结构健康监测Reliable, stand-alone data-acquisition systems for critical applications

Distributed Networks and Synchronization

Multiple GRANITE™ measurement modules can be distributed throughout the structure. Each module is connected to a central GRANITE™ DAQ. This networking capability decreases the quantity and lengths of the sensor cables between the sensors and the GRANITE™ DAQ. Fewer sensor cables reduces cost, improves system simplification, and lessens the risk of signal corruption from noise.

Synchronization is key to the success of a distributed network. There are three significant levels to the GRANITE™ DAQ synchronization:

1. 的GRANITE™ DAQ has a built-in GPS and precision master clock.
   1. 的pulse-per-second signal from the GPS is accurate to 1 µs. If enabled, the GRANITE™DAQwill phase lock its operating clock to within 200 ns of the GPS clock. So, multiple independent DAQ systems spread over potentially vast geo-spatial regions can be synchronized with a maximum timing error between DAQ systems of 1.2 µs.
   2. 独立于GPS，一个由温度补偿的高精度，板载，实时时钟将以±3分钟/年的精度保留自己的时间。
2. Within a single DAQ system, comprised of a GRANITE™ DAQ and GRANITE™ measurement modules, the measurements are all synchronized to the master clock of the GRANITE™ DAQ (sourced by either the GPS or precision on-board clock) via the CAN Peripheral Interface (CPI) or Ethernet Peripheral Interface (EPI) measurement buses.
1. CPI synchronization between measurement modules in the same DAQ is ±5 µs. The overall physical range of the bus varies up to 2,000 ft depending on the data rate.
2. EPI synchronization between measurement modules in the same DAQ is ±50 ns. The physical range of the bus is 300 ft per network connection. Daisy-chained connections can span thousands of feet.
3. For extremely time-based-sensitive applications, the GRANITE™ SPECTRUM measurement modules are used with EPI synchronization. Within each module, the analog electrical signal delay is calibrated and compensated to reduce the timing delay mismatch to ±10 ns channel-to-channel.