accuracy of multimeters when measuring coil resistance

[gerry81611]

so i "upgraded" my radio shack pocket multimeter to an amprobe pm-55a and have not been able to get consistent measurements since. the numbers jump wildly and then settle on a number that i know is higher than normal (3-4 ohms for a 2.4 coil)

once in a while i'm able to get an accurate reading, but rarely. i called amprobe tech support and they told me that no meter except a 4 lead one will accurately measure tenths of an ohm. i think this is bullcrap since my old radio shack meter seemed to do just fine.

i'm wondering if you guys have any accuracy or repeatability issues with your meters? i rebuild genesis and silica wicks and coils and stick with 32g kanthal.

i even tried clipping a 2 inch length of kanthal to test the resistance against a known quantity and the meter just jumped around wildly.

would sanding the probes help?

are there any usa made meters?



thanks,


g

 

[jasl90]

so i "upgraded" my radio shack pocket multimeter to an amprobe pm-55a and have not been able to get consistent measurements since. the numbers jump wildly and then settle on a number that i know is higher than normal (3-4 ohms for a 2.4 coil)

once in a while i'm able to get an accurate reading, but rarely. i called amprobe tech support and they told me that no meter except a 4 lead one will accurately measure tenths of an ohm. i think this is bullcrap since my old radio shack meter seemed to do just fine.

i'm wondering if you guys have any accuracy or repeatability issues with your meters? i rebuild genesis and silica wicks and coils and stick with 32g kanthal.

i even tried clipping a 2 inch length of kanthal to test the resistance against a known quantity and the meter just jumped around wildly.

would sanding the probes help?

are there any usa made meters?



thanks,


g

Actually, it's not bull crap. A 4 wire measurement really is the only way to get truly precise low ohm measurements. Fortunately we don't need ultra precise measurements so handheld a DMM should work just fine.
Two things can help...
1) Get (or make) a set of leads that have alligator clips. They will make a more stable connection to the resistor.
2) It can take a little while for the meter to "settle down". Even my Fluke meters can take 30 seconds or more before they stabilize. This is especially true of auto ranging meters.

What I do... Turn on the meter, set it to "hi-res" mode, clip the leads together and let it sit while I prep all the other stuff. By the time I'm ready to take a measurement the meter has settled down to about 0.11 ohms (the resistance of the leads themselves). Hit the "Rel" button to zero it out and take my measurement.

Never sand your probes.

Most Fluke meters are made in the USA. Some of their lower end models are made over seas but be prepared to spend big money if you want one. Even their "cheap" Chinese made models start at $120 (retail)... And they go up very quickly from there. eBay is your friend when shopping for Flukes. There are good deals to be had and the fact that they are damned near indestructible means you can buy them used with a fair degree of confidence.

 

[Sarje]

I've had the same experience. I've got a regular meter that measures about .1 ohm above what my mods tell me. I ordered an autoranging meter that's WAAY out. I know you're supposed to touch the leads together and measure the resistance of the leads themselves, you then subtract that number from the ohms reading of your coil. When I do this, it's about right. If I swap the leads between the two meters I still get the same result (original meter measures fine, new meter doesn't). I suppose the new one is just badly calibrated and the old one is calibrated to subtract the lead resistance.
Frustrated though as I still find myself using my old cheapie non auto-ranging meter.

 

[gerry81611]

thank you both! i measured the leads and it seems to bounce between 1.1-1.3. that seems about right for the readings i was getting. i kind of wish i still had the cheapie radio shack meter, i was hoping good tools would be more of a joy to use

gerry