Changing minimum and maximum voltage that we expect to generate/measure

[Freestyler]

Hello!

Our application has one AO and one AI voltage task with minVal fixed to -10 and maxVal fixed to +10. We acquire/generate m samples n times (for a total of m*n samples). It's possible to reconfigure the minVal/maxVal each of the n times (depending on the generated/acquired samples) in a quick way? If I'm correct, this is possible by stopping and recreating the task (calling DAQmxClearTask, then DAQmxCreateTask and finally DAQmxCreateAIVoltageChan or DAQmxCreateAOVoltageChan), but as far as I know this is a slow operation and this is not a good thing for our application. Are there other ways to do this? Actually we're using the NI PCI-6229 card.

Thanks in advance!

[LiciaP · Accepted solution]

Hi,

it is possible to set (and also get) the minimum and maximum values for a DAQmx channel: in LabVIEW through DAQmx channel property nodes Analog Input:Maximum Value and Analog Input:Minimum Value, in textual programming languages with functions DAQmxSetAIMin, DAQmxSetAIMax (and similarly for AO channels).

However, for M-series boards it is not possible to set these properties while the task is running, so you will have to stop the task, set the new values and start the task again.

I hope that this will help!

Bye!

Licia  

[Freestyler]

Grazie 🙂  

So something like this should do the work (I've added the code that seeks for max and min values and the function calls to DAQmxSetAOMin and DAQmxSetAIMin: 

'=================================================== AO ===============================================
'** START AN ANALOG OUTPUT OPERATION AT GIVEN BITRATE, TASK ALWAYS OPERATIVE **
Public Sub StartAOTask(OutData() As Double, SampsNum As Long, Bitrate As Double)
    If mBoardEn Then
        Dim i As Long, min As Double, max As Double
        
        min = OutData(0)
        max = min
        For i = 0 To UBound(OutData)
            If OutData(i) < min Then min = OutData(i)
            If OutData(i) > max Then max = OutData(i)
        Next
    
        Call DAQmxErrChk(DAQmxStopTask(mAOTaskHnd))
        Call DAQmxErrChk(DAQmxSetAOMin(mAOTaskHnd, "AO0:2", min))
        Call DAQmxErrChk(DAQmxSetAOMax(mAOTaskHnd, "AO0:2", max))
        Call DAQmxErrChk(DAQmxCfgSampClkTiming(mAOTaskHnd, "", Bitrate, mDAQmx_Val_Rising, mDAQmx_Val_FiniteSamps, LI2Curr(SampsNum)))
        Call DAQmxErrChk(DAQmxWriteAnalogF64(mAOTaskHnd, SampsNum, mAutoStart, mTimeOut, mDAQmx_Val_GroupByScanNumber, OutData(0), mManagedSamples, 0&))
    End If
End Sub

 And the task was defined so:

    Call DAQmxErrChk(DAQmxCreateTask("", mAOTaskHnd))           'Create AO - task 4 analog output
    Call DAQmxErrChk(DAQmxCreateAOVoltageChan(mAOTaskHnd, "Dev1"/ao0:2", "AO", -10#, 10#, mDAQmx_Val_Volts, 0&))

Is this looking OK?