Siglent SDM3055 opinions? - Page 1
Forum section: electronics / testgear

author: LarryMartin
author_rank: Contributor
timestamp: December 24, 2014, 06:09:09 pm
content: I've seen a bit of discussion on this forum about the Siglent SDM3055 bench multimeter firmware problems, but no substantive information about its performance. I can't even find any quickie Youtube review/unboxing videos. Is it just too new for any reviews or other information to filter out? Is the firmware too buggy to even use it? Is the SDM3055 just a bust and nobody is actually buying them for whatever reason?Assuming the firmware bugs are worked out, does anyone have an opinion on whether this could be a decent meter?

author: tautech
author_rank: Super Contributor
timestamp: December 24, 2014, 07:41:48 pm
content: Not long had mine, firmware immediatly updated to the "09" version and is stable with no problems.My first bench DMM so I can't comment how it compares against others.The UI is pleasant to use, it is fan cooled and emits a low pitched sound very similar to the Siglent DSO's.Continuity is fast.Comes with a software suite that as yet I have not tried or installed.I un-boxed it in another thread:https://www.eevblog.com/forum/testgear/test-equipment-packaging-experiences-good-bad/msg566161/#msg566161Any futher info you need just ask.

author: MisterBiscuit
author_rank: Unknown
timestamp: December 24, 2014, 11:03:58 pm
content: Same here. Updated the firmware immediately after unboxing and haven't had a problem with it.

author: DJ
author_rank: Unknown
timestamp: December 30, 2014, 03:21:19 pm
content: How is the stability of the unit? (drift vs. a precision voltage reference)

author: tautech
author_rank: Super Contributor
timestamp: January 04, 2015, 06:03:32 am
content: Quote from: DJ on December 30, 2014, 03:21:19 pmSorry, I don't have a precision reference but detailed accuracy and 1 Yr drift specs are in the Datasheethttp://www.siglent.com/2014EnglishWebsite/Documents/Datasheet/SDM3055x_DataSheet_DS06035-E02B.pdf

author: DJ
author_rank: Unknown
timestamp: January 04, 2015, 06:34:24 am
content: Data sheets are good, but trying to get a feel for the short term wander of the last digit(s), say over days when lab temperature can go from cool overnight to warm in the afternoon. The graphical capability is intriguing, was all set to pull the trigger on the Agilent 34461A, which of course is 6.5 vs 5.5 and more than twice as expensive. If the Siggy is stable enough to give me confidence I am seeing my circuits drift, and not the instrument, I'd feel more comfortable.If I were to do a shootout between the two (Agilent vs Siglent), I would do a couple tests, with each instrument monitoring the same DUT.1. A very stable voltage reference, say 2.5, 5.0 or 10.0V over 3 days with 5-10C day/night ambient temperature variation.2. A very stable voltage reference in a constant temperature environment over a couple days, maybe 40C.3. A battery under load such that it runs down over a couple days (nice low noise DUT), temperature uncontrolled.With both instruments measuring the same load, the resultant data could be overlaid to see just how well the lower priced, lower resolution holds up against a (presumably) excellent meter. There are probably ways to simplify the test, but a fundamental instrument on one's bench should have numbers one can trust. Without getting into noise sensitivity, quantization error, unexpected thermocouples and all the other things that make low level measurements interesting, just want something to give a nice warm fuzzy feeling about those last digits. If that makes sense.

author: tautech
author_rank: Super Contributor
timestamp: January 04, 2015, 07:04:07 am
content: Makes perfect sense.I'll see if Siglent have a model comparison to share here.When the SDM3055 was announced a few months back, Dave made the comment Siglent had ripped off the Agilent 34461A's screen interface. They do appear very similar, but what about the features?You will have done some careful research on that, what are your findings?I got mine for personal use but it also doubles as a demo unit.It's my first bench meter and I'm astounded with the features incorporated in it. No doubt this is the norm, but to date I've only used basic HH's.Almost as complex as a DSO but it is intuitive to use.The little that I have used it to date is such that I can not offer much in assistance, but I'm happy to answer any questions I can.EditComparison PDF added.

author: Hugoneus
author_rank: Frequent Contributor
timestamp: January 04, 2015, 04:13:53 pm
content: My review of the unit is will be coming out in a week or two. Hopefully that will help.

