JPS55107341A - Standard unit of atomic frequency - Google Patents

Abstract

PURPOSE:To obtain the atomic frequency standard unit stable in the frequency at power failure, by applying the control voltage before power failure stored at the voltage storage circuit to the variable capacitor controlling the frequency of the crystal oscillator in the closed loop at the power failure of the main power supply. CONSTITUTION:The frequency of electromagnetic waves from the cell 4 enclosing Rb atoms is modulated with the output of the low frequency oscillator 10, this is discriminated with the phase discriminator 11, and the error signal voltage corresponding to the different frequency from the center frequency is fed to the variable capacitor 16 controlling the oscillation frequency of the crystal oscillator 15 via the voltage storage circuit 32. When the main power supply 19 is in failure, the crystal oscillation circuit 14 only is driven with the auxiliary power supply 31 consisting of batteries. The circuit 32 performs A/D conversion 41 for the output voltage of the discriminator 11, stores it in the digital memory 42, and the voltage in D/A conversion 43 is fed to the variable capacitor 16. Although the content of the memory 42 is eventually renewed, the renewal of memory is stopped by the power failure detection circuit 45, the voltage stored immediately before the power failure is fed to the variable capacitor 16, and crystal oscillator is oscillated with the frequency immediately before the power failure.