Sensing Systems in Construction and Built Environment: History
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Contributor:
Amin Malekmohammadi
,
Nima Farzadnia
,
Amir Hajrasouliha
,
Ashley Lyn Mayer

Embark on an illuminating exploration into the cutting-edge realm of built environment sensors with this comprehensive research. Tailored for relevance in construction, structural engineering, management, and planning industries, the research delves deep into the intricate landscape of state-of-the-art sensing systems and their integral components. Immerse yourself in a meticulous examination that categorizes and elucidates existing sensors, neatly organizing them into two expansive domains: structural health monitoring (SHM) and building environment monitoring (BEM). This research not only unveils the diversity of sensors but also provides a nuanced understanding of their pivotal roles in shaping the future of the built environment.

  • sensing systems
  • smart sensor
  • construction
  • smart cities

1. Introduction

1.1. Definition of Sensing Systems

Sensing systems are subcategories of non-destructive techniques (NDT) used for the continuous supervision and maintenance of civil structures. In general, NDTs have a wide variety of implementations, where some can be in a controlled testing environment or in situ (on-site) assessments of the properties of a structure without affecting the functional value. In this research, two main applications, namely, structural health monitoring (SHM) systems and building environment monitoring (BEM) systems, will be reviewed and discussed. The SHM systems are best suited for monitoring the long-term performance of structures, such as bridges and buildings, where structural health is crucial to the functional value. The SHM implements a sensing network that takes measurements of a structure’s physical and mechanical properties and a data analysis system to identify any damage or irregularities within the structure [1]. The SHM systems allow for the early detection of damage, degradation, and corrosion, even in areas not visible to the human eye. However, these methods do not substitute for regularly scheduled maintenance plans or compensate for poor architectural or mechanical designs. The critical components of a sensing system are the data-acquisition equipment (DAE) and the data-acquisition system (DAS). The DAE comprises the hardware and sensors needed to measure, store, and communicate the acquired data. The on-site sensors convert physical measurements into electrical signals to transmit to the off-site DAS for processing. In the DAS, the data is analyzed by an algorithm to extract the relevant features and identify significant results. Monitoring previous and real-time data can also allow the algorithm to predict future advancements in the current structural conditions. With these predictions, necessary maintenance can be performed to ensure the continuing functionality of a structure.
The SHM systems provide a way to monitor, in great depth, the current conditions and predict future conditions of a structure, which, with preemptive actions, can increase the design life, reduce rehabilitation costs, and provide public safety [2]. Recent advancements in SHM systems include integrating a sensing network into the construction of civil infrastructure and the various connection networks of these implementations. Such sensing systems have recently attracted enormous attention with the trend for additive manufacturing. That includes the in situ assessment of material properties before, during, and post-printing for optimized printability and the printed structure’s performance [3]. Such sensors are used to measure the properties of the printing materials and the printing parameters in real-time through intelligent control systems. The control systems facilitate the collision-free performance of robots as well as in situ modification of the printing material. On the other hand, BEM systems are employed to ensure the safety and comfort of building occupants, as well as the general monitoring of the environment for any required maintenance. This is fulfilled using a wide variety of different sensors that will be discussed.

