UC San Diego

PLCs (Programmable Logic Controllers) are the work horse of industrial control systems. Industrial control systems are usually both mission-critical and safety-critical systems. A single software bug in a control system program could cause hardware equipment damage and human life loss. The PLC programs in control systems must provide bug-free and failure-free behaviors in order to avoid accidents. A PLC program must be completely tested for correctness in functionality, reliability, predictability, and safety before it's released for production systems. At a PLC program development stage, hardware devices in the industrial control system are usually not available for testing the PLC program for safety reasons. The often used solution is to use a simulator to simulate the hardware devices' behaviors. The simulator is usually built as a hardware test stand which consists of toggle switches, lamp indicators, and analog signal generators. The shortcoming of this kind of simulators is they are not automated and require lots of user interactions. As a result, they cannot guarantee the accuracy of behaviors of the hardware devices being simulated. This research presents an automated testing tool which automates the hardware device simulation process by using "virtual" wires. The hardware device simulation is part of a test case which is defined in the presented testing tool and downloaded to the PLC controller. This testing tool requires no user interaction during a test run so it reduces the testing cost and time and it can precisely simulate the behaviors of hardware devices