Timebase

[Cluo]

1. what is the differences between master timebase and reference timebase? 2. what is convert clock? 3. when do function sync DAQ, the ai sample clock and ao sample clock are all divided from master timebase, so they just share a start trigger when do function sync DAQ in one module? Thank you.

[John_P1]

Hi Cluo,

Some older DAQ boards can accept an external Master Timebase.  For example, here is a functional diagram of the E Series Analog Input Timing Engine (taken from the E Series User Manual😞

Many newer boards can phase-lock their internal timebases to an external clock.  We refer to this external clock as a Reference Clock (rather than a reference timebase).  Here's the M Series equivalent of the above diagram--it's actually two separate diagrams in the M Series User Manual since everything upstream of the AI Sample Clock Timebase MUX is common to the whole board (which is also true for the E Series boards, but the complexity is not such that it would warrant an entire separate diagram):

           

Notice that both boards can also accept an AI Sample Clock Timebase, which is specific to Analog Input clocking and is not used for all subsystems like a Reference Clock or the Master Timebase.  AO has similar diagrams in the manuals, and counters are a bit unique but can also accept external "timebases".

The Convert Clock is when the A/D conversion actually takes place.  On multiplexed boards, a single pulse of the Sample Clock will initiate one convert clock pulse for every channel in the scan list.  The rate of the convert clock affects the amount of time allowed for settling between channels (remember, every channel is multiplexed into one ADC).  Simultaneous boards like S Series and a few X Series boards do not have a separate convert clock, and just perform the conversion based directly on the sample clock.

If you are synchronizing multiple subsystems on the same board, using the default clocking options would derive all the clocks from the same timebase so usually all that you need to share is a start trigger.  When synchronizing multiple boards, you would need to either:

    1. Share a timebase/reference clock + Start Trigger

    2. Share a sample clock directly -- note that on Multilpexed boards you might also want to share convert clocks.  Of course, on multiplexed boards the separate channels are not sampled at the same time so this may not be important to you.

Best Regards,

010-06-30_111141