Using NI USB-6218 with matlab r2009a for real-time purposes

[miskol]

Hi,

I've already programmed a GUI to communicate between USB-6218 and matlab r2009a. However the performance are relatively slow.

In theory the USB-6218 can support up to 250kS/s, and since i am using 16 channels the sample rate are divided with 16 = 15,625S/s thus for a single sample for each channels it will take 64microseconds. In between channel samplings a delay is introduced by the hardware which is called channel skew rate which is 4microseconds. Thus for a single channel it will take around 68microseconds to sample.

Let's say roughly a single channel will take approximately 100microseconds to acquire a single sample. Thus if 2 samples are acquired from each channels the total time taken will be = 3.2miliseconds(for 16 channels). Below in the example program the SamplesPerTrigger is set to 2 as that is the minimum setting allowed.

clc; clear;

ai = analoginput('nidaq','Dev1');
set(ai,'InputType','SingleEnded');
addchannel(ai, 0:15); %16 channels
ai.SampleRate = 15625; %supported max. sampling rate divided by 16 channels
ai.SamplesPerTrigger = 2; %minumum supported

out = zeros(2,16);

tic;

start(ai);
out = getdata(ai);

toc;

stop(ai);
clear ai
delete ai

The recorded time for this is around 50 miliseconds which is far from the calculated 3.2 miliseconds. Unfortunately Real-Time Windows Target does not support for this particular hardware (NI USB-6218).

is there any other way to program MatLAB to communicate with the hardware faster? did i miss or do anything wrong?

Please help and correct me if i'm wrong, Thank you.

p/s: getsample(ai) can be used to immediately acquire a single sample for each channels, however the speed performance are around the same still.