Trigger-On/Trigger-Off Data Acquisition?

[Scott and Jessica]

First, I'm an old-fashioned mechanical engineer and not a controls genius,
so don't expect too much from me.

My question is, can LabView use software triggers to trigger-on/trigger-off?
More specifically, can I scan continuously and indefinitely while acquiring
(to a file) only data that occurs after the occurrance of the trigger-on
condition and before the occurance of the trigger-off condition. I hope
that was clear. Thanks.

Scott.

[Paul Davey]

Hi Scott

There is a VI located on the functions pallette: Data Aquisition: Analogue
Input: AI Read.vi that you use to read data from the buffered data aquisition.
This VI has as one of its optional inputs (it appears greyed out) a cluster
"Conditional Retrieval". This cluster is comprised of a number of variables,
including
Mode: which you can set to "On" or "Off" (or leave unchanged).
Trigger Threhsold: which is the trigger condition in volts
Channel Index: which is the 0-based index of the channel that the VI searches
for the trigger condition (comparing the signal to the trigger threshold).

When the Mode is set to On, the aquisition only begins when the trigger
condition occurs, and you use "AI Read.vi" to capture pre-trigger data. When
it is set to Off, aquisition simply begins when the VI is called (the data
retrieval is unconditional). To continuously scan for data, place a second
"AI Read.vi" inside a while loop, with a Boolean test for the "trigger-off"
condition wired to the While loop's boolean input.

The online help for "AI Read.vi" is helpful - I hope I made sense to you.

Paul

Scott and Jessica wrote:

> First, I'm an old-fashioned mechanical engineer and not a controls genius,
> so don't expect too much from me.
>
> My question is, can LabView use software triggers to trigger-on/trigger-off?
> More specifically, can I scan continuously and indefinitely while acquiring
> (to a file) only data that occurs after the occurrance of the trigger-on
> condition and before the occurance of the trigger-off condition. I hope
> that was clear. Thanks.
>
> Scott.

--

Research Assistant
School of Physiotherapy, Curtin University of Technology
Selby Street, Shenton Park, Western Australia, Australia. 6008
email: P.C.Davey@curtin.edu.au
Tel. +61 8 9266 4657 Fax. +61 8 9266 3699

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