Time track with Rigol DSO

Correction - I mean plot the cylce-by-cycle pulse width with respect to time

Can you mention a few models with that feature?

There's an article on e.g. EDN about it, helpfully in EDN fashion they offer no insight into what models/price range of scopes offer this feature or even what scope the author is using for the examples:

"An oscilloscope's track and trend features add two measurement-based math functions that you can use to gain insight into measurements."

So whatever oscilloscope or class of DSO this guy uses that he assumes everyone has has this feature I guess, sorry I can't be more specific.

I did a little more research and it looks like plotting tracks of the measurement parameters may be possible on Rigol's lower-end scopes using their Scopeview software that connects to them which is also reported to be clunky and a pain to set up unnnnngh

Add an outboard lowpass filter to see duty cycle, or some sort of ramp thing to see pulse width.

Or suck out waveforms and process externally.

RMS is usually linear on duty cycle.

My Rigols will measure most any thing, but with numerical display, not a trace.

I'm having some difficulty setting it up to measure somewhat small changes in pulse-width, tenths of a percent which the numerical display measurements seem in theory to have enough precision to do.

If I set it to normal-acquire though looks to be some noise causing the pulse width readout to jump around randomly in the tenths of % place swamping the measurement. If I set it to time-average the waveform with equi-time sampling then it looks like I'm losing precision, the width measurement parameter seems to only step in increments of 1% or greater when it's averaging.

Being able to plot the pulse width wrt time on a cycle-by-cycle basis would help a lot

The PWM frequency is 500kHz

That's no good, then. I think you need to get yourself a Tektronix.

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Period is 2 us. 0.1% of that is 2 ns.

Are you sure the PWM isn't jittering that much?

One trick with the Rigols (and many other digital scopes) is to always trigger off a vertical channel, not external trigger. External will have a full sample-period of jitter, but they do some Shannon thing to reduce trigger jitter from a vertical input. I've measured 30 ps RMS on a modest Rigol.

I got rid of my Tek, for a much better Rigol.

Can your Tek scope display duty cycle vs time? To 0.1%?

What does a non-numerical measurement mean anyhow?

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The RMS value of a rectangular pulse wave is proportional to the *SQUARE ROOT* of the duty cycle.

Connects with the I squared R rule.

Power in a resistor varies linearly with duty cycle.

.... Phil

I was able to figure out what I needed to know by zooming in on the pulse and using the infinite persistence so I could see better what the extremes of the PWM were as the circuit outputting the PWM did its things, that's really all I needed to know. I can then read off from the timebase and do the math to get what RMS voltage deviation we're looking at.

Saving screencap .bmps to USB stick is also nice feature, whew 21st century stuff! however they mounted the USB port on the front upside-down. :|

What generates the PWM?

I like to put a post-it on the screen and take a pic with a real camera. Otherwise I have a bunch of files like TEK0001 and TEK0002, not unique over time, and I have to keep notes off to the side somewhere about which is which.

One could make a gated current source into cap and then use the 'scope trigger level to only trigger on pulses of a given length. (time to amplitude converter)

George H.

Is that the input clock waveform? What'sNC7SV74_1.JPG, etc.?

That's the Q output of the flop, when the flop is cleared and then clocked high.

The speed amazed me.

The pickoff resistor may have a bit of shunt capacitance, but it's still really fast, for a 16 cent flipflop.

Oh, don't be constantly obnoxious. You'll turn into a sad old prune like Sloman.

I meant power. PWM is great for things like temperature controllers with resistive heaters, because it keeps the loop linear.

Thanks John, I saved the images. Should come in useful!

There is a thing that I call actual or critical setup time, which is the actual time between D and CLK where the output transition happens, or gets flakey or metastable. That can be positive or negative for various parts. It is seldom specified. The data sheet required setup/hold times presumably straddle that critical setup time.

I've seen parts that had a combination of prop delay and critical setup time such that making a shift register is unreliable.

XOR as phase comparator