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 which 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.
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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 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 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 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 broadly 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 oximetery, 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 response when subjected to the same input under constant environmental conditions.
- 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 sensor requires to sense and report a change in the change in the output signal.
- 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-rangeradio protocols (such as LoRa). These technologies can be segmented based on wireless versus wireline, and the wireless technologies can be grouped by personal area network (WPAN), wireless local area network (WLAN) or wide area network (WWAN) technologies.
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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/
Coxial/Fiber |
Range
| Short | Intermediate | Long | Long |
| Bandwidth | Narrow | Broad | Intermediate/Broad | Intermediate |
| Battery Life | Long | Short | Intermediate | Short |