TIME-STAMPING AND SYNCHRONIZATION FOR SINGLE-WIRE SAFETY COMMUNICATION

摘要

A time-stamping layer is provided for time-stamping of events detected in an industrial safety system. The technique implemented by the time-stamping layer uses autonomous device counters and simple arithmetic to label detected events (e.g., safety switching events) with accurate time-stamps without the need to synchronize clocks of the individual safety input devices and safety relay on the safety circuit. In some embodiments, the time-stamping technique is implemented in a single-wire safety system architecture that yields reliable safety device monitoring without the need for dual redundant signal channels.

主权项

1. A safety relay device, comprising:
a memory that stores computer-executable components; a processor, operatively coupled to the memory, that executes the computer-executable components, the computer-executable components comprising:
a counter component configured to periodically increment a counter at a defined frequency;a device diagnostic component configured to output a diagnostic request message directed to a safety input device on an industrial safety circuit and to record a first value of the counter corresponding to a first time at which the diagnostic message was output; anda message processing component configured to extract a return counter value included in a diagnostic response message received in response to the diagnostic request message, and to generate a time-stamp for an event detected by the safety input device based on the first value, the return counter value, and a second value of the counter corresponding to a second time at which the diagnostic response message is received at the safety relay.