Internet of Things (CS-803 (C)) Unit 2 Notes

How unit 2 is examined

This unit covers sensors (definition, node, features, classes, types, errors) and actuators; Sensor Types (14 marks) and Actuator (7 marks) carry the marks.

Define Sensor

Not asked since 2022

Definition. A sensor is a device that detects a physical, chemical or biological quantity from its surroundings and converts it into an electrical signal that can be measured and processed.

Key points.

The measured quantity is called the measurand, for example temperature, light, pressure or motion.
A sensor converts one form of energy into another, so it is a type of transducer.
In IoT the sensor is the input device that feeds raw data to the microcontroller or gateway.
Its output is usually a voltage, current or digital reading proportional to the measurand.

Basic components and challenges of a sensor node

Definition. A sensor node is a small device that senses, processes and transmits data, made of a sensing unit, a processing unit, a transceiver and a power unit.

Key points.

The sensing unit holds the sensor and an ADC that turns the analog signal into digital data.
The processing unit is a microcontroller with memory that runs the program and processes readings.
The transceiver gives wireless communication with the gateway or neighbouring nodes.
The power unit is usually a battery, sometimes with a solar harvester.
Challenges are limited energy, small memory and processing power, unreliable wireless links, low cost, security, and node failure in harsh places.

Sensor features, Sensor resolution

Definition. Resolution is the smallest change in the measured quantity that a sensor can detect and show in its output.

Key points.

Range is the span of measurand values the sensor can measure, and sensitivity is the output change per unit input change.
Accuracy is closeness to the true value, and precision is repeatability of repeated readings.
Response time is how fast the output follows a change, and linearity is how straight the input-output curve is.
A finer resolution means smaller steps are seen; for an $n$-bit ADC the step is $\text{range}/2^n$.

Sensor classes: Analog, Digital, Scalar, Vector Sensors

Definition. Sensors are classed by output type as analog or digital, and by the quantity measured as scalar (magnitude only) or vector (magnitude and direction).

Key points.

An analog sensor gives a continuous output such as a voltage, for example an LM35 temperature sensor or an LDR.
A digital sensor gives discrete binary output, for example a DHT11 or a PIR motion sensor.
A scalar sensor measures magnitude only, for example temperature, pressure or humidity.
A vector sensor measures magnitude and direction, for example an accelerometer, gyroscope or magnetometer.

Sensor Types

Definition. A sensor is a device that senses a physical quantity from the environment and converts it into an electrical signal; in IoT it acts as the eyes and ears of the system.

Role in IoT. Sensors acquire data from the physical world, which is then collected, sent to the cloud, analysed, and used to monitor conditions and trigger automation through actuators.

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Key points.

Temperature sensors (thermistor, LM35, thermocouple) change resistance or voltage with heat, and are used in smart thermostats and cold-chain tracking.
Pressure sensors (piezoresistive, strain gauge) convert force per area into a voltage, and are used in weather stations and tyre-pressure monitoring.
Proximity sensors (inductive, capacitive, ultrasonic, IR) detect a nearby object without touching it, and are used in parking assist and object counting.
Image sensors (CCD, CMOS) turn light into pixel data, and are used in smart surveillance and face recognition.
Light sensors (LDR, photodiode) change resistance or current with brightness, and are used in automatic street lights.
Gas and chemical sensors (MQ series) change conductivity with a gas, and are used in air-quality and leak alarms.
Motion sensors (PIR, accelerometer, gyroscope) detect movement or orientation, and are used in security systems and wearables.
Humidity sensors (DHT11) measure moisture in air by capacitance change, and are used in smart farming and HVAC.

Example. In a smart home, a DHT11 reads temperature and humidity, a PIR detects people, and the values go to the gateway, which switches the fan through an actuator.

Answer frame. Open with the definition and role of sensors in IoT; draw the classification tree; develop the role (sensing, collection, monitoring, automation) in two lines, then points 1-8 each with principle and IoT example; close with the smart-home example and a line that sensors are the base of every IoT system.

Asked: [14 marks] (May 2023) Discuss the role of sensors in IoT. Explain the various types of sensors.

bias, drift

Definition. Bias is a constant offset of the sensor output from the true value, while drift is a slow change of the output over time when the input is constant.

Key points.

