DAQ-USB6251 acquisition time is slow with matlab

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Hi,

I'm using this product to acquire 4 voltage with 3 different  volt range (-2;2), (-5;5) and (-10;10) in Single Ended mode at the maximum frequency, which is 250kHz.

I'm using matlab with session mode to acquire the data from the DAQ. I've done some speed test on the code and I've noticed that when I require multiple samples per channel (doesn'matter if they're 10 or 20) the time to do that is over 170  milliseconds, wherease if I acquire a single sample for each channel it takes about 22 ms. I cannot use the inputSingleScan because the errors are over +- 10mV. So right now I'm acquiring 20 samples and using theit mean.

How can I reduce the time to acquire 20 samples?

Thanks in advance. 

P.s. I've put the code I use, maybe it's useful for the answer.

Andrea

%Activate Daq device
daqregister('ni');
daqUSB6251=daq.createSession('ni');
%Add Channels to digitalize
daqUSB6251.addAnalogInputChannel('Dev1','ai0','Voltage'); %power voltage
daqUSB6251.addAnalogInputChannel('Dev1','ai4','Voltage'); %Y voltage
daqUSB6251.addAnalogInputChannel('Dev1','ai1','Voltage'); %X voltage
daqUSB6251.addAnalogInputChannel('Dev1','ai7','Voltage'); %power meter voltage
daqUSB6251.Channels(1).set('Name','Power');
daqUSB6251.Channels(2).set('Name','Y Pos');
daqUSB6251.Channels(3).set('Name','X Pos');
daqUSB6251.Channels(4).set('Name','PowerMeter');
daqUSB6251.Channels(2).set('Range',[-5.0 5.0]); %output is in [-4.5;4.5]V
daqUSB6251.Channels(3).set('Range',[-5.0 5.0]); %
daqUSB6251.Channels(4).set('Range',[-2.0 2.0]);
daqUSB6251.NumberOfScans=20; % samples per channel
daqUSB6251.Rate=250000; %Frequency of sampling in Hz 
daqUSB6251.Channels.set('TerminalConfig','SingleEnded'); %Voltage is referred to AiGND
daqUSB6251.Channels %print the channel configuration as set above

%acquire data slow (>170ms) 
data=daqUSB6251.startForeground();

%acquire data fast (22ms)

data=daqUSB6251.inputSingleScan();