[time-nuts] Z3805 two frequency maxima

Hal Murray hmurray at megapathdsl.net
Wed Nov 28 07:10:49 UTC 2012


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paul.destefano at willamettealumni.com said:
> We have an application in which we plan to travel 7 hours with an SR620
> turned off, then turn it on for 1 hour and take measurements we expect to
> be accurate to less than 1ns.  I would appreciate more information about
> how to get reliable data out of this instrument. 

What do you mean by "accurate to less than 1ns"?  What are you trying to measure?

The internal clock in the SR620 may be off a bit.  The specs should be in the users manual.  In general, you have to wait a while for it to warm up and it will depend on which options you have.  (Some units have good crystals.  Some have low cost crystals to save $$ if they will normally run off an in-house reference clock.)

Suppose it's worst case 1 part in 1E9, just to pick a handy number to work with.

If you measure the width of a 1 microsecond pulse, the error from the clock will be 1E-15 seconds or 1E-6 ns.

If you measure the time between 2 consecutive PPS pulses, the error from the clock will be 1E-9 seconds or 1 ns.



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