1.2. Construction: Process, Materials, and Defects

The construction of a civil structure can use a wide variety of materials, but the most commonly implemented are the most cost-efficient and functional. Wood, steel, concrete, and asphalt are some of the many common materials that make up a large portion of our civil structures today. These materials, however, are subject to degradation over time and usage due to various predictable and unpredictable environmental factors. The well-being of these materials can determine if a structure is functional and safe for use, so it is important to ensure the internal strength of the elements.
Wood, common in construction applications for buildings, bridges, and many more, is highly susceptible to environmental and mechanical factors and internal defects that may influence its structural performance [4]. The inner strength of wood is dictated by the direction of stress that is applied, the internal and external humidity, and the length of time in which a load is applied [1]. Wood, in particular, is also vulnerable to many environmental factors, such as rot and insect infestation, which may remain undetected until the damage is too extensive for repair. These factors, especially over time, can lead to structurally fatal defects within the wooden components that may call for the comprehensive rehabilitation of a structure. Asphalt and concrete are other widely used materials for infrastructures such as roads and bridges, and the health of such infrastructure is crucial to its functional value. These structures endure large amounts of stress and heavy loads and are prone to damage over time [5]. Detecting any defects in the structure could prevent damage such as cracks and corrosion in bridges as well as potholes and sinkholes in roads by scheduling maintenance at an early stage. For example, with surface infrastructures being a major form of transportation, there is much dependence on the functionality of these structures. Small-scale rehabilitation for minor damage could potentially prevent an entire shutdown of a fatally damaged roadway [6].
Monitoring the health of these structures that are guaranteed to have defects over time is an essential mechanism for maintaining a functional civil design. Sending out humans for maintenance requires a lot of time and labor. It is not always practical, as some internal measurements require invasive techniques that may hinder the usage of the structure for a limited amount of time. Implementing sensors within these structures eradicates the need for a large amount of labor to take these measurements and allows for continuous monitoring of structural health and the environment that directly affects the service life of the structure [7]. Sensing systems can monitor material attributes that may cause damage that would require heavily invasive measurements with a manual labor team.

1.3. Sensing System Components

Commonly, the sensing equipment implemented in sensing systems is used to measure structures’ physical and performance characteristics. These sensors can detect physical properties and translate them into mechanical properties to be measured. Many of these sensors incorporate at least one standard hardware that can take measurements or generate signals and, create a cooperative sensing network. The common measurement instruments found in a basic sensing system can be of the following categories [1]:
  • Transducer: Transducers are pieces of hardware that are capable of converting one form of energy into another. In the SHM systems, these can be categorized as a sensor or an actuator based on the input or output of an electric signal.
  • Sensor: A sensor is a type of transducer that reacts to a stimulus by converting the stimulus into an electrical signal. This electrical signal is then processed and transmitted to the database, or DAS.
  • Section 2 and Section 3 of this research describe different types of sensors.
  • Actuator: An actuator is a type of transducer that converts an electrical signal into a different form of energy to be applied to a structure or structural element. These predefined excitations include but are not limited to, mechanical strain, vibrations, and ultrasonic signals. Actuators require an electrical energy source and a control signal to operate.
  • Gauge: An instrument that measures the amount of a property, usually through a visual display on mechanical instruments. These instruments provide quantifiable data measurements of the property under review. Examples are pressure gauges, vibrating strain gauges, and dynamic strain gauges.
Recent advancements in sensing systems have integrated a wireless sensor network (WSN) or wireless smart sensor network (WSSN) that allows the transmission of sensor data through a wireless network. Compared to the wired communication networks of a typical sensing system, these ‘smart’ sensing systems require a few more hardware elements to increase the scalability of the network. These systems use the typical hardware involved in a sensing system, along with the following additional hardware [7]:
  • Global positioning system (GPS): A position tracking system to identify the locations of the placed sensors and where the data they transmit originates from. These instruments allow for localization of damage detection and locating where maintenance may be required.
  • Analog to digital converter (ADC): Converts the analog electrical signal from the transducer into a digital signal that can be transmitted across networks. These digital signals are data bits, which can be communicated and translated between technological systems.
  • Radio transceiver: A network transceiver that connects an internal sensor antenna to an external one that connects the sensor node to the greater network, such as the DAS. Transceivers may also support communication between sensors within the same network for cooperative sensing.
All sensing systems require a connection to a power source and some means of transferring the data from the sensors to the database, whether through a wireless network or ethernet cables. The various sensing components can be incorporated to formulate a complex sensing network, which may be unique to the structure that is being monitored. Depending on what properties are under review and what resources are available, the sensing network may or may not implement all these components. Either way, the network undergoes rigorous design to find the most effective sensing method and respective units for its application. Together, these hardware components create the physical network needed to monitor the properties of the intended structure.

