Introduction
Much of the functionality of IoT, and the data transmitted in the M2M and M2P notions of the IoT, are determined by the nature of sensor measurement. The other machines associated with IoT include actuators,
the devices that can be directed to perform a physical activity such as opening an irrigation dam or closing a livestock fence. However, in the context of development, the majority of current applications utilize connected sensors.
Sensors are one of the primary modes of realizing the full potential of value-added to the companies, communities, and individuals who employ them for IoT purposes. In general, sensors host a heterogeneous school of functions. They can detect everything, from changes in temperature and humidity to the amount of force and pressure being simultaneously applied to thousands of products on a manufacturing floor. Sensors can be broadly deployed to overcome a host of challenges but in some cases, they may need to be highly customized. It is this customization that enables sensors to provide real added value for IoT and ICT4D initiatives.
Range Of Common Sensors
The below figure illustrates some commonly found sensors available in the commercial market.
Types of Sensors
Sensors are often categorized based on their power sources: active v/s passive.
Active sensors emit energy of their own and then sense the response of the environment to that energy. Radio Detection and Ranging (RADAR) is an example of active sensing.
Passive sensors simply receive energy (in any form) that is produced external to the sensing device. A standard camera is embedded with a passive sensor - it receives signals in the form of light and captures them
on a storage device.
Position Sensors
Position sensor measures the position of an object; the position measurement can either be in absolute terms (absolute position sensor) or in relative terms (displacement sensor). Position sensors can be linear, angular, or multi-axis.
Example - Potentiometer, inclinometer, proximity sensor
Occupancy and Motion Sensors
Occupancy
sensors detect the presence of people and animals in a surveillance
area, while the motion sensors detect the movement of people and objects.
The difference between the two is that occupancy sensors will generate a
signal even when a person is stationary, while a motion sensor won't.
Example - Electric eye, RADAR
Velocity and Acceleration Sensors
Velocity (speed of motion) sensors may be linear or angular, indicating
how fast an object moves along a straight line or how fast it rotates.
Acceleration sensors measure changes in velocity.
Example - Accelerometer, gyroscope
Force
Force sensors detect whether a physical force is applied and whether the magnitude of the force is beyond a threshold.
Example - Force gauge, viscometer, tactile sensor (touch sensor)
Pressure
Pressure sensors are related to force sensors and measure the force
applied by liquids or gases. Pressure is measured in terms of force per
unit area.
Example - Barometer, bourdon gauge, piezometer
Flow
Flow
sensors detect the rate of fluid flow. They measure the volume (mass
flow) or rate (flow velocity) of fluid that has passed through a system
in a given period of time.
Example Anemometer, mass flow sensor, water meter
Acoustic
Acoustic sensors measure sound levels and convert that information into digital or analog data signals.
Example - Microphone, geophone, hydrophone
Humidity
Humidity sensors-detect humidity (amount of water vapor) in the air or a mass.
Humidity levels can be measured in various ways: absolute humidity,
relative humidity, mass ratio, and so on
Example - Hygrometer, humistor, soil moisture sensor
Light
Light sensors detect the presence of light (visible or invisible).
Example - Infrared sensor, photodetector, flame detector
Radiation
Radiation sensors detect radiations in the environment. Radiation can be sensed by scintillating or ionization detection.
Example - Geiger–Müller counter, scintillator, neutron detector
Temperature
Temperature
sensors measure the amount of heat or cold that is present in a system.
They can be broad of two types: contact and non-contact. Contact
temperature sensors need to be in physical contact with the object being
sensed. Non-contact sensors do not need physical contact, as they
measure temperature through convection and radiation.
Example - Thermometer, calorimeter, temperature gauge
Chemical
Chemical
sensors measure the concentration of chemicals in a system. When
subjected to a mix of chemicals, chemical sensors are typically
selective for a target type of chemical (for example, a CO2 sensor
senses only carbon dioxide).
Biosensors
Biosensors detect various biological elements such as organisms, tissues, cells, enzymes, antibodies, and nucleic acids.
Example - Blood glucose biosensor, pulse oximetry, electrocardiograph
Factors Driving Adopting Sensors Within IoT
There are three primary factors driving the adoption of sensor technology i.e. price, capability, and size.
Cheaper sensors
The
price of sensors has consistently fallen over the past several years,
and these price declines are expected to continue into the future.
Sensors vary widely in price, but many are now cheap enough to support
broad business applications.
Smarter Sensors
Sensor
does not function by itself—it is a part of a larger system that
comprises microprocessors, modem chips, power sources, and other related
devices. Over the last two decades, microprocessors’ computational
power has improved, doubling every three years
Smaller Sensors
There
has been a rapid growth in the use of smaller sensors that can be
embedded in smartphones and wearables. Micro-electro-mechanical systems
(MEMS) sensors—small devices that combine digital electronics and
mechanical components—have the potential to drive wider IoT
applications.
Generic Factor To Determine The Suitability Of Sensors
There are, however, several generic factors that determine the suitability of a sensor for a specific application.
Any of these factors can impact the reliability of the data received and therefore the value of the data itself.
- Accuracy - A measure of how precisely a sensor reports the signal.
- Repeatability- A sensor’s performance in consistently reporting the same responsewhen subjected to the same input under constant environmentalconditions.
- Range - The band of input signals within which a sensor can perform accurately. Input signals beyond the range lead to inaccurate output signals and potential damage to sensors.
- Noise - The fluctuations in the output signal resulting from the sensor or the external environment.
- Resolution- The smallest incremental change in the input signal that the sensorrequires to sense and report a change in the change in the outputsignal.
- Selectivity - The sensor’s ability to selectively sense and report a signal.
Sensor Connectivity
The connectivity requirements of different types of IoT networks vary widely, depending on their purpose and resource constraints. A range of different wireless and wireline technologies can be used to provide full IoT connectivity.
IoT devices communicate using a range of different communication
protocols, which may include: short-range radio protocols (such as
ZigBee, Bluetooth, and Wi-Fi); mobile networks; or longer-range radio
protocols (such as LoRa). These technologies can be segmented based on
wireless versus wireline and wireless technologies can be grouped
by personal area network (WPAN), wireless local area network (WLAN) or
wide area network (WWAN) technologies.
Comparing IoT Sensor Connectivity Technologies
Each technology has distinct characteristics,
including the range of their signal, the extent of their
data, Throughput (or bandwidth), and the power needs of the
communications device (or battery life), among other attributes.
| | Personal Area Network ANT + Bluetooth + RFID + NFC 802.11.4 + ZigBee | Local Area Networks(/WLAN)+ WiFi | Wide Area Network(WWAN) | Wireline(Copper/DSL/Ethernet/Coaxial/Fiber |
| Range | Short | Intermediate | Long | Long |
| Bandwidth | Narrow | Broad | Intermediate/Broad | Intermediate |
| Battery Life | Long | Short | Intermediate | Short |