Enormous latency while working with NI USB-6521

[Pavel_47]

Hello,

The setup of my testbend is shown on Fig.1, Fig.2.

Here are its features:

• "Simulate Signal" block generates Sawtooth signal with adjustable parameters - ampl, freq, offset, phase
• the output of "Simulate Signal" is wired to the driver of the output AO0 (block "USB-6521 AO0") of the USB-6521 device
• the output AO0 is cabled to the input AI0 of the USB-6521 device
• the output of the driver of the input AI0 (block "USB-6521 AI0") is wired to Waveform Graph (blue line) as well as the input to the driver "USB-6521 AO0" (red line)

Playing with thist testbend I've observed 2 strange phenomenas:

• when I modify some of Sawtooth parameters (i.e. ampl, freq, offset) the latency is about 15 seconds
• while the signal, generated by "Simulate Signal" is perfect Sawtooth, the "USB-6521 AO0" output is not perfect ... in other words its shape doesn't always follow the source shape (I control also by oscilloscope).

Any comments welcome.

Thanks in advance

Pavel

Fig.1

Fig.2

[Pavel_47]

I've copied this post on Most Active Hardware Boards\Multifunction DAQ

[NIquist]

There is no point in posting a picture of Express VIs.  We can't see how they're configured.  Post the code.  

I also suggest you learn to program with real DAQmx functions and dump the crutch of Express VIs.  They have limitations and most of the experienced posters here would never use them so it's hard to advise on them.  

[Dennis_Knutson]

Please use the other thread.

[NIquist]

Thanks Dennis.  Link:  http://forums.ni.com/t5/Multifunction-DAQ/Enormous-latency-while-working-with-NI-USB-6521/td-p/32418...