Subject: AELEX 211 (SENSOR TECHNOLOGY)

Course description: This course provides knowledge and understanding on sensors field usage and their role in
control system which is divided in two topics. The first part deals with discrete and solid state devices wherein
analog and digital signal voltage are applied and interface to microcontrollers and the second parts focuses mainly
on industrial applications being used for process control, automation and robotics which includes the interfacing
with programmable logic controllers and computers.

COURSE OUTLINE:

- Different types of sensors according to: capacitance, magnetism, inductions, piezoelectric and
temperature.
- Sensor technology ( materials, surface processing, nanotechnology, types of sensors)
- Proximity sensors (magnetic proximity sensor, capacitive proximity sensor, ultrasonic proximity sensor,
and pneumatic proximity sensor.)
- Thermal sensors, LVDT, level sensor, load cells, motion sensors, accelerometer, pressure sensor, magnetic
flow meter.)
- Optical sensors ( optical proximity sensors, optical proximity sensor with fiber optic cable.)

What is Sensor?

-In electronics, a sensor is a device that detects and responds to a physical input from the environment, converting it
into a measurable electrical signal. This signal can then be used to monitor, control, or analyse a process. Essentially,
sensors act as the interface between the physical world and electronic systems.

Here's a more detailed breakdown:

 Input: Sensors respond to various physical stimuli like light, heat, pressure, motion, sound, or chemical
changes.

 Conversion: The sensor converts this physical input into a corresponding electrical signal, such as a voltage,
current, or frequency change.

 Output: This electrical signal can then be used by other electronic components, like microcontrollers or
computers, to perform tasks like displaying information, triggering an action, or controlling a system.

Examples:

 Temperature sensor (thermistor): Measures temperature and outputs a voltage signal that varies with
temperature.

 Light sensor (phototransistor): Detects light intensity and converts it into an electrical signal.

 Pressure sensor (strain gauge): Measures pressure and outputs a voltage change proportional to the
pressure.

 Motion sensor (infrared sensor): Detects movement and can trigger an alarm or turn on a light.

Key functions of sensors:

 Monitoring:

Sensors can continuously track physical parameters, providing real-time data for observation and analysis.

 Control:
They can be used to automatically adjust or regulate processes based on sensed conditions.

 Automation:

Sensors play a crucial role in automated systems, enabling machines and devices to respond to their environment.

 Data acquisition:

They provide the data that enables systems to understand and interact with the physical world.

In essence, sensors are fundamental components in a wide range of electronic applications, from everyday devices
to complex industrial systems.

What is a Sensor?

Definition

An electrical sensor (also called an electronic sensor) is a device that detects a physical parameter of interest (e.g.
heat, light, sound) and converts it into electrical signal that can be measured and used by an electrical or electronic
system.

The detected quantity is usually a form of energy that is analog (continuous) in nature and is converted into electrical
energy using a transducer (e.g. a microphone is a transducer that converts sound energy into electrical energy).

How Are Sensors Used?

The signal generated at the output of an electrical sensor is typically used for the purpose of making a measurement
which can then be used to trigger a subsequent response. For example, a temperature sensor could be used to
measure the temperature of a room and convert it into an electrical signal. If the measured room temperature is too
low (below a pre-determined threshold) this information could be used by an electronic system that automatically
switches on a heater to increase the temperature of the room back towards the pre-determined threshold.
Alternatively, if the measurement from the sensor indicates that the room is too hot (above a pre-determined
threshold), the system could automatically switch on an air-conditioning unit to reduce the room temperature. The
common name for a sensor used to measure temperature is a thermometer.

Nowadays, the output signal from an electrical sensor is usually processed by a digital processor. To make this
possible, the continuous analog electrical signal must first be converted into a discrete digital representation using
an Analog-to-Digital converter.

Types of Sensors

Apart from heat and sound, electrical sensors can be used to detect and measure other quantities including light,
pressure, speed, acceleration, and mass. The size of the signal produced by a sensor depends on the application e.g.
Industrial sensors produce electrical signals typically between 20 and 30V while biosensors, used in health and
fitness wearables (Figure 1) and which are used to make human body measurements, typically produce electronic
signals of only a few millivolts or even smaller.

Sensors can be categorized based on their sensing principle into capacitive, magnetic, and inductive types. Capacitive
sensors detect changes in capacitance, magnetic sensors detect magnetic fields, and inductive sensors detect
changes in inductance. These principles are used in various sensor applications, including proximity sensing, position
sensing, and more.

1. Capacitive Sensors:
 - Principle: Capacitive sensors work by detecting changes in capacitance, which is an electrical property that
describes how well a device stores electrical energy. They operate by measuring the change in capacitance
between a sensing electrode and a target object.

- Detection: They can detect both conductive and non-conductive materials.

- Applications: Capacitive sensors are used in various applications, including proximity sensing, level sensing
(e.g., detecting fluid levels in a tank), and touch-sensitive interfaces.

- Types: They can be further categorized into active and passive types, where active sensing involves an
electronic component to detect capacitance changes.

Example: Capacitive touchscreens rely on capacitive sensing to detect finger touches.

2. Magnetic Sensors:

- Principle: Magnetic sensors detect the presence and strength of magnetic fields. They rely on various
physical phenomena, such as the Hall effect, magnetoresistance, or changes in magnetic permeability, to
convert magnetic field variations into electrical signals.

Types: Common types of magnetic sensors include:

 Hall effect sensors: These sensors measure the voltage difference caused by a magnetic field on a
current-carrying conductor.

 Magnetoresistive sensors: These sensors detect changes in resistance caused by a magnetic field.

Applications: Magnetic sensors are used in various applications, such as position sensing, speed sensing, and
magnetic field measurement.

Example: Reed switches are a simple type of magnetic sensor that use a magnetic field to close or open an electrical
circuit.

3. Inductive Sensors:

- Principle: Inductive sensors detect the presence of conductive objects by measuring changes in
inductance. Inductance is the property of an electrical circuit that opposes changes in current flow.

- Detection: Typically used to detect metallic objects, as the eddy currents induced in the object by the
sensor's magnetic field affect the inductance.

Applications: Inductive sensors are commonly used in proximity sensing, position sensing, and eddy current testing.

Types: Inductive proximity sensors can be further classified into different types based on their operating principle,
such as high-frequency oscillation, magnetic, or electrostatic capacity types, according to Keyence.

Example: Inductive sensors are used in automatic door systems to detect the presence of a person or object near the
door.