DAQ interchannel delay

[jjjohnson]

Hello,

I have a USB-6009 which I am reading analog values from. I tried reading AI0 using the DAQ assistant and everything is perfectly fine. The problem comes when I read 2 analog inputs at the same time. I do get the reading value correctly but it seems like it goes to ground every now and then. Find the attached files to see what I am donig.

thanks!

[mikeporter]

I'm at a place right now where I can't look at your code (I do wish NI would hurry up with the beta test for the Android version of LV) but the data does look very strange. What should the data look like?

Mike...

[jjjohnson]

Android version of LV? that sounds great!

The signals should look like the image attached. Hope you can spot the difference. When I sample 1 ADC it works like I would expect an ADC to work but if I add more ADC, it starts messing up.

any ideas?

[jjjohnson · Accepted solution]

hmm I think I got it sorted now!

I was using a DAQ assistant for each ADC and I needed to use 1 DAQ assistant with all the ADCs configured in it and later on a divider to separate each data channel 🙂

thanks for the help though

[mikeporter]

One thing to bear in mind is that one man's fix is another man's workaround. The basic problem is the DAQ Assistant -- which is an Express VI. The underlying problem is that each time it's called, the VI opens the daq, confirgures it, reads the data and then closes the task. Put that inside a loop and you have a very inefficient way of reading the data.

A good way of learning what calls are needed for DAQ is to create a DAQ Assistant that does what you want, and then turn it into a conventional VI by right clicking on it and selecting Open Front Panel. One it has been converted you can open it and see what it was doing.

Basically, what you want is all the initialization and configuration logic outside the loop and to the left. The read VI is inside the loop and the close logic is outside the loop and to the right. Pass the DAQ reference and Error Cluster into and out of the loop through Shift Registers.

Mike...