Same source but different signals between the Data Aquisition Toolbox and the NI softwares

Hello,

I have some trouble with the data acquisition toolbox. The simple program below works great for transient signals centered in 0. However, for signals with a voltage offset, the signal is set to zeros as if an high pass filter was applied. This is not an hardware problem as the signal acquired via NI softwares with the same source is correct.

We have a NI 6110 acquisition card.

Could you help me on this ?

Best regards

NB : We have exactly the same issue with the Oscilloscope enbedded in the data acquisition toolbox

The program:

daqreset;
fe=20000; % frequence d'echantillonage
varniv=5; % Niveau d'entrée en V (à checker)
duree=5; % en seconde
Nb_echant=duree*fe;
AI=analoginput('nidaq','Dev3'); 

input=addchannel(AI,0,{'angle'}); 
AI.Channel.InputRange = [-varniv varniv];
AI.Channel.SensorRange = [-varniv varniv];
AI.Channel.UnitsRange = [-varniv varniv];
set(AI, 'InputType','PseudoDifferential')
set(AI, 'SampleRate', fe)
set(AI, 'SamplesPerTrigger',Nb_echant); 
set(AI,'TriggerType','Immediate'); % 

start(AI);
wait(AI,duree*1.3);
data = getdata(AI,AI.SamplesAcquired);

Answer 1

[Manisha]

Hi Pierre,

Is the Coupling property set to the same value ('AC' or 'DC') in both the NI software and the Data Acquisition Toolbox?

Thanks,

Manisha

Answer 2

[Pierre]

Hi Manisha,

Thank you for answering. In both NI and Data Acquisition Toolbox, the property 'InputType' is set to Pseudodifferential (which corresponds to DC, I think). We investigated further the toolbox with a sine wave and it clearly behaves as a low cut filter under 10 Hz.... but not with the NI software!! Here is what we get with the 'get(AI)' command:

 BufferingConfig = [16384 1]
        BufferingMode = Auto
        Channel = [1x1 aichannel]
        ChannelSkew = 0
        ChannelSkewMode = None
        ClockSource = Internal
        DataMissedFcn = @daqcallback
        EventLog = [1x3 struct]
        InitialTriggerTime = [2012 3 15 14 10 6.90933]
        InputOverRangeFcn = []
        InputType = PseudoDifferential
        LogFileName = logfile.daq
        Logging = Off
        LoggingMode = Memory
        LogToDiskMode = Overwrite
        ManualTriggerHwOn = Start
        Name = nidaqmxDev3-AI
        Running = Off
        RuntimeErrorFcn = @daqcallback
        SampleRate = 2000
        SamplesAcquired = 10000
        SamplesAcquiredFcn = []
        SamplesAcquiredFcnCount = 1024
        SamplesAvailable = 0
        SamplesPerTrigger = 10000
        StartFcn = []
        StopFcn = []
        Tag = 
        Timeout = 1
        TimerFcn = []
        TimerPeriod = 10
        TriggerChannel = [1x0 aichannel]
        TriggerCondition = None
        TriggerConditionValue = 0
        TriggerDelay = 0
        TriggerDelayUnits = Seconds
        TriggerFcn = []
        TriggerRepeat = 0
        TriggersExecuted = 1
        TriggerType = Immediate
        Type = Analog Input
        UserData = []

        NIDAQMX specific properties:
        ExternalScanClockSource = PFI7
        HwDigitalTriggerSource = PFI0

[Manisha]

What does

AI.Channel.Coupling

return?

Answer 3

[Pierre]

There is no AI.Channel.Coupling

Here is AI.Channel:

Index:  ChannelName:  HwChannel:  InputRange:  SensorRange: UnitsRange:  Units:

1  'angle'       0           [-5 5]       [-5 5]        
[-5 5]       'Volts'

Answer 4

[Pierre]

Hi Manisha,

We did find a kind of solution. We installed the old NI-DAQ 7.4.4. driver and we do have access to discontinuous signal now, and the AI.InputType is now Differential.... However it is not very satisfying as the NI-DAQmx driver is no longer working. I think there is a bug in the data acquisition toolbox.

Regards