novice DIO acquisition question

[Stu@TCD]

I am using Labview RT running on a PXI. Apart from collecting analog data such as accelerometer traces, joystick responses (my experimental subjects make responses via a joystick) and other sources of data, I am interested in integrating eye movement data into my data stream. Specfiically we have an external eye movement measurement device that provides 12-bit H & V pupil position for each eye, plus 12-bit H & V corneal reflection data. There's some other data coming off teh eye tracker as well, in all we have about 56 bits of data to record. Later we may have up to 96-bits to record (when we add head-tracking to teh eye tracker).The eye movement system spits all of this out at 240S/s via a Measurement Computing PCI DIO-96 card. We want to
know what is the best way to integrate our digital eye movement data into our analog data file such that digital and analog data are timestamped. Someone suggested that the NI 6508 (96-bit, unstobed I/O) would be satisfactory given we have a RT system. Someone else told me this was bollocks and that for acquisition rates of 240S/s across 96-bits or more of digital data as well as 10 analog channels would require the high speed NI6534 DIO card (and a couple of them at that!). Any clues, I am a psychologist interested in eye movements, not an engineer interested in psychology. Cheers, Stu

[JustinBritten]

Stu,

If you acquire one bit of data from each of the 96 lines 240 times per second, then you are transfering 23040 bytes of data per second. Therefore, you will need a card that can perform at a minimum of 23.04kbytes/s. The PXI-6508 has a maximum rate of around 50kbytes/s. Transfer rates vary due to programming language, code efficiency, CPU speed and utilization, etc. Typical sustainable rates are around 1-10kbytes/s for this board. At the worst-case scenario of 1kbyte/s you would only be sampling 96 lines at 10.4S/s. I would recommend a high-speed digital I/O card. As was suggested to you, the PXI-6534 would be sufficient for your needs. Unfortunately, our high-speed cards have 32 lines maximum. Again, your friend was correct in saying that 3 ca
rds would be necessary.

The User Manuals for the PXI-6534 and PXI-6508 can be found on our web site at http://www.ni.com/manuals. The manuals include the card specifications.

Regards,
Justin Britten

Applications Engineer
National Insruments