Hi,
I have two PCI 6289 DAQ boards installed in a WinXP sp3 PC with NI-DAQmx 8.8.0f2, Measurement & Automation Explorer 4.5.049152, and VI Logger Lite 2.0.1. The 6289 cards are connected in the PC via a RTSI ribbon cable. My question has to deal with how Measurement & Automation/VI Logger handles signal timing, and interacts with the computer clock. I would like the two 6289 cards to collect data (analog voltage inputs, about 100 pts/sec on all 32 channels, both cards) synchronously; I would like data colelcted at input 00 on both boards to coincide in time, followed by the data collected on channel 01 on both boards, etc. To that end, I have the RTSI cable installed. I have two identical tasks, one for each board, set up in the Measuremetn and Automation Explorer program, since one task apparently can't control two 6289 board. I am fully aware that the 6289 cards multiplex analog signals to the on-board A/D converter, and do not collect data on all channels on the card synchronously.
My first question has to do with the RTSI cable. When I right click on either of the NI-DAQmx devices corresponding to either 6289 card, and select 'Properties', followed by 'RTSI configuration', I find that there is a pull down window for 'RTSI cable', though when I check to see what choices there are, the only option I find is 'none'. Why is this?
My other question has to do with how Measurement & Automation interacts with the system clock. In order to get the data logging to be synchronized between both 6289 cards, I have the two tasks controlling the cards set up identically. I have experimented with several ways to start and stop data logging with mixed results. I start both tasks manually, so there is a time delay between the start of one task and the other. The data logging however, is started via a digital trigger signal, easily implimented within the task. If 'begin logging when acquisition starts' is checked, the data files generated by both daq cards shares the same file name/creation date & time, and the 'time' of each data point in the data files from each daq board coincides with the other. At least the samples from both boards appear to be acquired synchronously, if the 'time' value is to be believed. If however, I leave the 'begin logging when acquisition starts' box unchecked in each task, start the task manually, and start data logging via a digital signal/trigger, the file names of the data files from each board (essentially date and time) are different, and within each data file, the 'time' values associated with each corresponding data point differ slightly, in other words, data point 0 from board 0 was apparently acquired a few seconds before or after the first data point from channel 0 on board 1. Also, if the tasks are started, and there is a delay actually starting the data logging, the time values associated with the data collected and saved are offset by the time delay between starting the task, and starting data logging. In other words, the 'time' associated with each data point is earlier than it was actually collected by the amount of the delay between starting the task and starting data logging. I tried using a digital signal to control data logging, both starting and stopping, of both boards, but didn't have any better results, at least as far as the signal synchronizign goes.
So, my question is, how do I get these cards to collect data synchronously: the acquisition time of channel 00 on card 0 to coincide with the acquisition time of channel 00 on card 1, followed by channel 01 on both cards, followed by channel 02, etc.?
thanks,
Brian
