need help understanding AI Clock Config and AI Control

[Fred R.]

Most of my experience has been with Labview 7 and 8 and I am investigating this VI made with Labview 5.
A portion of the block diagram is attached as a JPEG. The hardware used is a PCI-6025E.
Could some of you experience members please tell me if I am understanding this properly?


After doing some reading, my thought is that this portion is performing a single shot waveform acquisition using external clock (Counter 0) which is being routed to RTSI0 and RTSI1. The routing is done with the Route Signal VI of course.

The trigger config VI looks like it is using RTSI0 (a.k.a GPCTR0 source) as the trigger and the trigger type is "digital trigger a" which I found out stands for the first trigger.

What I don't understand is the two clock config VIs that are being used back to back.  The first one is configuring the 2nd clock but there is no clock source specified.

What ends up happening there when no source is specfied? My first guess is nothing changes.
Also, am I right by thinking  the second clock config VI is configuring the 1st clock to be equal to RTSI-1(CTR0 gate)?

Lastly, why is the AI Control VI there? I haven't seen it used in any examples.  From reference, its purpose is to control the task and specify the amount of data to acquire. In this case the minimum is 0, but is it necessary to have this VI?

Thanks in advance to whoever helps me out!
 

[Fred R.]

I appologize if some of my questions were confusing. I have a better understanding of how this works now.

If someone could just confirm what I said is true then I would greatly appreciate it.
The one thing that still bothers me is the 4th subVI from the left. The control VI has no source connected to it and the target is channel clock1.
Is there anything being changed here or could I remove the subVI and nothing would change?


Message Edited by Fred R. on 01-17-2008 09:41 PM

[samantham]

Hello,

Yes, you are correct with your understanding of the functional operation of the Route Signal VI and AI Trigger Config VI. 

The two AI Clock Config VIs are / can be important in this code.  This code is using an external scan clock (RTSI1) (scan clock - more commonly known as a Sample Clock in the DAQmx Driver).  The first AI Clock Config VI is configuring the Channel Clock and the second AI Clock Config VI is configuring the external Scan Clock.  Please use the LabVIEW Help to view the article titled AI Clock Config (Continued).  This Help article explains why one would first want to configure the Channel Clock when using an external Scan Clock.  The code you posted does configure the Channel Clock; however it does not change the channels per second since the clock frequency or alternative clock rate terminal inputs are not wired.  I would assume the first AI Clock Config VI was included to allow for testing when the code was beginning developed.

I saw you also asked what happens when no source is wired into the AI Clock Config VI.  The default input is “0” when nothing is wired into the input.  Please refer to the Help article titled AI Clock Config for other options.

The AI Control VI in your code is allowing for the setting of minimum pretrigger scans to acquire to be set to “0”, where acquisition is strictly posttriggers instead of the default input.  Thus, I would say that it is necessary.

[Fred R.]

Samantha, thanks for the clarification!