New technologies and applications
Sub-millisecond event logger30 September 2004
The ability to accurately pinpoint and record faults is critical for utility companies, as shown by the fallout from last year's power failures in Europe and the northeast USA. To address this type of problem, Rockwell Automation has produced a sequence-of-events input module for the Allen-Bradley ‘ControlLogix’ control platform.
The SOE module can timestamp to an I/O-point level, and discriminate between events that occur within 100 microseconds of each other, a function that is unachievable with standard input modules. With a purpose-built Allen-Bradley power supply and a global positioning satellite (GPS) module from Rockwell ‘Encompass’ partner Hiprom, the SOE module is sutable for for a variety of power applications including utility and sub-station automation, emergency shutdown systems, energy management and load shedding.
Rockwell claims that because the SOE module is integrated with the controller, and not a separate add-on, it provides the benefit of seamless data flow throughout the system.
SOE modules operate in two modes: co-ordinated system time (CST) per point and first in/first out (FIFO). In CST-per-point mode, a module provides two timestamps per input point, one for on/off transitions and the other for off/on. As a result, the module can capture timestamps for events on rising- and/or falling-edge transitions, which is essential when determining the order of a sequence of events. A module in FIFO mode can timestamp multiple transitions of any of its input points and store this data in an on-board buffer. Given that engineers can record every transition of every input in this mode, it is suitable for monitoring, analysing, optimising and troubleshooting the sequencing of any process. The power supply can work from any appropriate DC source (eg battery backup systems) to allow the system to continue operating and recording data in a blackout.
An SOE-driven solution can also give an absolute real-time reference for all timestamped data in the controller by addition of the 1756HP GPS module which helps users determine the exact order of events in their systems and correlate those events to a real-time microsecond-accurate clock. It also allows the application of a common time base for control components scattered across a wide geographic area.