multimeter with low continuity test voltage? - Page 1
Forum section: electronics / testgear

author: FrankBuss
author_rank: Unknown
timestamp: July 07, 2014, 11:20:14 pm
content: Is there are a good multimeter with a fast continuity test and low test voltage? I was thinking of buying a Fluke 87, but the manual says it uses up to 7.9 V test voltage for the ohm range. It doesn't say anything for the continuity test, unless I missed it, does it use the same voltage? I do measure sometimes in-circuit to find shorts when I solder PCBs, and this could destroy sensitive parts like FETs or RF transistors.My current old Voltcraft multimeter uses 1.2 V and 0.4 mA max current, but it is slow (half a second to beep). I've read that some cheap chinese multimeters are fast and are using low voltages, but I would like to have a good quality multimeter. I can build a simple tester myself, but there should be a good multimeter, with a fast continuity test,andlow test voltage and current, all in one device.

author: mjkuwp
author_rank: Unknown
timestamp: July 07, 2014, 11:33:12 pm
content: as one reference the manual of Agilent U1272A states"Maximum open voltage is <+3.3 V"this is on page 139 of the user guide.

author: FrankBuss
author_rank: Unknown
timestamp: July 08, 2014, 12:23:34 am
content: Thanks, the Agilent looks like a nice multimeter. 3.3 V is still a bit high, but less likely that this voltages destroys anything. And even cheaper than the Fluke 87, but more features, like the data logging. I just watched the EEVblog review:http://www.eevblog.com/2012/02/29/eevblog-249-agilent-u1272a-multimeter-review/

author: tautech
author_rank: Super Contributor
timestamp: July 08, 2014, 01:03:02 am
content: Fluke 15B uses 2x 1.5V AA supply.440mV @ 0.14mAFast beep too.

author: hlokk
author_rank: Contributor
timestamp: July 08, 2014, 02:17:52 am
content: If the test voltage was "high" but was severely current limited would it damage the components? Obviously if you apply 7v to a led you'll blow it, but only if you're assuming its not current limited, which I presume the multimeter would be? Just wondering as that may change how you read the specs (I.e. "Up to 3v test"). No idea, but curious as to what the answer would be.

author: FrankBuss
author_rank: Unknown
timestamp: July 08, 2014, 02:50:28 am
content: Quote from: tautech on July 08, 2014, 01:03:02 amNice, and the Fluke 17B doesn't cost much more and has temperature measurement as well, which can be useful. I have already a good benchtop multimeter with connection to a PC for data logging, so I think this would be a good choice then.Quote from: hlokk on July 08, 2014, 02:17:52 amI think the current limitation doesn't help, if the component has a high input resistance. There are a lot of microcontrollers with high impedance inputs that are rated for 3.6 V max. Might be not a problem if the input has ESD protection and the current flows to the positive supply rail (assuming you are measuring from the input to GND), which then powers the microcontroller and the voltage drops, but there are components without ESD protection. And many components might not like it, if you apply -7 V, which you don't think about when doing continuity tests.Would be an interesting test: If the ESD protection diode of a microcontroller input starts to conduct because of the high testing voltage, it might show a false short (for example you are testing data inputs on a PCB for shorts to ground), which should be no problem with the 440 mV of the Fluke 15B.

author: tautech
author_rank: Super Contributor
timestamp: July 08, 2014, 02:58:01 am
content: Quote from: FrankBuss on July 08, 2014, 02:50:28 amFYI Fluke 15B has the 17B functionality, just missing the buttons as far as I know.Check for previous EEVblog posts on this subject.

