SampClk.timebase.rate changes after Generation Task?

[dpwave]

I have a DAQmx Timing property node associated with a continuous AO task that pulls SampClk.Timebase.Rate each time before a new waveform (with different parameters) is created. After the waveform is created,  the task is started and stopped after data acquisition on other channels.  The weird thing is, there are instances where the value of SampClk.Timebase.Rate changes, even though nothing in particular changes the task properties except for the signals. I was under the impression that timebase rate is associated with the internal clock (NOT using an external clock here), and should be constant. Can anyone think of anything that could have caused this to happen? I am using a NI-4461, LabView 2010, and the latest NiDAQmx for this task, and SampClk.Timebase.Rate changes between 2.62144E+7 and  1.67772E+7 from time to time. Please help me explain this. Thank you!

Dan

[jmoody]

Hi Dan,

Are you using the PCI or PXI version of the NI 4461?  Also if you wire up a SampClk.Timebase.Src property, is it the same when the rate changes?  The 2.62144e7 is correct for the NI 4461 as shown here:

http://www.ni.com/pdf/manuals/373770j.pdf

on page 2.  Multiply any of the top of the ranges by their multiples (ie. 1.6e3*16384).