Scope trigger

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grad1618
Posts: 24
Joined: Sun Nov 20, 2016 5:24 pm

Scope trigger

Postby grad1618 » Wed Feb 01, 2017 8:09 am

Hello,

I am using the scope feature and it works well, but I am not able to trigger at a resolution lower than 500 ms.

I have a stimulus waveform (square wave, 10 Hz, 200 us, 0 to 5V) that I am using to trigger the scope, but this only triggers properly for 500 ms and above, anything lower (200 ms, 100 ms, etc.) and nothing triggers.

I have tried to adjust the trigger settings but nothing seems to work.
It's a very clean trigger signal.


Any ideas on what might be happening?
Thanks!

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tbroughton
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Joined: Mon Mar 25, 2013 8:28 am
Location: United Kingdom

Re: Scope trigger

Postby tbroughton » Wed Feb 01, 2017 4:52 pm

Hi there,

When you say you're unable trigger at a resolution less than 500ms, what specifically do you mean here? Are you referring to the recording duration? How are you generating the Stimulus - using LabChart's Stimulator function, or through some external signal coming into one of the PowerLab's Inputs?

I presume you've set this to trigger sampling on detection of a Stimulus artefact? More detail on this would be helpful so that I can advise.
Tom Broughton
Education Support Specialist | ADInstruments Europe

grad1618
Posts: 24
Joined: Sun Nov 20, 2016 5:24 pm

Re: Scope trigger

Postby grad1618 » Wed Feb 01, 2017 8:53 pm

Hi Tom,

I have an external trigger signal (stimulus) that is passed into channel 1 (0-5V square wave, 10 Hz, 200 us). In channel 2, I am recording an evoked electrical response to said stimulus (delay of ~30-50 ms).

I understand that the Scope View normally uses blocks/events/comments to split up individual responses into different pages.

The Scope View has the option to change the amount of data shown on the screen (to the left of the Start button at the bottom right-hand corner of the window). If I setup my trigger and response channels in Scope View and gradually decrease the size of the time window so that only one response fits the window, I get down to 500 ms. If I decrease the time scale further (200 ms or lower) my waveforms no longer trigger for some reason.

I am only using a single page in Scope View as I am not separating responses into blocks, using an event signal, or creating comments.

Given my setup above, I am not sure why it triggers on my stimulus signal (channel 1) only for time windows 500 ms and above.


Hope that adds a bit more information.

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tbroughton
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Joined: Mon Mar 25, 2013 8:28 am
Location: United Kingdom

Re: Scope trigger

Postby tbroughton » Thu Feb 02, 2017 9:17 am

Hi there,

Are you able to attach a recorded file that shows your data?

I assume you're triggering using LabChart's Sampling dialogue?

Note that the only thing Scope View actually does is overlay data by Events / Blocks / Comments so you can view changes around these events - using it without overlaying doesn't actually achieve much, as it makes it essentially the same as the Chart View!

Chart View has exactly the same scaling function, albeit the ratios are X:Y rather than explicit time windows in ms.
Tom Broughton
Education Support Specialist | ADInstruments Europe

grad1618
Posts: 24
Joined: Sun Nov 20, 2016 5:24 pm

Re: Scope trigger

Postby grad1618 » Sun Feb 12, 2017 1:21 pm

Hi Tom,

I have attached a small portion of one my data files. There are no comments or blocks.

Channel1: stimulus trigger
Channel2: EMG response signal

Using the LabChart 8 file playback feature and use the 'Stop at end of file' mode so it does not create blocks when it loops again, you can recreate what I am seeing.

If you open Scope View and set the horizontal scaling to 500 ms and run the file, you can see that channel1 and channel2 are in fact triggering as if I had used blocks for each stimulus trigger (except I did not). This does not create any pages unless you playback the file multiple times.

Increasing the horizontal scaling above 500 ms and the signals trigger, but any lower and it is lost.

I like using this feature because I don't want to make blocks and comments in my file while I am viewing the waveforms but I want a smaller horizontal scaling.
Attachments
scope_trigger.adicht
(224.5 KiB) Downloaded 13 times

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tbroughton
Posts: 128
Joined: Mon Mar 25, 2013 8:28 am
Location: United Kingdom

Re: Scope trigger

Postby tbroughton » Tue Feb 14, 2017 3:32 pm

Hi there,

I admit I am slightly perplexed by your inquiry here!

The way you've configured the Scope View makes it appear like the Scope View is overlaying by the spike in Channel 1, when in actuality this is just because you're setting to view 500ms of the signal at a time, and your trigger spikes are exactly 500ms apart, and as such the spikes will appear at exactly the same 'point' visually within Scope View.

The key thing to understand here is that all Scope does is allow you to view data in a different way to Chart View - overlaid by a time window as opposed to a continuous recording.

No data is ever lost - it probably looks like you're 'missing' data at 200ms or below because things are scrolling so quickly, but in actuality nothing is ever lost - just use the scroll bar to navigate through your recorded data after the fact! (See attached image)

Note that you don't have any Triggering set up on this recording at all. Triggering is when you use something other than the 'Start' button to commence recording, and is configured under Setup | Sampling.

You can also go to Chart View and configure a similar Scaling - something like 5:1 gives you an ~500ms Window.
Attachments
Data with 200ms window.jpg
(351.08 KiB) Not downloaded yet
Tom Broughton
Education Support Specialist | ADInstruments Europe

grad1618
Posts: 24
Joined: Sun Nov 20, 2016 5:24 pm

Re: Scope trigger

Postby grad1618 » Wed Feb 15, 2017 2:44 pm

Hi Tom,

I think you hit the nail on the head.

I somehow thought that LabChart was triggering at 500 ms when in fact it was just a coincidence given my signal period. Any time scale that matches signal period would do this.

I am familiar with Scope View triggering using blocks/comments/events in post-collection analysis, but don't like using those in real-time because it clutters up my file or creates discontinuities for DataPad.

Thanks for clearing that up.


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