IoT Sensing and Actuation.pdf
3 likes•4,860 views
This document discusses IoT sensing and actuation. It defines transduction as the process of energy conversion from one form to another. Sensors convert various forms of energy into electrical signals, while actuators convert electrical signals into various forms of energy, typically mechanical energy. The document describes different types of sensors and their characteristics like resolution, accuracy, and precision. It also discusses sensor errors and deviations. Finally, it categorizes sensing into four types - scalar sensing, multimedia sensing, hybrid sensing, and virtual sensing - based on the nature of the environment being sensed.
IoT Sensing and Actuation.pdf
- 1. Chapter 5 IoT Sensing and Actuation Introduction to IoT Dr. Loganathan R
- 2. 1 Introduction • The basic science of sensing and actuation is based on the process of transduction • Transduction is the process of energy conversion from one form to another • A transducer is a physical means of enabling transduction • Transducers take energy in any form and convert it into another • IoT applications involves Sensing/Actuation in one form or the other 2 Dr Loganathan R
- 3. 1 Introduction 3 Dr Loganathan R Parameters Transducers Sensors Actuators Definition Converts energy from one form to another Converts various forms of energy into electrical signals Converts electrical signals into various forms of energy, typically mechanical energy Domain Can be used to represent a sensor as well as an actuator It is an input transducer It is an output transducer Function Can work as a sensor or an actuator but not simultaneously Used for quantifying environmental stimuli into signals. Used for converting signals into proportional mechanical or electrical outputs Examples Any sensor or actuator Humidity sensors, Temperature Sensors Anemometers (measures flow velocity), Manometers (measures fluid pressure), Accelerometers (measures the acceleration of a body), Gas sensors (measures concentration of specific gas or gases), and others Motors (convert electrical energy to rotary motion), Force heads (which impose a force), Pumps (which convert rotary motion of shafts into either a pressure or a fluid velocity)
- 4. 2 Sensors 4 Dr Loganathan R • Sensors can measure or quantify or respond to the ambient changes in their environment or within the intended zone of their deployment • Generate responses to external stimuli or physical phenomenon through input functions and their conversion into electrical signals. • It is insensitive to any other property besides what it is designed to detect • A sensor does not influence the measured property Simple Sensing Operation
- 5. 2 Sensors 5 Dr Loganathan R • Sensors can be classified based on: 1. Power requirements, 2. Sensor output 3. Property to be measured. • Power Requirements: The way sensors operate decides the power requirements i. Active: Active sensors do not require an external circuitry or mechanism to provide power. It directly responds to the external stimuli from its ambient environment and converts it into an output signal. For example, a photodiode converts light into electrical impulses. ii.Passive: Passive sensors require an external mechanism to power them up. The sensed properties are modulated with the sensor’s inherent characteristics to generate patterns in the output of the sensor. For example, a thermistor’s resistance can be detected by applying voltage difference across it or passing a current through it.
- 6. 2 Sensors 6 Dr Loganathan R • The output of a sensor helps in deciding the additional components to be integrated with an IoT node or system i. Analog: Generates an output signal or voltage, which is proportional (linear/non- linear) to the quantity being measured and is continuous in time and amplitude. Physical quantities such as temperature, speed, pressure, displacement, strain, and others are all continuous and categorized as analog quantities. For example, a thermometer continuously respond to changes in the temperature. ii.Digital: These sensors generate the output of discrete time digital representation (time, or amplitude, or both) of a quantity being measured, in the form of output signals or voltages. Binary output signals in the form of a logic 1 or a logic 0 for ON or OFF. The generated discrete (non-continuous) values may be output as a single “bit”, eight of which combine a single “byte” output (parallel transmission). • Digital sensors can be directly integrated to the processors • Analog sensors to these Processors or IoT nodes requires interfacing mechanisms such as analog to digital converters (ADC), voltage level converters, and others.
- 7. 2 Sensors 7 Dr Loganathan R • Measured Property: Some properties to be measured based on temporal variations in the measured property, such as ambient temperature, atmospheric pressure, and others. Whereas some properties to be measured show high spatial as well as temporal variations such as sound, image, and others. Depending on the properties to be measured, sensors can be of two types. i. Scalar: Scalar sensors produce an output proportional to the magnitude of the quantity being measured. The output is in the form of a signal or voltage. A thermometer is an example of a scalar sensor that has the ability to detect changes in ambient, changes in sensor orientation or direction do not affect these sensor ii. Vector: Vector sensors are affected by the magnitude as well as the direction and/or orientation of the property they are measuring. Physical quantities like velocity and images that require additional information besides their magnitude for completely categorizing a physical phenomenon are categorized as vector quantities. For example, an electronic gyroscope, which is commonly found in all modern aircraft, is used for detecting the changes in orientation of the gyroscope with respect to the Earth’s orientation along all three axes.
