DAQCad 6024E Problem

[saint]

I have a problem with my DAQCard 6024E running under Windows XP. I am using the card to continuously acquire data on multiple channels, typically at 500Hz per channel although the sampling rate is configurable by the user. I am using NIDAQ Dll calls from a C++ program, and I am using DAQ_Monitor in a timer loop to read data from the acquisition buffer.

The problem is that at certain sampling rates, the driver doesn't supply data in a 'smooth' fashion - I'm checking for new data every 25ms or so. DAQ_Monitor reports no new data available for about half a second, and then reports loads of data is available very quickly - the net result being that data is being captured in bursts rather than in equal chunks.

I don't see this problem using a PCI602
3E board in a desktop PC, and I also don't see this happening with an old DAQCard 500 running on XP.

What is going on here, and what can I do to resolve it?

[Spencer S.]

Saint,

Because you are performing a hardware-timed acquisition, the data is not being captured in bursts. It is acquired at a specific rate. The transfers from the FIFO on the 6024E into the memory on the computer are in bursts. Because PCMCIA cards do not have DMA capabilities, they have to use interrupts. Interrupts are very system dependent. Do you have other processes running on your system?

Spencer S.