author: retiredcaps
author_rank: Super Contributor
timestamp: July 08, 2014, 05:46:13 am
content: On my Greenlee DM-200A (aka Brymen BM250 series), I get the following when set to continuity mode:0.494V DC157uAThe Greenlee uses 2 AAA batteries.Seehttp://www.brymen.com.tw/product-html/cata250/Bm250L4.htm

author: retiredcaps
author_rank: Super Contributor
timestamp: July 08, 2014, 05:50:08 am
content: You may know the BM257 is very popular here and others can verify those readings I posted with the Greenlee DM-200A.Dave also did a quick look video of the BM257 along with Martin Lorton.http://www.eevblog.com/2013/02/28/eevblog-432-brymen-multimeters/

author: Lightages
author_rank: Unknown
timestamp: July 08, 2014, 06:11:16 am
content: If you want low voltage, the Digitek DT2843R and DT-4000P-2 both have a continuity test of 0.44V! The DT2843R is dog slow but the pocket meter DT-4000P-2 is lightning fast.The Brymen BM257 has around 0.63V.

author: FrankBuss
author_rank: Unknown
timestamp: July 08, 2014, 07:51:51 am
content: Quote from: retiredcaps on July 08, 2014, 05:50:08 amThanks, looks good, too. And it has a serial connection for data logging with a PC as well, which is usually much more expensive. Maybe they don't spend as much for marketing than Fluke, so they can sell it cheaper. The new BM257s has true RMS and capacity measurement.PS: I found another confirmation that high continuity test voltage might destroy components:http://electronics.stackexchange.com/questions/56066/continuity-tests-risksAnyone with a Fluke 87? I can't believe that it is that worse and the datasheet is not clear about the voltage used in continuity mode.

author: retiredcaps
author_rank: Super Contributor
timestamp: July 08, 2014, 09:44:01 pm
content: Quote from: FrankBuss on July 08, 2014, 07:51:51 amMy Fluke 87V puts out 7.30V and 1.00mA in continuity mode. I have an original 87 (series 1) as well, but currently it has no battery. If you want that info, I can do it later or tomorrow.

author: FrankBuss
author_rank: Unknown
timestamp: July 08, 2014, 10:42:11 pm
content: 7.3 V is really bad. Thanks, no need to measure the Fluke 87, too, I already ordered the Brymen BM257sI'll post an update here if the test voltage is different from the BM257.

author: haoleboy
author_rank: Unknown
timestamp: July 09, 2014, 03:01:26 am
content: Wow, I had no idea my 87 V put out 7.3v in the continuity mode! I've been happily probing away on devices to find common grounds/paths as I'm learning, never even thought of the potential danger.Just how dangerous is that amount of voltage on a low power circuit (like maybe a cell phone or wireless router)?

author: KedasProbe
author_rank: Frequent Contributor
timestamp: July 09, 2014, 07:49:27 am
content: Anyone tried a zener to reduce the voltage?

author: FrankBuss
author_rank: Unknown
timestamp: July 10, 2014, 07:20:53 am
content: Just for the record: I got my BM257s today and I can measure 0.49 V for the continuity test and 0.16 mA, so the same as the old BM250.

author: Wh1sper
author_rank: Regular Contributor
timestamp: July 10, 2014, 07:48:54 am
content: MyMetraport 32 Shas 0.6xx Volts in ContinuityMy UT61e near to 4 Volts :-(It would be a nice project idea to build an 0.1 Volts Continuity Tester. One could safely measure on a PCB which has semiconductors already installed.

author: Lightages
author_rank: Unknown
timestamp: July 10, 2014, 08:05:15 am
content: I just remeasured my BM257 to be sure and it outputs 0.62V.... I wonder why the difference.

author: Yago
author_rank: Frequent Contributor
timestamp: July 10, 2014, 10:43:01 am
content: Could it be differing input impedances of the measuring device?

author: gdewitte
author_rank: Unknown
timestamp: July 10, 2014, 06:17:12 pm
content: Quote from: Wh1sper onYesterdayat 05:48:54 PMMetraport 32 Shas 0.6xx Volts in ContinuityMy UT61e near to 4 Volts :-(It would be a nice project idea to build an 0.1 Volts Continuity Tester. One could safely measure on a PCB which has semiconductors already installed.

author: Wh1sper
author_rank: Regular Contributor
timestamp: July 10, 2014, 07:53:03 pm
content: Quote from: gdewitte on July 10, 2014, 06:17:12 pmI'm pretty sure I could build something like that by myself. But would I have the spare time? I would gues: No!So Yes I would second that thumbs up!.If not to much time consuming, please do it!

