Autonomous monitoring unit, signs and registration for Cobalt-60 irradiator safety system

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, the 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 besides a monitoring the entire process by a synoptic table on the computer screen, also keeps records of all events on the computer's hard drive. The electronic management has proven to be efficient and has not produced any failure that had compromised the safety. The PLC along with the relay logic has always taken the right decisions ensuring proper radiation protection of operators and the integrity of radioactive sources, but it presented over the years of operation (beginning in 2004) less than a dozen flaws in system event log. The deficiency was found between the process of sending events via serial communication (EIA232) to the supervisory program. When failure occurs 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. This work aimed to build a standalone electronics connect the inputs and outputs of the security system, fully optocoupled to avoid any interference to the security system. It records each event on a memory card, waits for the right decision of the security system and in case of an incorrect decision an independent alarm notifies its own synoptic picture, and sends a text message to a group of defined cell phones. The circuit uses two microcontrollers called 'main' and 'secondary'. The main is responsible for the control and monitoring of peripheral inputs and outputs of the security system. The main is monitored by the secondary, thus creating a redundant. Again, if a wrong operation is detected an auxiliary alarm is triggered. (author)