Data Rates

The frequency of the master timebase (f_M) controls the module data rate (f_S), PWM, and dither frequencies of the NI-9470. The NI-9470 includes an internal master timebase with a frequency of 12.8 MHz, but the module can also accept an external master timebase or export its own master timebase. To synchronize the data rate of a NI-9470 module with other modules that use master timebases to control sampling, you must configure all the modules to share a single master timebase source.

The following table lists the available data rates of the NI-9470.

Because the NI-9470 has a limited set of module data rates available, you must configure other modules to run at the same sample rate as the NI-9470 module data rate to synchronize and phase-align samples. Data rates of 3.125 KS/s or 2.000 KS/s with a 12.8 MHz master timebase or 3.200 KS/s or 2.048 KS/s with a 13.1072 MHz are compatible with other dynamic signal acquisition (DSA) modules for phase-aligned samples. If correlated and non-phase-aligned samples are acceptable for your application, then you can configure other modules using the same master timebase to a faster sample rate than the NI-9470 module data rate.

You can configure the PWM divisor of each channel of the NI-9470 independently with a range of one to 511 to further divide down the module data rate to a channel PWM frequency. Software will operate the NI-9470 I/O nodes at the per-channel frequency. If I/O nodes from different channels or modules with different data rates are combined in the same loop, then the I/O node that runs the slowest will determine the loop time. The faster node will repeat output setpoints, drop readback samples, and a software warning will appear.

You can configure the dither divisor of each channel independently with a range of four to 4,095 that further divides down the channel PWM rate. Larger dither divisor values will increase the number of data points in the generated dither triangle waveform operating around the output setpoint.