Can anyone tell me if there is a setting on a digital multimeter for testing the value of resistors? I know they are color coded, but I’ve been told you can’t always trust those.
Thanks
Chris Peasley
Can anyone tell me if there is a setting on a digital multimeter for testing the value of resistors? I know they are color coded, but I’ve been told you can’t always trust those.
Thanks
Chris Peasley
If it’s a good meter, it will be auto-rangeing and all you have to do is set it to ohms.
Remember to set the selection switch back to volts after each use. Trying to measure volts on a meter set to OHM will blow the fuse or damage the meter. Some meters use the greek letter omega (upside down U) to mark the ohms scale.
A multi-meter should be able measure in ohms (for resistors) Keep in mind that a resister can be off 1% maybe 2% and still be “good”. So a 1000 Ohm resister might be 980 to 1020 ohms. This small difference is unimportant except in the most critical applications (space probes some to mind)
Ohms is the setting, but I just thought I’d toss in that I’ve never seen a color code that was wrong (though I’m sure it can happen). But, most are 5% (some even 10%)tolerance, unless you pay more. The difference is almost always unimportant, if it is important you can usually change what you’ve designed to make it less so. If you think those tolerances are wide, you don’t want to count on a capacitor value!
For a meter that isn’t auto-ranging, you want to use the next jighest setting, ie if the resistors you are testing are all 1K or less, use the 2K setting. If they are all 100K or less, use the 200k setting.
It’s all a question of how accurate the measurement is. Typical inexpensive meters only have 2 or 3 places after the decimal, so using the 2meg setting to measure a 480 ohm resistor is just going to show 0. And using the 1K setting to measure a 1meg reistor is going to show as an open. It doesn;t damage the meter if you are ont he wrong setting, so hook up a known resistor and try the different settings to see how this works.
Do NOT use the wrong setting when measuring current! that WILL damage something, hopefully just a fuse in the meter.
–Randy
I believe the color code he’s talking about is on the resistor itself to tell you the value. The color bands are usually off center on the resistor body, so start with the band closest to the end. The first two bands are the first two numerals, and the third is called the multiplier. The easiest way to think of the multiplier is “how many zeros after the first two digits.”
The code:
Black= 0
Brown= 1
Red= 2
Orange= 3
Yellow= 4
Green= 5
Blue= 6
Violet= 7
Grey= 8
White= 9
For example, a resistor with a code of Brown, Red, Green would be 1 (brown), 2 (red), followed by 5 zeros (green) or 1,200,000 ohms, also stated as 1.2 Megohms
Some have a fourth band for tolerance gold= 5%, silver = 10%
There are a million sayings to memorize the order of the color code, too. But none I know are suitable to post in a family forum.
For measuring the resitance I just use my Fluke 22. It’s a good, cheap, reliable knock around the house kind of meter.
I never really got the hang of the color code so I use a resistor calculator on my Palm.
A nice feature on a DMM is Min/Max/Average. It does a recording of lowest and highest readings. An audible tone sounds when the value changes. It will also average them out for you. The tone is nice when crawling around looking for an open or short.
To add to what rrinker mentioned about measuring current, DMMs have a low amp and a high amp jack as well as a setting. A good idea is to start out on the high one if there is any doubt as to the amount of current. Most DMMs measure current up to 10A although some go up to 20A. Above that you need a clamp-on inductive pickup. Remember when using a DMM you are measuring a circuit unless you are on Amps. While measuring Amps, you become part of the circuit.
A DMM is a lot like an air compressor, nobody ever complains they bought too large of a compressor. Get a good one and you will not regret it. Sears, Home Depot and Lowes are good places to look.
The Fluke meters are the best, most come with a lifetime warranty. They have come down in price and have some new inexpensive models out. Here is a link to their website: http://us.fluke.com/usen/support/demos/default.htm Select the 80 series DMM on the right and it will give you a virtual demo on a meters buttons and functionality. Dialup will take a bit to load but it is worth it.
Jim
Returning a multi-meter to the volts range after using it to check resistance preserves the internal battery, and protects the meter from releasing the magic smoke…
Checking resistance start with ensuring that there is NO power to the circuit, track, ext. Start at the highest range, unless you know what you expect to see, then work down to find the best reading. In this case a reading that makes sense for your application. You don’t want to see reading in the 0.003 ohm range unless you work with microelectronics. Just use common sense.
For continuity checks, most meters have that capability. Usually marked as a diode teste of check. There is a small beeper in the meeter, or you can watch the needle / display for the continuity reading.
Have fun…
Tom D… Thanks for the resistor color code… I misplaced mine. And it;s a good thing this is a family forum…
Dunno if they still sell it, but Radio Shack used to have a small cardstock color wheel for resistor values - just set the three dials to match the resistor you have and read off the number. Sometimes I misplace mine for months at a time but eventually it turns up, a very handy gadget to have. Or just get some colored markers and make one on a 3x5 card and keep at your bench.
–Randy
Here is one you can print: http://www.elexp.com/t_resist.htm
Here is a virtual one: http://www.webcalc.net/calc/0231.php
Jim
Hi can someone help out is a Tools-600-Amp-AC-Digital-Clamp-Meter good is over qualified should I buy a cheap one thanks?
Cranial Nerves: “On Old Olympus’ Towering Tops, A Fin And German Viewed Some Hops”
Now you show me yours.
I looked up that meter and in my opinion it is for a electrical contractor, generator or appliance repair.
The price is not terribly expensive but it lacks some features. What besidesMR do you plan on using it for?
LION looks at meter. Maybe dial moves. Maybe dial does not move. Maybe the reading means something, maybe it does not mean anything at all. What does the LION know? Him knows watt volts are; him knows watt amps are; him nose if ewe mutliply these things you will know watt the whats are, but who cares about whatts anyway.
Head of LION hurts thinking about it. Him will curl up in the den of him and nibble the tail of him. Numbers! Watt felid ever cared a paw’s claw about numbers.
ROAR
Thanks Jim! I thought it would be good for testing my transformers and tracks. I seen it in Home Depot what tester should I buy at a resonabel price ? Thanks
Thats really up to you. Spend what you can afford. If its never going into a wall and you only plan on MR usage, then maybe the Harbor Freight low end models are OK.
If you want to be able to check home electrical safely, spend a little more. 25-50 should buy a nice meter with a large display.
Working on cars takes a high end model. Typically 300 and up.
I just went to Home Depot bought a Klein mm500 for one penny ! I could not believe my ears when she said one penny she rang me up,I asked why she said because it was discontinued model,and I could not return it ! That made my day I hope it’s good ,and it dose the job its self adjust no dials… I hope it has vac