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Session 2259

Real-time Actuator Simulator Using Digital Signal Processing Robert Lynn Mueller The Pennsylvania State University New Kensington Campus

Abstract

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.

Introduction

There is no question that the lab is the place to drive home complex control theory. There have been papers suggesting methods [1] – [4] and there are companies that provide equipment [5] – [6]. But sometimes when the equipment is set up, things aren’t quite right for the topic that is being demonstrated. This paper describes a module that can be added to training simulators that can be used to modify the control characteristics to achieve desired results without destroying the realism of hands-on learning. While the module described in this paper is for a flow simulator application, its generalized design makes it easily modifiable for other applications.

The flow simulator is based on one designed by Jim Rehg[4] and is shown in Figure 1. It consists of a vertical tube with a squirrel cage blower at the bottom and a small fan at the top. The fan is used as a generator to measure relative airflow. The damper valve towards the bottom of the tube is used to control the airflow. Either the pneumatic actuator on the left of the tube or the stepper motor on the right side of the tube can control the valve’s position. The actuator not being used must be physically disconnected. The blower’s input is partially blocked so that when the valve is around 90% open, the flow sensor detects approximately 100% relative airflow; this makes the loop gain a little more than 1. This is necessary so that a gain crossover exists when experiments involving phase margin are conducted.

“Proceedings of the 2003 American Society for Engineering Education Annual Conference & Exposition Copyright © 2003, American Society for Engineering Education”

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Mueller, R. (2003, June), Real Time Actuator Simulator Using Digital Signal Processing Paper presented at 2003 Annual Conference, Nashville, Tennessee. 10.18260/1-2--11460