Multithreading and daq acquisition

Question

I�m trying to run 2 DAQ�s (PCI MIO 16 XE) devices in one PC (Win XP) to acquire N-data samples from 5 AI channels each using LV 7.0. For the acquisition to starts, each device is independently triggered (5KS/s) . It works fine and I can get the data. The problem is that the second DAQ starts the acquisition probably only after the first has finished its acquisition. (I cannot be sure about that because actually I do not know how to get the start time of an acquisition). At least the DAQ�s are starting the acquisition at different times and this could be a problem if the time difference is to big( >500 micro seconds).
1. is this a classical Multithreading problem? Is there a solution?
2. how can I assure that both DAQ�s start
the acq. nearly at the same time?
3. how can I get the start time of the Acq. ?
4. if I have to use 4 DAQ�s on one PC will this work? Known problems?
Thanks
Alberto

Answer 1

Let me try to explain my problem using the DAQmx example VI �Cont Acq&Graph Voltage-Ext Clk- Dig Start.vi�.
Making few changes to the above VI, you can use it as a Sub-Vi. ( I also limited the number of scans to 1000). I used 2 PCI MIO 16XE-10 devices and wrote a program using two of this sub.vi. I used one trigger signal and one clock for both devices and scanned the same channel. As input I used a Sinus voltage. After the program runs, If I plot the obtained data time independent, i.e the x-axis is now the scan number rather than time (relative or absolute) I get a shift in the signals of about 90 clocks, this means that for example, the scan position for the max amplitude came for one device 90 clocks later than for th
e first device. This is unacceptable for my application
In other test , If I just did copy the block diagram of the example in a new VI twice and made the necessary changes (trigger channel, channel names, etc). Now I got NO shift in the Graph. Both sinus waves were exactly the same. But I still have no idea about the difference on the start time of both devices. I suppose, in this case both devices started at the same time. But how can I be sure of that?
Without the possibility of using that Sub-Vi�s and because I have to use 1, 2 or 4 devices selectively, my program will be looking very complicated. I�m sure there must be a better way to solve this.
Thanks