Real-time actuator simulator using digital signal processing

This paper describes an actuator module that was originally built to convert 4-20 mA control signals into stepper motor command signals. The stepper motor is used to position a valve in an airflow process simulator and this actuator module now allows standard PID controllers to be used to control the airflow in the simulator. It is also now possible to use PLCs that don't have stepper motor commands as part of their PID algorithm. However, by using digital signal processing techniques in the module, it is now possible to simulate actuator delays and time constants. To help appreciate different actuator responses, it is also possible to replace the stepper motor actuator with a pneumatic actuator. This simulation system enables students to modify an actuator's transfer function without destroying the realism of a hands-on simulator. The paper describes the interface module's hardware and digital signal processing techniques as well as some of the lab experiments associated with the module.