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How to get the PreTrigg function to work for Trigger-Sequence in DIAdem DAC

I don't get the PreTrigg function to work.
Attachment include DAC-scheme, datafile and Word-document with further description.

In my saved data I'm not able to see any "PreTrigger"-data !!?
(On the contrary there is a delay of 0.3 seconds / 30 cycles until the "SaveFast" sequence occur !! NI Support: Refer to SRN 165992 )
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Message 1 of 6
Hello Mr.

The problem is hat DIAdem can only work Step by Step, that means the following:

Start measurement
Wait until stop trigger is true
Jump into the next line
Wait for stop trigger
And so on

If there is not enough time to collect values for pre-trigger the values are stored without them. In this case the last values of the line before are the pre-trigger values.

I hope this answer can help you.

Kind regards

Walter Rick
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Message 2 of 6
As there is a TriggerSequence WITH a PreTrigger function, IT HAS TO BE possible to use it !!

The question is how to configure the setup correct.

The speed could not be the problem since the clock is set to 100Hz (I intend to run it at 1kHz when I get it working).

I look forward to have a new answer to this question.


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Message 3 of 6
Indeed the speed is not the problem. Only in a special situation - such you described - it is not possible to collect pre-trigger values, because the current clock step reacts to the stop-trigger and the next clock step reacts to the start-trigger (in the next line). So there is no time to collect any pre-trigger values.

I hope this explains this special behaviour a little bit.

Walter Rick
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Message 4 of 6
Hello again,

yes, now I think I know how it work (unfortunately!).
I't seems the trigger-sequence won't help me in this application.
( I tried a couple of setups and found out that a stop-trigger is required, ... if you want to switch to the next sequence !)

Background / Application
The intention is to record data at a slow rate (say 10Hz) while slowly applying load to the test-object. At some point the contol-system (PLC, not DIAdem!) detects a possible breakdown of the test-object, the control-system then signals DIAdem to "record at fast rate (100-1000Hz) with pre-trigg" to capture the interesting part of the test.

How can I do this with DIAdem ?
(Is Trigger-Sequence out of the quest


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Message 5 of 6

If in your application it is necessary to have a pre-trigger the Trigger-Sequence is not the best choice.
Attached you find you DAC-Scheme with some small modifications to solve the problem (I hope).
I'm working with a second clock, a Copy-Block and start-/stop-trigger for the Save-Block. In the Save-Block I used the parameter "Retrigger".

I hope you can use the principle in you application.


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Message 6 of 6