- 8. A sensor node 8 Dr Loganathan R • Combination of a sensor or sensors, a processor unit, a radio unit, and a power unit • The nodes are capable of sensing the environment they are set to measure and communicate the information to other sensor nodes or a remote server The functional blocks of a typical sensor node in IoT
- 9. A sensor node 9 Dr Loganathan R Some Commercially Available Sensors
- 10. 3 Sensor Characteristics 10 Dr Loganathan R • Sensors can be characterized by their ability to sense the phenomenon based on the following three fundamental properties • Sensor Resolution: The resolution of a sensor is the smallest change in the measured quantity that it is capable of detecting. A sensor's resolution determines how accurate and precise it is. The accuracy of a sensor is independent of resolution. Sensor A can detect changes in temperature up to 0.5◦C, whereas B can detect changes up to 0.25◦C. B has a greater resolution than A • Sensor Accuracy: The accuracy of a sensor is the ability of that sensor to measure the environment of a system as close to its true measure as possible. For example, a weight sensor detects 100 kg mass as 99.98 kg, than sensor is 99:98% accurate, with an error rate of 0:02%. • Sensor Precision: The repeatability principle controls a sensor's accuracy. When the sensor is repeatedly tested and proven to have the same error rate, it is said to be very precise. For instance, the sensor accuracy is not considered great if the same sensor provides values of 98.28 kg, 100.34 kg, and 101.11 kg after three repeat measurements.
- 11. 4 Sensorial Deviations 11 Dr Loganathan R Sensorial deviations are considered as errors in sensors • Sensitivity error: attributed to sensor fabrication errors and its calibration. For Example the sensor output is truncated to its maximum or minimum value, which is also the sensor’s limits • Offset error or Bias: The output of a sensor differs from the actual value to be measured by a constant. For example, while measuring an actual temperature of 0◦ C, a temperature sensor outputs 1.1◦ C every time, this sensor have an offset error or bias of 1.1◦C. • Non-linear behaviour: If a sensor’s transfer function (TF) deviates from a straight line transfer function, it is referred to as its non-linearity • Drift : the behaviour of output signal of a sensor changes slowly and independently of the measured property. Physical changes in the sensor or its material may result in long-term drift, which can span over months or years.
- 12. 4 Sensorial Deviations 12 Dr Loganathan R • Hysteresis error: a sensor’s output varies/deviates due to deviations in the sensor’s previous input values • Quantization error(Digital Sensor): the difference between the actual analog signal and its closest digital approximation during the sampling stage of the analog to digital conversion. • Aliasing error: dynamic errors caused due to mishandling of sampling frequencies. Aliasing leads to different signals of varying frequencies to be represented as a single signal in case the sampling frequency is not correctly chosen, resulting in the input signal becoming a multiple of the sampling rate • Environment: sensors may be prone to external influences, which may not be directly linked to the property being measured by the sensor. For example, as most sensors are semiconductor based, they are influenced by the temperature of their environment
- 13. 5 Sensing Types 13 Dr Loganathan R • Sensing is divided into 4 categories based on the nature of the environment being sensed and the physical sensors being used to do: 1) scalar sensing, 2) multimedia sensing, 3) hybrid sensing, and 4) virtual sensing
- 14. 5.1 Scalar sensing 14 Dr Loganathan R • Scalar sensing encompasses the sensing of features that can be quantified simply by measuring changes in the amplitude of the measured values with respect to time. • Quantities such as ambient temperature, current, atmospheric pressure, rainfall, light, humidity, flux and others are scalar values as they do not have a directional or spatial property assigned with them. • Simply measuring the changes in their values with passing time provides enough information about these quantities. • The sensors used for measuring these scalar quantities are referred to as scalar sensors, and the act is known as scalar sensing. • Example Sensors: Color sensor, Current sensor, Digital temperature and humidity sensor, • Example Event: A simple scalar temperature sensing is a fire detection event.
