High speed PXI 6259 synchronization problem

[liron_m]

Hello,

After spending couple of days looking answers to my problem, I got lost and asking for little help.

Well I'm trying to build high speed data-acquisition system, using PXI chasis and two PXI-6259 device.  It's actually kind of a calibartion system.
The First Device :
    -  signal source transmitting analog signal at 100khz, at sample rate of 1Mhz.
    -  Analog input channel sample at 1Mhz
The Second Device
    -  Analog input channel sample at 1Mhz

The two device must be synchronized without any phase different.
I am using DAQmx driver in matlab.

I've tried couple of different setup:

1. Each task using 20MhzTimebase as sample clock, divided by 20.
   
• Using PXI_CLK10 as referenceClock for all 3 tasks.  
• Set Digital Edge start Trigger for the slave device, using the master ai/StartTrigger.
  
• Getting 1.9*10^-6 sec (~510Khz) difference between the two AI devices.
  
2. Same as before, but setting Slave sampleclock as master/ai/SampleClock
• Getting the same 1.9*10^-6 sec (~510Khz) difference
3. Each task using PXI_CLCK10 as sample clock, divided by 10.
• Same setting as before
• Getting 3.9*10^-8 sec (~25MHz) difference between the two AI devices.

Is that really system's limitations? I can't get accuracy better than 0.4 nanosec ?



Regards,
Liron Mizrahi

[David L.]

Hi Liron,

How many analog channels are you measuring on each 6259? If you are measuring multiple channels on each device, all channels will not be phase aligned as this board does not do simultaneous sampling. The 6259 uses a multiplexor, and scans through all channels in the program to latch the channel values on a single board (I.E. – ch0 will have a different phase than ch1,2,3, etc). Also, how are you measuring the phase difference of your signals?