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Abstract
| For distributed data acquisition and control system, clock synchronization between devices is key. The internal CPU clock of a CompactRIO has an accuracy of 40 ppm at 25 degree Celsius, which can cause up to 3 sec of drift per day. To compensate for this drift, common practice is to use a central clock (such as NTP) to synchronize the systems. In addition, the cRIO has an onboard FPGA which has its own 40 MHz clock. This clock is not synchronized with the CPU, and will also cause time drift. For short measurements, this drift is usually negligible, but for continuous data acquisition systems, running 24/7, the accumulated error has to be compensated. This article will show how we synchronized all clocks across multiple systems used for monitoring seismic activities in the LHC underground and surface areas. It will also describe the mechanism used to cross check synchronization by using the CERN developed White Rabbit timing system. |