Fastest trigger for Rigol 1054Z

[rpetitho]

I was trying to measure the frequency of a 32.768KHz clock thru my 1054z. I fed the clock out to channel 1 and triggered off it. Looked good on the scope, 5v peak to peak at around 32.768KHz. I fed the trigger out to my frequency counter but could not get that dialed into the 32.768KHz. The trigger out frequency shifted with the sample size (which made sense), so I adjusted the timebase in an effort to make the scope trigger on every edge. It seemed to miss some edges because the most I could get out of the frequency counter was around 28KHz when processed thru the scope. I also sent the clock out directly to my frequency counter and that showed 32.768KHz. Am I missing something? Is there a max trigger speed for the 1054z? Does anyone else have issues with the 1054z trigger reliability? Trigger Hold off was set to 16ns.

-Bob

[Fungus]

The maximum waveforms/sec is 30,000 in dots mode.

Presumably it's slightly less in other modes.

[Gandalf_Sr]

This sort of doesn't make sense to me. The trigger out only tells you how often the scope is triggering but you can't assume that the frequency on the trigger out of any O'scope will tell you the frequency of the waveform input.  If I were to repeat the test with a 1 MHz input, do you assume that the trigger out will show 1 MHz on a frequency counter?  It won't, not even on a $5,000 o'scope.

[2N3055]

Every scope, digital and analog,  will have retrigger time. Digital scopes will have slower retrigger time because they have to process captured data before proceeding with new capture.

What you're trying to do won't work well on pretty much any digital scope. It might work better on some (Keysight Megazoom based scopes that claim high wfm/s numbers like 3000/4000/6000 series) but even that only on lowish frequencies.

Also, that trig out frequency might not be very stable (it will have jitter) because in most digital scopes nowadays trigger is not analog comparator connected to sweep circuit, but a digital pattern engine working off a digitized data from A/D converter (hence digital trigger). So not only that it will be quantized to sampling clock of the scope, but it will have some delay to output and that one might not even be constant, depending of what is scope doing or what trigger you are using, so it will vary and you end up with jitter on trigger out.

What you are trying to measure with digital scope and counter is not a proper way to measure frequency .

Some analog scopes had outputs from their vertical amps so you could connect other equipment (like counter in your case) using scope as a sort of preamp (that was cool, I miss that). Also, their trigger circuit was analog comparator connected to sweep circuit, and by virtue of that completely synchronous to input signal.  So you could measure frequency by measuring trig out, but even then you could do that for maybe 100s of Khz(depending on scope). It would work for your specific case, but not good universal practice even then.

Today's digital scopes have none of that.

That is a crux of many discussions here about scopes. New digital scopes are not only digital.  They are different and should be used differently that analog scopes.
This is one example of what digital scopes cannot do.  On the other hand , my Keysight scope has same order of magnitude stability of TCXO compared to my TF930 counter so most of the time I just use counter built in to the scope to measure frequencies. More than enough for most of the work because it is better than any normal crystal oscillators (that are order of 10s of ppm) and anything that isn't high end TCXO, OCXO, rubidium, cesium or GPSDO frequency source.

If I need more precision that 8 digits, (or like you trying to check and/or calibrate watch crystals and need reciprocal counting for that), then I connect counter directly and pay more attention...
On clock chips, and Atmel AVR processors I enable clock out and measure that. It gives nice buffered strong signal that is easy to measure directly with counter.

[Gandalf_Sr]

Great summary by 2N3055.

I did some tests on my MSO5074 with a frequency counter connected to the trigger out but what I see is nowhere near the same as the 32,768 Hz square wave I feed into the triggering channel; the counter reading also varied as I changed timebase.

It's useful to think about what's going on; samples per second are different to triggers per second.  Assume the scope hasn't captured anything yet and then the trigger threshold is passed, a digital scope now starts capturing samples into memory until the memory buffer is full (I believe that, by default, the DS1054Z automatically sets the memory buffer size to be however many samples will fit on the screen for the selected timebase) so the scope will not 'rearm' the trigger until a screen full of samples has been captured so it makes sense that, as you make the screen contain more samples, the triggering will be less frequent.

