Hi AEC ENGINEER,
0.00001 Hz accuracy on a ~512 Hz signal is a little shy of 20 ppb.
You should technically be able to get this order of accuracy with the PXI-6608, which is calibrated to 11 ppb (10 ppb tolerance to the measurement + 1 ppb measurement error), but be wary that the oscillator will drift over time (see user manual) and will need to be recalibrated to maintain the 20 ppb accuracy that you require. The first year of normal use you can expect up to a 45 ppb drift in the timebase, but as the board ages the oscillator should drift less than this. You can perform the calibration yourself if you happen to have a 0.75 ppb rubidium clock source handy, or you can work through NI to calibrate the board as necessary.
The 6608 has 8 counters, but you need to use a 2 counter method to get enough resolution (the maximum timebase on the 6608 is 80 MHz, so the measurement error from the standard 1 counter method would be higher than your requirement). The "Large Range 2 Counter Method" is what you will want, and you will need to set the divisor high enough (1024 should work, and would give you an update every 2 seconds). Luckily, the 8 counters on the 6608 gives exactly enough counters for your 4 input signals when using the 2 counter method.
If you have a clock source that can drive the chassis backplane 10 MHz clock to the degree of accuracy that you require, then 6602s can be used instead (they PLL to the backplane). The 6608 is capable of driving the backplane clock, but you can also use the 6653, or if you're interested in PXIe the 6674T. Either of the Timing/Synch modules have the same caveat as the 6608--they would require warm up and would need to be calibrated more frequently than the recommended 1 year interval to maintain the accuracy you are asking for.
There are other factors like tolerance in the chassis power supply that could be a factor as well, but I think overall what you are asking is right on the threshhold of the aforementioned mentioned products (6608, or 6653/6674T + 6602) assuming they are properly warmed up and calibrated. If you're on a PXIe chassis then X Series cards would be an option to replace the 6602 and would give you 4 counters per slot (but you have to give them the high-accuracy backplane clock from a timing/synch module to get the accuracy you require). X Series cards have a sample-clocked frequency measurement that gives similar accuracy to the large range method but does not require 2 counters.
Best Regards,
John Passiak
