On 27/12/12 23:22, Magnus Danielson wrote:
Sometimes when you have isolated machines, the absolute time may not
need to be very accurate, but the relative timing between them can be.
Adjusting from wrist-watch every once in a while may suffice for
absolute time.
Yes, but what happens to the relative time when you adjust one of the
machines?
The requirement seems to be to have a deviation of less than 10ms, but
using a wristwatch is only going to give about a second resolution, so
there could be a step change a couple of orders of magnitude bigger than
that whilst the new time is propagated to subordinate machines.
Surely, either don't bother (ever) to resynch to real time, or the
problem remains. Wherever you get the master time from, you must be able
to get it with a resolution of 10ms or better and you must measure how
frequently you need to update the time so that the deviation is never
greater than 10ms at resynch time.
Rgds
Ken
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