Error -200802 While Trying to Output a Continuous Signal with DAQ Assistant

Issue Details

I am using LabVIEW with an NI USB-6211 DAQ device to control a machine by outputting analog signals. My project uses Express VIs and is configured for continuous sample generation because I need the signal to run for about two minutes.

However, when I execute the code, I encounter the error showed below.

Why does this error occur and how to resolve this?

Solution

The error message in the screenshot above has several possible reasons and the one applicable here is "Sample timing type is something other than On Demand". The error is caused by a mismatch between:

• Signal Generation Mode of the Simulate Arbitrary Signal configuration (e.g., One point per iteration)
• Timing Settings in DAQ Assistant (e.g., On Demand vs. N Samples)

As an example, the Simulate Arbitrary Signal could have been set to generate one sample per loop iteration whereas the DAQ Assistant could have been set to write 1000 samples per iteration.

To resolve this, you can use one of the following approaches: 

1. Set the Simulate Arbitrary Signal node to output the Entire Signal each iteration and configure the DAQ Assistant to N Samples. Remove the loop. Make sure the Samples to write value in DAQ Assistant is the same or less than Number of points defined in the Signal Simulator. This method sends the complete signal to the USB-6211, which then outputs it automatically.

2. Leave the Signal Generation setting of the Simulate Arbitrary Signal node as One Point per iteration but set the DAQ Assistant to 1 Sample (On Demand). Add timing control code into the while loop to handle the needed timing.

Additional Information

Both methods have drawbacks:

1. The first method has the drawback that as the signal is generated and transferred to the DAQ hardware at once, it is not possible to easily change the signal waveform while it is being output.
2. The 2nd method introduces jitter because LabVIEW relies on Windows timing, which is less precise than the DAQ hardware internal clock.