The Cesium Beam Primary Frequency
Standard is a rugged, compact, militarized, hybridized, solid-state,
Atomic Frequency Standard and Real-Time-Of-Day Clock, which provides
Standard and sinusoidal
output frequencies of 5 MHz, 1 MHz and 100 kHz accurate to ±5x10-12
with a long-term stablity of ±1x10-11.
Timing information in hours, minutes and seconds,
in the form of a direct real-time LED display Time-Of-Day Clock,
and 1 PPS and PPM outputs for driving external clocks.
The Standard owes its exceptional accuracy and stability
to a unique frequency comparison-and-control system, in which a
cesium atom (Cs133) is used to stabilize
the output frequency of a precision voltage-controlled quartz crystal
oscillator using an SC cut crystal to provide improved performance
under dynamic environments. The oscillator output is multiplied
and drives the cesium tube.
The signal induces transitions from one hyperfine
energy level to another, and those atoms which have undergone this
transition are detected by a hot wire ionizer and electron multiplier.
The output of the electron multiplier is fed back through an oscillator
control circuit to correct the oscillator frequency, maintaining
the Standard's accuracy.
Meters and Displays
Major circuit functions and signal levels are metered via a front
panel circuit switch and meter in combination, providing a convenient
means for determining the operational status of major circuits.
Operating status and alarm LED displays indicate operational status
of the primary and secondary loops.
The Standard may be transported, used as a bench-mounted
unit or rack-mounted by using the four mounting screws on its front
Three Power Sources
The Standard may be operated from three power
First Priority115 or 230 Vac, 47 to 400 Hz, single-phase.
Second PriorityExternal 22 to 30
Third PriorityInternal battery supply.
Simultaneous connection of ac and dc power source inputs can be
Front panel indicators advise of input power
availability, power source in use, and changing status of the internal
In the event of a power failure in any mode, automatic
transition between power sources takes place without any effect
or perturbation of time and frequency accuracy.
The standard utilizes modular
construction for ease of maintenance and maximum operational reliability.
All modules are removeable, minimizing downtime should a module
require replacement. Most modules may be easily replaced in only
a few minutes. All modules are interchangeable, minimizing spare