The whole acquisition system is scattered in various parts of the bridge. The bridge is divided into several sections according to the region. In the main sections, signal collector stations are placed. Each collector station is several kilometers or even more than ten kilometers away. Each group of collector stations is connected to the GPS synchronous clock receiver. The GPS PPS receiver receives the GPS clock synchronization signal, performs corresponding processing to obtain the clock synchronization signal and absolute time stamp, and sends them to the PXI acquisition equipment. The acquisition equipment receives the processed GPS synchronization signal, Achieve synchronization of the entire distributed acquisition system.

　　The clock synchronization here has two meanings:

　　The synchronization of data sampling frequency includes pulse synchronization and phase synchronization of sampling clock signal.

　　Synchronization on the timeline, that is, the synchronization of the time stamp at the sampling point.

　　Only when both aspects are synchronized can it be called a real synchronous acquisition.

　　At present, in addition to the GPS PPS clock synchronization technology scheme, there are two other clock synchronization technology schemes:

　　1. Chassis direct connection clock synchronization technology:

　　The clock frequency sharing technology of PXI-6653 clock synchronization module is mainly adopted. Each acquisition device is equipped with PXI 6653 clock synchronization module, and then the 6653 modules of each acquisition device are connected with coaxial cables, with one module as the master module and the rest as the slave modules; The clock signal inside the master module synchronizes the clock signal inside the slave module through the coaxial cable. The PXI-4472B uses the secondary signal as the sampling clock. The network time server can be used for timestamp synchronization.

　　2. GPS IRIG-B clock synchronization technology:

　　This technology is very similar to the GPS PPS technology. Both receive the GPS synchronization signal through the GPS receiver, do the corresponding processing and send it to the acquisition equipment for acquisition synchronization. The difference between this technology and the GPS PPS is that the IRIG-B clock synchronization signal contains absolute time, so PXI-6608 needs to receive this signal and parse it into a usable timestamp.

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