author: AintBigAintClever
author_rank: Regular Contributor
timestamp: July 10, 2014, 09:08:38 pm
content: Fluke 79-IIIOhms: 760mVContinuity/40 ohms: 3.08VDiode test: 3.04VAll of the above were into a 10M x10 probe on myDS2072A-SDS2302A-S(yes I had x10 selected in the menu)Unfortunately I can't measure the current availability as my other meter only has 400/1000 amp ranges.

author: MagicSmoker
author_rank: Super Contributor
timestamp: July 10, 2014, 09:23:29 pm
content: Quote from: retiredcaps on July 08, 2014, 09:44:01 pmDitto for my Fluke 179. However, in regular resistance mode the open circuit voltage is ~2.7V and the maximum current is 1.0mA (ie - current is the same as for continuity mode).

author: zaoka
author_rank: Frequent Contributor
timestamp: July 10, 2014, 09:32:48 pm
content: You need multimeter with low power ohm feature. Older Tektronix DMMs had that feature, or new Yokogawahttp://www.tequipment.net/YokogawaTY720.html?v=7231

author: FrankBuss
author_rank: Unknown
timestamp: July 10, 2014, 09:55:37 pm
content: Quote from: Wh1sper on July 10, 2014, 07:53:03 pmGoogle finds a lot of circuits when searching for the right words. Add "OpAmp" in your search query and you'll get more advanced circuits with modern OpAmps like the LM741:http://www.zen22142.zen.co.uk/Circuits/Testgear/connectiontester.htmTest voltage: 2 mV, test current: 200 uA. Maybe such a low voltage is not useful, because it could false alarm if the capacitors of a circuit are not completely discharged, but you can change the resistors as you like, and you could add one of those self-buzzing piezo speakers to the output.Of course, such a simple tester would be not as safe as using a Fluke (or better) multimeter. At least you should add a fuse in series to the 10 ohm resistor, and two 1N4004 or other big diodes in parallel (both directions, to clamp the voltage, if applied externally).

author: Wytnucls
author_rank: Super Contributor
timestamp: July 10, 2014, 10:16:22 pm
content: If you want a Fluke, the cheap 101 has an open voltage of 0.53V and a test current of 178uA. The buzzer stops above 80 Ohms.

author: FrankBuss
author_rank: Unknown
timestamp: July 10, 2014, 10:23:56 pm
content: That's interesting, so they know how to do it. Why did they use a higher voltage for the other Fukes? Saving some cents to avoid switching the voltage when in diode test or in continuity test mode?One more measurement from a colleague, high price benchtop Fluke 8845A: 6.2 V continuity test voltage.

author: Rick Law
author_rank: Super Contributor
timestamp: July 11, 2014, 06:44:55 am
content: Quote from: KedasProbe on July 09, 2014, 07:49:27 amBut a zener clamps the voltage by becoming a conductor once the zener voltage is reached. So you will be measuring the conductivity of the zener instead of the DUT.

author: Joule Thief
author_rank: Regular Contributor
timestamp: July 11, 2014, 07:13:06 am
content: Fluke 87-IIIOhms: 670mVDiode test: 3.73Vmeasured with Fluke 8800A

author: KedasProbe
author_rank: Frequent Contributor
timestamp: July 11, 2014, 09:04:45 am
content: Quote from: Rick Law on July 11, 2014, 06:44:55 amYou don't place your zener in parallel but in series with your DUT.(I may be doing some test myself later, obviously the 'beep' threshold will change a lot, maybe too much)Edit: I tried a 5v1 zener with my 5.3V DM3068 (needs a lower zener, I don't have one here now to test)(0.7mA, 4V -> 5700ohm but the beep threshold is max. 2000ohm, hence no beep)

author: mimmus78
author_rank: Unknown
timestamp: July 12, 2014, 07:13:34 pm
content: On my BM257 (not BM257s) is 0,497V too.