author: sotos
author_rank: Frequent Contributor
timestamp: January 04, 2015, 05:05:26 pm
content: Quote from: Hugoneus on January 04, 2015, 04:13:53 pmThanks, will wait

author: DJ
author_rank: Unknown
timestamp: January 05, 2015, 05:03:14 am
content: Quote from: Hugoneus on January 04, 2015, 04:13:53 pmSplendid! Will look forward to it.

author: MisterBiscuit
author_rank: Unknown
timestamp: January 05, 2015, 11:30:08 am
content: After having my unit for a few weeks, there are pretty much only two gripes that I have with it:5-1/2 digits are only available when using the "Slow" sample speed. On "Medium" & "High" speeds you only get 4-1/2 digits. Understandable, I guess...The Continuity test voltage is 6.7V! Yikes! Very disappointing. I've got handheld meters with Continuity test voltage of less than 0.5V.

author: rf-loop
author_rank: Super Contributor
timestamp: January 05, 2015, 03:27:07 pm
content: It is good to note also in this thread that here is@belbamade "first impression" including also internal images.There is not visible base part of serial so can not know how early manufacture lot or version it is.https://www.eevblog.com/forum/testgear/siglent-sdm3055-first-impressions/msg541312/#msg541312If we look some critical components selection Siglent have made related also with accuracy, it is clear that they have take seriously this HW design. As is typical today with Siglent.Voltage reference (Maxim) is good and also selected best C grade. (MAX6325 C... )Same with Analog Devices sigma-delta ADC is selected B grade instead of WB. (AD7190 B...)Also Omron relays are not bad in this price and accuracy class of meter.Also some resistor networks are quite good quality Caddock and IRC(tti)What I do not understand at all is how they have thinked continuity test and diode test.(but other way, if I have this kind of meter I also have some handheld multimeter what is perhaps much more handy for simply continuity testing and diode test.)If this kind of tabletop DMM is with diode and continuity test feature at all then it need design so that it really give some more value for user than 3$ shit handheld peep box.Please Siglent, redesign these functions agen from scratch and fist study what these functions need be for more value for user when he use tabletop 5 1/2 digit DMM for these functions. What is useful information when we test diode or other semiconductor? What it must not do! And what is useful information and what is not. And exactly same for continuity: need redesign. Continuity testing inside expensive sensitive equipment with 8V max open circuit voltage. Is it clever?

author: Siglent
author_rank: Regular Contributor
timestamp: January 07, 2015, 07:18:31 am
content: Quote from: MisterBiscuit on January 05, 2015, 11:30:08 am1. you can only get 5-1/2 digits while at slow speed, this is not only Siglent do, but also other brands;2. I don't understand what you mean, please see attachment. you mean our SDM3000 is not better than a handheld meter?

author: SimonD
author_rank: Regular Contributor
timestamp: February 06, 2015, 10:43:52 am
content: Quote from: Hugoneus on January 04, 2015, 04:13:53 pmHi Shahriar,When do you think we will see this review ?Thanks!

author: MisterBiscuit
author_rank: Unknown
timestamp: February 06, 2015, 03:03:05 pm
content: Quote from: Siglent on January 07, 2015, 07:18:31 amHey Sig,I think the issue here is "Open Circuit Voltage '<8V'". Mine is 6.7V. This is quite high for two reasons:1) It will forward-bias semiconductors that may be in parallel with the two points in the circuit that you're testing for continuity (to determine whether those points are shorted or not), giving a false positive.2) Its beyond the safe voltage range for many low voltage digital logic. So if I'm trying to see if there's a "difficult to see" solder bridge across two adjacent pins, there's the potential of damaging the IC.So yes, I'm saying the SDM3055 is *not* better than my handheld DMM which has open continuity testing voltage of 0.5, which is generally less than the voltage required to forward bias a diode or apply too much voltage to low voltage (1.8V or 3.3V) digital logic IC pins.

author: Hugoneus
author_rank: Frequent Contributor
timestamp: February 06, 2015, 03:05:51 pm
content: Quote from: SimonD on February 06, 2015, 10:43:52 amSorry, I have been very busy. There is one more review coming out and then it will be the multimeter review!

author: SimonD
author_rank: Regular Contributor
timestamp: February 16, 2015, 09:40:48 am
content: Hi,In the European sitehttp://www.siglent.eu/sdm3055.htmlwith bold characters says :With Firmware 1.01.01.11R1 installedHave anyone try it or knows something more about that ?

