Conflicts using Simulated Modules 9231 and 9204 (with cDAQ-9177) - Channel Order and Sampling Rate Limits

[daniela21]

Hi everyone,

I'm working with a simulated cDAQ-9177 with two simulated AI modules: the 9231 for IEPE (max rate 51.2 kS/s per channel) and the 9204 for Voltage (max rate 250 kS/s total). I am reading from both modules in the same task using continuous samples (batches of 100). I have encountered two problems:

1. Channel order affects the (simulated) readings:
   If I add 2 IEPE channels and 4 Voltage channels (in this order), the 2 IEPE channels read a sine wave with almost-zero amplitude, the first 2 Voltage channels read full-scale noise, and the last 2 Voltage channels read the expected sine wave.
   If I add 4 IEPE channels and 2 Voltage channels, the first 2 IEPE channels read the expected sine wave, the last 2 IEPE channels read the almost-zero-amplitude sine wave, and the 2 Voltage channels read full-scale noise.
   Basically, each IEPE channel gets mixed with the closest Voltage channel.
   If the order is reversed (Voltage channels first, then IEPE channels), every channel reads the expected sine wave.
2. Sampling rate limitation with ≥5 Voltage channels:
   Starting from 5 Voltage channels (regardless of the number of IEPE channels), an error appears saying the maximum sampling rate is 34.13 kS/s. For 5 Voltage channels, I would expect the sampling rate to work up to 50 kS/s because this would still be within the 9204’s maximum total rate, and it does not exceed the 9231’s maximum rate either. Also, the maximum sampling-rate value shown in the error does not change for any higher number of Voltage channels.

I thought these problems might be related to clock synchronization because the modules belong to different C-Series groups (the 9231 is a Delta-Sigma device while the 9204 is a SAR-Scanned device), but after reading the article "NI: Signal-Based Synchronization of Analog Input C Series Modules with NI-DAQmx in LabVIEW" I didn’t find any explanation for these issues.

Are these conflicts happening only because I'm working with simulated devices?

Notes: With a cDAQ-9179, the first conflict is reversed (the order that works is IEPE channels first, then Voltage), and the second conflict is the same. I am using the most recent LabVIEW version and corresponding drivers (including DAQmx). 

[santo_13]

Please do not create duplicate posts - https://forums.ni.com/t5/Multifunction-DAQ/Issues-using-Simulated-Modules-9231-and-9204-in-One-Task-...