Author Topic: multimeter with low continuity test voltage?  (Read 17922 times)

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Online FrankBuss

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multimeter with low continuity test voltage?
« on: July 07, 2014, 11:20:14 pm »
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, and low test voltage and current, all in one device.
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Offline mjkuwp

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Re: multimeter with low continuity test voltage?
« Reply #1 on: July 07, 2014, 11:33:12 pm »
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.
 

Online FrankBuss

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Re: multimeter with low continuity test voltage?
« Reply #2 on: July 08, 2014, 12:23:34 am »
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/
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Online tautech

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Re: multimeter with low continuity test voltage?
« Reply #3 on: July 08, 2014, 01:03:02 am »
Fluke 15B uses 2x 1.5V AA supply.
440mV @ 0.14mA
Fast beep too.  :-+
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Offline hlokk

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Re: multimeter with low continuity test voltage?
« Reply #4 on: July 08, 2014, 02:17:52 am »
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.
 

Online FrankBuss

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Re: multimeter with low continuity test voltage?
« Reply #5 on: July 08, 2014, 02:50:28 am »
Fluke 15B uses 2x 1.5V AA supply.
440mV @ 0.14mA
Fast beep too.  :-+
Nice, 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.

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.
I 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.
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Online tautech

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Re: multimeter with low continuity test voltage?
« Reply #6 on: July 08, 2014, 02:58:01 am »
Fluke 15B uses 2x 1.5V AA supply.
440mV @ 0.14mA
Fast beep too.  :-+
Nice, 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.
FYI Fluke 15B has the 17B functionality, just missing the buttons as far as I know.
Check for previous EEVblog posts on this subject.  ;)
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Offline retiredcaps

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Re: multimeter with low continuity test voltage?
« Reply #7 on: July 08, 2014, 05:46:13 am »
On my Greenlee DM-200A (aka Brymen BM250 series), I get the following when set to continuity mode:

0.494V DC
157uA

The Greenlee uses 2 AAA batteries.

See

http://www.brymen.com.tw/product-html/cata250/Bm250L4.htm
 

Offline retiredcaps

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Re: multimeter with low continuity test voltage?
« Reply #8 on: July 08, 2014, 05:50:08 am »
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/

 

Offline Lightages

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Re: multimeter with low continuity test voltage?
« Reply #9 on: July 08, 2014, 06:11:16 am »
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.
« Last Edit: July 08, 2014, 06:15:49 am by Lightages »
 

Online FrankBuss

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Re: multimeter with low continuity test voltage?
« Reply #10 on: July 08, 2014, 07:51:51 am »
You may know the BM257 is very popular here and others can verify those readings I posted with the Greenlee DM-200A.
Thanks, 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-risks

Anyone 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.
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Offline retiredcaps

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Re: multimeter with low continuity test voltage?
« Reply #11 on: July 08, 2014, 09:44:01 pm »
Anyone 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.
My 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.
 

Online FrankBuss

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Re: multimeter with low continuity test voltage?
« Reply #12 on: July 08, 2014, 10:42:11 pm »
7.3 V is really bad. Thanks, no need to measure the Fluke 87, too, I already ordered the Brymen BM257s :) I'll post an update here if the test voltage is different from the BM257.
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Offline haoleboy

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Re: multimeter with low continuity test voltage?
« Reply #13 on: July 09, 2014, 03:01:26 am »
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. :scared: Just how dangerous is that amount of voltage on a low power circuit (like maybe a cell phone or wireless router)?
 

Offline KedasProbe

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Re: multimeter with low continuity test voltage?
« Reply #14 on: July 09, 2014, 07:49:27 am »
Anyone tried a zener to reduce the voltage?
Not everything that counts can be measured. Not everything that can be measured counts.
[W. Bruce Cameron]
 

Online FrankBuss

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Re: multimeter with low continuity test voltage?
« Reply #15 on: July 10, 2014, 07:20:53 am »
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.
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Offline Wh1sper

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Re: multimeter with low continuity test voltage?
« Reply #16 on: July 10, 2014, 07:48:54 am »
My Metraport 32 S has 0.6xx Volts in Continuity
My 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.
 

Offline Lightages

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Re: multimeter with low continuity test voltage?
« Reply #17 on: July 10, 2014, 08:05:15 am »
I just remeasured my BM257 to be sure and it outputs 0.62V.... I wonder why the difference.
 

Offline Yago

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Re: multimeter with low continuity test voltage?
« Reply #18 on: July 10, 2014, 10:43:01 am »
Could it be differing input impedances of the measuring device?
 

Offline gdewitte

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Re: multimeter with low continuity test voltage?
« Reply #19 on: July 10, 2014, 06:17:12 pm »


Quote from: Wh1sper on Yesterday at 05:48:54 PM
My
Metraport 32 S has 0.6xx Volts in Continuity
My 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.

Many, many years ago, I built a continuity tester from a kit (which may have been from Audio Amateur), but can no longer find any info for it. The tester still works fine, and I frequently use it. Its PCB is labeled PE301A, uses an LM324 with a buzzer, is powered by a 9V battery, fits nicely in a 2.75"×4" black plastic box, has Voc = ~ 215mV, and Isc = ~ 270µA. If there's enough interest, I could try to generate a schematic from the PCB.


 

Offline Wh1sper

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Re: multimeter with low continuity test voltage?
« Reply #20 on: July 10, 2014, 07:53:03 pm »

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.
Many, many years ago, I built a continuity tester from a kit (which may have been from Audio Amateur), but can no longer find any info for it. The tester still works fine, and I frequently use it. Its PCB is labeled PE301A, uses an LM324 with a buzzer, is powered by a 9V battery, fits nicely in a 2.75"×4" black plastic box, has Voc = ~ 215mV, and Isc = ~ 270µA. If there's enough interest, I could try to generate a schematic from the PCB.

I'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!
 :-+
 

Offline AintBigAintClever

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Re: multimeter with low continuity test voltage?
« Reply #21 on: July 10, 2014, 09:08:38 pm »
Fluke 79-III
Ohms: 760mV
Continuity/40 ohms: 3.08V
Diode test: 3.04V

All of the above were into a 10M x10 probe on my DS2072A-S DS2302A-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.
 

Online MagicSmoker

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Re: multimeter with low continuity test voltage?
« Reply #22 on: July 10, 2014, 09:23:29 pm »
...
My 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.

Ditto 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).

 

Offline zaoka

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Re: multimeter with low continuity test voltage?
« Reply #23 on: July 10, 2014, 09:32:48 pm »
You need multimeter with low power ohm feature. Older Tektronix DMMs had that feature, or new Yokogawa http://www.tequipment.net/YokogawaTY720.html?v=7231

 

Online FrankBuss

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Re: multimeter with low continuity test voltage?
« Reply #24 on: July 10, 2014, 09:55:37 pm »
I'm pretty sure I could build something like that by myself. But would I have the spare time? I would gues: No!
Google 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 ;D :

http://www.zen22142.zen.co.uk/Circuits/Testgear/connectiontester.htm

Test 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).
« Last Edit: July 10, 2014, 10:02:54 pm by FrankBuss »
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