimFox
author_rank: Super Contributor
timestamp: November 04, 2021, 08:03:48 pm
content: If you are trying for < 1% accuracy, don't forget to include the effect of the meter's input capacitance driven by 25 ohms (50 ohm source plus 50 ohm termination).My Marconi 2610 true-rms bench digital voltmeter, useful up to 25 MHz, has an input capacitance of 40 pF, which with the 25 ohm impedance gives -3dB at 160 MHz, or about 1% attenuation at 1.6 MHz

author: voltsandjolts
author_rank: Unknown
timestamp: November 04, 2021, 08:10:07 pm
content: TheTTi 1908uses anAD8436for the TRMS measurement, which has rated 3dB bandwidth of 1MHz.I've never tested this DMM for such low-level wide bandwidth as required by OP, but could make some measurements if its of interest.Also, perhaps a x10 pre-amp in front of whatever-meter-you-choose would improve accuracy.

author: 2N3055
author_rank: Super Contributor
timestamp: November 04, 2021, 08:23:16 pm
content: Quote from: Kleinstein on November 04, 2021, 07:43:57 pmI must agree with you. You can buy Micisg scope with 1mV/div sensitivity for less than the price of MTX3293...

author: Bobson
author_rank: Regular Contributor
timestamp: November 04, 2021, 08:32:20 pm
content: Quote from: bdunham7 on November 04, 2021, 07:41:44 pmSure, I've just failed to google proper voltage probe.

author: Bobson
author_rank: Regular Contributor
timestamp: November 04, 2021, 08:33:09 pm
content: Quote from: TimFox on November 04, 2021, 08:03:48 pmNo, I don't need sub 1% accuracy, 5% is ok.

author: Bobson
author_rank: Regular Contributor
timestamp: November 04, 2021, 08:41:03 pm
content: Quote from: RoGeorge on November 04, 2021, 07:50:47 pmJust tested my handy APPA-506 DMM with UNI-T UTG-932E DDS monitoring with Hantek DSO-1202B.APPA 506 miserably failed not only 1mV, but also 10mv tests up to 100 KHz! Only at 100mV it's kept the level at 100 KHz.But, I suddenly realized that my portable Hantek DSO-1202B has 2mV/div plus 640x480 and is absolutely adequate for my task.PROBLEM SOLVED! And no need to buy additional equipment.P.S. Very discouraged by my APPA-506 bandwidth at mV ranges.

author: evava
author_rank: Regular Contributor
timestamp: November 06, 2021, 04:25:12 pm
content: Quote from: Bobson on November 04, 2021, 06:21:31 pmFYI, Velleman HPS140 has 1mV/div sensitivity, unfortunately you have to choose that sensitivity by hand (see picture with square wave 420kHz), this IMHO is more usable for your requirements than your Hantek DSO-1202B (has 2mV/div sensitivity).Of course Hantek is otherwise much better tool/scope.

author: HKJ
author_rank: Super Contributor
timestamp: November 06, 2021, 05:12:44 pm
content: I measured frequency response of some DMMs here:https://lygte-info.dk/info/DMMFrequencyResponse%20UK.html

author: evava
author_rank: Regular Contributor
timestamp: November 06, 2021, 05:33:53 pm
content: Quote from: HKJ on November 06, 2021, 05:12:44 pmBrymen 869 300kHzVery nice!What about its mV range?

author: Kleinstein
author_rank: Super Contributor
timestamp: November 06, 2021, 05:47:34 pm
content: The analog RMS to Dc converters can be quite fast, with a large signal. However the BW usually gets lower when the amplitude is reduced. The 1 mV case would be usually at only a small fraction of the range.For the AD8436 chip the BW is at some 300 kHz with 100 mV, but only some 10 kHz with 1 mV.It may be a good thing to limit the BW before the RMS chips to get better linearity.Some DMMs have additional amplification in the low range, but not all and even with 10 mV the BW is aready down.This is different from the DMMs that use digital RMS (e.g. KS3446x, DMM6500, but also some handhelds with usually not so geat BW to start with). The the BW stays constant with amplitude and thus more linear response also down to relatively low readings (if the calibration is correct).

author: Bobson
author_rank: Regular Contributor
timestamp: November 06, 2021, 07:31:20 pm
content: Quote from: evava on November 06, 2021, 04:25:12 pmShame on me! Sure it has 1mv. Yes, it more usable, and gives direct power readings (only should correct it to my load resistance), the only problem I have to replace the deteriorated battery.Thanks a lot!

author: Bobson
author_rank: Regular Contributor
timestamp: November 06, 2021, 07:37:37 pm
content: Quote from: HKJ on November 06, 2021, 05:12:44 pmYes, I visit your site often, since it is really good source of information, and one of the very rare which contain BW information.Unfortunately, BW@1mV is very different from BW@1V on most DMMs.And I've decided to use scopes, since they are more predictable, albeit not so precise.

