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Limitations of NI-DAQmx Simulated Devices

Updated Apr 2, 2020

Reported In

Driver

  • NI-DAQmx

Issue Details

  • I created a NI-DAQmx simulated device. What are the limitations of these devices with respect to NI-DAQmx physical devices?
  • I'm trying to use a simulated device clock as an external clock to my data acquisition, is this possible?

Solution

The purpose of simulated devices is to offer the possibility to start programming without hardware, check the syntax of the program and verify that written data meets specifications of the board. However, NI-DAQmx simulated and physical devices have some differences:
  • As of DAQmx 8.3 and later, simulated devices will reflect proper timing types for analog and digital tasks. For example, 1000 samples acquired at 1 kS/s will now take 1 second to return on a simulate device. See the note in Additional Information below which describes the timing behavior in versions prior to 8.3.
  • Simulated devices will not detect Error -200078, which is caused by an analog input task attempting to use a counter at the beginning of its acquisition when the counter is already in use. This is due to the fact that this error is generated by hardware, not the DAQmx Task State Model.
  • Simulated devices do not support triggering and it's clock can't be used as external timing sources for other tasks
  • NI-DAQmx simulated devices support software events. However, events that rely on the hardware, such as a sample clock event, are not supported. 
  • Watchdog timers do not expire.
  • NI-DAQmx simulated devices cannot be included in the same task with physical devices.
  • Counter data is always returned as 0. 
  • Timing is not simulated for counter tasks.
  • When reading data, all analog signals will be returned as a full-scale sine wave with three percent of full-scale noise. Digital data is returned as if each 8-bit port were counting up. 
  • It is not possible to read back the data you write to the output lines, as that data is not kept anywhere in memory (data returned will be as described above). There is no way to get feedback about the signals you write to the output lines, besides an error if the value is not within limits. 

Additional Information

Simulated devices In DAQmx 7.4 - 8.1 do not reflect proper timing rates. Task reads and writes will be returned immediately regardless of the sampling rate and number of samples per read/write specified in the task.