1.4. Modeling Processes

The modeling process for a sensing system typically calls for a 3D model of the structure to be monitored. Using a 3D image-based model allows for the location of any damage detected to be recognized with a visualized specification rather than a verbally described place. The model creates a virtual replica of the structure and the sensing network implemented throughout it. This way, the sensor locations can be planned (before implementation) and identified (after implementation) with a visual description of the components they monitor. The data reported from the implemented sensors is transmitted to a database, analyzed for relevant details, and the model is updated according to the reported measurements. These updates can happen in real-time and allow for continuous monitoring of a physical structure through a virtual environment. The data can be localized to a specific region, and the model can help identify where any maintenance or rehabilitation is needed. The model of the structure, paired with some algorithm or AI for data analysis, creates a Digital Twin of the system that simplifies remote monitoring of structural health and the building environment.

2. Sensors for Structural Health Monitoring

2.1. Fiber Optic Sensors

Fiber optic sensing technology is an optic measurement strategy that utilizes light waves and fiber-optic channels to measure the physical properties of a structure. The characteristics of light, such as its wavelength and frequency, are altered by the physical characteristics of the measured structure. Compared to a control waveform of a healthy structure, changes in the light properties can indicate a change in the structure’s internal physical properties. Palma and Steiger (2020) [1] describe the instrumentation for this system as optic fibers that can operate as a “both sensor and signal transmission medium”, where one optic fiber can house up to 10 sensors with a process known as multiplexing. The sensors embedded in the optic fibers reflect only a specific wavelength and allow others to transmit, known as fiber Bragg’s gratings (FBG), Figure 1 [8], With multiple sensors in a single fiber and the dual-function of the optic cables, this technology allows for long-range data transmission and high-frequency measurements. Banda et al. [9] employed analytical modeling, simulation, and experimental test of a structural damage sensing system based on fiber Bragg grating strain sensors to predict structural decay. The authors reported that the strain measured from the FBG sensors could be used to predict the damage of locations even if those locations are not instrumented if the sensor placement is optimized. Such fibers are best suited for measuring strain and temperature because the light waves are hardly affected by external variables such as electromagnetic or vibrational interferences. However, the FBG sensors are affected by temperature, but this can be accommodated through additional measurements and data adjustment. The optic fibers are delicate and complex, requiring careful, sophisticated installation and implementation. Despite the high production costs, the fiber optic method has been popularized as a durable and efficient measurement system for long-term structures [10][11].
Figure 1. Schematic diagram of an FBG [8].
Another type of fiber optic sensor that plays a crucial role in structural health monitoring is the fiber optic demodulator. Demodulators are essential components in optical fiber sensor systems, facilitating the extraction of information encoded in the optical signals transmitted through the fiber. These devices are designed to recover the modulation imposed on the light wave, allowing for the measurement of various physical parameters.
In the context of monitoring structural health, fiber optic sensors are often used to measure both temperature and strain. However, to decouple the effects of temperature and strain induced by external loads, innovative techniques are employed. One common method involves using a combination of different fiber optic sensor types, each sensitive to either temperature or strain. For example, a fiber Bragg grating (FBG) sensor is highly sensitive to strain variations, while an interferometric sensor, such as a Fabry–Perot interferometer or a Mach–Zehnder interferometer, can be specifically designed to be more responsive to temperature changes. By strategically placing and integrating these sensors within the structure, it becomes possible to separate the contributions of temperature and strain, enabling more accurate and reliable monitoring of structural conditions under varying environmental and loading conditions. This approach allows for the extraction of precise and independent measurements of temperature and strain, enhancing the overall effectiveness of fiber optic sensor systems in structural health monitoring applications [12][13].

