Innovative approach for dual control of electromechanical plant

In an attempt to optimize investment in training equipment, a methodology has been developed to allow an electromechanical plant to be controlled by either an embedded PLC or an embedded microcontroller without any physical or wiring modifications to the system. All sensors and effectors are wired to both control devices, which are in turn under the command of a supervisory control that allows only one of the two devices to be powered at any time. This allows a single electromechanical trainer to be used for teaching of PLC ladder logic, and/or microprocessor control using LabVIEW or C. An example electromechanical plant is presented in the form of a two-car, three-floor elevator system containing 8 actuators, 22 sensors, 14 switch inputs and 14 indicators. One of the challenges faced was developing an isolation scheme to accommodate both the standard 24V PLC control voltages and the 3.3/5V microprocessor control voltages. Another hurdle was designing for the variety of input interface specifications between the two platforms. A methodology was developed to allow for safe system operation by allowing the supervisory control to appear transparent to the user, yet allow it to modulate outputs when necessary to protect the plant equipment. The overall approach is presented; the final designs are being made available under an open-source license.