Frequency and Dutycycle Measurement in Multimeters

Thread Starter

SajyTvm

Joined Jan 4, 2022
1
What is the principle of measurement of Dutycycle in a Digital Handheld multimeter?
I have noticed, in some multimeters, the duty cycle measurement is very sensitive to the input signal amplitude. The reading go mad if the signal amplitude is more than say 4V (it shows 99%, where the actual duty cycle is 30%). It was a brand new meter purchased through Amazon. I tried two nos - same result.
Someone, please suggest a method to solve this problem.
 

DickCappels

Joined Aug 21, 2008
8,710
If I were to make a cheap duty cycle to voltage converter I would pass the input signal through an open drain comparator (or even an NPN transistor) to make it nice and "rectangular" followed with a zener diode or something more stable and precise to limit the pulse amplitude then just pass it through a low pass filter and you are done. I think it I were to make it for benchtop measurements I would protect it from excess voltage -wouldn't you?

Duty cycle is proportional to the time average of (clipping level x duty cycle). What's in your particular meter I cannot guess, but somebody will probably come along who does know.
 

MrSalts

Joined Apr 2, 2020
1,762
It's a sad day when you cannot measure frequency and duty cycle of line voltage to check for harmonics or if you cannot cancel out higher frequency PWM in a motor drive to find the base frequency. Even sadder if you have to bring the VFD to your bench to test as @DickCappels suggested.

@SajyTvm , it's time to invest in a meter, not spend on a meter. An investment helps you make more money, an expensive is simply spending money. A Fluke 87V seems expensive until you have to buy a second and their device to get your work done in addition to the discount meter you found on Amazon. Even more expensive is building unsafe duty cycle to voltage converters or bringing your motor assembly to a bench for testing. Buy the right handheld meter.

https://www.fluke.com/en-us/learn/blog/digital-multimeters/how-to-measure-duty-cycle
 

MB107

Joined Jul 24, 2016
290
I use an Innova Equus 3140 for my automotive work. I used the duty cycle setting for the first time setting up the fuel system on my 1988 Mercedes 560SL, several months ago. Since I was the first time doing it I verified the output with my O scope and it was perfect. If I recall it was a 5V signal. But this is an automotive meter.
 

KeithWalker

Joined Jul 10, 2017
2,354
What is the principle of measurement of Dutycycle in a Digital Handheld multimeter?
I have noticed, in some multimeters, the duty cycle measurement is very sensitive to the input signal amplitude. The reading go mad if the signal amplitude is more than say 4V (it shows 99%, where the actual duty cycle is 30%). It was a brand new meter purchased through Amazon. I tried two nos - same result.
Someone, please suggest a method to solve this problem.
Did you check the operators manual and read the specifications for making those measurements? I doubt it! I am pretty sure that you will find that the meter is working as it should.
If all else fails, read the @#X&$% manual!
 

tindel

Joined Sep 16, 2012
876
What is the principle of measurement of Dutycycle in a Digital Handheld multimeter?
I have noticed, in some multimeters, the duty cycle measurement is very sensitive to the input signal amplitude. The reading go mad if the signal amplitude is more than say 4V (it shows 99%, where the actual duty cycle is 30%). It was a brand new meter purchased through Amazon. I tried two nos - same result.
Someone, please suggest a method to solve this problem.
The most common way to read duty cycle of a PWM signal is to use the voltage mode and measure the voltage at the switch node. Most of the time the switch node is much faster than the bandwidth of the meter. dutycycle ~= measured voltage / input voltage. That is, a measurement of 1.65V will be 50% of 3.3V, and hence a duty cycle of 50%. Of course, this varies a lot based on what you're measuring and what the references are, etc. We'd need more information to advise on specifics... what are you measuring, what meter you have, schematics, etc. to advise fully.
 
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