Author Topic: Continuity vs Ohms  (Read 985 times)

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Offline DannnyGTopic starter

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Continuity vs Ohms
« on: May 09, 2024, 02:12:39 pm »
I recently watched a YouTube video where the technician was checking the output +&- (supposed to be dc) on a treadmill controller board.  (Board is not plugged in) He got .4 ohms and said that it was a direct short.  I'm using a treadmill board to practice using my multimeter because I retired a while back and got hooked on diddling with electronics.  I have no idea if it works or not and dont care at this point. Ive tested my board on the ohms setting of my MM and also got .4 ohms.  I set my MM to the continuity tone setting which also reads ohms and it gave no tone and OL?  I moved over to the ac input +&- and measured 345 ohms on the MM Ohms setting and 345 Ohms on the tone setting and got a tone.  Why am I confused about that?  Thanks for patience.
 

Online themadhippy

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Re: Continuity vs Ohms
« Reply #1 on: May 09, 2024, 02:28:46 pm »
Quote
I set my MM to the continuity tone setting which also reads ohms and it gave no tone and OL?
Is it a continuity range or continuity/diode test range
 

Offline DannnyGTopic starter

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Re: Continuity vs Ohms
« Reply #2 on: May 09, 2024, 02:43:13 pm »
Correction .42 mohms
MM reads ohms with continuity ( speaker icon with delta beside it)
MM also has Ohms setting ( sel button takes you there)
MM is a Mastfuyi Mk06
 

Offline ebastler

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Re: Continuity vs Ohms
« Reply #3 on: May 09, 2024, 03:05:23 pm »
Correction .42 mohms

Might it be 0.42 MOhm? Please be careful with capitalization. The "M" prefix means "Mega" (1 million), while "m" means "milli" (1/1000).

0.42 MOhm = 420 000 Ohm is a high resistance which will certainly not trigger the continuity beeper. In contrast, 0.42 mOhm is a very low resistance, probably well below the resolution of your multimeter, and it would certainly cause the continuity beeper to sound.
 
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Offline DannnyGTopic starter

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Re: Continuity vs Ohms
« Reply #4 on: May 09, 2024, 05:37:48 pm »
The word triggering shows me the difference and put me on the right track.  I checked my MM and it was milliohms.
Thanks
 

Offline pcprogrammer

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Re: Continuity vs Ohms
« Reply #5 on: May 09, 2024, 05:49:37 pm »
Guess this song applies.  :-DD

https://youtu.be/Z8aKoMmMZnI?t=158

.42mOhm means 420 micro Ohm. Not very likely that a cheap multi meter will be able to measure such a small resistance. Even 42 milli Ohm is already a very small resistance. The leads of your multi meter most likely have a higher resistance than that.

Edit: Added the picture of the album cover of the song.
« Last Edit: May 09, 2024, 05:54:29 pm by pcprogrammer »
 
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Offline ebastler

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Re: Continuity vs Ohms
« Reply #6 on: May 09, 2024, 06:32:21 pm »
I checked my MM and it was milliohms.

Please check again!  ;)

I looked up the Mastfuyi Mk06, and it does not have a milli-Ohm range at all. (Hardly any multimeter has that -- the resistance of  probe wires and contacts is easily in the 100s of milli-Ohm, so measuring resistances well below that requires special connections and equipment.) Since you mentioned that you are getting into electronics, getting a feel for the order of magnitude of the relevant quantities is important, as is getting a solid handle on the notation.
 
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Offline IanB

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Re: Continuity vs Ohms
« Reply #7 on: May 09, 2024, 06:48:12 pm »
0.4 Ω (ohms) is a reasonable measurement for a direct short. Such a low resistance should definitely cause the continuity test on the meter to beep.
 
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Offline BeBuLamar

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Re: Continuity vs Ohms
« Reply #8 on: May 09, 2024, 08:08:37 pm »
Correction .42 mohms

Might it be 0.42 MOhm? Please be careful with capitalization. The "M" prefix means "Mega" (1 million), while "m" means "milli" (1/1000).

0.42 MOhm = 420 000 Ohm is a high resistance which will certainly not trigger the continuity beeper. In contrast, 0.42 mOhm is a very low resistance, probably well below the resolution of your multimeter, and it would certainly cause the continuity beeper to sound.

