In 2011, many of us read a startling news report of an experiment conducted by CERN claiming that neutrinos appeared to be traveling faster than the speed of light.
The collaboration of the experiment, called OPERA (Oscillation Project with Emulsion-tracking Apparatus), made headlines with its claim that a beam of neutrinos made the 730-kilometre journey from CERN, Europe's particle-physics lab near Geneva in Switzerland, to the Gran Sasso National Laboratory near L'Aquila, Italy, faster than the speed of light by about 60 nanoseconds. The result defied Albert Einstein’s special theory of relativity, which states this cannot happen.
After I saw the news report, I spoke with one of my colleagues and remarked that the result was probably due to someone messing up the calibration of the time clocks for the whole test.
It turned out that a discrepancy of 62 nanoseconds of measurement was indeed caused by a clock oscillator on an electronic board ticking faster than it was supposed to have been.
As a result of this huge embarrassment and disturbance to the scientific community, CERN’s spokesperson Ereditato and their leading scientist Autiero resigned their leadership positions.
(To read more about this interesting story, click on the following link: https://en.wikipedia.org/wiki/Faster-than-light_neutrino_anomaly)
The clock on each Crystal Instruments Spider board plays the same critical role when the Spider system takes cross-channel measurements. The electronic boards of Spider systems can have separate locations hundreds of meters away through an Ethernet cable connection. However, all the boards must have clocks accurately synchronized within a range of nano-seconds. Without clock synchronization, cross-channel measurements such as the frequency response function will be completely invalid.
Crystal Instruments is one of the companies in our industry pioneering the use of IEEE PTP technology to synchronize clocks. A Spider system with multiple front-ends uses precision time protocol to synchronize the internal clocks of each front-end over the Ethernet network so that all input channels can be accurately phase-matched. Each front-end is connected to a central switch that routes messages from each connected front-end through its ports. PTP synchronization will work regardless of whether the switch is PTP-enabled or not. PTP works by measuring the signal path delay between each front-end, and the more precisely this delay can be measured and predicted the more accurately the clocks can be synchronized.