Sampling frequency of analogue input

Hardware
,
10

Dear Mario,

Thank you for your kind reply on Jan 21th in this forum. After that, I tested the
DaqAInScan/Continue/End to read out analogue signal from the DAQ (USB-1208FS,
Measurement Computing). The following is the Matlab script:

PsychDefaultSetup( 2 );

DaqID = DaqFind;

% Define options
options.channel = [ 8 9 ]; % 8: horizontal, 9: vertical position of the eye
options.range = [ 1 1 ];
options.f = 250;
options.immediate = 1;

warning off

array_H = ;
array_V = ;
array_T = ;

% Start collecting eye position
DaqAInScanBegin( DaqID, options );

T1 = GetSecs; T2 = GetSecs;
while ( T2 - T1 ) < 1
[ params, data ] = DaqAInScanContinue( DaqID, options, 1 );
if ~isempty( data )
for i = 1:length( data )
array_H = [ array_H; data( i, 1 ) ];
array_V = [ array_V; data( i, 2 ) ];
array_T = [ array_T; GetSecs ];
end
T2 = GetSecs;

else
    array_H = array_H; 
    array_V = array_V; 
    array_T = array_T; 
    T2 = GetSecs;
end

end

% Stop collecting eye position
DaqAInScanEnd( DaqID, options );

% Draw a graph of the eye position
figure;
plot( array_T, array_H, ‘r.-’ ); hold on
plot( array_T, array_V, ‘g.-’ ); hold off

The data was collected by using a static dummy eye. The obtained position was plotted in the
attached figure (eye_position_DAQ1). The red and green line indicates the horizontal and
vertical position, respectively. As you can see there, I could read out about 250 points per second with
the DaqAInScan/Continue/End. However, it seems that the horizontal and vertical position switches
randomly when a new chunk is read out (32 chunks per second). I tested with the other two DAQs and
obtained the similar result (attached figure ‘eye_position_DAQ2’ and ‘eye_position_DAQ3’).
The output signal from the eye tracker was bifurcated and monitored by using PowerLab
(ADInstruments), but the horizontal and vertical position did not switch during the whole test.
So, my questions are:

  1. How can I stop switching the horizontal and vertical position, or are there any mistakes in my
    usage of the DaqAInScan/Continue/End?
  2. During the test, I got the following message lines regardless of the statement of warning off:
    Missing 992.5 sample/channel, 3970 bytes.
    Missing 992.0 sample/channel, 3968 bytes.
    ………
    Nothing received.
    How can I stop the message lines?

I would be appreciated if you could give me any suggestion.

Sincerely,

Daq

eye_position_DAQ1
eye_position_DAQ2
eye_position_DAQ3