2.2. Piezoelectric Sensors

Piezoelectric sensors play a crucial role in structural health monitoring (SHM), providing a versatile and effective means of assessing the integrity of various civil and mechanical structures. These sensors operate on the principle of piezoelectricity, where certain materials generate an electric charge in response to mechanical stress. In the context of SHM, piezoelectric sensors are often employed to monitor structural vibrations, strain, and impact events. One of the key advantages of piezoelectric sensors is their high sensitivity, allowing for the detection of subtle changes in a structure’s behavior. These sensors can be strategically placed on or within a structure, such as bridges or buildings, to capture dynamic responses and identify potential issues, including fatigue, cracks, or other structural anomalies. The real-time monitoring capabilities of piezoelectric sensors make them valuable tools for ensuring the safety and reliability of critical infrastructure.
Piezoelectric sensors for structural monitoring come in various types, each designed to address specific monitoring needs. One common type is the accelerometer, which measures accelerations and vibrations in structures. Accelerometers based on piezoelectric materials are ideal for capturing dynamic responses, enabling the detection of vibrations caused by environmental factors, traffic loads, or other external forces. Another type is the piezoelectric strain sensor, which measures changes in strain or deformation within a structure. These sensors are often used to identify subtle shifts in structural elements, helping to pinpoint areas experiencing excessive loads or stress. Additionally, piezoelectric pressure sensors can be employed to monitor changes in pressure within structural components, providing insights into load distribution and potential structural weaknesses. The versatility of piezoelectric sensors allows them to be customized for specific applications, and advancements in sensor technology continue to lead to the development of new sensor types that further enhance their capabilities in structural health monitoring. The ability to choose from various sensor types allows engineers and researchers to tailor monitoring systems to the unique requirements of different structures and environments, contributing to more effective and targeted structural health assessments.
Furthermore, piezoelectric sensors offer benefits beyond their sensitivity and real-time monitoring capabilities. They are relatively compact and lightweight, making them easy to integrate into existing structures without causing significant alterations. This characteristic is particularly advantageous for retrofitting older infrastructure with monitoring systems. Additionally, piezoelectric sensors can be part of a broader sensor network, working in conjunction with other types of sensors to provide a comprehensive understanding of a structure’s condition. The data collected from these sensors can be analyzed to assess structural health, predict potential issues, and guide maintenance activities, ultimately contributing to the longevity and safety of civil and mechanical infrastructure [14][15][16][17][18][19][20][21].

2.3. Piezoresistive Sensors

Piezoresistive sensors operate similarly to piezoelectric sensors. These sensors, however, are purely vibration-based and are best suited for flexible structures that require low-frequency vibration measurements [22][23]. In the vibration-based approach, the identification of the “existence, location, type, and extent” of structural damage depends on the relationship between the measured and “model parameters” [1]. This type of analysis requires measurements to be taken on the frequency response of a healthy structure to compare data to and differentiate between healthy and damaged structural members. In the low-frequency responses of a structure, actuators, such as shakers, are used to apply a forced vibration or excitation to the structure. These vibrations impact all modes of the structure equally, allowing for a global damage detection technique. These shakers can operate in a constant frequency white noise mode or sine sweep mode, where the actuator alternates between low and high-frequency excitations. The response of the vibration is captured by the sensors and transmitted for comparative analysis. The system can also use ambient excitations, where the environment applies the vibrational force. Still, this method requires complex modal parameters, the ability to operate without knowing when the system is to be excited, and the identification of low amplitude vibrations. This can make it difficult to extract significant and relevant data from the responses. Kuo et al. [22] studied the problems associated with temperature stability and time drift when using piezoresistive sensors in bridges. Their results showed the sensors with higher boron doping concentrations and lower stiffness were less sensitive to temperature variation and time drift problems, respectively. Overall, piezoresistive sensors in a low-frequency application allow for possible damage detection in a structure through global changes.
Piezoresistive sensors exhibit both advantages and drawbacks that impact their suitability for various applications. One of the significant advantages is their sensitivity to changes in strain, making them effective in measuring deformation and stress in structural elements. Their high sensitivity allows for precise detection of subtle variations in the material, providing valuable insights into structural health. However, piezoresistive sensors are susceptible to environmental factors, with moisture being a notable concern. Moisture can affect the resistivity of the sensing material, leading to inaccuracies and reducing the sensor’s reliability over time. Consistency is another consideration, as piezoresistive sensors may exhibit variations in performance due to manufacturing tolerances. Achieving consistent results across sensors can be challenging, impacting the overall reliability of a monitoring system. On the positive side, these sensors often offer good linearity in their response to applied strain, simplifying the interpretation of data. Additionally, piezoresistive sensors can provide accurate measurements when properly calibrated, offering valuable data for structural health monitoring applications when environmental conditions are carefully controlled. Despite these challenges, ongoing research and technological advancements aim to mitigate drawbacks and enhance the overall performance of piezoresistive sensors in structural monitoring contexts. Figure 2 shows a typical piezoresistive strain gauge using a Wheatstone bridge.
Figure 2. Piezoresistive strain gauge measurements are made using a Wheatstone bridge circuit [24].

