Data transmission using SCB68 starts, then halts and then, starts again. What is causing this?

[Ayush]

I am using the SCB68 as an interface for connecting an ultrasound sensor operating at 40kHz to my DAQ card. My data consists of a chirp signal of 5ms followed by a certain number of zeros. The number of zeros depend upon the pulse repetition interval (pri) so as to make one unit of data correspond exactly to one unit of pri. This unit of data is subsequently repeated after each pri seconds for a fixed period of time. The sampling frequency is 250 kHz. The problem is that if the pri is lower than 50ms, the data transmission starts, than abruptly stops for 100-300ms and then, resumes again for as long as I want without any halts. However, this halt in the middle affects the processing of the received signal. I have checked all the properties of the analog output object and they seem to be set correctly. Please help as soon as possible.

[Ayush]

Also, sometimes, when the card has been in use for a long time continuously, the following error message is displayed :

Error event occurred at 17:10:34 for the object: nidaqmxDev1-AO. NIDAQmx error : Onboard device memory underflow. Because of system and/or bus-bandwidth limitations, the driver could not write data to the device fast enough to keep up with the device output rate.  Reduce your sample rate, alter the data transfer method (from interrupts to DMA), use a product with more onboard memory, or reduce the number of programs your computer is executing concurrently. Task Name: MWDAT0151  Status Code: -200016

Why does this happen only sporadically and not always? It does not cause any interference with the working of the card but is this error and the problem I mentioned previously somehow inter-related?

[TCPlomp]

Do you use one task continous or do you start/stop the task for every output?

Ton

[Ayush]

I use one task continuously with the 'RepeatOutput' propety set to infinity. The transmission is stopped only once in the end.