For accuracy, I have a Trimble GPSDO which has a 10 MHz output that I can feed into any of my scopes or counters to get crazy accurate frequency (less than 100 ppt - parts per trillion).  It's reassuring that my Rigol DG4062 counter reads 10.000000 MHz when I feed the 10 MHz ref signal in from my GPSDO to its frequency counter input (no I'm not feeding the GPSDO ref frequency into the Ext freq in connector).

[Fungus]

Yep, this is NOT an analog comparator that echos its output to the connector on the back. There's software in the loop.

[StillTrying]

Does the trigger out need a pull up resistor.

[2N3055]

Does the trigger out need a pull up resistor.

No.

[rpetitho]

Thanks all, good info above. It was the test circuit from this datasheet (http://www.conwin.com/datasheets/cx/cx205.pdf) that sent me down the path of using the scope, but I guess the digital scope is not the tool for the job. Anyways I got the answer I needed by using my frequency counter alone. Confirmed when it matched with the scope's counter display.

-Bob

[ebastler]

Does the trigger out need a pull up resistor.

To pull up its frequency? 

[David Hess]

Rigol calls it a "trigger output" but it really is not.  It is more like a "gate output" on an analog oscilloscope which is active during the sweep and is related to the unblanking signal.

Some analog scopes had outputs from their vertical amps so you could connect other equipment (like counter in your case) using scope as a sort of preamp (that was cool, I miss that). Also, their trigger circuit was analog comparator connected to sweep circuit, and by virtue of that completely synchronous to input signal.  So you could measure frequency by measuring trig out, but even then you could do that for maybe 100s of Khz(depending on scope). It would work for your specific case, but not good universal practice even then.

That is the common way with an analog oscilloscope.

Some analog oscilloscopes support a real trigger output although the examples I can think of are tied to a counter/timer module like the 7D15 which can be used as a trigger and operates more like a trigger recognizer.  The reason for this capability is that the 7D15 is a universal counter/timer with oscilloscope like trigger capability which can be used to trigger on multiple levels of a waveform to measure things like slew rate or rise time and some way is needed to display where the triggers are actually occurring.

[2N3055]

Rigol calls it a "trigger output" but it really is not.  It is more like a "gate output" on an analog oscilloscope which is active during the sweep and is related to the unblanking signal.

On DS1000Z Rigol calls it "Trigger Out and Pass/Fail", and is multi-function 50 Ohm output. It is configurable in software. On DS4000 you can use it to output cal signal with pretty fast edges (500 ps range)..

Everybody in digital scope land calls it somewhat different (Aux Out usually), and it works mostly the same nowadays with everybody, with some differences.. That are big enough to bite you back sometimes..

Some has option (like Keysight MSOX/DSOX3000T ) to output either "TRIGGER" which is, like you said, sweep indicator, and if you set it to output "TRIGGER SOURCE" than it will output pulse any time there is a trigger qualified event, which would, for instance with edge trigger, be every time signal passes trigger threshold, even during the sweep. That setting would follow signal frequency accurately up to max trigger frequency (up to some 20ish MHz on 3000T), but still would be digital and jittery compared to input signal, which could or not be a problem. But not every digital scope has this option.  Some scopes can output Trig ready (for conditional triggers).

It is what it is and it will be highly dependent on exact scope model you have.

I still miss Preamp OUT. That was useful at times. Although, with today's scopes timebase accuracy in low ppms and many, many, built in measurements, it is not as important as it used to be.

Most important is that you NEED to read manual for your instruments to know exactly what it can and cannot do and how to use it properly.

For Keysight 3000T, manual only for Power measurement application is exactly 100 pages. And if you ask me, it is very tersely written and could benefit from more explanation at some moments...