Objectives

7.1.1 Discuss a range of control systems. 7.1.2 Outline the uses of microprocessors and sensor input in control systems. 7.1.3 Evaluate different input devices for the collection of data in specified situations. 7.1.4 Explain the relationship between a sensor, the processor and an output transducer. 7.1.5 Describe the role of feedback in a control system. 7.1.6 Discuss the social impacts and ethical considerations associated with the use of embedded systems.

Control System Videos

Centralized Control Systems

A control system is a device or set of devices that manage the behavior of other devices.

Depending upon whether a human body (the operator) is physically involved, a control system can be categorized as either a Manual Control System or a Automatic Control System.

Manual Control System

A simple example of a manual control system is a shower.

When the operator (a person) starts the shower the water is cold. To start the heating process the valve in the hot water line is opened. The operator can then determine the effectiveness of the control process by standing in the shower. If the water is too hot, the valve should be closed a little or even turned off. If the water is not hot enough then the valve is left open or opened wider.

4 Functions of a Control System

The shower control system, completed by the operator, includes the following functions:

Automatic Control System

The manual shower control system can easily be converted to an automatic control system as shown in the figure below.

Hardware of an Automatic Control System

An automatic control system contains the following hardware.

7.1 Control
Centralized Control Systems
7.1.1	Discuss a range of control systems. You can find control systems working in just about ever area of society including industry, business, healthcare, transportation, education, energy, military, government, and the home. The IB curriculum states, "Technical knowledge of specific systems is not expected but students should be able to analyse a specified system. Examples automatic doors heating systems taxi meters elevators washing machines process control device drivers, domestic robots GPS systems traffic lights ... other common devices Several of the control systems listed above are discussed below. Automatic Doors Automatic doors consist of a sensor, a processor and an automator. The sensor is often infrared and sends out infrared signals which then bounce off of objects. These signals can also be microwaves. The sensor then receives the signal and then sends a signal to the processing unit which then processes the information and sends it to the automator, in the form of two motors that cause the doors to open for a brief moment, and then close. Photocells in the elevator make sure that the door does not close on people walking through. These sensors sense if there is someone in the way and sends a signal to the processor. If this signal is true, stating that there is somebody in the way, the doors will not close. The processor will then see whether the doors should open or close, based on the information that it has received from the sensors. If the infrared sensor senses a person, the processor will tell the motors to open the door. Then, if the photocells do not sense a person in the way, the processor will send the signal to close the door again. Elevator An Elevator Control System consists of buttons on the floors of a building and within the elevator, a motor to move the elevator up and down, motorised doors, and a computer to control everything. A person will first press a floor button to call an elevator. The computer will receive this and send the best suited elevator to that floor, this is determined by not only the position of the elevators but also the direction of the elevators currently in use. The computer can 'see' where the elevator cab is in the shaft as the cab has magnetic sensors on its side that read a series of holes in a long magnetic tape along the shaft. The computer will send the cab to the floor with motors that control the movement of the elevator. The motor will control the movement of the elevator cab with suspensions cables. When the elevator reaches the floor the doors will only open when the cab reaches a certain point (read with the magnetic sensor), the cab door will also have a timer to ensure it does not stay open without a passenger pressing the close door button. The passenger will then press the button of which floor he/she wishes to go to. This is request is sent to the computer. The computer will then proceed to activate the motors pulling the elevator cab to the passengers desired floor. When the elevator is approaching the floor the computer (recognized with the magnetic sensors) tells the motors to slow down gradually until a full stop at the desired floor. When the floor is reached, the doors will open. Traffic Light Pedestrian crossing often use traffic lights to ensure safety for both the drivers and the pedestrians. The pedestrian pushes a button which sends a signal to the microprocessor. This then waits for an appropriate time to trigger the signal to change with the use of other sensors. Traffic lights use underground electrical wire to induce an electromagnetic field which will detect any presence of metal. The Global Positioning System (GPS) Each of these 3,000- to 4,000-pound solar-powered satellites circles the globe at about 12,000 miles (19,300 km), making two complete rotations every day. If you know you are 10 miles from satellite A in the sky, you could be anywhere on the surface of a huge, imaginary sphere with a 10-mile radius. If you also know you are 15 miles from satellite B, you can overlap the first sphere with another, larger sphere. The spheres intersect in a perfect circle. If you know the distance to a third satellite, you get a third sphere, which intersects with this circle at two points. The Earth itself can act as a fourth sphere -- only one of the two possible points will actually be on the surface of the planet, so you can eliminate the one in space. Receivers generally look to four or more satellites, however, to improve accuracy and provide precise altitude information.