author: Muttley Snickers
author_rank: Unknown
timestamp: February 25, 2015, 07:34:05 am
content: For those in Australia interested in getting their hands on one of these meters Trio Test and Measurement are now stocking them.Trio Test.http://www.triotest.com.au/shop/555-siglent-technologies

author: tautech
author_rank: Super Contributor
timestamp: February 25, 2015, 07:59:18 am
content: I want those chocolates you owe me with the cheque.

author: Muttley Snickers
author_rank: Unknown
timestamp: February 25, 2015, 08:05:15 am
content: I'm glad that you accept cheque's because my cash bounce's.Muttley

author: SimonD
author_rank: Regular Contributor
timestamp: March 05, 2015, 12:13:40 pm
content: Quote from: Hugoneus on February 06, 2015, 03:05:51 pmHi again Shahriar,any progress with this review ?I' m ready to buy a desktop multimeter but i' m waiting for your allways trusted review !Thanks !Simon

author: sotos
author_rank: Frequent Contributor
timestamp: March 05, 2015, 03:27:52 pm
content: Me too, waiting.

author: fremen67
author_rank: Frequent Contributor
timestamp: March 06, 2015, 05:36:59 pm
content: Quote from: Hugoneus on February 06, 2015, 03:05:51 pmIt seems that your review is eagerly awaited. What about a trailer?

author: giovannirat
author_rank: Regular Contributor
timestamp: March 07, 2015, 03:48:04 pm
content: I have two questions regarding SDM3055:1) Is there a service manual available ?2) Is the multimeter factory calibrated (with certificate) ?

author: Bryan
author_rank: Frequent Contributor
timestamp: March 07, 2015, 08:06:53 pm
content: QuoteLooking forward to the review as well

author: tautech
author_rank: Super Contributor
timestamp: March 08, 2015, 02:22:18 am
content: Quote from: giovannirat on March 07, 2015, 03:48:04 pmWelcome to the forum.The Service manual is in the process of being translated in English. This was the reply from China when I requested one last week.I did not recieve one with mine, however I am not sure of the latest shipments.

author: nowlan
author_rank: Frequent Contributor
timestamp: April 24, 2015, 02:25:44 pm
content: Quote from: Hugoneus on February 06, 2015, 03:05:51 pmCant seem to find it

author: SimonD
author_rank: Regular Contributor
timestamp: April 25, 2015, 08:00:50 am
content: Quote from: nowlan on April 24, 2015, 02:25:44 pmMaybe two things can happen ... or the device is very good for the price and did not want to disappoint the " Big names - Siglent competitors" or is just for the rubbish and Shahriar feel ashamed to create a video review ...

author: seabell
author_rank: Contributor
timestamp: September 03, 2015, 09:47:09 pm
content: Quote from: LarryMartin on December 24, 2014, 06:09:09 pmYour last question is the most important. Wish I had known about this site before taking a chance buying this meter. Mine refused to boot the third time it was switched on.The vendor sent me to Siglent USA, saying they don't take returns after 30 days. Siglent USA said I have to pay to send it back to them, non-negotiable. I pointed out my annoyance as this cost me US$150. Tough luck, apparently.I sent it via the most economical courier, because, as I pointed out to Siglent, our postal service is seriously unreliable. They sent it back a couple days after receipt via - guess what - regular postal service.That was two weeks ago, and no sign of it yet. More than likely it will cost me less to pay the duties and taxes a second time than to jump through all the hoops necessary to prove I am reimporting after repair.Don't know how useful or reliable it will be until I get it back, but one thing is absolutely certain. I will NEVER buy Siglent again. If a customer is to be used as a beta tester, and is required to pay for that dubious privilege, they should make it clear at the point of purchase.Learning now that this was a known issue when I bought the unit just makes me angrier about the whole situation. Couldn't they have arranged to email known customers and warn them about the urgent necessity of upgrading the firmware?

author: tautech
author_rank: Super Contributor
timestamp: September 04, 2015, 09:03:54 am
content: Quote from: seabell on September 03, 2015, 09:47:09 pmIt is unfortunate your vendor did not offer greatly better support.You should name and shame them.

