Fast array building from two independent acquisitions

Question

Hi all,
I'm trying to figure out a way to build an array very quickly (up to 5 kHz) from two independent acquisitions.  For the two acquisitions I have a counter input from an encoder and a normal analog input, the purpose is to correlate with high resolution a position to an output voltage.  I can run each independently fast enough, but the problem I'm having is figuring out how to line up the two signals into a single array simultaneously and at a consistent rate (5 kHz) to write out to a file.  My first hack was to read the two outputs into a while loop clocked by a wait timer, but the best I think I can do there is a 1 millisec wait which gives me no better than 1 kHz.  Any ideas?  Hopefully something simple I'm overlooking.  Running LabVIEW 7.1 on a PCI-6036E card.  Thanks in advance.

Answer 1

You're going to have to use hardware timing on the DAQ card and acquire multiple samples on each scan.
If you're using DAQmx (and you really should be), change the Read VI to
acquire multiple smaples from multiple channels. This single VI can
scan both channels and output a 2D array with each channels data in one
row of the array.
You'll also need to change your configuration setup to specify both channels and the smapling rate.
If you look in the Example Finder (Help menu>Find Examples...)
double click through "Hardware Input and Output">"DAQmx">"Analog
Measurments">"Voltage" you'll see several examples that do this sort
of measurment. Most of them only show how to acquire a single channel,
but can be easily modified to include a second channel.
Let us know if you need more help.
Ed
Ed Dickens - Certified LabVIEW Architect - DISTek Integration, Inc. - NI Certified Alliance Partner
Using the Abort button to stop your VI is like using a tree to stop your car. It works, but there may be consequences.