# Duty Cycle test on DMM?

Discussion in 'Electronic Basics' started by Lumpy, Aug 3, 2005.

1. ### LumpyGuest

My DMM has a scale to measure
Duty Cycle %.

Exactly what is that measuring?

L

2. ### DBLEXPOSUREGuest

I suppose there is more than one way to say it. To me Duty Cycle is the
percentage of time the circuit is on vs. off in one period of the cycle.

Usually a term used when talking of square waves. Lets say the period is
one second for the entire cycle and the circuit is on for .5 sec. Then this
is a 50% duty cycle. Now say it is on for .25 sec. and off for. 75sec.
This is a 25% duty cycle...

3. ### John FieldsGuest

---
Sorry, but that's wrong. duty cycle is the ratio of ON time of a
periodic waveform to the period of one complete cycle of the
waveform, expressed as a percentage.

for instance, for:

_____ _____
SIG_____| |____________________| |_____

5-->| |<--- ton
20-->| |<-- tcy

100 ton 100 * 5
D = --------- % = --------- = 25% (1)
tcy 20

If it was, as you said,

"the percentage of time the circuit is on vs. off in one period of
the cycle", then we'd be looking at:

_____ _____
SIG_____| |____________________| |_____

5-->| |<--- ton
15->| |<-- toff

100 ton 100 * 5
D = --------- % = --------- = 33.3% (2)
toff 15

Which is wrong.
----

4. ### LumpyGuest

Ok. What, in practical terms, might someone
want to measure to know the duty cycle % ?

L

5. ### chuckGuest

What field are you in?

Auto mechanics often need to measure the duty cycle of fuel injectors.

6. ### DBLEXPOSUREGuest

Well, hello John!

I do see your point, the "vs. off" should be removed from the first
definition. Hopefully the second paragraph clarified my point.

To the OP, Duty cycle adjustments are made in many electronic applications.
In my experience I have had to tweak duty cycle when performing servo and
timing circuit alignments. A common application might be your VCR.
However, I have never done this with a DMM. Typically an O'scope is used
but I suppose there are applications where one can use a DMM.

7. ### LumpyGuest

I'm a musician.

L

8. ### Michael BlackGuest

Well in that case, old analog synthesizers counted on variable duty
cycle in order to get the right "tone", but they were only vaguely
calibrated when it came to most functions. Actually, calibration is
the wrong word, it's more like a scale so you could reset the controls
at a later time. Most likely you'd be listening, and you had the
right duty cycle when it sounded like you wanted ( in other words,
you weren't concerned with how much duty cycle a violing had, but
you'd adjust duty cycle until you had the same level of harmonic
content out of the oscillator, based on a mental comparison with
a real violin). I suppose if you actually needes something specific,
you'd pull out an oscilliscope and look at the waveform.

Michael

9. ### LumpyGuest

[what's a duty cycle measurement for]

Thanks! That's an analogy that I can understand.

I played an Arp 2 voice analog synth in the 70's.
My understanding (my guess) was that as we altered
the shape of the waveform, we made the wave look
more sawtooth or squarewave, less sine.

If that's a correct understanding, then how does
duty cycle relate to those saw or square waves?

Or in the specific case of this DMM of mine,
does the ability to measure duty cycles mean that
I could measure and then repeat the settings on
the hypothetical analog synth?

Thanks everybody for the education.

Lumpy

10. ### DBLEXPOSUREGuest

On second thought, if I read your notation correctly, I don't think you can
substitute "divided by" for "vs.". You can say Ali vs. Frazier and it
means, opposed by (my meaning was, "as opposed to") you can't say Ali
divided by Frazier. That would not make sense.

To re phrase, Percentage of time the circuit is on as opposed to off in one
period.

At any rate, probably still more word than needed and not very eloquently
put, hence the second paragraph.

New topic

Do you have an understanding of Quantum Entanglement?