Keeping zoo safety on track

The Zoofari monorail is a popular attraction at a well known UK zoo, ­carrying in excess of 2,000 passengers on busy days. But legally it is not a pleasure ride. Because it has four automated unmanned trains and two stations, it is officially classified as a transportation system and is ­therefore subject to operational and safety requirements laid down by the Office of the Rail Regulator (ORR). Control and safety equipment from Omron is meeting these requirements dependably and cost effectively

Originally put into service in 1991, the Zoo monorail had for most of its life given excellent service but recently it was becoming difficult to maintain and there was a need to upgrade the safety systems to a more modern design.

To determine the best way to remedy these problems and to provide the monorail with an assured future, the Zoo’s management team commissioned a detailed report. This strongly recommended that the existing control and safety systems should be completely replaced, as this would not only mean that modern equipment could be used throughout, but would also allow the monorail to be upgraded to meet today’s increasingly strict safety requirements.

The contract for the control and safety systems was won by a local integrator, a company that had already had considerable experience of working on the monorail, and that had put forward an offer based on Omron safety and control equipment for all major functions, including modern EtherNet/IP technology – wireless, wired and fibre-optic based – to link the various components of the system.

The integrator says: “We chose Omron for several reasons, one was that much of the monorail’s original equipment was from Omron and it had given excellent service in this demanding application for more than 17 years, which is no mean feat when you remember that the monorail operates 364 days a year.”

The scale of the new Zoo monorail control and safety installation is large. Each of the four trains has two independent PLCs that, among other functions, monitor and control the variable speed drives that provide the motive power for the trains. Each train also has a Handy NSH handheld HMI terminal with a colour touch screen, which provides dead-man and emergency stop functions. This HMI terminal is used for driver operation and control during maintenance and it also provides access to the extensive on-board diagnostic systems.

The trains are made up of four carriages, and remote I/O (input/output) modules connected to the on-board PLC and safety network controllers are provided in each carriage. When the system is running, the train PLCs and safety controllers communicate with a master PLC in a central control room via an EtherNet/IP wireless connection that uses Omron smart roaming technology. This provides multiple access points and handles multiple clients, as well as supporting very rapid switching as the trains move in and out of range of the individual access points.

The master PLC, in turn, communicates with a SCADA (supervisory control and data acquisition) in the control room at Station One. The SCADA installation incorporates a large widescreen display that provides the monorail supervisor with comprehensive real-time information about the precise locations and performance of the trains and about the status of the safety systems.

In order to meet the highest possible standards for safety, the installation also makes extensive use of Omron safety network controllers; seven Ne1a safety controllers are used. These are, for example, fitted to each train, where one of their functions is to provide interlocking of the carriage doors on the basis of motion and position to ensure that their operation coincides with the opening of the trackside passenger gates in each station.

The safety network controllers conform to Category 4 in line with EN954-1, and SIL3 in line with IEC61508. In this application, however, they are used to meet EN954-1 Category 3 requirements on the platforms, where they work in conjunction with the proximity safety laser scanners on each station platform to detect the presence of passengers who may still be near to closing exit doors.

Additional safety network controllers are used in a fixed installation that covers each station and to provide safe interlocking of two track switch points in the maintenance areas. These controllers are linked by a fibre-optic Ethernet IP network that uses ring topology with dual redundancy. This means that even if a fibre-optic cable is completely severed, the network remains operational, and trains that are in motion can proceed safely to the stations.

To transfer safe data between safety network controllers, an Omron Safe Devicenet-to-Ethernet controller is employed, ensuring high transmission integrity over nearly a kilometre.

One of the key requirements for the control and safety installation was it should employ the most effective measures possible to ensure a collision between trains can never happen. To achieve this three independent systems were deployed and the overall system has been evaluated and approved by the ORR.

The Zoofari monorail is proving as popular as ever with visitors to the zoo and, thanks at least in part to its new safety and control systems based on Omron equipment, it is now on track to provide many more years of safe and reliable service.

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