- 15. 5.2 Multimedia sensing 15 Dr Loganathan R • Multimedia sensing encompasses the sensing of features that have a spatial variance property associated with the property of temporal variance. • Multimedia sensors are used for capturing the changes in amplitude of a quantifiable property concerning space (spatial) as well as time (temporal). • Quantities such as images, direction, flow, speed, acceleration, sound, force, mass, energy, and momentum have both directions as well as a magnitude. • These quantities follow the vector law of addition and hence are designated as vector quantities. • They might have different values in different directions for the same working condition at the same time. • Example Sensor: Camera sensor, Compass and Barometer • Example Event: A simple camera-based multimedia sensing using surveillance
- 16. 5.3 Hybrid sensing 16 Dr Loganathan R • The act of using scalar as well as multimedia sensing at the same time is referred to as hybrid sensing. • To measure vector and scalar properties of an environment at the same time, a range of various sensors are employed to measure the various properties of that environment at any instant of time, and temporally map the collected information to generate new information • For example, to measure the soil conditions at regular intervals of time to determine plant health, moisture and soil temperature are deployed underground to estimate water retention capacity and the moisture being held • Additional camera sensor with the plant may be able to determine the actual condition of a plant by additionally determining the color of leaves • The aggregate information from soil moisture, soil temperature, and the camera sensor will be able to collectively determine a plant’s health
- 17. 5.4 Virtual sensing 17 Dr Loganathan R • Farmer A ’s sensors are being used for actual measurement of parameters, whereas virtual data (which does not have actual physical sensors but uses extrapolation-based measurements) is being used for advising Farmer B. • if the data from farmer A’s field is digitized using an IoT infrastructure and this system advises him regarding the appropriate watering, fertilizer and pesticide regimen for his crops, this advisory can also be used by farmer B for maintaining his crops
- 18. 6 Sensing Considerations 18 Dr Loganathan R • The following major factors influence the choice of sensors in IoT-based sensing solutions: 1. Sensing range 2. Accuracy and Precision 3. Energy 4. Device Size
- 19. 6 Sensing Considerations 19 Dr Loganathan R • Sensing range: The sensing range of a sensor node defines the detection fidelity of that node. • Approaches to optimize the sensing range in deployments are fixed k-coverage and dynamic k-coverage. (an area of a deployment field is said to be k-covered if each point belongs to the intersection of sensing ranges of at least sensors) • A lifelong fixed k-coverage tends to usher in redundancy as it requires a large number of sensor nodes, the sensing range of some of which may also overlap. • Dynamic k-coverage incorporates mobile sensor nodes post detection of an event, which is a costly solution and may not be deployable in all operational areas and terrains • For example, a proximity sensor has a sensing range of a couple of meters, in contrast, a camera has a sensing range varying between tens of meters to hundreds of meters. • As the complexity of the sensor and its sensing range goes up, its cost significantly increases.
- 20. 6 Sensing Considerations 20 Dr Loganathan R • Accuracy and Precision: The accuracy and precision of measurements of sensor are critical in deciding the operations of specific functional processes. • Typically, off-the-shelf consumer sensors are low on requirements and often very cheap, but their performance is limited to regular application domains. • For example, a standard temperature sensor can be easily integrated with conventional components for hobby projects and day-to-day applications, but it is not suitable for industrial processes. • Energy: The energy consumed by a sensing solution is crucial to determine the lifetime of that solution and the estimated cost of its deployment. • If the sensor or the sensor node is so energy inefficient and it requires replenishment of its energy sources quite frequently, the effort in maintaining the solution and its cost goes up and its deployment feasibility goes down. • For example sensor nodes deployed on the top of glaciers, access to these nodes is not possible.
- 21. 6 Sensing Considerations 21 Dr Loganathan R • Device Size: Most of the applications of IoT require sensing solutions which are so small that they do not hinder any of the regular activities that were possible before the sensor node deployment was carried out. • Larger the size of a sensor node, larger is the obstruction caused by it, higher is the cost and energy requirements and lesser is its demand • For Example, human activity detector, If the detection unit is too large to be carried or too bulky to cause hindrance to regular normal movements. • The wearable sensors are highly energy-efficient, small in size, and almost part of the wearer’s regular wardrobe
- 22. 7 Actuators 22 Dr Loganathan R • A machine or system’s component that can affect the movement or control the said mechanism or the system • Control systems affect changes to the environment or property they are controlling through actuators • The system activates the actuator through a control signal, which may be digital or analog • The outline of a simple actuation system.
- 23. 8 Actuator Types 23 Dr Loganathan R • Actuators are divided into seven classes: 1. Hydraulic 2. Pneumatic 3. Electrical 4. Thermal / magnetic 5. Mechanical 6. Soft memory polymers 7. Shape memory polymers.
- 24. 8.1 Hydraulic actuators 24 Dr Loganathan R • Works on the principle of compression and decompression of fluids • Facilitates mechanical tasks such as lifting loads through the use of hydraulic power derived from fluids in cylinders or fluid motors • The mechanical motion applied to a hydraulic actuator is converted to either linear, rotary, or oscillatory motion. • The almost incompressible property of liquids is used for exerting significant force. These hydraulic actuators are also considered as stiff systems • The actuator’s limited acceleration restricts its usage.