author: HKJ
author_rank: Super Contributor
timestamp: November 06, 2021, 07:53:41 pm
content: Quote from: Bobson on November 06, 2021, 07:37:37 pmIf you want me to test a specific DMM you can ask. I will only test DMM's that are supported by TestController and that I have (That is a rather broad selection).I would not be surprised if the band width at 1mV was better than 1V, because you do not use the standard input divider, but feed the signal more directly into the DMM. That is only a guess and need tests to confirm.

author: Wolfgang
author_rank: Super Contributor
timestamp: November 06, 2021, 08:02:39 pm
content: A lot of cheap spectrum analyzers could be helpful. Rigol DSA7 or 8 series, they start from 9kHz and go up to way above what you need. Sum up the spectral powers, and you have your RMS value. On top, you see the harmonic contents immediately. Low levels of 1mV or even lower are no problem at all.

author: Bobson
author_rank: Regular Contributor
timestamp: November 06, 2021, 08:11:30 pm
content: Quote from: HKJ on November 06, 2021, 07:53:41 pmOn the contrary, BW@1mv is not wider, but narrower at least on my home DMMs APPA-506 and CEM-DT9979.I'll add some measurements in an hour.Here are some results, very, VERY weird. All measurements done using UNI-T 932 generator, 9999 Ohm load settings (since i didnt attach any terminator), sine wave, 0 DC offset. DMMs are set for AC mV range. Measurements repeated twice: 1st time two DMMs were in parallel, 2nd time alone.Some remarks:CEM is unstable at 1mV with F>2KHz, but has very wide BW at 10mV.It showed bad results in V AC mode.APPA showed better results in V AC mode, than in mV AC mode !!!I guess I should repeat the test with proper terminator attached, but not now.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 06, 2021, 08:19:11 pm
content: The calculated RMS value from the scope is not so bad. It is essentially the same as digital RMS used in some higher end DMMs, just with a faster and usually 8 bit only ADC. The faster sampling rate and usually 1:2:5 gain settings can help somewhat to reduce the effect of the limited ADC resolution.The results can be different, as the BW of the scope is often higher and at 1 mV the noise may already be significant.A spectrum analyser often lacks the input protection and often has a 50 Ohms input. So depending on the source it many work or now.

author: Wolfgang
author_rank: Super Contributor
timestamp: November 06, 2021, 08:41:15 pm
content: Quote from: Kleinstein on November 06, 2021, 08:19:11 pm...well, the levels to be measured are in the 1mV range, which is way below the destruction limit of spectrum analyzers (mostly above 20dBm). 50ohms may be an issue, but regarding noise the spectrum analyzer declasses any scope (even the cheap one have a DANL below -150dBm). Cheap scopes are noisy at low voltages !

author: HKJ
author_rank: Super Contributor
timestamp: November 06, 2021, 08:59:39 pm
content: Quote from: Bobson on November 06, 2021, 08:11:30 pmAs I said: It need testing.I have only tested one DMM in the mV range and it had better bandwidth.But then I tested at near full mV range and not at a low level that is outside specifications for most DMM's. A good idea if you want to use a DMM at 1mV is to add a 100 times amplification with a OpAmp.

author: Bobson
author_rank: Regular Contributor
timestamp: November 06, 2021, 09:44:34 pm
content: Quote from: HKJ on November 06, 2021, 08:59:39 pmI agree, it differs and depends.I've updated my prev post with some test results, which are rather strange.CEM has flat BW up to 350 KHz at 10mV, better than @ 100 or 1 mV. But it is unusable @1mV at F>2KHz.Will test Fluke 8846A and some other DMMs at Monday. Especially interested in Escort 89s, which is very unusual.

author: 1audio
author_rank: Frequent Contributor
timestamp: November 07, 2021, 01:36:16 am
content: After seeing this I just checked my vintage Fluke 8860A. On the 10V range is down about 3% at 1 MHz, on the 100 mV range its about the same with 10 mV in. Those seem to usually change hands for around $100 or less. Pretty good value for 4 1/2 digits. Better performance than my Fluke 87 mkIII which barely makes it to 100 KHz and is way down by 300 KHz. The 8060A is more accurate even though is been 30+ years since it was calibrated or adjusted.

author: 1audio
author_rank: Frequent Contributor
timestamp: November 07, 2021, 02:00:36 am
content: Sorry, operator error here. While the 8060A is much better than the 87, it drops starting at 200 KHz. The 87 is more like 20 KHz it seems. My calibrator has too many knobs to watch. I'll have to park a counter on it to make sure I don't miss something.

author: bdunham7
author_rank: Super Contributor
timestamp: November 07, 2021, 02:47:13 am
content: Quote from: 1audio on November 07, 2021, 02:00:36 amTypical high-end bench DMMs seem to roll off at 300kHz or lower, with some exceptions. The only ones I know of that do 1MHz and TRMS are the Fluke 8505A/8506A, although there may be others. But even those are getting into the 3-4% error range and at that point almost any DSO will do as well or better.

