Continous period, overwritte​n error

Question

I am working for a project to counting every photon for about 10 seconds.
I used the pci-6602 and a computer with a 2.8Ghz Core i5-2300 CPU and a 16GB RAM.
The software is Measure studio 2010 SP1 and NI DAQmx 9.5.
But there will be an error:
Data was overwritten before it could be read by the system.
If Data Transfer Mechanism is Interrupts, try using DMA. Otherwise, divide the input signal before taking the measurement.
For average 300kHz input signal, the error appeared immediately, but for average 1kHz input signal, the error still appeared after 3-5 seconds.
Here is my setting:
myTask.CIChannels.CreatePeriodChannel(counterCombo​Box.Text, "",
                    Convert.ToDouble(minValueTextBox.Text),
                    Convert.ToDouble(maxValueTextBox.Text), edge,
                    CIPeriodMeasurementMethod.LowFrequencyOneCounter, 0.001, 4, CIPeriodUnits.Seconds);
        myTask.Timing.ConfigureImplicit(SampleQuantityMod​e.ContinuousSamples, 100000);
        myTask.CIChannels.All.DataTransferMechanism = CIDataTransferMechanism.Dma;
        myTask.CIChannels.All.DuplicateCountPrevention = false;
        myTask.Stream.ReadWaitMode = ReadWaitMode.Poll;
        myTask.Stream.ConfigureInputBuffer(1000000);
I tried many solutions and changed many setting, but the result didn’t changed.
I heard that the on board memory of pci6602 is small, but for 1kHz signal it still can’t work.
Please help me to solve this problem.
Thanks very much.

Answer 1

1. The basic idea is that instead of measuring the period between each individual photon detector pulse, you simply count the # of pulses occurring within a fixed interval.  The fixed interval would be a constant rate sample clock and you could use another counter to create it.  You may need to look into the "Duplicate Count Prevention" property because you will want to capture the many intervals in which 0 pulses occur.
2. Impossible for me to judge what resolution or format you need for your data.  In general, count-binning will give you a measurement of average photon activity per sampling interval.  If you get 10 counts in 1 msec, you'll only be able to see that as an *average* of 10 kHz.  Reality may be 10 pulses at > 100 kHz and a lot of idle time.
  Freq or Period measurement on individual pulses gives you much more information about photon activity and you can also do some binning-like averaging after the fact.  But the occasional fast bursts may cause a data acq error.  The high precision trades off against the chance of losing all the data due to a data acq error.
If it was me, I'd lobby for a more suitable data acq board like an X-series and measure individual pulses.  But it may be that your particular experiments & studies don't demand that precision, in which case binning is a method that should work with the data acq board you've already got.
-Kevin P