7.1.2

Outline the uses of microprocessors and sensor input in control systems. Microprocessors A microprocessor is an integrated circuit that contains the entire central processing unit of a computer on a single chip. Microprocessors take on the role of controller in most automatic control systems. Having a microprocessor in a control system has several advantages They can process data very quickly much faster than a human Due to these fast speeds they can react very quickly to change in the control system Control systems can run 24/7 They can work in places where it would be dangerous for humans Outputs are consistent and error free However there are several disadvantages It may cost a lot of money to develop the software for a control system as they are specialized The system will not be able to run in the case of a power shortage The system will not be able to run in the case of a computer malfunction A computer can't react to events that it has not been programmed for, unlike a human Sensors Sensors are input devices that measure physical quantities. There are sensors for a lot of conditions such as temperature, pressure, sound, and humidity. If the sensor is an analog device it sends its readings to an Analog to Digital Converter which then sends the data on to the CPU for processing. For example: Temperature sensors in buildings are used to maintain specific temperatures. Security alarm systems use infrared and pressure plates to sense movement within an environment. Magnetic sensors are used to detect metal and can be placed in roads to monitor traffic flow. What is an ADC An Analog to Digital Converter(ADC), converts analog data, from sensors, to readable data for a computer, which is digital data. A computer can't read analog data because it is constantly changing, so an ADC samples the data to obtain digital information that can be processed by a computer.

7.1.3

Evaluate different input devices for the collection of data in specified situations. There are numerous input devices used to gather information. Some examples are shown in the table below. Kinect A motion sensing input device by Microsoft for the Xbox 360 video game console and Windows PCs. It enables users to control and interact with the Xbox 360 without the need to touch a game controller, through a natural user interface using gestures and spoken commands. Passive Infrared Sensor (PIR) An input device that measures infrared light emitted from objects that generate heat, and therefore infrared radiation, in its field of view. They have many uses including security lighting and alarm systems. Laser Rangefinder An input device that bounces the energy of a laser beam off a target, and then measures the return time back to the sensor. Since the speed of light is a constant, the return time gives an accurate reading of the distance to the target. Golfers often use them to determine the distance from their ball to the hole. Temperature Sensor An input device that gathers data concerning the temperature from a source and converts it to a form that can be understood either by an observer or another device. These sensors come in many different forms and are used for a wide variety of purposes, from simple home use to extremely accurate and precise scientific use.

7.1.4

Explain the relationship between a sensor, the processor and an output transducer. Transducer - an electronic device that transforms energy from one form to another. A tranducer can be either an input device (sensor) or an output device (actuator). Sensor - an input device acquires information from the "real world" by detecting/measuring a signal or stimulus. Senors take some sort of physical energy - such as sound waves, temperature, or pressure - and converts it into a electronic signal that can be read. Processor (Controller) - manipulates/stores the input data from a sensor. Output Transducer (Actuator) - is an output device that takes an electronic signal and converts it into physical energy. A good example of this relationship is the process of speaking through a microphone, amplifying the sound, and listening to the modified sound through speakers. Microphone - converts the sound waves that strike its diaphragm into an electrical signal. Amplifier - increases the power of the signal received from the microphone. Speakers - converts the electrical signal back into a sound.

7.1.5

Describe the role of feedback in a control system. A feedback control system examines the output produced by the system so that it can make changes that will improve its efficiency. In a feedback control system, information about performance is measured and that information is used to correct how the system performs. An example of feedback control system is the autopilot in an airplane. The autopilot control system continually monitors the airplanes speed and altitude and makes adjustments as needed to maintain the desired speed and altitude.

7.1.6

Discuss the social impacts and ethical considerations associated with the use of embedded systems. Examples - considerations for using the following types of systems tagging prisoners surveillance CCTV improved safety systems An embedded system is a dedicated computer system designed for one or two specific functions. This system is embedded as a part of a complete device system that includes hardware, such as electrical and mechanical components. The embedded system is unlike the general-purpose computer (like a PC), which is engineered to manage a wide range of processing tasks. Most people don't realize that the most common form of computer in use today is by far the embedded computer. In fact, 98% of computing devices are embedded in all kinds of electronic equipment and machines. Computers are moving away from the desktop and are finding themselves in everyday devices like credit cards, mobile phones, cars and planes or places like homes, offices and factories. Embedded systems are being increasingly used in critical applications such as Safety-critical applications potential for death, injury, loss or damage to property Examples: anti-lock brake system, laser used to perform lasik surgery, missiles Societal-critical applications potential for major disruption to everyday life Examples: traffic lights, airport flight scheduling systems, toll booths, ATM Ethical-critical applications potential for unethical use Examples: survelliance, CCTV, tagging prisoners or child sex offenders Business-critical applications potential for large economic loss to company/business exposure to litigation

Distributed Systems
7.1.7	Compare a centrally controlled system with a distributed system.

7.1.8

Outline the role of autonomous agents acting within a larger system.

Activities Required Reading: Topic 7 : Control Student Booklet Complete the handout: Control Systems Reference for handout: BWagner.org Navigate to IB HL 2 on the left menu, then read Unit 16 Control.