7N7 said:
Or an ohm meter with a kelvin (four wire) measurement option, otherwise I will second the above comment - no two wire meter is going to give a very accurate result below 10 ohms or so..
When doing two wire measurements with a conventional dvm if you subtract the lead resistance you can usually get pretty close with a decent meter.
My Fluke 77 has always been good to about a tenth of an ohm from zero to ten, but the weak point is the test leads. My guess is the bond to the probes and the bananas is friction or compression, as the lead resistance changes slightly with time and movement. Home constructed leads with soldered bananas are much more reliable for low resistance measurements. Still, for low ohm measurements you're much better off to build an opamp current source, then measure the voltage drop across the resistor. Or, use any supply to push some current through the DUT (device under test) and another accurately known resistor, measure the drop across both, then calculate the result.
I use a fluke meter when I need very accurate readings, but I use my Radio shack digital autoranger for most work. Why? It was cheap ( 30 USD) and it works to almost as good of accuracy as a fluke. Close enough for tube work. It also has a nice hold feature on it. I have had it through several over voltages and accidental over-amperages, and all it did was blow the internal fuse. Unlike my other meters such as my craftsman ones, it has a fuse on the 10amp section.
Its not the best out there but its safe to say that its a bit better quality in terms of construction and accuracy than your average outlet store brand.
Its not the best out there but its safe to say that its a bit better quality in terms of construction and accuracy than your average outlet store brand.
I used to use a lot of cheaper meters for general use, I now use them only for measuring multiple circuit points where I won't be changing ranges or modes.
Fluke meters are protected against inadvertent overloads such as those that occur when you absent mindedly attempt to measure voltage while the meter is still in resistance mode. Try that with most cheap meters and you will see plenty of magic smoke..
I no longer recommend the cheap meter to most newbies as anything other than a back up for this reason. (Unless they really need only to measure things infrequently.) Cheap used Flukes are easy to find on eBay for little more than a cheap new meter in many cases.
I don't find the accuracy of cheap meters particularly bad, but they don't come close to my Keithley 2002 either.
Fluke meters are protected against inadvertent overloads such as those that occur when you absent mindedly attempt to measure voltage while the meter is still in resistance mode. Try that with most cheap meters and you will see plenty of magic smoke..
I no longer recommend the cheap meter to most newbies as anything other than a back up for this reason. (Unless they really need only to measure things infrequently.) Cheap used Flukes are easy to find on eBay for little more than a cheap new meter in many cases.
I don't find the accuracy of cheap meters particularly bad, but they don't come close to my Keithley 2002 either.
How about this?
http://support.metermantesttools.com/meterman-sales/download/asset/1646419_a_6118_eng_w.pdf
You can zero the readings for the 20 ohm scale.
http://support.metermantesttools.com/meterman-sales/download/asset/1646419_a_6118_eng_w.pdf
You can zero the readings for the 20 ohm scale.
astouffer said:
That's much better, and probably pretty useful but still, even if you adjust for your leads there are still no guarantees about contact resistance when testing a particular component.
For very small resistors the best option is a known voltage applied to the resistor and measure the current - or a bridge!
7N7
Get the $30 Radio Shack meter... Works great for the money and is reliable with internal protection.... Auto ranging is really important. I've had mine for 2yrs blew fuses when misused and beeps when your in the wrong mode. I use mine a lot with no regrets. They usually last 6 yrs then start acting wacky. I'd be very leary of used Ebay meters. Meters age and have wear and tear on them. I don't care what brand it is, electronics don't age well. Stick with new and you know what you got. .... Happy Holidays to all!!
How true. That's the main reason burning DVMs. I did my share and now its almost a reflex to switch dial back to VAC setting after every measurement.
Protection helps, but I dont think it will hold if you discharge high voltage 100uF capacitor through DMM when it is set on resistance measurement.
Anyway, I am using couple Radioshack DMMs (bought them 10 years ago for around $80). They are quite accurate.
Tony said:
now this is the tester i grew up with,got my first one in 1972...
I can't believe they still make these. The remains of a well used specimen are still lying around somewhere. It served me well in the early days...
I didn’t read the whole thread but my humble advice would be to buy one good meter and a few el-cheapos for the ‘dirty work’.
/Hugo
George (aka tubelab) has some good information about choosing and using digital mutimeters. Give this a look as well:
http://www.tubelab.com/MeterUse.htm
http://www.tubelab.com/MeterUse.htm
Meters
I have had several meters since 1985, mostly cheap RS analog types.....bit the bullit & got a Sears large display autoranging digital version...had it for some ten years replaced leads three times & one battery change, three fuses...OOpps.
Unfortunately it has no zeroing function so I get lead resistance.
I was told in class way back when, one good Digital & one more NICE analog will do.
Have an ancient Simpson analog.....I need to refurbish.
________________________________________Rick.........
I have had several meters since 1985, mostly cheap RS analog types.....bit the bullit & got a Sears large display autoranging digital version...had it for some ten years replaced leads three times & one battery change, three fuses...OOpps.
Unfortunately it has no zeroing function so I get lead resistance.
I was told in class way back when, one good Digital & one more NICE analog will do.
Have an ancient Simpson analog.....I need to refurbish.
________________________________________Rick.........
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