I think it's MOhm (megaohms) because I doubt that the OP has a meter that can read in 0.42 milliohms.
 
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Offline Solder_Junkie

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Re: Continuity vs Ohms
« Reply #9 on: May 09, 2024, 08:30:29 pm »
My Fluke 177 has this in the manual for continuity:
"Product beeps at <25 Ω"

Whereas my Brymen BM235 has this in the manual:
"Continuity Threshold: Between 30 Ohms and 480 Ohms"

Which leads me to be wary using continuity for anything critical... I think the Brymen is particulaly vague!

SJ
 
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Offline ebastler

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Re: Continuity vs Ohms
« Reply #10 on: May 09, 2024, 09:22:08 pm »
Might it be 0.42 MOhm? Please be careful with capitalization. The "M" prefix means "Mega" (1 million), while "m" means "milli" (1/1000).

0.42 MOhm = 420 000 Ohm is a high resistance which will certainly not trigger the continuity beeper. In contrast, 0.42 mOhm is a very low resistance, probably well below the resolution of your multimeter, and it would certainly cause the continuity beeper to sound.

I think it's MOhm (megaohms) because I doubt that the OP has a meter that can read in 0.42 milliohms.

I think so too, which is why I wrote that.  ;)
 
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Offline CatalinaWOW

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Re: Continuity vs Ohms
« Reply #11 on: May 09, 2024, 10:18:32 pm »
There is a lot going on here.  The meter in question is only specified to read values greater than 1 ohm, though it does claim to have 0.1 ohm resolution on the lowest scale.   There is no such thing as AC resistance in a meter of this type.  Who knows what that weird combination of buttons does, or why it fires the continuity buzzer.  Stick with the resistance setting.  How to interpret the results is another big issue.  Unless you know that the maker of the Utube video knows what he is talking about, and you have the same make and model card as was being tested in the video an apparent short circuit should only indicate the possibility that the card is bad, not a certainty. 

here a link to the manual

https://images.homedepot-static.com/catalog/pdfImages/59/59692c5b-a816-4a6f-8210-2e85dfdb5e25.pdf
 
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Offline DannnyGTopic starter

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Re: Continuity vs Ohms
« Reply #12 on: May 10, 2024, 12:33:53 am »
You are all right.
I wasn't reading the milli, mega etc correctly
I didn't know that continuity stopped at a certain resistance depending on the multimeter
But I know and understand a little more thanks to your help.  I having fun when I'm not scratching my head...lol
Thanks kindly
 

Offline Solder_Junkie

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Re: Continuity vs Ohms
« Reply #13 on: May 10, 2024, 09:37:29 am »
From the linked manual, courtesy of CatalinaWOW, continuity is really ambiguous, I suspect they really mean below 50Ω:

"Continuity check: Provides an audible indication above 50Ω"

A continuity check is perhaps best used for nothing more involved than identifying wires in a bundle.

SJ
 

Offline pcprogrammer

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Re: Continuity vs Ohms
« Reply #14 on: May 10, 2024, 10:18:32 am »
A continuity check is perhaps best used for nothing more involved than identifying wires in a bundle.

True, diode test is much better for fault finding.

Offline BeBuLamar

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Re: Continuity vs Ohms
« Reply #15 on: May 10, 2024, 11:27:01 am »
There is a lot going on here.  The meter in question is only specified to read values greater than 1 ohm, though it does claim to have 0.1 ohm resolution on the lowest scale.   There is no such thing as AC resistance in a meter of this type.  Who knows what that weird combination of buttons does, or why it fires the continuity buzzer.  Stick with the resistance setting.  How to interpret the results is another big issue.  Unless you know that the maker of the Utube video knows what he is talking about, and you have the same make and model card as was being tested in the video an apparent short circuit should only indicate the possibility that the card is bad, not a certainty. 

here a link to the manual

https://images.homedepot-static.com/catalog/pdfImages/59/59692c5b-a816-4a6f-8210-2e85dfdb5e25.pdf

The meter can display a resistance value less than 1Ω but the unit is Ω and not mΩ. It would never displays 0.4 mΩ. If the OP see an m it would be the upper case M and it means MΩ.
 


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