With the advancements in laser technology and improvements of the operation robustness,the fountain clocks can not only be used as frequency standards to calibrate atomic time scales,and improve the long-term stability and accuracy,but also be used to steer a hydrogen maser as a time-keeping clock.The ground state hyperfine transition of rubidium atoms,as a secondary representation of the second definition,has the advantages of small collision cross-sections and highly robust cooling lasers.It is a better candidate for commercial clocks.The prototype of a commercial rubidium fountain clock developed at the National Institute of Metrology(NIM)with a bi-metal microwave-vacuum integrated Ramsey cavity to increase the temperature adaptability of the system.A miniaturized optical system and a cage structure detection light system to improve operational reliability.A long-term quasi-continuous operation with an operation rate of 97.5％in a year is realized.Though the one-year comparson tese,the long-term fractional frequency instability achieves 3.7×10-16 for the comparisons between the Rb fountain clock and NIM5 cesium fountain clock.The frequency instability of a single fountain clock is better than 2.6×10-16.
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