Week 1 Lecture Material PDF

Sensing Dr. Sudip Misra Associate Professor Department of Computer Science and Engineering IIT KHARAGPUR Email: [email protected] Website: http://cse.iitkgp.ac.in/~smisra/ Introduction to Interne...

Sensing Dr. Sudip Misra Associate Professor Department of Computer Science and Engineering IIT KHARAGPUR Email: [email protected] Website: http://cse.iitkgp.ac.in/~smisra/ Introduction to Internet of Things 1  Definition  A sensor detects (senses) changes in the ambient conditions or in the state of another device or a system, and forwards or processes this information in a certain manner. “A device which detects or measures a physical property and records, indicates, or otherwise responds to it”. References: ‐ Oxford Dictionary 1. http://www.businessdictionary.com/definition/sensor.html 2. https://en.oxforddictionaries.com/definition/sensor Introduction to Internet of Things 2 Sensors  They perform some input functions by sensing or feeling the physical changes in characteristics of a system in response to a stimuli.  For example heat is converted to electrical signals in a temperature sensor, or atmospheric pressure is converted to electrical signals in a barometer. Introduction to Internet of Things 3 Transducers  Transducers convert or transduce energy of one kind into another.  For example, in a sound system, a microphone (input device) converts sound waves into electrical signals for an amplifier to amplify (a process), and a loudspeaker (output device) converts these electrical signals back into sound waves. Introduction to Internet of Things 4  Sensor vs. Transducer  The word “Transducer” is the collective term used for both Sensors which can be used to sense a wide range of different energy forms such as movement, electrical signals, radiant energy, thermal or magnetic energy etc., and Actuators which can be used to switch voltages or currents. References: 1. http://www.electronics‐tutorials.ws/io/io_1.html Introduction to Internet of Things 5 Sensor Features  It is only sensitive to the measured property (e.g., A temperature sensor senses the ambient temperature of a room.)  It is insensitive to any other property likely to be encountered in its application (e.g., A temperature sensor does not bother about light or pressure while sensing the temperature.)  It does not influence the measured property (e.g., measuring the temperature does not reduce or increase the temperature). Introduction to Internet of Things 6 Sensor Resolution  The resolution of a sensor is the smallest change it can detect in the quantity that it is measuring.  The resolution of a sensor with a digital output is usually the smallest resolution the digital output it is capable of processing.  The more is the resolution of a sensor, the more accurate is its precision.  A sensor’s accuracy does not depend upon its resolution. Introduction to Internet of Things 7 Sensor Classes Based on Based on Output Data type Analog Scalar Vector/ Digital Multimedia Introduction to Internet of Things 8 Analog Sensors  Analog Sensors produce a continuous output signal or voltage which is generally proportional to the quantity being measured.  Physical quantities such as Temperature, Speed, Pressure, Displacement, Strain etc. are all analog quantities as they tend to be continuous in nature.  For example, the temperature of a liquid can be measured using a thermometer or thermocouple (e.g. in geysers) which continuously responds to temperature changes as the liquid is heated up or cooled down. Introduction to Internet of Things 9 Digital Sensors  Digital Sensors produce discrete digital output signals or voltages that are a digital representation of the quantity being measured.  Digital sensors produce a binary output signal in the form of a logic “1” or a logic “0”, (“ON” or “OFF”).  Digital signal only produces discrete (non‐continuous) values, which may be output as a single “bit” (serial transmission), or by combining the bits to produce a single “byte” output (parallel transmission). Introduction to Internet of Things 10 Scalar Sensors  Scalar Sensors produce output signal or voltage which is generally proportional to the magnitude of the quantity being measured.  Physical quantities such as temperature, color, pressure, strain, etc. are all scalar quantities as only their magnitude is sufficient to convey an information.  For example, the temperature of a room can be measured using a thermometer or thermocouple, which responds to temperature changes irrespective of the orientation of the sensor or its direction. Introduction to Internet of Things 11 Vector Sensors  Vector Sensors produce output signal or voltage which is generally proportional to the magnitude, direction, as well as the orientation of the quantity being measured.  Physical quantities such as sound, image, velocity, acceleration, orientation, etc. are all vector quantities, as only their magnitude is not sufficient to convey the complete information.  For example, the acceleration of a body can be measured using an accelerometer, which gives the components of acceleration of the body with respect to the x,y,z coordinate axes. Introduction to Internet of Things 12 Sensor Types Light Dependent resistor Light Photo‐diode Thermocouple Temperature Thermistor Strain gauge Force Pressure switch Potentiometer, Encoders Position Opto‐coupler Reflective/ Opto‐coupler Speed Doppler effect sensor Carbon Microphone Sound Piezoelectric Crystal Liquid Chemical sensor Chemical Gaseous chemical sensor Introduction to Internet of Things 13  Pressure Sensor Ultrasonic Distance Sensor Tilt Sensor Infrared Motion Sensor Source: Wikimedia Commons Source: Wikimedia Commons Source: Wikimedia Commons Source: Wikimedia Commons Analog Temperature Sensor Camera Sensor Source: Wikimedia Commons Source: Wikimedia Commons Introduction to Internet of Things 14  Sensorial Deviations  Since the range of the output signal is always limited, the output signal will eventually reach a minimum or maximum, when the measured property exceeds the limits. The full scale range of a sensor defines the maximum and minimum values of the measured property.  The sensitivity of a sensor under real conditions may differ from the value specified. This is called a sensitivity error.  If the output signal differs from the correct value by a constant, the sensor has an offset error or bias. Reference: https://en.wikipedia.org/wiki/Sensor 15