Error 200281: Read relative to the reference trigger

[Tyzack]

I am trying to set up a DAQMx task that, when commanded to start, reads data continously, until it reads a stop trigger (hardware, rising). At that point I want to get back n number of total samples with p samples before the trigger (conceptutally n total, p before trigger, n-p after trigger)

I believe that I want to use a "reference trigger" to do this. So I have setup my task thusly:

// Create the channel

m_DAQmxTask.AIChannels.CreateVoltageChannel(m_Device.AIPhysicalChannels[channelIndex], channelName,

AITerminalConfiguration.Differential, m_ScalingFactor * -1.0, m_ScalingFactor, "BinaryCodes");

m_DAQmxTask.Timing.ConfigureSampleClock(

string.Empty, m_ClockFrequency, SampleClockActiveEdge.Rising, SampleQuantityMode.FiniteSamples, m_NScans);

m_DAQmxTask.Triggers.ReferenceTrigger.ConfigureDigitalEdgeTrigger(

"PFI0", DigitalEdgeReferenceTriggerEdge.Rising, m_PreTriggersScans);

m_DAQmxTask.Stream.ReadAllAvailableSamples =

true;

m_SingleChannelReader =

new AnalogSingleChannelReader(m_DAQmxTask.Stream);

m_SingleChannelReader.BeginReadMultiSample(m_NScans,

new AsyncCallback(singleChannelRead), null);

then, in singleChannelRead, the line:

double

[] dataArray = m_SingleChannelReader.EndReadMultiSample(iasResult);

Gives me a DAQmx error 200281 read relative blah blah blah.

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I added the "m_DAQmxTask.Stream.ReadAllAvailableSamples = true;" as a shot-in-the-dark fix though it didn't work.

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Am I setting this task up correctly for what I want to do? If so, what I am doing wrong? If not, what is the proper way to set up this task?

[MartyMcDAX]

Hello Tyzack,

This error is probably occurring, because you have set up a reference trigger (which is designed to acquire pretrigger samples prior to being triggered), but the trigger is occurring before enough pretrigger samples have been acquired.  

If you are new to data acquisition in Measurement Studio, I would recommend you check out the program structure of some of our examples, such as AcqVoltageSamples_IntClkDigRef, located in the National Instruments directory on your machine:

\National Instruments\NI-DAQ\Examples\DotNET2.0\Analog In\Measure Voltage\AcqVoltageSamples_IntClkDigRef\cs

This is a very helpful example that demonstrates the overall structure of data acquisition in Measurement Studio.  I hope that helps.