2.4. Nanosensors

Nanosensors refer to sensors that exist and can take measurements on the nanometer scale. These sensors are mainly piezoelectric materials that typically take the form of fine powders or liquids, as well as nanofibers that can be applied to a structure to measure its material performances or conditions [25][26]. Nanosensors have been integrated into a large variety of forms, including smart paints. The smart paint sensor is made from a mixture of piezoelectric material and polymers and is applied to a surface like paint. The paint can also be made with a mixture of epoxy resin and carbon nanofilaments that increase the sensor’s sensitivity to vibrations and its conductivity. The sensor is flexible and even suited for curved surfaces, welded joints, or complex geometries [7]. Operating in a similar fashion to a traditional sensor, the smart paint can detect damage, impacts, and other dynamic responses through voltage signals generated between a silver paste and the surface to which the paint adheres. These sensors are easy to implement, low cost, and require minimal power to operate.
Carbon nanofilaments such as carbon nanofibers, nanotubes, as well as graphene pellets are other commonly used nanosensors in construction [27]. Using such materials can replace the disadvantages of traditional sensors like strain gauges. A small percentage of such materials (1% of the total volume) can increase the ductility of concrete by 100 times [28]. This will provide a continuous path of conductivity that can transfer the change in the electric resistance when an external load is applied to sensors. The deformation in members can be measured by correlating the electric resistance and stress.

2.5. Laser Displacement Sensors

Laser displacement technology is a method of optic-based measurements that utilizes a laser beam to measure the distance and displacement of a structure over time. The laser displacement system consists of mounted equipment that takes periodic scans of a structure and measures the distance between the components. The distance is calculated using either a “time-of-flight measurement of a laser pulse or phase comparison between as transmitted and reflected continuous laser beam” [1]. The distance measurement is compared to previously stored data to detect any structural position differences. This method is generally not suited to detect any minor damage or deformations that would be smaller than a centimeter, but it is able to assess larger, more significant deteriorations of a structure. One major advantage of this method is the ability to operate independently of a natural light source and the direct access to the measured structure, despite equipment costs and lower accuracy relative to alternative methods. This method can also be applied to the displacement measurement of large-scale structures [29]. Park et al. [30] proposed a wireless displacement measurement system for a large-scale irregular structure to monitor the vertical displacements of the truss elements during construction.

