The 5071A uses a fundamental property of the element cesium to define frequency.
Inside the cesium beam tube assembly, an applied microwave signal causes
energy-level transitions to occur in the cesium atoms. The microwave signal is synthesized from a 10 MHz voltage-controlled crystal oscillator (VCXO). Patented Cesium II
circuit and software technology detects departures of the microwave frequency from
the cesium energy-level transition frequency and corrects them by tuning the VCXO to
run precisely at the proper rational-fraction of the cesium frequency. The microprocessor (an integral part of this servo loop) performs the error determination and correction
several times a second to ensure that the VCXO is always closely locked to the
cesium-transition frequency.
Many functions within the 5071A are under Cesium II software control. The software
manages the initial warm-up and alignment, then continuously monitors the appropriate signals using this information to control all key operating parameters for optimum
performance. Starting the 5071A merely requires connecting AC or DC power.
After a typical warm-up time of 15 minutes, the standard is fully operational and the
operator may optionally press three keys to display a continuous operation signal.
There are no maintenance procedures or adjustments needed even when necessary
to replace the cesium beam tube. The 5071A