Bias is a fixed error present at all readings and is removed by calibration or by subtracting the offset.
Drift grows gradually with time, temperature change or ageing of the sensing element.
Drift needs periodic recalibration, whereas bias is corrected once.
Both reduce accuracy even when the sensor is precise.

Hysteresis error, quantization error

Definition. Hysteresis error is the difference in output for the same input depending on whether the input is rising or falling, and quantization error is the difference between the real analog value and its digital representation.

Key points.

Hysteresis comes from friction, magnetic or material lag in the sensing element.
It is measured as the maximum gap between the rising and falling curves.
Quantization error appears in ADC conversion because a continuous value is rounded to the nearest step.
Its maximum is $\pm \tfrac{1}{2}$ of the step size, and it falls when ADC bits increase.

Actuator

Definition. An actuator is a device that converts a control signal into physical action such as movement, heat or force.

Key points.

In IoT it is the output device, working opposite to a sensor: the controller sends a signal and the actuator acts on the environment.
Types are electrical (motors, relays, solenoids), hydraulic (liquid pressure) and pneumatic (compressed air).
Working is signal, then energy source, then motion, for example a relay switching a pump.
Applications are smart locks, valves in irrigation, robotic arms and fan or light control.

Asked: [7 marks] (May 2023) Write short note on Actuator.

Actuator types: Hydraulic, Pneumatic

Definition. Hydraulic actuators use pressurised liquid (oil) and pneumatic actuators use compressed air to produce linear or rotary motion.

Key points.

Hydraulic actuators give very high force, so they suit heavy machines, but they need pumps and can leak.
Pneumatic actuators are fast, clean and cheap, but the compressible air gives less force and less precise control.
Both use a cylinder and piston moved by fluid pressure through a valve.

electrical, thermal/magnetic, mechanical actuators, soft actuators

Definition. These actuators convert electrical, thermal, magnetic or mechanical energy, or a deformable soft material's response, into motion.

Key points.

Electrical actuators (DC, stepper and servo motors) are easy to control and most common in IoT.
Thermal or magnetic actuators use heat expansion, shape-memory alloys or magnetic fields, as in solenoids.
Mechanical actuators use gears, cams, screws or levers to transform one motion into another.
Soft actuators use flexible materials such as silicone that bend when air or voltage is applied, and suit soft robots and grippers.

Last-minute revision

A sensor converts a physical quantity into an electrical signal; an actuator converts a control signal into physical action.
A sensor node has sensing, processing, transceiver and power units.
Resolution is the smallest detectable change; quantization step is $\text{range}/2^n$.
Analog sensors give continuous output, digital give discrete output.
Scalar sensors give magnitude only, vector sensors give magnitude and direction.
Sensor types: temperature, pressure, proximity, image, light, gas, motion, humidity.
Bias is a constant offset; drift is a slow change over time.
Hysteresis depends on the direction of input change.
Maximum quantization error is half a step.
Actuator types: electrical, hydraulic, pneumatic, thermal or magnetic, mechanical, soft.

Memory hooks

Node = SPTP: Sensing, Processing, Transceiver, Power.
Bias is a Barrier (fixed), drift is a Drive-away (slow).
Sensor is the ear, actuator is the hand.
Hydraulic = liquid = heavy force; pneumatic = air = light and fast.

Coverage checklist

Define Sensor: definition, measurand, transducer.
Basic components and challenges of a sensor node: four units, challenges.
Sensor features, Sensor resolution: range, sensitivity, accuracy, resolution.
Sensor classes: Analog, Digital, Scalar, Vector Sensors: four classes with examples.
Sensor Types: Q1 (14 marks, May 2023).
bias, drift: definitions and difference.
Hysteresis error, quantization error: definitions and causes.
Actuator: Q2 (7 marks, May 2023).
Actuator types: Hydraulic, Pneumatic: working and comparison.
electrical, thermal/magnetic, mechanical actuators, soft actuators: four kinds.

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Internet of Things (CS-803 (C)) - Unit 2 Short Notes

How unit 2 is examined

Define Sensor

Basic components and challenges of a sensor node

Sensor features, Sensor resolution

Sensor classes: Analog, Digital, Scalar, Vector Sensors

Sensor Types

bias, drift

Hysteresis error, quantization error

Actuator

Actuator types: Hydraulic, Pneumatic

electrical, thermal/magnetic, mechanical actuators, soft actuators

Last-minute revision

Memory hooks

Coverage checklist