2.6. Rotation Measurement Sensor

Rotation measurement sensors play a critical role in various applications where monitoring and quantifying angular displacement or rotational motion is essential. These sensors are designed to detect and measure the extent of rotation around a specific axis. One common type of rotation measurement sensor is the gyroscope, which utilizes the principles of angular momentum to determine the rate of rotation. Another example is the rotary encoder, which converts mechanical rotation into electrical signals. These sensors find widespread use in industries such as aerospace, automotive, robotics, and manufacturing, where precise control and feedback on rotational movements are crucial. The data obtained from rotation measurement sensors can be utilized for tasks such as navigation, stabilization, and positional feedback in machinery and equipment. The continuous advancements in sensor technologies, including the integration of micro-electromechanical systems (MEMS) and fiber optics, contribute to the development of more accurate and compact rotation measurement sensors, expanding their applications in diverse fields [31][32].

3. Sensors for Building Environment Monitoring

The many aspects of a building’s internal environment can be measured using a wide variety of different sensors. These sensors can be used to ensure the safety and comfort of the building occupants, as well as general monitoring of the environment for any required maintenance [33]. Below, widely used sensors to measure environmental variables and their working mechanism are listed.

3.1. Temperature Sensors

Temperature sensors measure the ambient temperature of the environment they are placed in through different hardware elements. Available temperature sensors meet the requirement of temperature monitoring in buildings; however, their performance in terms of simplicity of operation, accuracy, range, and response time may vary [33][34]. Figure 3 shows different types of temperature sensors.
Figure 3. Types of temperature sensors [35].
Common types of temperature sensors are:
  • Semiconductor-based sensors: Constructed with identical diodes that use temperature-sensitive voltage compared with current conditions to detect changes in atmospheric temperature.
  • Thermocouple: Two wires of different metals are placed at different points, where a change in atmospheric temperature will reflect as a change in voltage between the two wires.
  • Resistance temperature detector: Constructed as a film or wire wrapped around a ceramic or glass core, and a change in the element’s electrical resistance reflects a temperature change. These tend to be the most accurate but also can be the most expensive type of sensor.
  • Negative temperature coefficient thermistor: These sensors provide a high resistance in low environmental temperatures, and the resistance drops quickly as temperature increases. Reflects temperature changes quickly and accurately.

3.2. Humidity Sensors

Humidity sensors are used to measure the amount or percentage of water vapor in ambient air. They can also be used within a structure to continuously measure the internal humidity, evaporation rate, and water penetration levels [36]. Figure 4 shows a capacitive humidity sensor. Three common types of humidity sensors are:
Figure 4. Capacitive humidity sensor [37].
  • Capacitive: The sensor uses a capacitor and water vapor to measure humidity levels. The capacitor has a porous dielectric core surrounded by two electrodes. The voltage across the capacitor changes when water vapor is present at the electrodes.
  • Resistive: A similar operation to the capacitive sensor, this sensor uses an electrical charge to measure the humidity levels of the external environment. They use ion salts to measure the voltage difference across the electrodes and are generally less accurate than the capacitive sensors.
  • Thermal: As illustrated in Figure 5, two matched thermal sensors, one coated in dry nitrogen and the other in ambient air, conduct electricity based on the humidity in the environment. The difference in electricity between them calculates the humidity reading of the environment.
Figure 5. Thermal humidity sensor [37].
Some of these sensors require complex circuit design as well as regular calibration. Those are mainly categorized under expensive sensors such as capacitive sensors. On the other hand, other sensors, such as resistive sensors, have a low cost but offer a narrow measurement range and are less accurate but have a good response time.

