LabVIEW
how to trigger from analog input channel
Hey Henry,
First, let me clarify something: Are signals A, B, X, and Y all analog input signals being read by the same card? If so, you can't really "control" one analog input with the other analog inputs. Although, you could acquire ALL this signals at the same rate (most likely a fast rate to catch the triggers). Then in software you can setup a condition where if A is above a certain value, then save the corresponding value of X, and when B is above a certain value (or within a certain range) then save the corresponding value on Y. This would essentially be a software workaround for what you are trying to do.
To split the signals, you can just use the index array function to grab the individual channels like shown below:
Also, how often and how many samples are you wanting to acquire per trigger? If you just want one sample each time you receive a trigger, you can monitor the trigger lines and start an analog input task for the specific channel that you receive a trigger for. If you are planning on receiving the triggers at the same time, then you could make an analog task that always acquires your X and Y channels not matter if B or A triggers, but then only saves channel data that corresponds to which trigger hit. For example, every time A OR B triggers, you will collect a sample from X & Y, and then if trigger A was the one that actually fired, you would only save the sample from channel X.
Basically, there are various ways you can implement this in software, but you have the limitation of not being able to simultaneously record analog at different sample rates with different triggers (i.e. - all analog inputs that you want to acquire at the same time must be on the same task, and acquiring at the same speed. What you do with the data after you acquire it though can produce the functionality you’re looking for). I hope this helps!
-Nathan H
Hey Henry,
The device number is just whatever the name is in Measurement and Automation Explorer. For example Dev1 is a common device name. So your channel would be "Dev1/ai0" for analog input zero of that device (you could also enter "Dev1/ai0:1" for channels 0 AND 1 of device 1).
I'm not sure what VI you are referring to when you say "AI Sample Channels.vi", do you mean DAQmx Create Virtual Channel.vi? Press CTRL+H to bring up context help, then hover over the VI in question to see the actual name. Most DAQmx VIs that require a channel name will allow you to add a constant or control to the input, and that constant or control will have an arrow button on the right side that allows you to expand a drop down menu as shown below, which makes it easier to find your device name.
I hope this helps!
-Nathan H
