Gathering data BEFORE the trigger event, How?

[stuman]

Just a general question. I know about analog triggers in VB6 and they work fine. My question is, is it possible to get some of the data before the trigger was triggered. Example record for 1 second, trigger at 1 volt. When the CWAI1_AcquiredData is fired, it will return 1 seconds worth of data after the trigger, can I get at the data 0.1 seonds before the trigger happened?

No I cannot just lower the trigger value, it is already set at 0.05 volts and goes to 5 volts within 0.01 seconds.

Thanks

Stuman

[CKap]

Hello Stuman,

You havent mentioned what hardware you are using. The functionality that you are looking for is definitely possible but not all hardware support it.

You need to define a stop trigger (Traditional DAQ) which is also referred to as Reference Trigger (DAQmx).

The specific property that you would need to define is CWAICondition.PreTriggerScans.

Look into the Measurement Studio DAQ help for more information on other properties that you would need to also define. I have attached it for your reference.

Regards,

Chetan K.

Application Engineering

National Instruments

[stuman]

Thanks for getting back to me, I appreciate it. I have tried what you have suggested but it does not seem to acquire any data from before the trigger event. I am using a 6070E Firewire DAQPad. Is this hardware capable of doing what I require? If not, is it mentioned in the documentation anywhere, not trying to screw you, just want to know for future purposes, what to look for.

Thanks

Stuman

[stuman]

I am using traditional DAQ, can someone give me a list of that hardware supports PreTriggerScans?

Thanks

Stuman

[Matt_A]

Hello Stuman,

You can normally examine the device user manual or specifications to determine what triggering options the device supports. For example, on page 9 the NI 6070E/6071E Family Specifications here has a sections called "Analog Trigger". Within this section is a specification called analog input purpose, which lists the following:

"Analog input ...............................Start, reference, and pause trigger, sample clock"

This confirms that the NI 6070E support the use of reference triggers.