CLASSIFICATIONS OF CONTROL SYSTEMS - Motion Control

Motion control is a broad term used to describe an open-loop or closed-loop electromechanical  system wherein things are moving. Such a system typically includes a  motor, mechanical parts that move, and (in many cases) feedback sensor(s). Automatic  assembling machines, industrial robots, and numerical control machines are examples.
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CLASSIFICATIONS OF CONTROL SYSTEMS - Process Control

Process Control

Process control refers to a control system that oversees some industrial process so that a uniform, correct output is maintained. It does this by monitoring and adjusting the  control parameters (such as temperature or flow rate) to ensure that the output product  remains as it should.

Figure 7  A closed-loop oven-heating system.

The classic example of process control is a closed-loop system maintaining a  specified temperature in an electric oven, as illustrated in Figure 7. In this case, the  actuator is the heating element, the controlled variable is the temperature, and the sensor is a thermocouple (a device that converts temperature into voltage). The controller  regulates power to the heating element in such a way as to keep the temperature (as reported by the thermocouple) at the value specified by the set point.
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Introduction to Control Systems

INTRODUCTION

A control system is a collection of components working together under the direction of some machine intelligence. In most cases, electronic circuits provide the intelligence, and electromechanical components such as sensors and motors provide the interface to the physical world. A good example is the modern automobile. Various sensors supply the on-board computer with information about the engine’s condition. The computer then calculates the precise amount of fuel to be injected into the engine and adjusts the ignition timing. The mechanical parts of the system include the engine, transmission, wheels, and so on. To design, diagnose, or repair these sophisticated systems, you must understand the electronics, the mechanics, and control system principles.In days past, so-called automatic machines or processes were controlled either by analog electronic circuits, or circuits using switches, relays, and timers. Since the advent of the inexpensive microprocessor, more and more devices and systems are being redesigned to incorporate a microprocessor controller. Examples include copying machines, soft-drink machines, robots, and industrial process controllers. Many of these machines are taking advantage of the increased processing power that comes with the microprocessor and, as a consequence, are becoming more sophisticated and are includ- ing new features. Taking again the modern automobile as an example, the original moti- vation for the on-board computer was to replace the mechanical and vacuum-driven subsystems used in the distributor and carburetor. Once a computer was in the design, however, making the system more sophisticated was relatively easy—for example, self- adjusting fuel/air ratio for changes in altitude. Also, features such as computer-assisted engine diagnostics could be had without much additional cost. This trend toward com- puterized control will no doubt continue in the future.
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