Author Topic: multimeter with low continuity test voltage?  (Read 26663 times)

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Offline Wytnucls

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Re: multimeter with low continuity test voltage?
« Reply #25 on: July 10, 2014, 10:16:22 pm »
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.

« Last Edit: July 10, 2014, 10:20:17 pm by Wytnucls »
 

Offline FrankBussTopic starter

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Re: multimeter with low continuity test voltage?
« Reply #26 on: July 10, 2014, 10:23:56 pm »
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.
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Offline Rick Law

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Re: multimeter with low continuity test voltage?
« Reply #27 on: July 11, 2014, 06:44:55 am »
Anyone tried a zener to reduce the voltage?

But 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.
 

Offline Joule Thief

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Re: multimeter with low continuity test voltage?
« Reply #28 on: July 11, 2014, 07:13:06 am »
Fluke 87-III
Ohms: 670mV
Diode test: 3.73V

measured with Fluke 8800A
Perturb and observe.
 

Offline KedasProbe

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Re: multimeter with low continuity test voltage?
« Reply #29 on: July 11, 2014, 09:04:45 am »
Anyone tried a zener to reduce the voltage?

But 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.

You 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)
« Last Edit: July 11, 2014, 04:54:22 pm by KedasProbe »
Not everything that counts can be measured. Not everything that can be measured counts.
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Offline mimmus78

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Re: multimeter with low continuity test voltage?
« Reply #30 on: July 12, 2014, 07:13:34 pm »
On my BM257 (not BM257s) is 0,497V too.
 

Offline WVL_KsZeN

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Re: multimeter with low continuity test voltage?
« Reply #31 on: July 12, 2014, 08:04:00 pm »
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.
« Last Edit: July 12, 2014, 08:10:34 pm by WVL_KsZeN »
 

Offline KedasProbe

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Re: multimeter with low continuity test voltage?
« Reply #32 on: July 13, 2014, 10:10:45 am »
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 0.34mA

Although it's good that you know this about your meter it will not replace a good 0.4V continuity tester.
« Last Edit: July 13, 2014, 10:37:11 am by KedasProbe »
Not everything that counts can be measured. Not everything that can be measured counts.
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Offline retiredcaps

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Re: multimeter with low continuity test voltage?
« Reply #33 on: July 14, 2014, 07:29:03 am »
I have an original 87 (series 1) as well, but currently it has no battery.
Original 87 puts out 1.240V and roughly 300uA when set to continuity.
 

Offline tautech

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Re: multimeter with low continuity test voltage?
« Reply #34 on: July 14, 2014, 08:55:34 am »
Fluke 15B uses 2x 1.5V AA supply.
440mV @ 0.14mA
Fast beep too.  :-+
Who would have thought the Fluke 15B would have fared so well against supposedly much better meters.  :-DMM

So I thought I had better check my Vichy VC99 and:

0.641 V @ 0.25 mA 

Not too bad either.  :phew:
Beep not quite as instant as the Fluke 15B but still quick.
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Offline Wh1sper

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Re: multimeter with low continuity test voltage?
« Reply #35 on: July 16, 2014, 04:32:00 pm »
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: [Select]
      .-------------.
      |          .--|-----------------------
      |  .---|   |  |      |
      | -|   |  / \ |      -
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      |          '--|-----------------------
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An ASCII Art Schematics :-)
« Last Edit: July 16, 2014, 07:40:56 pm by Wh1sper »
 

Offline tautech

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Re: multimeter with low continuity test voltage?
« Reply #36 on: May 07, 2015, 09:13:24 pm »
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
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Offline gdewitte

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Re: multimeter with low continuity test voltage?
« Reply #37 on: May 08, 2015, 01:46:22 am »
Not a multimeter, but many (many, many) years ago I built a small kit (from Audio Amateur?) that has Voc = ~ 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.
 

Offline Fungus

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Re: multimeter with low continuity test voltage?
« Reply #38 on: November 17, 2017, 06:46:28 am »
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.

7.3 V is really bad. Thanks

It'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.

 

Offline FrankBussTopic starter

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Re: multimeter with low continuity test voltage?
« Reply #39 on: November 17, 2017, 07:00:48 am »
It'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.

Yes, 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.
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Offline David Hess

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Re: multimeter with low continuity test voltage?
« Reply #40 on: November 20, 2017, 01:04:03 am »
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.

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.

The 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.
 

Offline Muxr

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Re: multimeter with low continuity test voltage?
« Reply #41 on: November 20, 2017, 06:43:17 am »
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 \$\Omega\$). Current is 0.5mA by the way.
« Last Edit: November 20, 2017, 06:48:30 am by Muxr »
 

Offline HalFET

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Re: multimeter with low continuity test voltage?
« Reply #42 on: November 20, 2017, 07:11:56 am »
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.
 

Offline Fungus

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Re: multimeter with low continuity test voltage?
« Reply #43 on: November 20, 2017, 07:33:42 am »
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.

So that's why it's 20000 counts - so you can measure industrial drive electronics to 4.5 digits in the rain.  :-+

on the other hand the 15b+ is more geared towards bench use I think.

Unlike a bench meter, which would never need that accuracy.
 

Offline HalFET

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Re: multimeter with low continuity test voltage?
« Reply #44 on: November 20, 2017, 08:26:16 am »
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.

So that's why it's 20000 counts - so you can measure industrial drive electronics to 4.5 digits in the rain.  :-+

on the other hand the 15b+ is more geared towards bench use I think.

Unlike a bench meter, which would never need that accuracy.

Stop 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. Also http://en-us.fluke.com/products/digital-multimeters/fluke-87v-digital-multimeter.html 

But 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!
 

Offline David Hess

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Re: multimeter with low continuity test voltage?
« Reply #45 on: November 21, 2017, 05:22:40 pm »
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.

The 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 volts
Fluke 87-1 1989 Diode Test   <3.9 Volts
Fluke 87-2 ---- Ohms Test   <1.3 volts
Fluke 87-2 ---- Diode Test   <3.9 Volts
Fluke 87-3 1997 Ohms Test   <1.3 volts
Fluke 87-3 1997 Diode Test   <3.9 Volts
Fluke 87-4 1999 Ohms Test   <5 Volts
Fluke 87-4 1999 Diode Test   <5 Volts
Fluke 87-5 2004 Ohms Test   <7.9 Volts
Fluke 87-5 2004 Diode Test   <7.9 Volts

It 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.
 


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