MATLAB Central Newsreader - Data Acquisition with multiple NI PXI-4472 boards

Data Acquisition with multiple NI PXI-4472 boards

Christopher — Mon, 10 Mar 2008 11:52:17 -0400

I have a NI PXI chassis with several PXI-4472 boards
installed. Using the Data Acquisition Toolbox (v2.11 Matlab
R2007b) I'd like to capture data from channels that span
several boards.

The code I have at the moment initialises one of the
PXI-4472 cards like this :

ai = analoginput('nidaq','PXI1Slot2');
addchannel(ai, 1:2);

In labview I would be able to specify a range of boards, for
example, 'PXI1Slot2, PXI1Slot3' but this does not work as a
parameter to 'analoginput()' .

Does anybody have any suggestions of how I can
simultaneously acquire 8 channels from PXI1Slot2 and 8 from
PXI1Slot3 ?

Thank you for your help,

Chris Lowis

Re: Data Acquisition with multiple NI PXI-4472 boards

Christopher — Tue, 11 Mar 2008 09:43:02 -0400

I managed to get multiple channel acquisition spanning
multiple boards working using the NI-DAQmx Tools available
from the NI website
(http://zone.ni.com/devzone/cda/tut/p/id/3005) and the
following code :

Physical_Channel = 'PXI1Slot2/ai0:7, PXI1Slot3/ai0:7';
Minimum_Value = -10;
Maximum_Value = 10;
Sample_Rate = 2000;
Measurement_Time = 3;
Samples_per_Channel = Sample_Rate * Measurement_Time;
Timeout = -1;

[data, time, initial_time, timed_out] =
AcqNUpdates(Physical_Channel,
Minimum_Value, Maximum_Value, Samples_per_Channel,
Sample_Rate, Timeout);

It seems to me, however, that this toolbox is a series of
interfaces into compiled ".dll" files, and that, for
example, the callback/continuous calculation functions of
the data acquisition toolbox are not available through
MATLAB code. Is this correct ?

I'd like to be able to do continuous processing of my
acquired data, and update a MATLAB plot window with the
results using all 16 available channels on my two PXI-4472
cards. Is this possible with either the NI-DAQmx tools, or
the Data Acquisition Toolbox ?

Thank you for any help,

Chris

Re: Data Acquisition with multiple NI PXI-4472 boards

Sherryl Radbil — Wed, 12 Mar 2008 11:28:01 -0400

Hi Chris,
Your statement in the 1st post that with Data Acquisition
Toolbox (DAT) you cannot create one analoginput object that
spans 2 devices is correct.
But you can created an object for each:

ai2 = analoginput('nidaq','PXI1Slot2');
ai3 = analoginput('nidaq','PXI1Slot3');

Many of the DAT commands take an array of objects:
start([ai2 ai3])
They will not start simultaneously, but it will be pretty
close and each data point you will get with getdata has a
timestamp so you can correlate.

Look at abstime on the getdata help page
http://www.mathworks.com/access/helpdesk/help/toolbox/daq/getdata.html

All the best,
Sherryl