Manual trigger with pre-trigger buffer?

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Wally
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Re: Manual trigger with pre-trigger buffer?

Post by Wally » Wed Dec 18, 2013 5:46 pm

Chilehed - In your last post

Picture 1 Chan A Plus or minus 5V DC - Chan B turned Off

Picture 2 Chan A Plus or minus 5V DC - Chan B turned Off

Picture 3 Chan A Plus or minus 50V AC - Chan B Plus or minus 20V AC

Is it something as simple as this that is causing your problem?

The other thing is the filters on each chan - what are these set at?

Post the PSD file and people will be able to see how you have this set up and post where and how you have connected to the sensors.

Wally

hbr
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Re: Manual trigger with pre-trigger buffer?

Post by hbr » Wed Dec 18, 2013 6:28 pm

CrankAnd2Cams.10SperDiv1.jpg

chilehed
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Re: Manual trigger with pre-trigger buffer?

Post by chilehed » Thu May 15, 2014 5:52 pm

hbr, yes, thank you, that was my problem with aliasing. I didn't realize that the number of samples referred to the time scale shown in the window. With 10 s/div and sampling at 1 GS I get good resolution.

I still haven't solved the end-of-sampling issue: I can't be there when the event occurs. I need sampling to stop when the voltage goes high and stays there longer than 5 seconds. The half-minute before that is what I need to capture, and it might be days before the event happens.

AuthorMike
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Re: Manual trigger with pre-trigger buffer?

Post by AuthorMike » Fri May 16, 2014 11:32 am

chilehed wrote:.....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.
Hi,

I've managed to do what you are after (although I am only using 1 Channel, hence triggering on A. Change this as you need).

Collection time = 5 s/div.

Trigger settings:
Single
ChA
Pre-Trigger 60 % (this gives you your 10 seconds between 4.5 V and 5 V, and around 20 seconds before the trigger starts)

Window Pulse Width
Threshold 1: 4.5 V
Threshold 2: 5.5 V
Time: 10 s

Tools>Alarms
:

Event - Capture (ensure the tick box is active)
Edit>
Action=Save Current Buffer
File=Location to save file
"OK"

Ensure tick is also showing next to "Save Current Buffer [xxxxxxx]".
"Apply"
"OK"

Now, another important part. Get the car and scope running, but do not connect channel A until the blue trace reaches the trigger point (should be 30 seconds). Once it has reached the trigger point, connect the Channel A lead BNC to the scope ChA input.

When the scope detects the V with the parameters we have set, it will then continue to fill ONE buffer. At the end of that buffer it will automatically save your capture.

chilehed wrote:I still haven't solved the end-of-sampling issue: I can't be there when the event occurs. I need sampling to stop when the voltage goes high and stays there longer than 5 seconds. The half-minute before that is what I need to capture, and it might be days before the event happens.
You've changed your requirments in the above post to that of the one on the first page. From your quote change my above settings to:

Trigger settings:
Single
ChA
Pre-Trigger 85 % (this gives minimum 5s capture in the threshold range, and around 30 seconds before the trigger event occurs).

Window Pulse Width
Threshold 1: 4.5 V
Threshold 2: 5.5 V
Time: 5 s


Now, another important part. Get the car and scope running, but do not connect channel A until the blue trace reaches the trigger point (should be 42.5 seconds). Once it has reached the trigger point, connect the Channel A lead BNC to the scope ChA input.

When the scope detects the V with the parameters we have set, it will then continue to fill ONE buffer. At the end of that buffer it will automatically save your capture.
Mike Valentine
Technical Author @ Pico Technology UK

chilehed
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Re: Manual trigger with pre-trigger buffer?

Post by chilehed » Fri May 16, 2014 3:23 pm

Mike, thanks for your help. Yes, I've been unclear. What I need is an ending trigger, that is, as soon as the voltage stays high for 5 seconds I need to capture the data that's already been recorded: the previous 30 seconds or so.

AuthorMike
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Re: Manual trigger with pre-trigger buffer?

