# Noob frequency question



## Rotzy (Dec 12, 2017)

Hello everyone. I'm a new member with a frequency testing question.

I recently purchased a duramax XP10000EH generator and have been doing some initial testing. I am having trouble getting an accurate frequency reading with my Uni-T UT204 multimeter. I have been using the "Hz / Duty%" setting and have tested across the hot and neutral terminals on the 120V generator outlet/plug. I've also tried testing the end of the extension cord that is powering an electric heater as a test load. My readings fluctuate wildly from 300-500Hz under no load and 160-190Hz under load. I assume I'm getting some sort of feedback that is preventing me from getting an accurate reading?

Can anyone tell me what I'm doing wrong or exactly what to do to get a proper frequency test?

Thank you.


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## motormonkey (Jul 10, 2016)

You may well have already done these things, but gotta cover the bases.

Are you using the supplied leads in the "Hz/Duty%/V/Diode/Ohms" and "COM" jacks?

Are the leads okay? (Verify this by doing a simple continuity or resistance check.)

Do you have the selector in the "Hz/Duty%" positon?

Do you have "Hz" selected with the function button?

Is the battery okay? (Might not hurt to try another battery.)

Have you tried measuring the frequency of the power line in your home? (Harmonics and noise from a generator can drive a lot of electronics crazy.)

Test all the functions of the meter out on known good sources.

I have seen situations where large power transformers, radio transmitters, radar antennas, etc. nearby can drive the electronics crazy. Any of that around?

Aside from that, there's not a lot more to check. The meter is a fairly inexpensive one. Maybe it's defective.


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## Rotzy (Dec 12, 2017)

motormonkey said:


> You may well have already done these things, but gotta cover the bases.
> 
> Are you using the supplied leads in the "Hz/Duty%/V/Diode/Ohms" and "COM" jacks?
> 
> ...


Hi and thanks for the response.

Yes to all of your questions, except for the last one: No known sources of radio frequency interference. I should have mentioned that I tested the unit on the power line in my home a number of times and get rock steady frequency readings between 59.99 - 60.01.

Are you suggesting that "noise" from the generator can be causing the bonkers readings that I'm seeing? If so, would a higher quality meter be less susceptible to this? Do you think a basic Kill-A-Watt meter would work better?

Here'a a short video of the readings with a 1500W load.


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## motormonkey (Jul 10, 2016)

The meter functions normally when hooked to commercial power, but goes bonkers when hooked to your generator output. That pretty much nails it that the generator is producing a bit of a "noisy" output (non-sinewave components, bad crest factor, etc.) That's not really that abnormal. Lots of generators do it. Most electronics can deal with it, but sometimes this happens. Your meter is clearly not dealing well with it. Some other meter might do better but you never know. If you can, test different meters and see, preferably without buying them until you know.


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## exmar (Jun 29, 2015)

Dumb Question, why are you testing for Frequency? Are you trying to troubleshoot something or just spooked because you didn't purchase an inverter unit? Came back to finish, I've had regular gensets for outage use for a long time and nothing in my house has ever been harmed. I'd guess we have as many smart tv's, computers, etc. as anyone else.


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## Rotzy (Dec 12, 2017)

I'm simply trying to test output and adjust engine speed as needed before I feed this thing into my panel.


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## Rotzy (Dec 12, 2017)

Somehow my reply to motormonkey's first post did not post.

The answer is yes to all of your questions except for the last one. As to your last question, I don't believe there is any high powered interference close by. I should have mentioned in my original post that multiple times during testing, I plugging the meter into an outlet in my home and the readings are rock steady at 59.99hz - 60.01hz.


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## KRE (Nov 29, 2011)

Rotzy said:


> Somehow my reply to motormonkey's first post did not post.
> 
> The answer is yes to all of your questions except for the last one. As to your last question, I don't believe there is any high powered interference close by. I should have mentioned in my original post that multiple times during testing, I plugging the meter into an outlet in my home and the readings are rock steady at 59.99hz - 60.01hz.


Your doing the right thing by testing before hooking it up.
If the readings are that bad I'd look at it with an O-Scope before I hooked it to anything. If no O-Scope an you want to chance it, simple fix for testing only, small machine tool transformer (or two hook in series) with load applied, should cancel out most of the glitch crossovers to allow correct reading. The info says your meter is true RMS if that is in fact true, I'd make sure I O-Scope'd it first. If it is as bad as I suspect I'd return it, an get something else. Induced harmonics are very hard on motors an many delicate power supplies.