3.3. Motion/Occupancy Sensors

Motion and occupancy sensors use thermal detection to record the placement and movement of people within a space. These sensors operate by emitting ultrasonic waves or radio waves and detecting the time that it takes for the waves to bounce back to the emission spot. When a person or persons enter the sensor’s field of view, a portion of the emitted waves bounce back to the sensor before the rest, indicating there is an object in view. The proper use of such sensors in buildings can lead to energy savings, improved climate control, and higher building security [38][39]. At the same time, no images or personal information is stored or transmitted, making these sensors privacy-compliant. Common types of these sensors are:
  • Motion sensors/passive infrared: These sensors use heat maps of peoples’ body heat in the sensor’s field of view. These sensors monitor continuously and can report the occupancy and movement of people. They can have a 180-degree or 360-degree field of view, depending on their location of implementation (underside of a table or desk versus on the ceiling). They are unobtrusive, cost-effective, easy to install, and low maintenance; however, they are only suitable for short-distance measurements (up to 10 m) [40].
  • Time-of-flight sensors: These sensors emit an infrared light beam that reflects off an obstruction, such as a person, and back to the sensor. The time it takes for the light to return to the sensor reflects the distance and movement of the object reflected off. These sensors can determine if someone is moving towards or away from the sensor, allowing the detection of entry and exit, as well as the flow of foot traffic in an area.
  • Infrared array sensors: These sensors use temperature measurements to detect objects (moving or motionless), temperature distribution, and moving direction. The objects must be closer to the sensor for more accurate temperature readings.

3.4. Contact Sensors

Contact sensors in buildings operate as a two-piece system that detects the magnetic field between the pieces to determine whether they are in contact. This sensor is usually used as a mechanism to determine if a door or window has been opened. On a door, one piece of the sensor is placed in the door frame, and the other is placed on the door itself. When the door is open, the magnetic field is disturbed, and the sensor transmits a corresponding signal. These sensors can be very useful in maintaining safety and observing the activity within a building.

3.5. Gas/Air-Quality Sensors

Air quality sensors monitor changes to the air quality and detect the presence of various gasses (hazardous and safe) in an environment. This device is useful for creating and maintaining a safe and healthy environment in buildings. The three most common air quality sensors are:
  • Oxygen: An electrochemical sensor that can detect any gasses that can be reduced electrochemically or oxidized. Maintaining healthy oxygen levels is vital to the health and well-being of the occupants.
  • Carbon monoxide: An electrochemical sensor that works similarly to the oxygen sensor. Carbon monoxide is a hazardous, invisible gas that is a large safety concern if left unattended in an occupied building. It is important to monitor the levels of this gas to protect the building community [41].
  • Carbon dioxide: An infrared detection sensor that transmits an infrared light beam through a light tube, then detects how much of the beam’s energy levels remain (or are lost). This energy is then calculated into how much carbon dioxide is present in the air [42]. In highly insulated spaces, high carbon dioxide levels cause stale and stuffy environments, where occupants have complained of fatigue and headaches, affecting comfort and productivity.
  • Smoke sensors: These sensors detect levels of airborne particulates and gasses, and recent developments allow for the notification of any issues immediately.

3.6. Electrical Current Monitoring Sensors

Electrical current (CT) sensors measure the energy consumption of a circuit in real time. This allows for identifying areas where energy is being wasted or there are abnormal operating conditions. To prevent energy waste, assets can be powered off when they are not necessary. Identifying any abnormal operations of a circuit can be a sign that maintenance is needed in that specific area. The different types of CT sensors are:
  • Split core: These sensors can be opened and fitted around a preconfigured conductor in a circuit. These are ideal for existing circuits.
  • Hall effect/DC: These make use of the Hall effect to measure AC and DC current by measuring the changing voltage of a device in a magnetic field. The Hall effect is the electromagnetic phenomenon that occurs when an electric current flows through a magnetic field, generating a voltage difference across a capacitor [43]. An open loop type of this sensor is compact, low-cost, and accurate. A closed-loop type of this sensor offers quick response and consistency of results across environmental temperatures (low-temperature drift).
  • Rogowski coils: These are a type of flexible current transformers that consist of a thin coil that is wrapped around a conductor. These are easy to install on pre-existing circuit configurations and are snapped closed [44].
  • Solid core: Best for new installations, these sensors are complete loops with no way of opening and are accredited for their high levels of accuracy.

This entry is adapted from the peer-reviewed paper 10.3390/s23249632

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