author: seabell
author_rank: Contributor
timestamp: September 04, 2015, 10:30:36 pm
content: Quote from: tautech on September 04, 2015, 09:03:54 amThat's easily done, of course (It was Tequipment). However, the thread is about Siglent's SDM3055.Tequipment's 'Return Policy' does state that there is a 30 day limit on returns though it isn't very clear about the apparent fact that this also applies to defective products. My complaint was made five months after receipt.Having re-read my communications with Siglent USA, it appears that I did NOT clearly state the potential issues with using 'regular' postal services, so I am not making that an issue either.My beef remains with the reprehensible practice of Siglent releasing a poorly programmed/tested product to market and then not compensating the buyer for his costs in shipping and handling to get the thing sorted out. I will never be able to switch on this DMM in future without some doubt in my mind that it will even make it through the boot process, let alone give reliable measurements, and I thoroughly resent the 40% cost increase incurred.Siglent's attitude is that this "is common in the electronics industry" - and that is a direct quote.As far as I am concerned Siglent crashed and burned on this one, and the damage is irreparable. Never again.

author: VasinD
author_rank: Contributor
timestamp: September 24, 2016, 04:26:28 pm
content: 8 volts for continuity test?? What?? This is just ridiculous. Wanted to buy this meter before, but after this forum - don't.

author: tautech
author_rank: Super Contributor
timestamp: September 24, 2016, 08:27:47 pm
content: Quote from: VasinD on September 24, 2016, 04:26:28 pmWelcome to the forum.That's the trouble with the internet.....not all info is up to date.I've just checked a demo unit with latest FW I have and indeed it's higher than I'd like to see @6.8V but as listed in the Datasheet @ 1 mA.I'll forward your concerns to the factory for consideration by the engineers.More up to date info on the Siglent bench DMM's is in this thread:https://www.eevblog.com/forum/testgear/siglent-new-bench-dmm-sdm3055/

author: nctnico
author_rank: Super Contributor
timestamp: September 24, 2016, 09:16:42 pm
content: With today's trend towards 1.8V logic 6.8V is way too much. Some of today's jelly-bean MOSFETs don't want to see more than a few Volts on their gates.

author: tautech
author_rank: Super Contributor
timestamp: September 25, 2016, 09:01:01 am
content: I got a PM today after I replied to VasinD from a member that also has a SDM3055 confirming the continuity test values posted above. While they are what they are I was reminded in the PM of the continuity test burden applied by the revered Fluke 87V of in excess of 7V @ 1mA.These Fluke values were of concern in this thread:https://www.eevblog.com/forum/testgear/multimeter-with-low-continuity-test-voltage/Nevertheless concerns will be passed to Siglent for their consideration.

author: VasinD
author_rank: Contributor
timestamp: October 04, 2016, 09:41:44 pm
content: tautech, thank you for the link!

author: tautech
author_rank: Super Contributor
timestamp: October 04, 2016, 10:25:20 pm
content: Quote from: VasinD on October 04, 2016, 09:41:44 pmI'm in a dialogue with the Siglent engineers on the OC Continuity test voltage and they make some valid points.The design (currently) uses theContinuityvalues that are primarily a current source that being presently 1mA and even this level I argue is still too high.Diodetest mode supplies the same parameters although there is not the same risk as there might be fault tracing using Continuity mode on a populated PCB.However IMHOContinuitytest levels need be less than 500mV and well under 1mA under any test conditions.From this thread we can see even the revered Fluke 87 (some variants) have the same Continuity test values along with many other "A" brand DMM's. AFAIK most bench DMM's have high Continuity test values too.https://www.eevblog.com/forum/testgear/multimeter-with-low-continuity-test-voltage/I have offered the argument that if reverse engineering is undertaken there is a risk of damage to componentry and further member support and reasoning would be appreciated to pass on to the engineers once they return from the Chinese spring break after the 8th of October.

author: VasinD
author_rank: Contributor
timestamp: October 07, 2016, 08:42:15 pm
content: I am looking for a bench DMM with price below 500$. Have read datasheet for rigol DM3058... Guess what?"Continuity / Diode Test : 1 mA ± 5% constant - current source, < 8 V open - circuit voltage"It seems to me that most of bench DMM has continuity test voltage far above a reasonable 0.5V. Hmm... Maybe I don't understand something...Also I am curious to know, from where this 8V came from? Why not 12V or 20V? I can not imagine what this 8V can be dedicated for?Maybe some one can explain this?Sorry for my english by the way.

