Ad-hoc synchronization of industrial control networks

摘要

A method and apparatus are disclosed to provide ad-hoc synchronization in industrial networks between a programmable logic controller and each I/O device without any specific protocol extensions or distributed clock scheme. An embodiment of an industrial control network comprising a Programmable Logic Controller (PLC), a network coupled to the PLC, and a plurality of networked input/output (I/O) devices coupled to the network is provided. Each I/O device comprises: inputs coupled to the network to receive data from the PLC as device input data; and outputs coupled to the network to transmit output data from the I/O device to the PLC. The embodiment further comprises a programmable timer initiating an I/O cycle for the device on a periodic basis. The I/O device is operable to determine a first time period starting at the time at which specific output data arrives from the PLC and ending when the period of the timer ends. The first time period is compared to a predetermined time period. The I/O device is operable to adjust the period of the timer such that the first period approaches the predetermined time period and ad-hoc synchronization is provided between production time of the PLC and timing of the I/O device.

主权项

1. An industrial control network comprising a programmable logic controller (PLC), a network coupled to said PLC, and a plurality of networked input/output (I/O) devices coupled to said network, each I/O device comprising:
inputs coupled to said network to receive output data from said PLC; outputs coupled to said network to transmit input data to said PLC, said input data being produced by said each I/O device after receipt of said output data; a periodic programmable timer to provide a programmable base period for I/O device I/O cycles, said periodic programmable timer providing an output trigger at a base frequency corresponding to said programmable base period; apparatus to capture an arrival time of receipt of said output data and to determine a time delay between said receipt of said output data and a next output trigger from said periodic programmable timer; a filter coupled to said apparatus to provide a filtered average time delay; and a comparator responsive to said filtered average time delay to adjust said programmable base period of said periodic programmable timer to be equal to said filtered average time delay to thereby provide device ad-hoc synchronization with said PLC.