author: WVL_KsZeN
author_rank: Regular Contributor
timestamp: July 12, 2014, 08:04:00 pm
content: I can confirm the low test voltage (around 0.5V) of the Fluke 17b. The 187/289 have voltages of 4 and 5V though!I also tested my agilents (1232a and 1272a), they had test voltages of 2.something and 3.something volts.. darnit. Why does every multimeter have a serious disadvantage? So far I like my Fluke 187 best, but maybe I'll turn to the 17B for cont. testing on sensitive circuits.

author: KedasProbe
author_rank: Frequent Contributor
timestamp: July 13, 2014, 10:10:45 am
content: I just did a few test with extra diodes (instead of a zener) but it doesn't really do the job.On my DM3068 with 5.8V you have 1mA source, you can add up to 3 diodes in series creating a drop of 1.85V (@1mA, 1.5V @0.1mA)and this will change the threshold from max 2000ohm to max 150ohm. (due to 1mA source and 2000ohm limit --> max diode/zener voltage drop is 2V)Measuring a (fourth) diode will not make it beep but there will go current through it (1mA)This means the voltage between 5.8V and 2V of their source is completely useless, a 2.5V source would have done the same job.Obviously a short <150ohm will make it beep.On my Brymen 869 I get 3V open, a 0.42mA source.It does not beep for 1 diode and the current though it is 0.34mAAlthough it's good that you know this about your meter it will not replace a good 0.4V continuity tester.

author: retiredcaps
author_rank: Super Contributor
timestamp: July 14, 2014, 07:29:03 am
content: Quote from: retiredcaps on July 08, 2014, 09:44:01 pmOriginal 87 puts out 1.240V and roughly 300uA when set to continuity.

author: tautech
author_rank: Super Contributor
timestamp: July 14, 2014, 08:55:34 am
content: Quote from: tautech on July 08, 2014, 01:03:02 amWho would have thought the Fluke 15B would have fared so well against supposedly much better meters.So I thought I had better check my Vichy VC99 and:0.641 V @ 0.25 mANot too bad either.Beep not quite as instant as the Fluke 15B but still quick.

author: Wh1sper
author_rank: Regular Contributor
timestamp: July 16, 2014, 04:32:00 pm
content: This wouldn't let me sleep, so I found a very simple solution.For proof of concept I used my UT61e which has near to 3 Volts while in continuity mode with open test leads.I simply put a spare Germanium Diode (AA114 or something like that) parallel to the leads and voilá thats is it!The diode is under the blue heat shrink tube.Edit:And at the photo one can see that the plus and minus pole is switched.Not tested if my other Multimeter have the same behavior.Just 4fun:Code:.-------------.| .--|-----------------------| .---| | | || -| | / \ | -| -| | (_/_)| ^| '---| \_/ | || | | || '--|-----------------------'-------------'An ASCII Art Schematics :-)

author: tautech
author_rank: Super Contributor
timestamp: May 07, 2015, 09:13:24 pm
content: For those doing PCB reverse engineering and concerned about continuity testing damaging delicate componentry, I thought it good to link to this post and thread:https://www.eevblog.com/forum/eda/pcb-reverse-engineering/msg668285/#msg668285

author: gdewitte
author_rank: Unknown
timestamp: May 08, 2015, 01:46:22 am
content: Not a multimeter, but many (many, many) years ago I built a small kit (from Audio Amateur?) that hasVoc = ~ 200mV, and Isc = ~ 270µA (https://www.eevblog.com/forum/testgear/low-voltage-low-current-continuity-tester/), and it's still my go-to continuity tester.

author: Fungus
author_rank: Super Contributor
timestamp: November 17, 2017, 06:46:28 am
content: Quote from: retiredcaps on July 08, 2014, 09:44:01 pmQuote from: FrankBuss on July 08, 2014, 10:42:11 pmIt'll be current-limited so you'll only see 7.3V if you measure it with a 10 MOhm impedance multimeter. Try it on a 10 Ohm resistor and see what the voltage is.

author: FrankBuss
author_rank: Unknown
timestamp: November 17, 2017, 07:00:48 am
content: Quote from: Fungus on November 17, 2017, 06:46:28 amYes, 1 mA current limited. So you will see the full voltage with e.g. 10 kOhm. 1 mA might be no problem for most parts, because they can survive much higher voltages and currents for a short time, if the pins are ESD protected, but I still think this is a bad idea.

