[jules]

I've been successfully using the same meter for some years now and it's proved to be accurate for all the DIY work i've done so far but I'm wondering if I've found its limits.

For 1/4W resistors the meter readings are always close to the specified values but I'm finding that the reading on each one of a number of 1 ohm, .5W Dale resistors are consistently high, [2 ohms in fact].

I seriously doubt that the resistors are all incorrectly labeled, so I'm wondering if lesser DMMs struggle with low resistance and high wattage values.

Jules

PS I changed the batteries in case they were the prob   

[markC]

I just bought some Dale .5W 1% R's last week & measured them. They were pretty much bang on. Mind you, the values were higher, (97.6 ohm). How's your battery?

[jules]

Thanks for the reply Mark ...

 The batteries are ok. I've got 24 of these Dale 1 ohm 5W resistors all measuring ~ 2 ohm so I'm doubtful that it's something as freak as a badly labelled batch. My meter also struggles with some .2ohm, 5W Dales so I suspect it's just too much for it to handle.

Jules

[gitarretyp]

Try touching the leads on your DMM together to see what their resistance is. It may be your leads have developed a loose or poor connection and are adding some resistance to your measurements, which you may only notice while measuring these small value resistors.

[mgalusha]

Most meters don't do well with really low values. Partly because of the leads but also because of the resistance of the probe to the resistor lead. Some meters have a relative mode that allows for the lead resistance and if one uses some clip leads to get a positive grip on the CUT the accuracy is much better. A Fluke 8050A is a nice piece, easy to find and affordable. eBay

[jules]

Gitarretyp:

The meter is accurate and consistent for high resistance low wattage resistors. It's also consistent for low resistance high wattage resistors but the measurement is consistently high  so I think Mike's suggestion hits the nail on the head.

Mike:

I'm reassured that the resistors are probably ok. I like to test that the values are right before soldering them in but in this case I think it's safe to assume they're ok and I might have to look at a better meter and procedure if I'm going to use resistors like this more often. Yes, an Ebay Fluke is a great idea [thanks for the link]!

Jules

[mgalusha]

I imagine your resistors are fine, it's rare that they are mis marked but I have seen it once or twice. More often that not it's me that makes the error reading the value so I measure them too.

The high readings on low values are exactly what happens without a relative mode. On the 200 ohm scale of the Fluke 8050A I get about .04 ohms with the leads shorted. If I short them and hit the relative button it zeros and then my readings are accurate, at least they seem to be. Think of it like the tare weight function of a scale.

[JoshK]

Much like Mike was saying you could try to shift the scale by adding a, say, 100ohm resistor.  Measure the 100 ohm resistor to get its precise reading.  Then clip your 1ohm resistor to the 100ohm with an aligator clip or something and measure the combo.  Then subtract the first reading.  This should give you a good reading hopefully.

[jules]

Josh:

I had a go at that with a medium value resistor in series with the test resistor but my meter probably isn't all that accurate at the third significant figure.

Mike:

I tried the lead shorting test to get a rough idea of what part they and other inbuilt resistance might play and the reading is .4 ohm so using that as a correction, the readings on a 1 ohm resistor are still high but basically the problem is solved. Those Flukes are a very good price on ebay.

Thanks all

Jules

[markC]

I shoted the leads on my UEI meter and was pleased when it read 0.00 ohms! It's a meter made for the HVAC trade, but I didn't expect it to read 0.
It is the auto ranging type.

[peranders]

What was the range? 200 ohms or 2kohms or? Normal test cables have 0.1-0.5 ohms.. at least

[markC]

It just displays 0.00 ohms. If I hook up jumper wires to the leads, (which I often use for diagnostic purposes and test them regularly to ensure continuitiy), I get a reading of about .01 to .02 ohms.