author: VasinD
author_rank: Contributor
timestamp: October 07, 2016, 08:52:08 pm
content: By the way my cheapest chinese no name multimeter from a couple of bucks range has much more reasonable 3V continuity voltage.

author: nctnico
author_rank: Super Contributor
timestamp: October 07, 2016, 09:57:34 pm
content: Somewhere between 3V and 4V is a good value. White leds have a typical forward voltage slightly over 3.0V and it would be handy if you can measure these. I just checked the 2 DMMs (Keysight and Vichy) on my desk and both use a current of 1mA for the continuity check.

author: tautech
author_rank: Super Contributor
timestamp: October 08, 2016, 12:06:39 am
content: Quote from: VasinD on October 07, 2016, 08:42:15 pmIt seems most Bench DMM's use common values for Diode and Continuity test, ie. 6-8V @ 1mA.However it is contant current AND variable voltage, so as a result of loading the output in a test the voltage will roll off to retain a 1mA supply.I did a quick check/test with a red LED to illustrate this:The image showing Diode test displays the conducting voltage of the LED @ 1mA.Values, both V and A confirmed with my Fluke 15B.In Continuity mode the display shows resistance (as expected) and the LED current and voltage levels remain the same.Another, this time a Schottky diode, again 1mA and voltage as per display.

author: Performa01
author_rank: Super Contributor
timestamp: October 08, 2016, 10:33:07 am
content: In the past, not many of the more serious bench DMMs have provided a continuity test mode. Some do not even have a diode test function, such as the Fluke 8842A (obsolete now, but top-notch in its time), but also the Keithley 2001, which is still in production (and one of the best DMMs ever made in my book).Quite obviously, most manufacturers couldn’t believe someone would use a super-accurate and expensive multi-digit bench meter for primitive tasks like continuity or diode testing. But users obviously demanded these features nonetheless, so they have been added to more recent designs – at no cost, by simply displaying the voltage drop of the existing ohms measurement mode with (programmable) voltage limits for “open”, “diode drop” and “short”.No surprise, my respectable collection of bench DMMs includes only three with continuity test mode; these are Fluke 45, Keithley 2015THD (which is essentially a Keithley 2000 plus some extras for audio measurements) and Picotest M3500A.I’ve just tested them and none of them makes a distinction between continuity and diode test.The Fluke 45 (30 kCnts) uses max. 0.8mA up to 3V (max. reading: 2.5000V).Keithley 2015THD (1.2 MCnts) uses const. 1.0mA up to 6.9V (max. reading: 3.02918V).Picotest M3500A (1.2 MCnts) uses const. 1.0mA up to 12.2V (max. reading: 1.19999V).Then I still have a couple of old meters that provide at least diode test – the venerable HP3466A and Tektronix DM2510 (the latter could simulate continuity by programming a limit test on the ohms measurement mode, but that’s not really practical). Here are the test results:HP3466A (20 kCnts) uses const. 1mA up to 4.55V (max. reading: 1.9999kOhms).Tektronix DM2510 (20 kCnts) can use const. 100nA, 10µA or 1mA up to 10V (max. reading: 19.999MOhms, 199.99kOhms, 1.9999kOhms).With most meters, the open circuit voltage is a fair bit higher than the actual measurement range. All, except for the Fluke 45, provide a constant current source. The best “diode tester” in this collection is the Keithley 2015THD, but even this instrument cannot measure much more than 3V.As a conclusion, Siglent didn’t do anything special with their SDM3055 – they apparently just copied what others have done before. On the other hand, by doing so, they missed the opportunity to be innovative and offer something better – which would have been neither difficult nor expensive: just add a switchable voltage clamp to the test current source that’s activated in continuity mode and use the most sensitive voltage range for the measurement. Even if the latter cannot be done easily for some reason, the 2V range would be enough for continuity testing with the voltage clamped to <0.5V, as the accuracy requirements for the threshold level are rather low anyway.Diode test, on the other hand, should use a higher voltage so we can also measure LEDs and zeners as well. Even an open circuit voltage of 8V or more wouldn't be of much use as long as the meter does the measurement in its 2V range. Ideally, the measurement range should cover the full compliance voltage, i.e. it would be the 20V range and the max. voltage of the current source could be made even higher (though it needs not really go up to 20V). A nice feature would be autoranging in diode test mode (alternatively a manually selectable high/low diode test mode), so that for low voltage drops (with ordinary diodes) the 2V range is engaged.EDIT: Corrected open circuit voltage for Keithley 2015THD and added max. displayed voltage. Updated the comment on the test results.

