Fractional Counts in Buffered Counting Operation Using NIDAQ Tools

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Thu, 12/04/2014 - 05:53 am

I am using NIDAQ Tools MX and a NI PCI-6353 to perform buffered counting from a PMT and associated photon counting circuitry. Inexplicably at seemingly random points in the buffer wave I am getting data points containing fractional counts. E.g.

320021 320040 320065 320112 320143 0.0509744 0.0506521 0.0467849 0.0471072 0.0467849 0.0419509 0.0377615 0.0387283 0.04324 0.0490408 0.0525857 0.0554861 0.0587088 0.0599979 0.0580643 320626 320650 320671 320700 320731 320753

These counts can also be negative.

21727 21746 21772 21781 -0.081155 -0.0640749 -0.0505397 -0.0353931 -0.0199243 -0.00735591 -0.00316644 -0.00187738 0.00456796 0.0116578 0.0168141 0.0168141 0.0174586 0.0197145 22122 22143 22165 22190 22212

After these blips, counting seems to return to normal within 15 or so samples.

The associated code for the counting operation is

DAQmx_CTR_CountEdges/DEV="Dev1"/CLK="pfi12"/SRC="pfi2"/WAVE=chan8AcqBuff 1

The wave that holds the counting data is initialized to NaN before use.

Does anyone have any explanation for this?