A second look at Chip Scale Atomic Clocks for long term precision timing

We compare the performance of 38 Chip Scale Atomic Clocks manufactured by Microsemi Corporation (originally Symmetricom Inc.) used in a fleet of Ocean Bottom Seismographs. CSACs have been available commercially since 2011, promising accuracy close to that of conventional “low power” Rubidium oscillators at one fortieth the power of the most efficient Rubidium. Ocean bottom seismology provides a particularly challenging requirement for timing: millisecond level or better accuracy over a one year interval or longer. While results from an early batch of CSACs have been largely positive, later units have not performed as well. The CSAC specifications have changed, reflecting a decrease in reliability and accuracy of more recent units. We will discuss the impacts of the degraded aging for long-term autonomous experiments. For the majority of applications this change is not very important. However since aging-related phase error increases with the square of time, applications requiring long-term accurate phase such as ocean bottom seismology may be significantly impacted. We will also compare the CSAC to the SISMTB Microprocessor Compensated Crystal Oscillator, designed and manufactured by Seascan, Inc. using lab testing to determine their performance relative to the range of CSAC performance.