author: _Wim_
author_rank: Super Contributor
timestamp: November 07, 2021, 07:40:20 am
content: A 200kHz BW 1mV AC-signal seems fairly easy to amplify with 1 or 2 opamp stages powered by a 9V battery. The amplified signal can than be read by any of the above multimeters with 200kHz TRMS BW. If 10k input impedance is enough, you could even "abuse" a µcurrent for this (although for sure not an optimal solution, but it is very useful for measuring small currents additionally)https://www.eevblog.com/files/uCurrentRev5schematic.pdfhttps://www.eevblog.com/projects/ucurrent/

author: Trader
author_rank: Frequent Contributor
timestamp: November 07, 2021, 03:27:36 pm
content: AD8362 -https://www.analog.com/media/en/technical-documentation/data-sheets/AD8362.pdf50 Hz to 3.8 GHz - 65 dB TruPwr™ DetectorAccurate rms-to-dc conversion from 50 Hz to 3.8 GHzInput dynamic range of >65 dB: −52 dBm to +8 dBm in 50 ΩWaveform and modulation independent, such as GSM/CDMA/TDMA

author: 1audio
author_rank: Frequent Contributor
timestamp: November 08, 2021, 03:59:15 am
content: "Typical high-end bench DMMs seem to roll off at 300kHz or lower, with some exceptions. The only ones I know of that do 1MHz and TRMS are the Fluke 8505A/8506A, although there may be others. But even those are getting into the 3-4% error range and at that point almost any DSO will do as well or better."This prompted me to look at some specs for scopes and for most I see - 3dB (-50%) specsSiglent gives this which is something BUT 1 dB is approx 20%. The 8506A is 3.5% at 1 MHz:Bandwidth Flatness DC- 10% (BW): ± 1 dB (20%) 10%- 50% (BW): ± 2 dB (37%) 50%- 100% (BW): + 2 dB/-3 dB (+37%-50%) (conversions mine from here:https://calculator.academy/db-to-percentage-calculator/#f1p1|f2p0 )Looking though my collection my HP3403 is .5% at 1 MHz. I'll need to check that it meets spec or can be adjusted. My 8506a is within spec but that is 3%. I also have a Fluke 8922 which is .7% at 1 MHz.Maybe its worth asking what it being measured that needs this accuracy at 1 MHz and 1 mV?

author: bdunham7
author_rank: Super Contributor
timestamp: November 08, 2021, 04:06:17 am
content: Quote from: 1audio on November 08, 2021, 03:59:15 amThat's quite a collection of unusual and accurate devices for AC voltage measurement!

author: 1audio
author_rank: Frequent Contributor
timestamp: November 08, 2021, 05:45:57 pm
content: Working in the audio trade got me started and then deciding I needed to maintain my own stuff since calibration, especially of vintage instruments, is costly if even possible. Also I accumulated this stuff almost 20 years ago when it was cheap and no one wanted it. I'm reluctant to mention too much or the prices on eBay will jump. The prices of thermal converters have already jumped so I'm glad I have a collection.

author: Fungus
author_rank: Super Contributor
timestamp: November 09, 2021, 06:39:42 am
content: The Fluke 8060A is still very sought-after for Audio work.

author: 2N3055
author_rank: Super Contributor
timestamp: November 09, 2021, 07:11:05 am
content: Quote from: Fungus on November 09, 2021, 06:39:42 amWhere it performs no better than any modern 100KHz BW meter, including UNI-T UT71It is cool old legendary meter, but that's it. It's nostalgia stuff.

author: Caliaxy
author_rank: Frequent Contributor
timestamp: November 09, 2021, 12:38:13 pm
content: Quote from: 2N3055 on November 09, 2021, 07:11:05 amUnlikely. Why would someone doing audio work would choose UT71, a meter whose lowest ACV range is 4V?

author: 2N3055
author_rank: Super Contributor
timestamp: November 09, 2021, 01:45:47 pm
content: Quote from: Caliaxy on November 09, 2021, 12:38:13 pmBandwidth wise... Sorry for not being clearer.

author: coromonadalix
author_rank: Super Contributor
timestamp: November 09, 2021, 03:25:25 pm
content: The venerable 3458 had / has a 2Mhz bandwith if i recall ??

author: 1audio
author_rank: Frequent Contributor
timestamp: November 09, 2021, 05:05:02 pm
content: I think this has veered quite far from where the OP started his inquiry.In any case comparing a current mid priced handheld multimeter to a premium handheld meter introduced in 1980 (41 years ago!) is not really all that valid. However the specs are roughly comparable (see attached PDF) which is a demonstration of the progress in technology in 40 years. The Fluke is slightly better but not enough to be a big differentiator.The Fluke 8506A uses a thermal TRMS conversion where the Keysight 3458 uses a sampling technique, which works best with sinusoidal repetitive waveforms for maximum accuracy. And there is a 20 dB difference in cost.in practical terms a fluke 8920-8922 or even better an HP 3403 are much better suited to measuring wide bandwidth AC signals. And once you are in RF land there is a constellation of different instruments depending on what you are attempting to quantify.

author: 2N3055
author_rank: Super Contributor
timestamp: November 09, 2021, 06:56:39 pm
content: Quote from: 1audio on November 09, 2021, 05:05:02 pmThank you for the effort to make comparison.I agree that rest of conversation veered quite far...OP asked about portable (handheld?) meters with 200kHz + bandwidth...