LAB_14 - Control Systems - Lab 14 Control Systems"That is...

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Lab 14 153 Control Systems Summary All disciplines of engineering deal with the design, development, testing and use of engineering systems. While there is an almost endless variety of systems, many of these rely on similar models or have underlying mathematical representations which are very similar. In this experiment, we will design, build and test various control systems applied to a model heating system. The model system integrates the use of sensors and measuring systems and is computer-controlled. Educational Objectives After performing this experiment, students should be able to: 1. Design and test various control schemes for a model heating system. 2. Design, build and test a "computer-controlled" control system. Background Information Classification of Control Systems In engineering, a system is an arrangement of components connected or related so that they act as an integrated unit. A control system is a system that commands, directs or regulates itself or another sys- tem. Control systems are classified into two major types; open-loop and closed-loop systems. An open-loop system is one in which the control process is independent of the output. A gas range is an example of an open-loop control system, it will give off a pre-adjusted amount of heat as long as it has the same setting. In open-loop systems, the control action is achieved by proper calibration of the sys- tem. A closed-loop system is one in which the control process depends on the output. Closed-loop sys- tems have a characteristic called feedback which distinguishes them from open-loop systems. Feedback allows the output of the system to be compared with the input so that the correct action may be taken to regulate the output. A building’s heating system is an example of a closed-loop control system. Figure 1 depicts the block diagram for such a system and is composed of smaller components that work together to regulate the temperature of a room and thus the building. It utilizes a thermostat to turn the heating ele- "That is by far the most stable pointing we have so far" - - "Except that the tar- get isn't in the aperture!!" - Conversation between Spacelab Mission Control and Astronaut
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Lab 14 154 ments on or off as the room temperature rises and falls. Note that each unit represented in the block dia- gram may be considered an individual system. The thermostat is shown as two elements because it has two functions: (1) to measure the room temperature and compare it with the desired temperature and (2) to decide whether to turn the furnace on or off. The variation in the outdoor environment is the primary reason for the unpredictable change in the room temperature. If the outside conditions (temperature, wind, cloudiness, etc.) were predictable, we could design an open loop heating system that would operate continuously to supply heat at a predetermined rate just large enough to replace the heat lost to the out- side environment. No feedback would be necessary. Of course, the real world does not behave so nicely, so we must adjust the heat-output rate of our system according to what the actual room temperature is.
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This note was uploaded on 12/16/2011 for the course ENGR 102 taught by Professor Cattell during the Fall '10 term at Community College of Philadelphia.

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LAB_14 - Control Systems - Lab 14 Control Systems"That is...

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