DCS (Distributed Control Systems) have been used in the pulp and paper industry since they were first developed. These instrumentation systems were used to automate the process and to save labor and energy costs. However, even while the number of sensors and actuators was increasing in the newer systems, instrumentation signal processing still used point-to-point wiring between the I/O cards of the DCS or PLC and the individual sensors/actuators.
Oji Engineering Co., Ltd. Fuji Mill considered automation for their new machine that makes paper from pulp. They determined that the number of automation points would increase, therefore they reviewed the wiring system between the DCS and the sensors/actuators, for reducing both the initial cost and installation time.
They focused on the following items for deciding on the system to use.
- Reliability: High performance that was supported by a large number of companies
- Operation: High-speed network that ensured proper system operation
- Maintainability: A system that was easy to maintain and that would allow for future expansion and changes.
Three additional points were considered in the Maintainability requirement above. They were:
- The data link should operate normally even when an error occurs in one of the network devices
- Each network device should be capable of being replaced online
- Each solenoid valve should be capable of being replaced online.
CC-Link was chosen as the field bus system that met the above requirements.
In this system, the control station of the DCS is connected to the PLC Controller by a PLC Controller level network system. CC-Link is controlled through this PLC and all of the solenoid valves and digital inputs are connected to the PLC by the CC-Link network. The solenoid valves and other digital I/O are installed in a wall-mounted panel and are connected to the process valves by pneumatic piping and cables.
The power supply circuit of the solenoid valves has been simplified in the new paper machine by using CC-Link Networking. Wiring in the panel has been sharply decreased because the individual interface boards (previously required) are no longer necessary. This reduces the number of components. Each solenoid valve wiring panel is now connected to the controller by a single CC-Link network cable which dramatically reduces wiring costs. Oji Paper can also expect increased reliability due to fewer I/O connections. By utilizing the CC-Link field-bus network, it is also easy to collect and compile process information that is useful for preventive maintenance. As a result, Oji Paper expects a reduction in overall operation costs.
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