- 25. 8.2 Pneumatic actuators 25 Dr Loganathan R • Works on the principle of compression and decompression of gases • These actuators use a vacuum or compressed air at high pressure and convert it into either linear or rotary motion • Pneumatic rack and pinion actuators are commonly used for valve controls of water pipes. • Pneumatic actuators are considered as compliant systems and has quick response to starting and stopping signals. • Small pressure changes can be used for generating large forces through these actuators. • Example: Pneumatic brakes, it convert small pressure changes applied by drives to generate the force required to stop or slow down a moving vehicle. • Responsible for converting pressure into force. • The power source in the pneumatic actuator does not need to be stored in reserve for its operation.
- 26. 8.3 Electric actuators 26 Dr Loganathan R • Electric motors are used to power an electric actuator by generating mechanical torque. This generated torque is translated into the motion of a motor’s shaft or for switching. • For example, solenoid valves control the flow of water in pipes in response to electrical signals. • The cheapest, cleanest and speedy actuator types • The use of thermal or magnetic energy is used for powering this class of actuators. • These actuators have a very high power density and are compact, lightweight and economical. • Example: shape memory materials (SMMs) such as shape memory alloys (SMAs) • These actuators do not require electricity for actuation. • They are not affected by vibration and can work with liquid or gases. • Magnetic shape memory alloys (MSMAs) are a type of magnetic actuators. 8.4 Thermal or magnetic actuators
- 27. 8.5 Mechanical actuators 27 Dr Loganathan R • The rotary motion of the actuator is converted into linear motion to execute some movement • The use of gears, rails, pulleys, chains and other devices are necessary to operate. • Used in conjunction with pneumatic, hydraulic or electrical actuators • Also work in a standalone mode. • Example: hydroelectric generator convert the water-flow induced rotary motion of a turbine into electrical energy
- 28. 8.6 Soft actuators 28 Dr Loganathan R • Consists of elastomeric polymers that are used as embedded fixtures in flexible materials such as cloth, paper, fiber, particles and others • The conversion of molecular level microscopic changes into tangible macroscopic deformations is the primary working principle of this class of actuators. • These actuators have a high stake in modern-day robotics. • They are designed to handle fragile objects such as agricultural fruit harvesting or performing precise operations like manipulating the internal organs during robot- assisted surgeries
- 29. 8.7 Shape memory polymers 29 Dr Loganathan R • Shape memory polymers are smart materials that respond to some external stimulus by changing their shape and then revert to their original shape once the affecting stimulus is removed. • Features such as high strain recovery, biocompatibility, low density and biodegradability characterize these materials, Functions similar to our muscles • Respond to a wide range of stimuli such as pH changes, heat differentials, light intensity, and frequency changes, magnetic changes and others. • Photopolymer/light-activated polymers (LAP) are a particular type of SMP, require light as a stimulus to operate. • LAP-based actuators are characterized by their rapid response times. • Using only the variation of light frequency or its intensity, can be controlled remotely without any physical contact. • LAPs shape can be changed by the application of a specific frequency, to change the polymer back to its original shape, a light stimulus of a different frequency has to be applied
- 30. 8 Actuator Types 30 Dr Loganathan R
- 31. 9 Actuator Characteristics 31 Dr Loganathan R • Weight: • The physical weight of actuators limits its application scope. • For example, the use of heavier actuators is generally preferred for industrial applications and applications requiring no mobility of the IoT deployment. • Lightweight actuators used in portable systems in vehicles, drones and home IoT applications. • This is not always true. • Heavier actuators also have selective usage in mobile systems, for example, landing gears and engine motors in aircraft.
- 32. 9 Actuator Characteristics 32 Dr Loganathan R • Power Rating: • This helps in deciding the nature of the application with which an actuator can be associated. • It defines the minimum and maximum operating power an actuator can safely withstand without damage to itself. • it is indicated as the power-to-weight ratio for actuators. • For example, smaller servo motors used in hobby projects typically have a maximum rating of 5 VDC, 500 mA, which is suitable for an operations-driven battery-based power source. Exceeding this limit might be detrimental to the performance of the actuator and may cause burnout of the motor. • Servo motors in larger applications have a rating of 460 VAC, 2:5 A, which requires standalone power supply systems for operations. It is to be noted that actuators with still higher ratings are available and vary according to application requirements.
- 33. 9 Actuator Characteristics 33 Dr Loganathan R • Torque to Weight Ratio: • The ratio of torque to the weight of the moving part of an instrument/device is referred to as its torque/weight ratio. • Indicates the sensitivity of the actuator. • Higher is the weight of the moving part, lower will be its torque to weight ratio for a given power.
- 34. 9 Actuator Characteristics 34 Dr Loganathan R • Stiffness and Compliance: • The resistance of a material against deformation is known as its stiffness, whereas compliance of a material is the opposite of stiffness. • Stiffness can be directly related to the modulus of elasticity of that material • Stiff systems are considered more accurate than compliant systems as they have a faster response to the change in load applied to it • For example, hydraulic systems are considered as stiff and non-compliant, whereas pneumatic systems are considered as compliant.