Solution
Devices with Delta-Sigma ADCs have different timing properties.
Delta-Sigma C Series devices have discrete sampling rates. Requesting a different rate will result in the module defaulting to the discrete rate closest to the requested sampling rate. The valid samples rate for these devices will be given by a formula that can vary with the module. The formula can be found in the module datasheet's
Data Rates section. For example,
NI 9234 Datasheet and
NI 9237 Datasheet show the valid sample rates are give by
where fs is the sampling rate, fM the internal timebase on the device and n a number between 1 and 31.
SC Express and DSA devices have a finer timing resolution given by the
Sample Rate Range and
Sample Rate Resolution specifications. For example, the
PXIe-4339 sample rates an be set between 1 S/s and 25.6 kS/s in increments of 181.9 µS/s.
It is possible to read the actually used sample rate using the DAQmx Timing Property Node:
Always refer to your Delta-Sigma device's documentation for accurate information about its valid sampling rates.