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Matt_Colie

Southeast Michigan

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Posted: 09/12/21 07:59am Link  |  Quote  |  Print  |  Notify Moderator

GD,

While that is a cheap version of an Oscilloscope, even with the suggested additional parts to look at the wave shape, you can't use it to do either a true THD (Total Harmonic Distortion) measurement. All you can do is look at it an see if it is pretty.

This came up recently when an acquaintance could not run his new inverter microwave from the CCV portable generator. We got things together and found that his machine produced a really big 3rd and fifth order that fooled the power supply of the microwave.

The microwave ran fine with the power from my 48yo Onan even with the distortion cause be cylinders firing.

Matt


Matt & Mary Colie
A sailor, his bride and their black dog (one is waiting for us at the bridge) going to see some dry places that have Geocaches in a coach made the year we married.


wa8yxm

Davison Michigan (East of Flint)

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Posted: 09/12/21 08:03am Link  |  Quote  |  Print  |  Notify Moderator

2112 wrote:

Gdetrailer wrote:


$50 says you are wrong.
Close. This scope has 50V pk input. You would either need a 10X probe or a step down transformer such as THIS to protect the input. That will cost you another $10. I use the transformer for isolation as well. I just wanted readers to be aware another component would be required.

120V RMS is about 170V pk so you would expect to measure 17V pk using this transformer. 60Hz would be 16.66 mS pk to pk.


I have one of those... A good scope will show you waveform. Not sure yet how good that one is.. It was "Good enough" for my specific need but not sure how good it would be for your need.

A Kill-A-Watt is about 1,000 worth of meters in a 20-30 dollar box. ONE of the meters is frequency.

Also some multi-meters (like my Crafstman clamp on AC/DC job) do frequency.


Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times


Gdetrailer

PA

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Joined: 01/05/2007

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Posted: 09/12/21 12:11pm Link  |  Quote  |  Print  |  Notify Moderator

Matt_Colie wrote:

GD,

While that is a cheap version of an Oscilloscope, even with the suggested additional parts to look at the wave shape, you can't use it to do either a true THD (Total Harmonic Distortion) measurement. All you can do is look at it an see if it is pretty.

This came up recently when an acquaintance could not run his new inverter microwave from the CCV portable generator. We got things together and found that his machine produced a really big 3rd and fifth order that fooled the power supply of the microwave.

The microwave ran fine with the power from my 48yo Onan even with the distortion cause be cylinders firing.

Matt


When looking at the waveform of a sinewave you do not "need" to have a THD readout.

You simply zoom in and VIEW the part of the waveform and you will easily see the distortion. That after all is what millions of "Techs" have done since the first Oscilloscope was born.

If you can't read a 60HZ waveform from a "O" scope, you are not a real Tech.. Now if you were trying to read say the distortion of a amplifier at 20Kz and higher it does get a bit more difficult to do but not impossible..

Folks now days are so spoiled.

I have repaired a lot of audio and video equipment over the yrs with just a DVM and "O" scope and no schematics.

60Hz is a piece of cake.

Gdetrailer

PA

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Joined: 01/05/2007

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Posted: 09/12/21 12:19pm Link  |  Quote  |  Print  |  Notify Moderator

2112 wrote:

Gdetrailer wrote:


$50 says you are wrong.
Close. This scope has 50V pk input. You would either need a 10X probe or a step down transformer such as THIS to protect the input. That will cost you another $10. I use the transformer for isolation as well. I just wanted readers to be aware another component would be required.

120V RMS is about 170V pk so you would expect to measure 17V pk using this transformer. 60Hz would be 16.66 mS pk to pk.


That was a quick "sample" of what is available now days, there ARE other portable versions out there that can easily handle higher input voltages.. You simply have to do some looking.

There also versions that have no readout, instead they can connect to a laptop or even a Tablet. and have many advanced features of storing and playing back the waveform.

And, in reality, with 60hz, you do not need a large bandwidth on the scope, most any scope will work even as low as 100 Khz will show noise spikes and if the waveform is badly distorted.

Gdetrailer

PA

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Posted: 09/12/21 12:28pm Link  |  Quote  |  Print  |  Notify Moderator

wa8yxm wrote:

2112 wrote:

Gdetrailer wrote:


$50 says you are wrong.
Close. This scope has 50V pk input. You would either need a 10X probe or a step down transformer such as THIS to protect the input. That will cost you another $10. I use the transformer for isolation as well. I just wanted readers to be aware another component would be required.

120V RMS is about 170V pk so you would expect to measure 17V pk using this transformer. 60Hz would be 16.66 mS pk to pk.


I have one of those... A good scope will show you waveform. Not sure yet how good that one is.. It was "Good enough" for my specific need but not sure how good it would be for your need.

A Kill-A-Watt is about 1,000 worth of meters in a 20-30 dollar box. ONE of the meters is frequency.

Also some multi-meters (like my Crafstman clamp on AC/DC job) do frequency.


Kill-O-watt is a nice device, but it doesn't give or show distortion, it will also have a small delay in frequency reading and voltage Kill-O-watt uses a "sampling" over time method and averages the samples to come up with a result with periodic updates.

"O" scope has zero delay, you will see the waveform change with distortion, voltage and frequency change all real time..

Not working with rocket science here, this is very basic 60HZ AC Sinewave theory. Distortion of the sinewave waveform means you have distortion which can be caused by AVR, gen head speed or in this case a gen inverter failure..

But my point was you do not need a stand alone $1,000+ THD meter to see if the gen output has distortion, noise, wrong voltage or is off frequency.

2112

Texas

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Joined: 07/16/2011

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Posted: 09/12/21 03:25pm Link  |  Quote  |  Print  |  Notify Moderator

Gdetrailer wrote:

2112 wrote:

Gdetrailer wrote:


$50 says you are wrong.
Close. This scope has 50V pk input. You would either need a 10X probe or a step down transformer.....
That was a quick "sample" of what is available now days, there ARE other portable versions out there that can easily handle higher input voltages.. You simply have to do some looking .......
Fair enough, but be aware the person asking the question doesn't know what he's looking for.

I use This DSO188. 1Mhz, 12 bit ADC, USB rechargeable. It has an auto feature. You don't have to know anything about setting up a scope. Just connect it and press AUTO. It samples the signal and makes the proper adjustments to properly display the signal. My Siglent has this same feature and I paid over 10X $ for that scope.

A strange thing is when I bought my DSO188 Amazon had mostly negative reviews on it. Mostly from people that didn't understand how this little thing worked and had unrealistic expectations. Now most of the Amazon listings doesn't have any reviews. It's like they pressed a reset button on these.


2011 Ford F-150 EcoBoost SuperCab Max Tow, 2084# Payload, 11,300# Tow,
Timbrens, PullRite SuperGlide 2700 15K
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