Post by AuthorMike » Mon May 19, 2014 9:54 am

chilehed wrote:Mike, thanks for your help. Yes, I've been unclear. What I need is an ending trigger, that is, as soon as the voltage stays high for 5 seconds I need to capture the data that's already been recorded: the previous 30 seconds or so.
Hi,

Perhaps I should have uploaded the psdata file on Friday, apologies. Here it is:
WindowPulseWidth50Seconds.psdata
(196.3 KiB) Downloaded 416 times
WindowPulseWidth50Seconds.png
Ignore the signal shown in the data file as I used an AWG on a different PicoScope to feed in a signal purely to meet the trigger conditions.

YOU WILL NEED TO: Change the threshold settings (TH1: 4.5 V & TH2: 5.5 V), and ensure the alarm settings are set as per my above post.

You will see 50 seconds across the screen. With the trigger point set at 85%, you will capture the trigger points and the previous 30 seconds, if you follow the settings I suggest above.

Unless I have totally missed what you are after, in which case I apologise :)

EDIT:

Having looked at this again, and discussed with a colleague I think this may be better suited to you. Window Dropout trigger.
WindowDropout50Seconds.psdata
(26.91 KiB) Downloaded 424 times
WindowDropout50Seconds.png
This first psdata file in this post waits for the signal to drop again, which means if your signal is in the threshold range for 30 seconds, the scope will continue to capture till the signal exits the threshold. With the WindowDropout the trigger merely waits for 5s to have passed, and then triggers, regardless of how long the signal is in the threshold for.

Let me know, :)


Mike
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Re: Manual trigger with pre-trigger buffer?

Post by chilehed » Mon May 19, 2014 2:17 pm

Thanks Mike, the Window Dropout looks like it's just what I need.

Funny, I'm certain that I had tried it previously with no success... I guess I must've screwed it up somehow. Oh well.

Testing resumed.
Thanks again.
Tom

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Re: Manual trigger with pre-trigger buffer?

Post by AuthorMike » Tue May 20, 2014 7:29 am

chilehed wrote:Thanks Mike, the Window Dropout looks like it's just what I need.

Funny, I'm certain that I had tried it previously with no success... I guess I must've screwed it up somehow. Oh well.

Testing resumed.
Thanks again.
Tom
Great news :D

Don't forget the important part though when you start the test:

"Get the car and scope running, but do not connect channel A until the blue trace reaches the trigger point. Once it has reached the trigger point, connect the Channel A lead BNC to the scope ChA input."

Otherwise you may not capture the event at the trigger point (and therefore miss out on seeing the previous 30 seconds or so).

Sounds an interesting test, why not do a case study? :) :)
Mike Valentine
Technical Author @ Pico Technology UK

chilehed
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Re: Manual trigger with pre-trigger buffer?

Post by chilehed » Tue May 20, 2014 6:06 pm

AuthorMike wrote:...Sounds an interesting test, why not do a case study? :) :)
It's quite interesting indeed, but unfortunately I'm not at liberty to discuss the details. It would end up a very boring case study, little more than "I needed to capture what happened before the signal went high, and here's the trigger that Mike kindly gave me." Even if I were allowed to talk about it, it wouldn't help anyone; I work for an OEM, and the study only makes sense if you know the details of the controller code and have access to the RAM.

But for what it's worth, the one scope we have in our group gets used a lot. It's pretty slick and the guy who holds it says they're thinking about getting another. My only complaint (and it's common in my group) had been that I have a hard time understanding the User's Guide and finding things in it, but now that I've gone back again I see that it's merely a consequence of style, terminology, and being more accustomed to a different scope s/w architecture. For example, with the other packages we use (e.g., ETAS Inca) you select a sampling rate for your signals, that's the rate regardless of the timescale of the scope, and the buffer runs indefinitely. But with Pico you scale the scope and select how many samples you want over that time scale, and if you rescale the scope you end up with a different sampling rate... that seems strange to me. The way you set up triggers is different as well... my luck that I'm the guy who ended up in front in terms of exercising the package! :mrgreen: I'll catch on eventually.

Thanks again.

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