Buffer underflow when using DAQcard 6024E to generate analog signal

[pcworld]

I am using DAQcard 6024E to generate continuous analog signal. If the update freqeuncy is above 500Hz, I will get the following 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.

My laptop is dell inspron 8500, 2.4GHz. Is there a solution in LabVIEW to increase the update freqeuncy above 500Hz?

[Brooks B.]

Hello:

This error occurs when you are trying to output data from the DAQ Device faster than your program is telling it what to write. This usually occurs if your while loop is taking too long to execute. Possible solutions would be to increase the number of points that you write at at time or decrease the rest of your code in you while loop. Start with the LabVIEW shipping example "Continuous Generation" located under Help >> Find Examples... See how fast that example will run because it is optimized for speed.

Good Luck!

Sincerely,

Brooks B
Applications Engineer

[pcworld]

Thank you for your reply. I tried the example "continuous generation of analog voltage" with 1000Hz update rate, I cannot see the signal on the scope. I also use MAX test panel to generate analog output with 1000Hz update rate, I will get the buffer underflow error within a few seconds. It will be fine if the rate is 500Hz.

I think this might be the hardware limitation because there is no on-board memory and DMA function on the DAQCard.

Regards,

Wei Lin

[Brooks B.]

Wei Lin:

You are absolutely right about the DAQCard 6024E. It has no DMA available since PCMCIA doesn't support DMA and has no onboard FIFO. The specs say that board will do 1 kS/s with interrupts, system dependent. This is something that is highly dependent on the system. Many of the newer laptops have built-in wireless LAN cards that might be taking some of the bus bandwidth. Do you have any other PCMICA cards in the laptop? If so, disable/remove them. Unfortunately, the DAQCard 6024E is really only good for static AO or very slow AO. If you need to do AO with a PCMCIA card, the DAQCard 6062E is a much better card because it has an 8192 sample FIFO for doing AO. Sorry for the limitations but that hardware device is just not really de
signed for doing fast AO.

Good Luck!

Sincerely,

Brooks B
Applications Engineer