Single-point vs. Waveform Acquisition in NI VeriStand

Issue Details

I am building up a VeriStand application and am selecting between single-point hardware and waveform hardware.  What considerations should I take when choosing hardware for a VeriStand system? 

Solution

The NI VeriStand Engine architecture is designed for single-point, closed-loop control.  The memory transfer mechanisms between different loops in the engine are primarily single-element FIFOs and as a result passing waveforms between loops is not a viable option for most applications.  

If you are doing any control in the application, it is strongly recommended to get a data acquisition module with a SAR ADC that can run in hardware-timed single-point mode.  X Series multifunction boards are a good example of this.  The module will acquire at the same rate that the primary control loop is running and feed new single-point information to the control loop at each of its iterations.  

If you are datalogging and are not actively controlling anything with your hardware acquisition, a simultaneously-sampled module with a delta-sigma ADC may be a viable option for the application.  You can create a waveform task, run the task faster than the Primary Control Loop, and log the acquired data to file.  DSA and SC Express modules generally have some amount of filter delay, so keep in mind that your acquisition may not be completely synchronized with a single-point card that doesn't offer the same front end signal conditioning.