author: David Hess
author_rank: Super Contributor
timestamp: November 20, 2017, 01:04:03 am
content: That is a real mistake if the open circuit voltage is that high on the Fluke 87. What were they thinking?Usually you want to stay below 5 volts to avoid base-emitter breakdown of bipolar transistors and higher than 2.2 volts so LEDs may be tested. The low voltage has increased with the introduction of blue and white LEDs but should still be kept low.The low voltage ohms mode in some meters is for making resistance measurements without forward biasing any PN junctions which would interfere with the measurement.Quote from: hlokk on July 08, 2014, 02:17:52 amThe gate oxide of a MOSFET can be destroyed instantly if the gate-to-source voltage is too high.Bipolar transistor base-emitter junctions suffer permanent damage lowering hfe if subject to reverse breakdown.

author: Muxr
author_rank: Super Contributor
timestamp: November 20, 2017, 06:43:17 am
content: Continuity test on 87v appears to be the same as the diode test. I assume they wanted high enough voltage for the same reason diode test voltage is high, to overcome forward voltage of a few diodes in series perhaps? When in Ohm range the voltage is low (100mV into 10K). Current is 0.5mA by the way.

author: HalFET
author_rank: Frequent Contributor
timestamp: November 20, 2017, 07:11:56 am
content: The Fluke 87 is meant for industry! You're supposed to toss that thing in your toolbox and shove those probes up a VFD's proverbial behind while standing in a pool of oil and piss. Industrial drive electronics will take 7V probe voltage easily, they'll also take 70V actually. It's designed for its use case, I'm not quite sure why it became popular among hobbyists.On the other hand the 15b+ is more geared towards bench use I think.

author: Fungus
author_rank: Super Contributor
timestamp: November 20, 2017, 07:33:42 am
content: Quote from: HalFET on November 20, 2017, 07:11:56 amSothat'swhy it's 20000 counts - so you can measure industrial drive electronics to 4.5 digits in the rain.Quote from: HalFET on November 20, 2017, 07:11:56 amUnlike a bench meter, which wouldneverneed that accuracy.

author: HalFET
author_rank: Frequent Contributor
timestamp: November 20, 2017, 08:26:16 am
content: Quote from: Fungus on November 20, 2017, 07:33:42 amStop assuming you don't need precision in the field and that you do need it on the bench... 1% error on something dealing with 10+ kW can be really bad. Alsohttp://en-us.fluke.com/products/digital-multimeters/fluke-87v-digital-multimeter.htmlBut there is no reason to go at 5% resistors with a >3.5 digit meter in most cases. It might not be a popular opinion, but don't glorify tools!

author: David Hess
author_rank: Super Contributor
timestamp: November 21, 2017, 05:22:40 pm
content: Quote from: HalFET on November 20, 2017, 07:11:56 amThe DMMs which are contemporaries to the Fluke 87 series do not suffer from this flaw and make no mistake, it is a flaw with respect to electronics applications. I never bought a Fluke 87 series but had I discovered that it used such a high test voltage, I would have disqualified it instantly for electronics use. Let's see ...Fluke 87-1 1989 Ohms Test <1.3 voltsFluke 87-1 1989 Diode Test <3.9 VoltsFluke 87-2 ---- Ohms Test <1.3 voltsFluke 87-2 ---- Diode Test <3.9 VoltsFluke 87-3 1997 Ohms Test <1.3 voltsFluke 87-3 1997 Diode Test <3.9 VoltsFluke 87-4 1999 Ohms Test <5 VoltsFluke 87-4 1999 Diode Test <5 VoltsFluke 87-5 2004 Ohms Test <7.9 VoltsFluke 87-5 2004 Diode Test <7.9 VoltsIt is disappointing that they kept the 87 model number on a meter which behaves so differently. I wonder how many mysterious failures will be caused by naive users of the Fluke 87 series 5 meters. It will be little consolation when Fluke points to the specifications and says that it is not their fault and the user should have known.