Resistor readings

[John Roman]

Got some wire wound sand cast power resistors from Jameco yesterday and I'm having trouble getting a consistent reading. They're value is:
5 watt  .15 ohm  @ 5% tolerance .  I'm using a Fluke with a new battery and the probes are in perfect condition. The value does increase with temperature as expected but never settles to less than .2 ohms which puts it within tolerance. Is my meter suspect or what?
I'd say they're fine, just checking.

[Doc B.]

It's just the resistance of the test leads adding onto the resistance of the resistor. You can try cleaning the test lead tips, but it's unlikely that you can remove the last .01 of an ohm of resistance.

[JC]

Also, does your Fluke let you "zero out" the resistance of the leads/probes?  Mine happens to have that feature, which is very handy indeed for measuring sub 1 Ohm resistors.  Otherwise, the leads/probes always read .1 - .2 Ohms with the probes shorted together.

[Grainger49]

No, there is no manual zero with any digital meter I am familiar with.  So just touch the two meter leads together and subtract that portion of an ohm from your readings.

[John Roman]

Thanks gentleman, back to the operating table......

[JC]

It is referred to as "Cal" on my Fluke, and it apparently tells the processor to "ignore" the reading it is getting of the leads/probes shorted together until the next time it boots up.

I've noticed with digital meters, it also helps to have a low Ohms range if you expect to need to measure lower valued resistors frequently. 

[Jim R.]

Both my digital meters have a button to zero out the probe lead resistance.  T hough it seems that if you switch scales you have to re-zero them.

-- Jim

[booangler]

You can always try something like this. Much more accurate but does require you to use some math.

Simple Low Resistance Test Jig

Cheers,

Alan