[time-nuts] HP5061B Cold Start

Donald E. Pauly trojancowboy at gmail.com
Sat Apr 8 18:02:03 EDT 2017


We performed an experiment with our working HP5061B which had been
cold overnight.  This was to better determine lock time from cold
ovens.  We found that the crystal oscillator oven heats up about twice
as fast as does the cesium oven.  Therefore the lock time is not much
different whether the crystal oscillator was cold or hot.  Our crystal
oven has been running 34 when hot.  The cesium oven has been running
about 14 when hot.  Here is our data as a function of measurement time
in minutes versus meter readings.  "+" denotes a pegged meter.

The instrument was powered on at 0 minutes except for the cesium
heater.  The cesium heater was turned on at 13 minutes. The crystal
oven had nearly stabilized by that time.  Oscillator heater current
was stable 15 minutes after power up and undershoots a bit at about 23

Note that first signs of beam current occur 7 minutes after cesium
oven was powered up.   First signs of 2nd harmonic occurred 9 minutes
after cesium oven was on.  We conclude that lock is feasible 23
minutes after a cold start.  If the crystal oven is left on, lock can
likely be achieved 20 minutes after the cesium oven is powered up.
The ion pump preserves beam tube vacuum if the crystal oven is left
on.  If it is left off for long periods, high ion pump current may
delay the application of power to the cesium oven until the vacuum is
pumped down.

For those who only occasionally need the stability of a cesium clock,
you can have full performance 23 minutes after a cold start, or 20
minutes if the crystal and the ion pump are hot.  If you use cesium
for an hour a day, tube lifetime will be extended by 24 to 1 over
continuous operation.  If a beam tube lasted five years in continuous
operation, it will last 120 years if used an hour per day.  A similar
benefit will occur if you use it continually for 2 weeks once a year.
It does no good to waste cesium unless you are using the instrument.

Time Ces Osc Beam 2nd

 0   +  0  0  0
 7   +  0  0  0
11 55  0  0  0
13 40  + 0  0
15 42 34 0 0
20 42 34 2 0
22 42 32 6 2
23 25 32 10 5 no lock
24 19 32 12 9 lock (free run back to OPR)
28 19 34 20 34 normal beam current

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