author: tautech
author_rank: Super Contributor
timestamp: October 08, 2016, 07:24:43 pm
content: Quote from: Performa01 on October 08, 2016, 10:33:07 amWe hope the design permits FW changes to allow a lower OC voltage for Continuity test.QuoteIt would be a good feature if it did go to 20V.I have had a need to check HV diodes, the Vf of which is often 8V or more, some I've encountered as much as 12V.Thanks for your enlightenment as not many of us have a # of DMM's of different breeds on the shelf to compare like you have.

author: Performa01
author_rank: Super Contributor
timestamp: October 09, 2016, 02:08:36 am
content: Quote from: tautech on October 08, 2016, 07:24:43 pmUntil someone (Siglent?) eventually comes up with a practical solution integrated in a decent DMM, my standard procedure for diode test is this (Diode_Measurement)A good old Knick J41 current calibrator provides 100nA ~ 150mA at voltages up to 30V. Then simply connect the D.U.T. and some DMM in parallel to measure the voltage drop.The picture demonstrates the measurement of a 27V/5W Zener diode, showing 26.9449V at 1mA.

author: snik
author_rank: Contributor
timestamp: October 09, 2016, 06:00:13 am
content: Quote from: tautech on October 08, 2016, 07:24:43 pmWould be really great

author: TurboTom
author_rank: Super Contributor
timestamp: October 09, 2016, 09:23:25 am
content: Your findings just made me curious what that rather high test voltage in diode mode - even if current limited - means to the device under test. I found my Rigol DM3068 to provide a quite high voltage as well, at 1mA test current setting, it's 5.7V into a 10MOhms multimeter. Hence I did some simple single-shot tests with a DSO and a crappy red LED.The initial test was without the LED, just tapping the DSO probe´s tip on the DMM (pos) probe, ground was connected to the neg DMM probe. It's amazing to seed the voltage initially climb above 9V to slowly settle down to the aforementioned 5.7V. Since this shot was taken at a rather slow time base (500µs/div), some bouncing is visible.The next test was exactly the same but with the LED across the DSO´s probe terminals. Since now everything takes place much more quickly, I reduced the timbase to 50ns/div, so bouncing wasn't an issue anymore - everything happens when the initial contact is established. The first spike exceeds 3V. Assuming a parasitic inductance of the LED's terminals of 30nH (they were partially bent so this assumption shouldn't be too far off) and after measuring a DC voltage drop of approx 2.07V@100mA (have to be quick...) and with an initial rise time of about 5ns, the current should have peaked out at round about 170mA, give or take a little. I didn't take into account the DSO probe/ LED junction capacitance, so the current was probably rather higher than lower than that.The ringing is the effect of the DMM probe leads`s inductance as is shown in the next DSO screen shot where I used extra short test leads (15cm). But once again, the situation of the inrush current is more or less the same.Selectring a different (lower) diode test current at the DM3068 wouldn't make any noticable difference regarding the initial voltages/currents.Finally, I decided to check a Voltcraft (Conrad Electronics brand -- probably Uni-T made) VC890´s diode test function under the same condition. Open-circuit voltage measures here 3.5V and the whole measurement (with long test leads) looks much less troublesome with the voltage only slightly exceeding 2V at the LED for a short duration.After this test, I would only reluctantly use an instrument with high open-circuit voltage to test highly sensitive semiconductors like laser diodes or maybe some GaAs circuits. For more general components (CMOS/Bipolar silicon semicunductor circuits), I guess the situation should be fairly safe.Cheers,Thomas

