SET Chapter 17.pdf

Learning Outcomes Describe the functions of timers Describe the functions of sensors, and use motion and light sensors as examples of sensors commonly used in home automation systems State how timers and sensors can be used to switch devices on and off automatically to conserve...

Learning Outcomes Describe the functions of timers Describe the functions of sensors, and use motion and light sensors as examples of sensors commonly used in home automation systems State how timers and sensors can be used to switch devices on and off automatically to conserve energy Describe and program timers and sensors to control lighting and electrical devices 2.6.1 Functions of Timers Fig. 2.6-1: Timer Timers are used to automatically turn lighting and other electrical devices on and off with pre- set timings to save energy. There are two kinds of timers: mechanical and electronic. Many people go for electronic timers as they are cheaper and more accurate. Today, many building automation systems use smart devices with built-in electronic timers. For example, large shopping malls use timers to perform more complex scheduling tasks. When the mall is closed, the system timer automatically turns off all the internal lighting within the mall while the external decorative lighting is left running. The next day, the system timer turns on the internal lighting and turns off the external lighting. At home, the washing machine uses the timer to control the various laundry processes and cycles, and the microwave oven uses it to set different heating durations. Unit 2.6 | Timing and Sensing 116  2.6.2 Functions of Sensors Many types of sensors are used in a building automation system. Sensors serve as input devices to send feedback to the system to perform the required responses. Here are some examples of how sensors are used in our everyday lives: In Singapore, almost everyone takes the lift every day; sensors operate the lift doors. A temperature sensor sends feedback to the controller to reduce or shut down the cooling system when it senses a drop in the surrounding temperature. A smoke detector triggers the fire alarm system when it detects smoke in the building. 2.6.3 Motion Sensors Fig. 2.6-2: Motion sensor A motion sensor, sometimes known as a motion detector, is a device that detects moving objects, particularly people. It is often integrated as a component of a system that automatically performs a task or alerts a user of motion in an area. Lighting can be automatically turned on and off by the device dsockeetecting motion within a range of 5 to 30 m. Passive infrared (PIR) sensors are sensitive to signals emitted by moving objects. 2.6.4 Light Sensors Fig. 2.6-3: Light sensor A light sensor, sometimes known as a photo sensor, is a passive device that converts light energy (visible) or infrared waves (invisible) into an electrical signal output. Light sensors are more commonly known as photoelectric devices or photo sensors because they convert light energy (photons) into electrical energy (electrons). Unit 2.6 | Timing and Sensing 117  2.6.5 Temperature Sensors Fig. 2.6-4: Temperature sensor A temperature sensor is a device that measures and detects changes in temperature. For example, temperature sensors can be used in fire alarms to detect a sudden rise in temperature, which could indicate that a fire has occurred. It can also be used in heaters and air conditioners to monitor and maintain the desired temperature, while at the same time, optimise energy consumption. The responsiveness and precision of a temperature sensor are crucial in many situations. 2.6.6 Window Sensors Fig. 2.6-5: A pair of window sensors Window sensors come in pairs. One fits onto the window itself, while the other attaches to the frame, and they are positioned right next to each other. Adhesives are usually used to keep the window sensors in place, though they can also be screwed directly onto the frame. Window sensors are either wired directly to the home security system or powered by battery to function wirelessly. When the two pieces of window sensors are separated (i.e., the window is opened), they will send a signal to the home security system. Unit 2.6 | Timing and Sensing 118  2.6.7 How Timers and Sensors Can be Used to Conserve Energy The most effective and practical approach to energy saving is to turn off lighting and other electrical devices when they are not in use. There are many examples of sensors and timers used in commercial and public buildings as well as residential homes: Sensors for activating automatic door openers provide convenience and improve the overall level of hygiene, especially in hospitals, as people can open the doors without touching them. Sensors for activating escalators in public buildings can put them in sleep mode when no one is using them. Sensors for activating a burglar alarm system can alert the homeowner or security service when they detect the motion of a possible intruder. Such detectors can also trigger a security camera in order to record the possible intrusion. Sensors for detecting light near windows can be used to adjust light levels within a building. Sensors for activating curtains and blinds can be used to improve the ambience of restaurants and other establishments. Timers can be used to turn on and off streetlights or indoor lights in walkways, lobbies and staircases at specific times. A more advanced system may have multiple timers to control the various types of lighting in a building compound, as shown in Table 2.6-1. Table 2.6-1: Timing system for lighting different parts of a building compound Lighting Location Turn-On Time (Hours) Turn-Off Time (Hours) Carpark 0700 – 1100 1130 – 0700 Garden 1930 – 1000 1000 – 1900 Corridor 1900 – 1100 1000 – 1900 Building Perimeter 1900 – 1130 1130 – 1900 To provide even greater user-friendliness, a combination of timers and sensors could be programmed to turn on the lighting for a brief period of time when the motion detectors sense someone leaving the building outside of the scheduled turn-off times. Unit 2.6 | Timing and Sensing 119