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## Rotzy (Dec 12, 2017)

Thanks for the continued replies.

I'm a little hesitant to buy an oscilloscope just for this purpose. I don't foresee myself having any use for it after initial generator testing and the learning curve looks a bit steep. I've looked at a few inexpensive ones on Amazon, but the reviews are all over the board. If an inexpensive unit will give me the results I need, then I'm open to the purchase but I don't have the time to really learn how to use the oscilloscope if it's not fairly simple to operate. Any product suggestions?

I intend to use the generator for emergency backup power. I need it to run our two forced hot air furnaces, high efficiency gas hot water heater, two refrigerators and other miscellaneous lights and household appliances. How bad can high THD units hurt these devices?


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## KRE (Nov 29, 2011)

If you don't want to buy an O-Scope just use two transformers with a small load an use you meter.

Above normal THD can substantially shorten the normal life cycle of any item. Remember caps an resistors live long on clean power, not so much on trashy electrical voltage. One reason I do not like any printed circuit boards in my last line of electrical defense.


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## Rotzy (Dec 12, 2017)

Sorry for my ignorance, but when you say a small transformer, what exactly do you have in mind? I'm a visual learner, so a link to a product would be most appreciated :tango_face_grin:

I did order an inexpensive oscilloscope. If it works, I guess we'll see how bad things look this weekend. I still plan to try a kill-a-watt meter and/or another multimeter to see if I can get a frequency reading. The oscilloscope I ordered only reads frequency in KHz, so accuracy is probably not all that great. Thankfully, the store has a good return policy.

Do you think that getting away from the generator would have any effect on the ability of my Uni-T meter to read frequency? What I mean is if I were to run a high quality extension cord away from the generator and plug a load into it, do you think a reading from there would have any less interference?


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## motormonkey (Jul 10, 2016)

You might try a power line conditioner. They usually use inductors and capacitors in filter networks to attenuate higher frequency noise and harmonics. Inexpensive consumer types can be had for as little as $50 or so, and quality, performance, and price go up from there. You get what you pay for.


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## KRE (Nov 29, 2011)

Rotzy said:


> Sorry for my ignorance, but when you say a small transformer, what exactly do you have in mind? I'm a visual learner, so a link to a product would be most appreciated :tango_face_grin:
> 
> I did order an inexpensive oscilloscope. If it works, I guess we'll see how bad things look this weekend. I still plan to try a kill-a-watt meter and/or another multimeter to see if I can get a frequency reading. The oscilloscope I ordered only reads frequency in KHz, so accuracy is probably not all that great. Thankfully, the store has a good return policy.
> 
> Do you think that getting away from the generator would have any effect on the ability of my Uni-T meter to read frequency? What I mean is if I were to run a high quality extension cord away from the generator and plug a load into it, do you think a reading from there would have any less interference?


Something like a small machine tool transformer, which can be had from e-bay very cheap.
The ext cord will only work if your meter is not shielded internally, but remember the longer the wire the more inductance you add as well. So with that in mind you might wrap the cord around a heavy piece of steel which will make a choke, an try to read the freq again.
The reading speed of the O-Scope is the max it will read/sample, it should read down to 1 hertz w/o issue, as well as give you the top an bottom of the sine-wave peaks to scale voltage with. After you get it look at your utility power to get an idea of how smooth the wave form should look, but remember your looking at a wave form that is going thru 10-30 transformers before it reaches you. That said the wave form directly from the gen set will have wave peaks closer together which is normal when not going thru all the transformers. Any glitch in the wave-form will produce a very visible sideways track if it's speed is below the max thresh hold of your O-Scope, which should be w/o issue.


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## Rotzy (Dec 12, 2017)

Well, I got home and picked up a Kill-A-Watt meter. It was able to produce a frequency reading. The generator was running at about 63Hz with a 50% load. I was able to scale it back to a little over 60 under load, but will let it break in a few more hours before doing a final adjustment. The oscilloscope also came and works, although screen detail is not the best. Power company readings look pretty nice. The generator graph is not as smooth, but doesn't look at bad as I thought. Although, that could just be the bad resolution of the oscilloscope!


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