Maintenance of UTC(MIKE) in Finland by using a delay generator as a micro stepper

Local time in the Centre for Metrology and Accreditation is derived from our master clock, a hydrogen maser. An often occurring phenomenon in hydrogen masers is a small, approximately constant frequency drift. As a consequence, the time error of a hydrogen maser typically follows a parabola. To compensate for this, a programmable delay generator is used to produce an opposite function. Thus, a local time UTC(k) is frequently a combination of master clock time and a programmable delay. In the Centre for Metrology and Accreditation we follow this approach. The delay generator is computer controlled to generate a parabolic delay d: d(t) = a+bt+ct², where c is aging factor in ns/day² (which is essentially stable), b is rate correction in ns/day, a is constant in ns, and t is time in days from start (MJD-MJD₀). The aging factor c of our master clock is less than 3 ps/day², equivalent to df/f <; 1×10^-16/day. The produced time UTC(MIKE) is compared to UTC via dedicated time and frequency receivers. Calculation of the parameters a, b and c, predicting the behaviour of the master clock, is the key problem of accurate time keeping. To maintain the time difference UTC-UTC(MIKE) within ±10 ns, as published in Circular-T, elaborate calculations with supporting data from other atomic clocks in the laboratory are required. Since October 1, 2009 up to the end of March 2009 UTC-UTC(MIKE) has stayed within ± 9 ns, which at the moment seems to be the tightest range of all the participating laboratories.