Digital Multimeter

[FlyingCarGuy]

Hey guys, I'm looking at the Fluke multimeters. Specifically the 170 series. I'll be receiving my first robot in the next couple of days and the cheap meter I have now does not inspire confidence. What kind of meter would be best for me if I'm building my own robots? I'd also use the same meter for wiring the house and working on the cars. Also, what is true RMS and when would I use it? What is a CAT IV rating?

Here's a link to the ones I'm looking at
http://www.farwestcorrosion.com/fwst/in ... series.htm

[JPKNHTP]

-JPKNHTP

[philba]

[note: somebody's been messin with the BBS SW, doesn't let me use parens and isn't doing url tags properly, sigh...]

well, I'd bet your cheapo DMM is a lot better than you think and won't make much difference. The one thing I would go for is a bigger, bright display. There is nothing more annoying than having a hard time seeing the reading.

On RMS, typically, the cheap meters assume a sine wave. The better ones actually do the calculations. It may be better but do you really to measure wierd AC signals for their RMS value? I've yet to really need it. Maybe for measuring inverter output?

For wiring your own house, with AC, I'd guess. I'd go and get one of those non contact voltage detectors - like this one

At minimum, I'd want the following in a meter:
- AC, DC, Current to 1A, min
- resistance
- Capacitance
- audible continuity
- Freq to a couple hundred K or so
- big and backlit display <-- don't skrimp on this
- decent built-in stand

Nice but not necessary
- temp, but depends on the probe quality
- diode - resistance doesn't do it
- Hfe
- serial connection

<small>[ December 14, 2005, 08:36 AM: Message edited by: philba ]</small>

[Dean Huster]

Regarding the Cat IV, III, II, I, etc. ratings --

The higher the Category number, the safer the meter is to use in high-energy circuits. In other words, using a Chinese, Korean, Taiwanese (i.e., Radio Shack) meter to troubleshoot 480-volt 3-phase systems is threatening to shorten your lifetime, fingers and/or arm. A good Fluke Cat IV meter is best on those circuits (along with eye/face protection, insulating gloves, proper clothing, etc. Cat I meters are mostly for probing around inside a computer; Cat II can be used for household electrical stuff all the way to the service panel; Cat III .... hey, it seems to me that you can hit up the Fluke web site and get all this information from an authoritative source.

Dean

[Robert Reed]

As to true RMS- cheap meters measure RMS based on the assumption that it is a true sine wave, and become inaccurate for any other waveform. My Fluke meter is touted as true RMS and is based on , among other things, the crest factor of the waveform. This gives actual reading in true RMS ( which is the equivalent DC voltage to produce the same the same power). Lately, I have been working with a lot of Triac power circuits producing very chopped up waveforms and the meter gave me useful info pertaining to that. Dont know what Flukes limits are on various waveforms, but it seemed to work fine for this application.