Dual PID controller for SLC 500
April 2003
PLCs, DCSs & Controllers
Using multiple PID loops with an Allen-Bradley SLC 500, is made easier with Red Lion Controls' DLCD. The device is a DIN-rail mounted module that implements two independent PID loops, communicating with a SLC 500 over the DH-485 network to allow a PLC program to control and monitor each loop's operation. By lifting the burden of PID control from the controller, the need for expensive I/O cards is avoided, and valuable PLC memory and processing power are made available for other tasks. The DLCD not only provides a more elegant and effective control solution, it also offers considerable hardware cost savings for each loop concerned.
The DLCD is designed to be a true plug-and-play solution. It controls all the communication between itself and the SLC 500, avoiding the need for any ladder programming. All of the device's features can be configured using Red Lion Controls' Windows-based configuration package. Alternatively, by setting a few bits inside the PLC, the DLCD can be configured to read all of its parameters from the controller's data tables. This allows hot-swapping of devices without the need for any configuration operations beyond the setting of a few DIP switches - ideal for OEMs wanting to simplify maintenance procedures in order to reduce the cost of ownership of their machines.
The PID control algorithm used in the DLCD has been tried and tested in the field, having been used in Red Lion's temperature controllers for many years. It provides advanced auto-tune facilities, multiple alarms, heat-cool operation, plus input and output filtering. The control accuracy of the DLCD makes the product suitable for extruders, injection and blow moulders, ovens and furnaces, or food processing applications. In fact, any application where a SLC 500 is being used in conjunction with temperature control will benefit from the DLCD's improved performance and reduced cost.
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