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DVM meters with Square waveform mode

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KrisBlueNZ

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User willwatts has started five threads within the past few hours. I am closing all of them temporarily.
 

willwatts

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Steve check it out again, it's not an oscope, its a DVM meter with a function mode with a square waveform output at only 50hz
It is right next to the Diode checker mode, it has a square waveform symbol
It only outputs at 50hz at 2 volts peak to peak

My question is the use of this mode? what can you test at 50hz? what circuits can I test using a 50hz square waveform

I heard that one of its use is to test line power transformers, but why would you test a transformer at 50hz? plus if you apply 50hz squarewaveform to the primary how do you measure the secondary of the transformer?

There is other brands of meters like this that output a square waveform at 30hz, but for what kinds of test? to test what at 30hz?

Sinometer UT30D Pocket-size Digital Multimeter with Square Wave Generator (50Hz)
http://www.amazon.com/Sinometer-UT30D-Pocket-size-Multimeter-Generator/dp/B005TLXNPO
 

hevans1944

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That's a handheld oscilloscope, not a DVM.

Can you be more precise in your question? Are you talking about a calibration output?
The link points me to a cheap imported 3 1/2 digit multimeter. Maybe the "unique build in square wave generator" could be used to stimulate a circuit? No information on what the peak-to-peak amplitude or current sourcing capability is, but for sixteen bucks (plus shipping and handling) I bet it ain't much. Probably a left-over from internal clock circuitry.
 
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(*steve*)

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Weird, the first time I followed Danny's now broken link it gave me a list of $US2000+ hand held oscilloscopes.

Now I know what you're talking about, the answer is simple.

It is a mostly useless feature added to differentiate the multimeter from others. It's pretty much the same as the transistor tester almost nobody will use it, but it seems like a nice feature to have.

It's also probably cheaper and easier than a frequency or counter option and maybe people will think that's what it is.
 

willwatts

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No, it's ment for testing or injecting into an input or circuit
1.) To test transformers, how can you?
2.) PWM motors , it's ment for PWM circuits but how so?
3.) Adjustable voltage control circuits?
4.) Synchronic clock?
5.) Calibrate flow meter displays?
6.) Tachometers
7.) Frequency input devices

Look at PAGE#31 of the BK meter it explains it B&K Precision Corp.'sModel 2890A
https://bkpmedia.s3.amazonaws.com/downloads/manuals/en-us/2890A_manual.pdf
 

(*steve*)

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Well there's your answer. Congratulations.

Are we finished now?
 

willwatts

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I don't get how they use it to measure , test, check for each one
can you give an example for each one in the list how it is used and tested?
 

willwatts

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1.) To test transformers, how can you?
2.) PWM motors , it's ment for PWM circuits but how so?
3.) Adjustable voltage control circuits?
4.) Synchronic clock?
5.) Calibrate flow meter displays?
6.) Tachometers
7.) Frequency input devices

How would it be used and i need examples of how to use it to test, check, measure for these circuits
 

(*steve*)

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Pick one of those and think about it. How do you think your very cheap (but clearly as good as a BK Precision) multimeter could be used with it?
 

willwatts

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1.) I put a 50hz square waveform on the primary of the transformer and use an oscilloscope on the secondary?
why is 50hz a good test frequency for transformers?

2.) 50hz to test a PWM circuit ? to see if the PWM circuit is outputting a waveform on the oscilloscope?

3.) not sure what an adjustable voltage control circuit is or does or what is it used for

4.) Synchronic clock, i have no idea what this is or used for

5.) Calibrating a flow meter display using a square waveform out?

6.) Testing a Tachometer using a 50hz square waveform, i have no idea how this is done
 

(*steve*)

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1.) I put a 50hz square waveform on the primary of the transformer and use an oscilloscope on the secondary?
why is 50hz a good test frequency for transformers?

I'll assume this is the one you chose.

Why do you think 50Hz might be a good frequency?

Would it be equally good for all transformers?

What output would you expect to see on the secondary?
 

willwatts

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Why do you think 50Hz might be a good frequency?

I have no idea why, why do you think it's a good frequency?
I would think 60hz because it's line frequency ,
but 50hz might work for testing line power transformers

The other DVM meters are at 30hz, which I have no idea what to test at 30hz

The BK meter is the only one that is a variable frequency and duty cycle square waveform output

Would it be equally good for all transformers?

No, just for 60hz line power transformers
not for testing audio transformers or output transformers
Maybe for step up and down transformers

What output would you expect to see on the secondary?

The same waveform on the primary to the secondary, same voltage and line frequency
 

hevans1944

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Just because some instrument has a "feature" doesn't mean that "feature" is useful. If I want a variable frequency, variable duty cycle waveform to test something I also want to (1) be able to select the waveform (2) adjust the frequency and (3) set the duty cycle (or pulse width)... preferably with knobs not buttons. But that's just me. A dedicated function generator, not a multi-meter, is what I would use.

Transformers don't pass square waves very well, so I fail to see how exciting their primary with a square wave would provide much useful information measured at the secondary. YMMV.
 

willwatts

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Someone told me the 50hz output is for testing cars fuel injectors pwm circuits. I'm not sure why fuel injectors use 50hz as an input to a pwm circuit
 

KrisBlueNZ

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Why do you think 50Hz might be a good frequency?
I have no idea why, why do you think it's a good frequency?
I would think 60hz because it's line frequency ,
but 50hz might work for testing line power transformers
Mains / line frequency is 50 Hz in many places outside the U.S. including the UK, Europe and Oceania. In any case 50 Hz is not too far from 60 Hz. So that might be the right answer - that the meter might be slightly useful for testing mains (line) transformers.
Would it be equally good for all transformers?
No, just for 60hz line power transformers
not for testing audio transformers or output transformers
Maybe for step up and down transformers
Good answer!
What output would you expect to see on the secondary?
The same waveform on the primary to the secondary, same voltage and line frequency
Different voltage, unless the transformer has a 1:1 turns ratio.
Same frequency, yes.
The transformer will change the waveform too. A transformer that's designed to operate at 50/60 Hz is designed to pass a sinewave, not a squarewave. A squarewave has lots of harmonics, which (by definition) are at higher frequencies than the fundamental, and a mains (line) transformer will not reproduce these very well.

If you have one of these meters, and an oscilloscope, you can do an experiment to see how the transformer modifies the squarewave.
 

willwatts

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Different voltage, unless the transformer has a 1:1 turns ratio.
Same frequency, yes.
The transformer will change the waveform too. A transformer that's designed to operate at 50/60 Hz is designed to pass a sinewave, not a squarewave. A squarewave has lots of harmonics, which (by definition) are at higher frequencies than the fundamental, and a mains (line) transformer will not reproduce these very well.


The square waveform output of the DVM meters is only 2volt p/p so i don't think a line transformer would do anything

Yes it passes a sine waveform at 120VAC

But a square wave at 2 volts p/p it might pass because the voltage is so low?

This goes back to maybe it's ment for a cars fuel injection or timing PWM circuits for cars
 
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