# DAQ output speed maximum

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Michael Leung on 15 Sep 2011
Hi,
I'm tring to use my NI card (PCI 6259) to output a "smooth" ramp function, similar to those you achieve from function generators.
function [] = Ramp(Vpp, Frequency, NumRepeat)
% Vpp = Voltage peak to peak
if isempty(NumRepeat)
NumRepeat = 1;
end
x = 0.5 * Vpp * linspace(-1,1,500/Frequency)';
x = [x; -x];
ao_Ref = analogoutput('nidaq','Dev1');
set(ao_Ref,'SampleRate',1000);
% set(ao_Ref,'TriggerType','Immediate')
for j = 1:NumRepeat
putdata(ao_Ref, x);
end
start(ao_Ref)
The code works fine. The only problem I am having is that the output voltage is given in tiny steps. The voltage is determining the position of an actuator, and thus the actuator does 1000 little "jumps" per second.
>> daqfind
Display Summary of Analog Output (AO) Object Using 'PCI-6259'.
Output Parameters: 1000 samples per second on each channel.
The NI card should be able to output alot more then 1000 samples per second, if I am not mistaken. Is there a way to "smotthen" out the output voltage? (make it a linear slope, rather then 1000 small steps.
Any help would be appreciated.
Thanks,
Michael
Michael Leung on 15 Sep 2011
Is there a simpler way to achieve a ramp function??

Walter Roberson on 15 Sep 2011
Ummm, you did set(ao_Ref,'SampleRate',1000) so why not try increasing that 1000 to a higher value?
Walter Roberson on 15 Sep 2011
For that card and single channel, the spec is 1.25 Msamp/second, so somewhere around 1250000 in theory. I don't know what the practical limit is (based upon MATLAB's overhead, the other operations happening on your system, and so on.)
Chirag Gupta on 15 Sep 2011
Once the data acquisition starts, there will be no MATLAB overhead as the data is queued on the board.

Chirag Gupta on 15 Sep 2011
You should be able to increase the sample rate of your AO to reduce the steps.
set(ao_Ref,'SampleRate',5000);
The default setting of the toolbox is to make it 1000.