author: Performa01
author_rank: Super Contributor
timestamp: October 09, 2016, 02:46:48 pm
content: Well, let’s see what the well established brands Fluke and Keithley as well as the young Picotest company have to offer in terms of limiting the risk of damage to devices in diode (or continuity) test mode.I’ve tried to resemble what TurboTom has shown us with the Rigol DM3068.Initial scenario is the voltage step with no load – except for the 1MOhm scope input – connected. I’ve fitted a 1.2m test cable with rocker switch for convenience and minimal contact bounce. It’s not worth showing any results at slow timebases like 500µs/div though, as nothing strange happened during this test. Consequently, a timebase of 50ns/div was used for the following screenshots.Fluke 45 (Fluke45_OC_EXT)Keithley 2015 THD (Keithley2015THD_OC_EXT)Picotest M3500A (PicotestM3500A_OC_EXT)Then I’ve tried hard and succeeded to find a crappy red LEDHere are the results:Fluke 45 (Fluke45_LED_EXT)Keithley 2015 THD (Keithley2015THD_LED_EXT)Picotest M3500A (PicotestM3500A_LED_EXT)Taking the usual test setup used with a DMM into account, including some 1.2 meters cabling with unknown characteristic impedance – but usually somewhere in the range of 100 ~ 1000 ohms – and complete impedance mismatch on both ends, we can expect quite some ringing and all kind of weird effects. This is just the test setup and we cannot blame the DMM.To verify this, I've run a simulation on a (very rough) equivalent circuit of my test setup (Diode Test Voltage)The DMM is modeled as a 1mA current source with the output limited by a 6.8V zener diode. Added 1MOhm and 47pF in parallel, because the current source won’t be ideal and every DMM has some capacitance at the input terminals (specified as <100pF for most bench DMMs).This is followed by a lossy transmission line, where I’ve assumed 100mOhms, 200nH and 50pF per meter and a total length of 1.2 meters.After that, there is the switch with 100mOhms contact resistance and some wiring inductance, which is driven by a step generator and switched on 100ns after the simulation starts.The LED is replaced by three 1N4148 switching diodes plus 15nH in series. Of course, a LED will most likely behave very different to this, but I don’t have a Spice model for a LED.Finally, after some further stray inductances comes the scope input with 1MOhm and 22pF in parallel. This takes the capacitance of the connector into account, the specified input capacitance of the scope is actually lower.As can be seen from the simulation, the positive spikes exceed 4V and while the frequency of the ringing is actually quite similar to the real measurements, the amplitude and duration is a fair bit worse. This was to be expected, as the real circuit includes many more lossy elements than the equivalent circuit.Another graph is showing the current through the diodes (Diode Test Current)According to the simulation, there is indeed one narrow peak >150mA right after the switch has closed. But the current exceeds 100mA for only 3.74ns in the simulation (Diode Test Current Zoom)Anyway, none of my real world tests showed anything near as bad. By far the worst contender was the Picotest M3500A – as was to be expected due to its high open circuit voltage – and even there the maximum voltage did not exceed 2.26V.The Fluke 45 on the other hand, behaved extremely well and did not show any overshoot at all.

author: tautech
author_rank: Super Contributor
timestamp: October 09, 2016, 09:39:12 pm
content: For some comparison, well sort of:SDM3055 red LEDFluke 15B(V measured with SDM3055 2V range 10G input impedance)Ohms measure AND Continuityboth open circuit0.44150V and current 138uADiode test:1.571V @ 470uA1N5819 Schottky diodeLots of noise induced by long DMM leads.But we see with a Fluke 15B Continuity and Diode measurements use very different voltages and currents, each optimised for their respective measurements.

author: Performa01
author_rank: Super Contributor
timestamp: October 10, 2016, 12:57:31 am
content: Quote from: snik on October 09, 2016, 06:00:13 amI very much doubt this can be done by a simple change in FW. Without a programmable (or at least switchable) voltage clamp at the output of the current source there is no way to limit the open circuit voltage. Quite obviously, this would require a HW change.But then, everyone can make their own clamp quite easily. Simply connect a diode in parallel to the DMM input for continuity test in a circuit with very sensitive components (Clamp)The voltage is limited to some 600mV, so potential damage to any components can be definitely ruled out. The continuity function still works correctly, as long as the threshold level is set to less than 600 ohms (for 1mA test current).In case of the Keithley 2015THD in continuity mode, it displays e.g. “0610.2 OHM instead of “OPEN” when nothing is connected, but still shows the correct reading when the actual resistance is lower than that and it will also beep as long as the programmable threshold level is set to a reasonable resistance value (default is 10 ohms).BTW. the diode in this example is a 1N914.And how about the open circuit voltage when connected to the scope? (Keithley2015THD_OC_LIM_EXT)I would say, there’s not much left to be desiredOf course it would be much more convenient, if DMM manufacturers just added this to their instruments as a standard. Since it has to be switchable in order to not limit diode test and ohms measurement, it would not be just a diode, but also a transistor or two and a couple resistors. Not a big deal, really.