Abstract
Nowadays there is a frequent demand to increase the quality of synchronization in industrial distributed systems. Node synchronization can be implemented in the Ethernet network using time protocols, e.g. IEEE 1588 Precise Time Protocol (PTP). However, active network components like switches and routers have negative influence on achieved accuracy of synchronization because they affect a packet delay variation in the network. To suppress this effect, special (but expensive) industrial switches, with a packet propagation delay correction, can be used. Another way using either low cost GPS receivers for synchronization of local clocks or a special timing for data transfer is described in the paper. It will allow a cheaper solution that preserves high quality of synchronization. Besides, a device for packet delay measurement (PTP tester) was designed and developed to be possible to evaluate the proposed methods.
Highlights
Real time operation is a very important aspect of industrial distributed systems
The offset of the Precise Time Protocol (PTP) tester caused e.g. by Physical Layer (PHY) and LAN connectors has to be determined before its application
The delay values measured by the PTP tester were subtracted from the Several predefined delays Ts were set in the Calnex Paragon X and a delay of the transfer path Ta was measured by the PTP tester
Summary
Real time operation is a very important aspect of industrial distributed systems. A special software and network components are applied in this case. Node synchronization can be implemented directly in the Ethernet network using time protocols, e.g. IEEE 1588 Precise Time Protocol (PTP) [2]. In this case, the accuracy of synchronization can be negatively influenced by active network components like switches and routers, which delay packet transmission. The existing ways of testing using lowcost instrumentation appreciate the secondary effects only, because the properties of network concerning time parameters are not measured directly, but only a possibility to synchronize slave devices to the master device is evaluated This way is not suitable for evaluation of a synchronization accuracy, because it is influenced by many secondary actions, e.g. with control algorithm of slave device etc. The PTP tester was connected with the Calnex Paragon X using the 100BASETX Ethernet and the separate 10 MHz clock signal for synchronization (see Fig. 5)
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