04-12-2015 04:02 PM
Hello,
I'm doing some very low level noise measurements, order of one uV where picked up stray mains voltage frequencies easily dominates. So I searched for the possibility to sample below the Nyqvist frequency of the mains frequency, as I'm measuring 10hz signals and below anyway.
In the datasheet, the specifications, NI Dynamic Signal Acquisition User Manual I find 1kHz stated as the lowest sampling rate for the 446x. However, the minimum sample frequency of my 4462 is actually 31.25hz, which I found "by accident", from the NIMAX test panel by setting a too low sample rate. The error message gave the valid sample range. I guess this can also be verified via a property call.
I think it would be valuable if te documentation would be updated, for example the filtering section.
my2c
04-14-2015 05:19 AM
Of course, that should have read "minimum sample rate comment".
Can someone tell me how to read the sample rate limits in .net. What's the property to look for? I really can't find it in the docs....
04-22-2015 12:12 AM
This is the propert for the driver (in C)
http://zone.ni.com/reference/en-XX/help/370471AC-01/mxcprop/attr1344/
I would guess myTask.Timing.ActualSampleRate or similar in .NET, check the helpfile for timing properties.
04-22-2015 11:19 AM
Thanks,
But that does not read back the valid limits, only sets rate values?
I'm OK now but it should be of general interest for all DAQ devices, to be able to read valid values.
I think the 1kHz comes from the lower limit using the internal clock in the ADC chip, but the PXI-4462 uses it's own DDS tunable clock.
Anyway, it works down to 31.25 Hz.
my2C
04-23-2015 01:44 AM
You are able to read it back, first you set a value and then you typically read it back to see that the value was actually set to what you wanted.
DAQmxGetSampClkRateis the C function described in previous post link. There is a similar one for .NET which you can find in the .NET help.