Capture of 4 analog chanels, using one of them as a trigger

Question

Hello there,
I posted a message a week or so ago about some issues I was having, and
I seem to have sorted them out (which is great!). Thanks for the
pointers.
So, I have one more quiery, and hopefully the last for a while. I've
attatched a copy of part of the VI I'm working with. All it does is
capture a user-specifiable number of analog input channels and write
them to a data file. It does so quite nicely, and with no problems. So..
My requirement is that the actual capture of the input channels must
occur only when a certain triggering voltage is met. This trigger will
come from a Berkley Nucleonics 500A pulse generator box. The precise
nature of how it might work I am not sure about because I'm a little
unsure about what my equipment can do. I was thinking the trigger could
be one of the input channels.. that would be great. My interface is an
SCB-68 board. It is currently set up for 4 analog input channels (and 2
output channels), using BNC connectors.
I've been doing some digging to try to avoid spamming a new message,
but haven't really got anywhere.. I'm a little concerned about whether
my system will even allow something like this. Will I have to wire in
(physically) some new channels into the SCB board? I read something
about only digital edge triggering being possible. If I have to use a
digital trigger, is there any way to use the current pulse generator..?
Again, any pointers are greatly appreciated. Regards,
mike
Attachments:
Input_only.vi ‏76 KB

Answer 1

Hi Mike,
You need to create a digital trigger task in MAX.
Open your Functions pallet on your block diagram, Measurement I/O, DAQmx – Data Acquisition, DAQ Task Name VI.
Once you have places the Task Name VI on your block diagram, right click it, choose New NI-DAQmx Task, MAX.
The NI DAQ Assistant window will open. Choose from the menus:
Analog Input, Voltage, your card, highlight your channels, Next, enter a name for the task, Finish.
Voltage Input Set-up Window should then open.
Are you using the TTL trigger to stream or as a clock?
If you are using it as a clock:
Go to the Task Timing tab and enter the number of samples you require.
If you are using it to stream:
Go to the Task Trigger tab and set start trigger type to Digital, Edge to Rising.
If you click on the Connection Diagram tab at the bottom of the window it show you how to wire the task.
When you have finished setting up the task click ok, this saves the task along with the configured settings within MAX.
I have attached an example piece of code which reads the 4 channels once triggered as configured in MAX.
If you require the channels to be read iteratively once triggered simply place a while loop around the read function and graph, so that the display updates.
Hope this helps
Emma R
NIUK& Ireland
Attachments:
Example code.vi ‏17 KB