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Cable Testing Question/Help

hthomas

Member
Messages
145
I am testing patch cables and instrument cables with my multimeter. Just want to verify I am doing it correctly. I have the meter set to Ohms. I am doing tip to tip and sleeve to sleeve. I get readings of 0.2-0.4 depending on the cable and either tips or sleeves. Are those cables a problem since they are not measuring 0.0? I have a mixture of pre made cables and ones I have soldered. All of which do not measure to 0.0

Is it a case of they are really close to 0.0 and it is not an issue?

I am just worried I am not getting the full benefit of quality cables.
 

John Coloccia

Cold Supporting Member
Messages
9,579
If you touch the two probes together, you probably won't get 0.0 either. If it does measure zero, it's only because your meter isn't precise enough or is out of calibration. My cheap meters measure 0 when I do that. My Fluke usually measures .2 or .3 or so, which is probably just contact resistance. There's resistance in everything, including the probes, the contact between the probes, etc. Your cables are fine, but check tip to sleeve as well to make sure you don't have a short.

To really measure low resistances like this, you need to do a 4 terminal measurement to remove things like contact resistance. What you're looking for when you're testing cables is much simpler than that. It's just a basic go/no-go continuity test. If you start getting higher numbers, like 10 ohms for example, you may have a problem somewhere, most likely some oxidation/oil/whatever on the connector or the probes that you might want to clean off and try again.
 
Last edited:

TheoDog

Silver Supporting Member
Messages
19,880
Tip to sleeve should measure OL.
Tip to tip and sleeve to sleeve should have very small resistance measurements. That is the capacitance which is mostly a function of length.
 

John Coloccia

Cold Supporting Member
Messages
9,579
I thought it meant "open line"
It's overload. For example, you'll also get it if you switch your meter to the mV range (instead of auto ranging), and stick 9V in there...you'll get an OL. It generally means that whatever you're measuring is too high to measure. :)
 

TheoDog

Silver Supporting Member
Messages
19,880
Gotcha.. And on continuity, if there is no current at all between the leads, resistance is full or "too high to measure."
 

John Coloccia

Cold Supporting Member
Messages
9,579
Gotcha.. And on continuity, if there is no current at all between the leads, resistance is full or "too high to measure."
Bingo. Honestly, I didn't actually know what it stood for until a few years ago...all I knew was that it meant "too much!". Then I saw a video and the guy said the word "overload", and it all clicked into place. I just figured it was some convenient arrangement of the LCD that obviously wouldn't be confused with a number. :)

How I managed to be engineering for nearly 20 years at the time, and somehow NOT know that, is beyond me.

edit:
I can answer that, actually. I'm an engineer, therefore I never read the destructions.
 




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