Manual trigger with pre-trigger buffer?

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Manual trigger with pre-trigger buffer?

Postby chilehed » Tue Dec 10, 2013 7:04 pm

I'm trying to identify something that happens very infrequently, and would like to be able to trigger manually on the event and have only the last 15 seconds (or so) recorded (rather than just record for hours at a time and end up with a huge data file). Is there a way to do that?
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Re: Manual trigger with pre-trigger buffer?

Postby Martyn » Wed Dec 11, 2013 7:11 am

Set a repeat trigger, move the trigger diamond to the right hand side and top of the screen, at a level that the signal will never reach. Set the collection time to 2s/div and when the event occurs stop the capture.
capture.bmp

You can now zoom in and look at the detail.
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Re: Manual trigger with pre-trigger buffer?

Postby chilehed » Thu Dec 12, 2013 2:57 pm

When the trace gets to the end of the screen there's about an 8-second time lag, during which no data is captured, before the second buffer screen starts populating. There's a very high probability that the event will happen during that time. Is there no FIFO buffer that elimitates holes in the data?
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Re: Manual trigger with pre-trigger buffer?

Postby Martyn » Thu Dec 12, 2013 3:39 pm

If you follow the instructions the trace will never get to the end of the screen because the trigger point is never reached. It will not pause whilst it writes the buffer to disk as the buffer is never full. You should see the trace scrolling continuously. This will mean you only ever have 1 screen of data and you can manually stop when the event of interest happens and then zoom in and inspect the data.

Is this what you meant by manual trigger ?
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Re: Manual trigger with pre-trigger buffer?

Postby Autonerdz » Thu Dec 12, 2013 5:11 pm

There is an animation here that illustrates what Martyn is saying:

http://www.autonerdz.com/cgi/yabb2/YaBB ... 5231719#13

As long as you use a long enough capture time and are there to stop the scope when the event occurs, if the signals you monitor are affected, there is no chance you will miss it. Just be sure to adjust for an adequate sample rate for the signals you are monitoring.

Tom Roberts
http://www.autonerdz.com/
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Re: Manual trigger with pre-trigger buffer?

Postby chilehed » Mon Dec 16, 2013 8:24 pm

Yep, that works, thanks.

I'm looking at the crank sensor voltage, and tried to use Window Dropout so it would trigger when the voltage stuck between 4.5 and 5.5 V for more than 10 seconds (indicating that the engine had stopped for that long), but nothing happens when that condition is met. So unless I can get that to work I'll just keep sticking my head out the door every 20 minutes or so to check on it.

Now I've got a more important question. I've got the crank, Cam W and Cam X sensors going into ports A, B and C. When the scope wakes up in Scope view it brings up the crank signal fine, but when I try to add views for B and C there's no option to select them: the scope doesn't appear to recognise that those ports are geting any voltage. When I run Cam W or Cam X to port A it shows good signals, so I know that's not the problem.

Then I tried Automotive/Advanced Tests/CamAndCrankSensors, but all it'll pull up is CamW.

I tried Cam, Crank, Injector and Ignition, and it pulls up all three sensors; it doesn't show the square waves very accurately and I really need the higher resolution, but you can at least see all of the crank teeth as well as the sync gap.. But when I save the data and open the file back up later the signal looks corrupted.

Here's what the crank signal should look like, you can see the sync gap clearly:
Capture1.JPG

And here's what the crank and cam signals look like from CamCrankInjectorAndIgnition. The cam should show a short/short/long/long pattern over two crank revs (58 crank teeth per rev), but most of the crank teeth have been lost and you can't see a good cam tooth pattern. Crank is on top, the cams are on the bottom.
Capture2.JPG


So what do I do? How can I view and record channels B and C? I prefer to use Scope view because I really need to resolve the short low time on the crank sensor.
Last edited by chilehed on Tue Dec 17, 2013 11:13 am, edited 1 time in total.
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Re: Manual trigger with pre-trigger buffer?

Postby Robski » Tue Dec 17, 2013 2:15 am

without the PSD file at first glance that looks like insufficient sample to me ..... :shock:

Also where are you grounding CH A ?
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Re: Manual trigger with pre-trigger buffer?

Postby chilehed » Tue Dec 17, 2013 3:20 pm

I've got a breakout harness in the sensor, and I know it's wired correctly.

It looks like the Automotive views have aliasing issues that are not present in the regular Scope views.
Here's what a cycle of Crank and Cam W look like on Ch. A, at 500 S/div (2 separate shots because I can't get to Ch. B in this mode):
Crank
Crank.500SperDiv.JPG


Cam
Cam.500perDiv.JPG


Here's a cycle of Crank and Cam W, seen in Cam and Crank Sensor view and recorded at 50mS/div. Notice the Cam voltage profile looks different, and it's not what the sensor actually outputs:
CrankAndCam.50mSperDiv.JPG


Here's a cycle of Crank and Cams W and X, as seen in Cam, Crank, Injector and Ignition view. 50 mS/division, with Ch. C rescaled to +/- 20 volts:
CrankAnd2Cams.50mSperDiv.JPG


Finally, here's a cycle of Crank, W and X in the same view, but taken at 10 S per division. This is obviously aliased, and it does the same thing in Cam and Crank view as well:
CrankAnd2Cams.10SperDiv.JPG


So it looks like, in the Automotive views, sampling rate drops as time/div goes up, which is useless for me.
And in regular Scope view it doesn't let me pull up channels B or C, even though they obviously are getting signals.
And the Window Dropout trigger seems to be broken as well.

Any ideas?
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Re: Manual trigger with pre-trigger buffer?

Postby Fat Freddy » Wed Dec 18, 2013 9:37 am

So it looks like, in the Automotive views, sampling rate drops as time/div goes up, which is useless for me.
And in regular Scope view it doesn't let me pull up channels B or C, even though they obviously are getting signals.
And the Window Dropout trigger seems to be broken as well.



If you posted the files some one will help. Looks like operator error to me.

Without too much effort I can dial up a sample rate of 250KsS at 10 seconds per division.
Not sure about your problems with the trigger either, again data files will help.

HTH
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Re: Manual trigger with pre-trigger buffer?

Postby Fat Freddy » Wed Dec 18, 2013 9:47 am

Also as Robski has mentioned. How are you hooked up. Your voltages look odd.
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