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Do I need a true RMS multi-meter?

leftymechanic

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Do I need a true RMS multi-meter?
« on: October 01, 2015, 04:11:AM »
Guys,
Do I need a true RMS multi-meter?

I have been given the green light at work to replace my cheap multi-meter with a new Fluke. Is there any need for me to buy a true RMS multi-meter? I see them listed in the catalog, but i don't think I need to go with one.

I typically check continuity, 480 volts, sometimes small current and it seems as though a standard multi-meter is all I need. Any advice?

Thanks!!
Lefty Mechanic
-- Richomond, Virginina --


Cheller

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Re: Do I need a true RMS multi-meter?
« Reply #1 on: October 02, 2015, 04:19:AM »
I have some advice, and it's based on a few decades of working as a maintenance technician.

First off,  RMS means root mean square...

RMS voltage measurements are determined by converting an AC signal to DC and applying a mathematical factor to convert the reading to a numerical value. This all takes place within a true RMS meter and you just get to see the true RMS value. Their counterpart would be what is called an averaging multi-meter, which calculates an average value within the circuitry and displays that value for you to read.

Why would you need a true RMS multi-meter?

Because it can provide an accurate reading of pure sine waves as well as any complex waveforms like semi-distorted sine waves, square waves, rapid pulses, noisy signal, and even signals from switching power supplies.

Would a maintenance technician need a true RMS multi-meter?

Not if your job is limited to basic electrical tasks such as checking fuses, verifying the presence of power, testing basic switches and relays, or checking the continuity of wires. But if you go beyond fundemental electrical tests, it may be a better investment.

A true RMS multi-meter would be more often used by a maintenance technician who is exposed to diagnosing elecrical and electronic problems associated with sensors, solid state controls, variable frequency drives, motor controls and industrial motors, power supplies, low voltage systems, circuit boards,and any other equipment that may produce an unusual electrical waveform.

Although it is not a requirement, and many maintenance techs in the field still use a less costly averaging multi-meter, it may prove a better investment in the long run. In the recent past, true RMS multi-meters priced much higher than good quality averaging meters. But this gap in pricing has narrowed considerably making true RMS multi-meters more affordable than they have ever been.

If you can get more accurate readings and faster results to your troubleshooting, the return on investment is there. I personally used common averaging meters like the Fluke 27 Series or the Fluke 73/77 Series over the bulk of my maintenance career, but in hindsight, I probably should have invested in a true RMS meter some time ago.

The more research I have done, the more certain I am that my next multi-meter will be a True RMS Multi-meter.

Does anyone have anything to add?
When in Doubt, Check eBay for Cheap Parts

--- Methodical Troubleshooting is the only troubleshooting! ---
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Re: Do I need a true RMS multi-meter?
« Reply #2 on: October 09, 2015, 03:28:PM »
I used what I thought was a good Fluke meter for many years. I broke down and bought a True RMS meter and after using it for just a few months, I know I'll never go back. I feel better about the readings when working with variable drives. That alone makes it all worth it.

You can get good deals on eBay. I think you'll find the best values there whether you buy a used one or go with new.
Thank You,
Adam from Scranton

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Re: Do I need a true RMS multi-meter?
« Reply #3 on: November 28, 2015, 05:37:AM »
I decided to investigate True RMS meters even more, as a matter of fact I bought one....



Everything looks good and so far it works great. As for fuse testing, checking for incoming power, and other basic use, I don't anticipate seeing any difference from my older Fluke 73. I think it will come in handy when I've used it on a Freq. drive though...



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