Comparative response time and fault logging with a PLC and supervisory software and a standalone unit developed for recording

Abstract

The Cobalt-60 irradiator of IPEN / CNEN, a category IV facility, has a security system for inter locking doors or exposure of radioactive sources made simultaneously by a programmable logic controller (PLC) model S7-200 from Siemens and a relay logic. From a set of information, both systems work together opening doors or exposing the sources. All incoming and outgoing information are sent serially via EIA232 communication to a personal computer with Windows® platform for a supervisory program which provides the monitoring of the entire process by a synoptic table on the computer screen and is also intended to keep records of all events on the computer's hard drive. A deficiency was found for the process of sending events via serial communication (EIA232) from PLC to the supervisory program. When failure occurred in a very short time, the PLC always took the right decision, but the registration process that had to go through the Windows® timeshare lost the information. In the previous work [1] developed a standalone electronics unit connected to the inputs and outputs of the security system, fully optocoupled to avoid any interference to the security system that records each event on a memory card. In this work, for checking the unit developed record time ability, transients incoming signals for simulating failures, were injected at security system inputs and the response time of security system, supervisory program and the autonomous unity were measured and compared.