You're reading from Architectural Patterns and Techniques for Developing IoT Solutions

Product typeBook

Published inSep 2023

PublisherPackt

ISBN-139781803245492

Edition1st Edition

Concepts

IoT Development

Author (1)

Jasbir Singh Dhaliwal

Sensor and Actuator Selection Guidelines

Sensors and actuators constitute a critical part of any IoT system. As was mentioned at the start of this book, sensors are akin to human body parts of perception (eyes, ears, touch, and so on), whereas actuators can be compared to human parts of action (hands and legs). Through sensors and actuators, the IoT system interacts with the physical realm, and it is the ability of the IoT system to effectively blend physical (data acquisition and action) and virtual (processing) worlds that make IoT systems so unique and powerful.

In this chapter, we will understand the different types of sensors and actuators (the intent here is not to provide an exhaustive list of sensors and actuators but a representative list). Elements from these lists can be mixed and matched to develop innovative and interesting use cases. As we will understand in the chapter, these lists can be used in two ways:

Given a problem statement, which sensors and actuators...

Key terms/definitions

In this section, we define some key concepts associated with sensors and actuators:

Accuracy: Accuracy refers to the ability of sensors to provide a result as close to real value as possible.
Precision: Precision refers to the capability of the sensor to give the same readings for the same measurement over time and under similar conditions. Although accuracy and precision seem like similar terms, they differ in the sense that accuracy refers to how close the reading reported by the sensor is to the actual value, whereas precision refers to the ability of the sensor to detect even small changes. The difference between accuracy and precision can be better understood by the following figure:

Figure 9.1 – Difference between accuracy and precision

Repeatability: Repeatability indicates the ability of the sensor to sense a particular value and report it as the same value consistently (under similar environmental conditions...

Usage scenarios of sensors

Different types of sensing technologies are used in a complementary manner to implement complex use cases. As an example, autonomous vehicles leverage different technologies to accurately determine the environment (current location and approaching obstacles) and make sense of the available information. An autonomous vehicle best illustrates this as it uses diverse technologies to understand its environment in real time, as is illustrated in the following figure:

Figure 9.5 – Autonomous vehicle leveraging multiple technologies for understanding the environment

The following table compares the different sensing technologies used in autonomous vehicles and provides an example of how diverse sensing technologies can be used in a complementary way:

...

Operation and usage scenarios of actuators

An actuator is a device that, based on some trigger mechanism, will make something move, rotate, oscillate, or initiate some operation. Actuators can perform actions on themselves (turn water sprinklers on/off, change temperature settings in a thermostat, and so on) or on the sensors (starting/stopping a sensor or moving a sensor from one location to another, for example). Generally, actuation requires more energy than sensing; accordingly, actuators are supplied with stronger batteries or are mains-powered. However, in a typical deployment, the count of sensors would far exceed the number of actuators.

For a completely automated and/or remote operation, sensors and actuator work in a complementary fashion to monitor and change the environmental state, as shown in the following diagram:

Figure 9.6 – Sensor and actuator working in a complementary fashion

Actuators can be broadly categorized into three categories...

Use case – connected coffee vending machine

The following figure shows the overall functionality of the connected coffee vending machine and the high-level interaction between the user and the coffee machine:

Figure 9.9 – Coffee vending machine operation and user interaction

For the coffee machine to provide the functionality specified in the preceding figure, various sensors and actuators need to be integrated and housed in assembly. In addition to the core data processing engine, diverse sensors and actuators would be required, which are shown in the following figure:

Figure 9.10 – Sensors and actuators present in the coffee vending machine

Let’s look at the elements shown in the figure in greater detail:

Keypad: The keypad serves as a primary input mechanism for selecting the specific coffee types and quantity of ingredients such as milk and sugar. Also, users can schedule the brewing process to...

Factors to be considered while selecting a sensor or actuator

Selecting a sensor and/or actuator is one of the most important design considerations as it involves balancing diverse (and often conflicting) requirements. As the number of sensors/actuators deployed in real/practical use cases is large, it is almost impossible to replace deployed field devices if they are found to be unsuitable later. Hence it is better to perform the required due diligence during the initial selection stage. Accordingly, this section provides guidance regarding the key factors that should be kept in mind while shortlisting the field devices:

Data and usage considerations: This covers the type of data required and its purpose and it will cover aspects such as the type and size of the sample. Most of the applications perform the following collectively or in isolation:
- Object recognition
- Object presence/absence
- Level/quantity monitoring
- Distance ranging
- Initiating movement either linear, rotary, or oscillatory...

Introducing wireless sensor and actuator networks

WSANs are generally controlled by a DG (also referred to as sinks or base stations). Mostly, WSANs are deployed in remote or obscure locations where they aren’t mains powered, which necessitates the need to employ aggressive energy optimization techniques (inducing regular sleeping/waking cycles and minimizing the data communication) so that batteries can last for a longer duration (unless energy is harvested from the environment, such as solar/vibrational energy).

Another desired property from WSANs is the ability to add or remove nodes (sensors or actuators) without impacting the overall performance of the WSAN. To achieve this, nodes need to be designed intelligently whereby they can dynamically route data packets with any change in network topology. Typically, this is achieved by following a distributed architecture whereby each node acts independently and maintains the information about its nearest neighboring node. WSANs...

Summary

This chapter covered the sensors and actuators that form crucial elements (similar to the eyes and ears) of any IoT network. A representative list of sensors/actuators was also provided as an aid that can help you while developing an IoT solution for novel use cases that can be implemented using a combination of the suggested sensors/actuators. Two specific examples (one related to a connected coffee vending machine and another to autonomous vehicles) were provided to illustrate how a diverse set of sensors and actuators are needed for implementing real-life IoT use cases. By now, you should be able to grasp key characteristics that need to be considered while selecting a sensor and/or actuators for the envisaged IoT use case.

You were also introduced to the different topologies in which sensors and actuators can be arranged (WSAN topologies) to serve diverse operating needs. Insights were shared regarding techniques or tactics used to optimize the data transfer in WSAN...

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Author (1)

Jasbir Singh Dhaliwal

Jasbir Singh Dhaliwal has over 26 years of software development and management experience, including 10 years in delivering complex IoT projects. Currently employed with IBM as a Principal Architect (IoT and cloud) and considered a thought leader with over 31 IoT patents, he has a deep understanding of IoT concepts/architectures and has delivered IoT projects in diverse domains such as consumer goods, smart buildings, healthcare, precision agriculture, automobile, and manufacturing. His extensive experience in both the public cloud and embedded domains gives him a unique edge in conceiving innovative end-to-end IoT solutions. He holds a bachelor's degree in computer science and engineering from Punjab Engineering College, India.
Read more about Jasbir Singh Dhaliwal

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