Confirming that I'm getting all samples

[sandheep]

Hello--

I have an application where I'm sending a 100Hz pulse to a device and I'd like to measure 27 analog inputs for each cycle of the pulse.  My DAQ is an NI-USB 6363 OEM.
I've configured the task to trigger off the counter output (PFI12 in this case), and have the system capturing a finite number of samples for each cycle (1M samples /27 channels @ 100Hz = 370 samples per cycle).  Despite this, I seem to be only getting about 22-24 samples for every 100 cycles.  I'm not getting any buffer overruns, so I'm not sure where the data is going.  Below is my code:

Public Function StartPulse(ByVal CycleParams As CycleParameterType, ByVal SampleRate As Double, ByRef ErrMsg As String) As Boolean
        With CycleParams
                PressHiTime = .PressureOnTime / 1000
                PressLoTime = (.Period - .PressureOnTime) / 1000
                VentHiTime = .VentOnTime / 1000
                VentLoTime = (.Period - .VentOnTime) / 1000
                VentLagTime = (.LagTime) / 1000
                SamplesPerSnap = Convert.ToInt32(SampleRate * .Period) / 1000
        End With

        If AIRunningTask Is Nothing Then
            Try
                AITask = New Task()
                AITask.AIChannels.CreateVoltageChannel("/" & DAQName & AIPort, _
                                                       "AnalogInputs", AITerminalConfiguration.Rse, AIMinVoltage, AIMaxVoltage, AIVoltageUnits.Volts)
                AITask.Timing.ConfigureSampleClock("", SampleRate, SampleClockActiveEdge.Rising, SampleQuantityMode.FiniteSamples, SamplesPerSnap)
                AITask.Triggers.StartTrigger.ConfigureDigitalEdgeTrigger("/" & DAQName & PressurePulseOutputChannel, DigitalEdgeStartTriggerEdge.Rising)
                AIReader = New AnalogMultiChannelReader(AITask.Stream)
                AIRunningTask = AITask
                AIReader.SynchronizeCallbacks = True
                AITask.Control(TaskAction.Verify)
                'Pressure Signal Generation
                PressurePulseTask = New Task()
                PressurePulseTask.COChannels.CreatePulseChannelTime("/" & DAQName & PressurePulseCounter, _
                                                            "PressureSignal", COPulseTimeUnits.Seconds, COPulseIdleState.Low, _
                                                            0, PressLoTime, PressHiTime)
                PressurePulseTask.Timing.ConfigureImplicit(SampleQuantityMode.ContinuousSamples)

                'Vent Signal Generation
                VentPulseTask = New Task()
                VentPulseTask.COChannels.CreatePulseChannelTime("/" & DAQName & VentPulseCounter, _
                                                            "VentSignal", COPulseTimeUnits.Seconds, COPulseIdleState.Low, _
                                                            VentLagTime, VentLoTime, VentHiTime)
                VentPulseTask.Triggers.StartTrigger.Type = StartTriggerType.DigitalEdge
                VentPulseTask.Triggers.StartTrigger.DigitalEdge.Edge = DigitalEdgeStartTriggerEdge.Rising
                VentPulseTask.Triggers.StartTrigger.DigitalEdge.Source = "/" & DAQName & PressurePulseOutputChannel
                VentPulseTask.Timing.ConfigureImplicit(SampleQuantityMode.ContinuousSamples)

                'Count the Signals
                CountPulseTask = New Task()
                CountPulseTask.CIChannels.CreateCountEdgesChannel("/" & DAQName & CountPulseCounter, _
                                                                  "CountPulses", CICountEdgesActiveEdge.Rising, 0, _
                                                                 CICountEdgesCountDirection.Up)
                CountPulseTask.CIChannels.All.CountEdgesTerminal = "/" & DAQName & PressurePulseOutputChannel
                CountPulseReader = New CounterSingleChannelReader(CountPulseTask.Stream)

                'Start 'em up!
                CountPulseTask.Start()
                VentPulseTask.Start()
                AIReader.BeginReadWaveform(SamplesPerSnap, AIAsyncCallback, AITask)
                PressurePulseTask.Start()
                Debug.Print(AITask.Timing.SampleClockSource)
            Catch ex As Exception
                AIRunningTask = Nothing
                AITask.Dispose()
                StatusCheckTimer.Enabled = False
                ErrMsg = ErrMsg & " " & ex.Message
                StartPulse = False
                Exit Function
            End Try
        End If
        StartPulse = True
    End Function

    Private Sub AICallback(ByVal ar As IAsyncResult)
        Dim ErrMsg As String = ""
        Try
            If (Not (AIRunningTask Is Nothing)) AndAlso AIRunningTask Is ar.AsyncState Then
                ' Retrieve data
                AIData = AIReader.EndReadWaveform(ar)
                'Plot your data here 
                DataToQueue(AIData)
                AIReader.BeginMemoryOptimizedReadWaveform(SamplesPerSnap, AIAsyncCallback, AITask, AIData)
            End If
        Catch ex As DaqException
            DAQError = ex.Message
            StopPulse(ErrMsg)
        End Try
    End Sub


    Private Sub DataToQueue(ByVal sourceArray As AnalogWaveform(Of Double)())
        Dim i As Byte = 0
        Dim tmpstr As String = ""
        Dim tmpAIdata(NumChannels - 1, SamplesPerSnap - 1) As Double
        Dim dataCount As Integer = sourceArray(i).Samples.Count
        For i = 0 To NumChannels - 1
            For j As Integer = 0 To (dataCount - 1)
                tmpAIdata(i, j) = sourceArray(i).Samples(j).Value
            Next
            If i = SystemPressureChannel Then
                AIPressure = tmpAIdata(i, dataCount - 1)
            End If
        Next i
        AISnap.Add(tmpAIdata)
    End Sub

Any thoughts on what the problem is?  Do I need to configure the sample clock source?Thanks!!!Sandheep

[Dane.S]

If you execute the code with only one channel are you seeing the same behavior?

[sandheep]

Dane--

Thanks for the response.  I did not try that, but remedied the situation by switching to a solution based on the ContAcqVoltSmpls_EveryNSamplesEvent example. 

That seemed to be the only option that did not use Endreadwaveform.  Perhaps I don't understand how things work, but it seems to be that if you have an async callback that has an endreadwaveform, data handling code, and beginreadwaveform, then there is a possibility to lose data in between the endread and beginread, right?  Or is the data streaming constantly, and endread finishes a "sip" of data, while beginread begins a "sip"?

Please let me know what you think.

Thanks!

Sandheep