how to output multiple scan in usb6008 with matlab

hi

i need your help to use ni usb6008 to output analog signal , the analog signal is the control signal from PID controller i used this code

% Initialization
global  Temperature 
global Irradiance
global current
global Vref
global data
global u
%%get connected devices
d = daq.getDevices
%create session
  s = daq.createSession('ni')
s1= daq.createSession('ni')
  %add analog channel  s.addAnalogInputChannel('ID',channel num, 'measurement type')
% s.addAnalogInputChannel('Dev1',0:3, 'Voltage')%irradiance
  s.addAnalogInputChannel('Dev1','ai0', 'Voltage')%irradiance
s.addAnalogInputChannel('Dev1','ai1', 'Voltage')%Temperature
% s.addAnalogInputChannel('Dev1','ai3', 'Voltage')%Temperature

s1.addAnalogOutputChannel('Dev1', 'ao0', 'Voltage')
% set rate of scan  1000 scans/second ,  run for 30 seconds

   s.Rate=1000;
  s.DurationInSeconds =10
  v.TerminalConfig = ' Differential';
  %v.TerminalConfig = ' SingleEnded';
  %_____________________________
  %aquire data and process
  lh = s.addlistener('DataAvailable', @plotData);
  %store data
  %h = s.addlistener('DataAvailable', @storedata)% Analog Output
  ao_value = u % duty cycle control signal 
  s1.outputSingleScan(ao_value)

s.startBackground()
   s.wait()
 delete (lh)
 delete (h)
 s.release()

but an error message appeared "The data argument must contain one column for each output channel in the session.

i also can't use queue output data

ao_value = u % duty cycle control signal 
s.queueOutputData (( ao_value)');

it gives me error that "There must be at least one analog output channel in the session before outputSingleScan or queueOutputData can be used.

[mado]

any help ?

Answer 1

[Walter Roberson]

When you use

global u

then "u" is initialized to [] unless you have already initialized it. The empty array [] does not contain at least one column and so cannot be used as a value for outputSingleScan