Ho, Clifford K. Miller, and Mary J. Watt, Louise. Wee, Sui-Lee and Adam Jouran. MD-D, ed. Fine, George F. Kumar, A. Kim, and G. Zhang, C. Zhang, D. Webb, and G.
Borisov, Sergey M. Mead, M. Bales, E. Singh, and S. James, George. Perrier Recalls Its Water in U. Czugala, Monika , et al. Cogan, Deirdre , et al. Radu, Tanja , et al. Yang, Chin-Lung , et al. Swensen, James S. McLachlan, Michael J. Nolte, and Timothy L. Arami, A. Vallet, and K. Metcalf, Cheryl D. Brown, L. Spulber, I. Reaston, P. Reaston, and B. Ng, J. McCaffrey, C. Chevalerias, C. O'Mathuna, and K. National Wellness Institute. Continua Health Alliance. Helmenstine, Anne Marie. How Do Smoke Detectors Work?
Bently, John P. Singapore: Longman, Wilson, Jon S. Burlington, MA: Newnes, You do not have permission under this licence to share adapted material derived from this chapter or parts of it. Skip to main content Skip to sections. This service is more advanced with JavaScript available. Advertisement Hide. Sensing and Sensor Fundamentals. Authors Authors and affiliations Michael J. Open Access. First Online: 04 January This process is experimental and the keywords may be updated as the learning algorithm improves.
Download chapter PDF. There are no uniform descriptions of sensors or the process of sensing. In many cases, the definitions available are driven by application perspectives. Taking a general perspective, a sensor can be defined as: A device that receives a stimulus and responds with an electrical signal. Fraden, Sensor definitions from a scientific or biomedical engineering perspective broaden the potential types of output signals to include, for example, an optical signal: A device that responds to a physical input of interest with a recordable, functionally related output that is usually electrical or optical.
Jones, Another common variation, which takes into account the observational element of the measurement, describes a sensor as follows: A sensor generally refers to a device that converts a physical measure into a signal that is read by an observer or by an instrument. Chen, et al. Instead, descriptions of transducers focusing on the process of converting a physical quality into a measurable output, electrical or optical, for example, have emerged. One such definition is: A converter of any one type of energy into another [as opposed to a sensor, which] converts any type of energy into electrical energy.
An alternative description is: A sensor differs from a transducer in that a sensor converts the received signal into electrical form only. Khanna, Sensors can be used to measure or detect a vast variety of physical, chemical, and biological quantities, including proteins, bacteria, chemicals, gases, light intensity, motion, position, sound and many others, as shown in Figure Sensor measurements are converted by a transducer into a signal that represents the quantity of interest to an observer or to the external world.
In this section, we will review the most commonly used sensing techniques for our target domains. Open image in new window. Figure The sensing process.
For any given quantity, there is usually more than one form of sensor that can be used to take a measurement. Each sensor type offers different levels of accuracy, sensitivity, specificity, or ability to operate in different environmental conditions.
There are also cost considerations. More expensive sensors typically have more sophisticated features that generally offer better performance characteristics. Sensors can be used to measure quantities of interest in three ways: Contact: This approach requires physical contact with the quantity of interest.
Table Common Mechanical and Electromechanical Sensors. Strain gauges are one of the most common mechanical sensors and come in many forms and types. They have been used for many years, and are the key sensing element in a variety of sensors types, including pressure sensors, load cells, torque sensors, and position sensors. Measurement is based on a change in resistance due to strain on a material or combination of materials. The entire structure is encapsulated within a protective polyimide film.
An excitation voltage typically 5V or 12V is applied to the input leads of the gauge network and a voltage reading is taken from the output leads. The output readings in millivolts are measured by a measurement circuit normally in the form of a Wheatstone bridge, as shown in Figure Kyowa, As stress is applied to the strain gauge, a change in resistance unbalances the Wheatstone bridge.
This results in a signal output, related to the magnitude of the applied stress. Both strain gauge elements and bridge resistors can usually be purchased in an encapsulated housing. This form of package is commonly called a load cell. Foil strain gauge attached to a wheatstone bridge. MEMS gyroscopes measure the angular rate of rotation of one or more axes, as shown in Figure Gyroscopes can measure intricate motions accurately in free space.
They have no rotating parts that require bearings, and therefore lend themselves to miniaturization and batch fabrication using semiconductor manufacturing processes. Almost all MEMS gyroscopes use vibrating mechanical elements proof-mass to sense rotation based on the transfer of energy between two vibration modes of a structure caused by Coriolis acceleration.
The most popular form of MEMS gyroscope is a tuning fork gyroscope, which contains a pair of masses that are driven to oscillate with equal amplitude but in opposite directions.
When rotated, the Coriolis force creates an orthogonal vibration that can be sensed by a variety of mechanisms Nasiri, Other forms of MEMS design include vibrating wheel, wine glass resonator hemispherical resonator gyro , cylindrical vibratory, and piezoelectric. MEMS gyroscopes can be found in smartphones, fall detectors, and games consoles. Photodetectors Photodetector sensors are based on the principle of photoconductivity, where the target material changes its conductivity in the presence or absence of light.
Sensors are sensitive for a given spectral region range of optical wavelengths from ultra-violet to infrared. Examples include: Active pixel sensors, such as those found in smartphone cameras and web cams. Charged-coupled devices CCD , such as those found in digital cameras. Light-dependent resistors LDRs , such as those found in street lighting systems.
IR sensors come in both active and passive forms, as shown in Figure In the active form, the sensor employs an infrared light source, such as a light-emitting diode LED or laser diode, which projects a beam of light that is detected at a separate detector photoelectric cells, photodiodes, or phototransistors. An object that passes through the beam disrupts the received signal at the detector.
An alternative configuration is reflectance-based detection, where the source and detector are located in the same enclosure. The amount of light received at the detector depends upon the reflectivity of the object surface. Infrared sensors can be used as counters, proximity sensors as with automatic doors , or to identify the presence of people or other mobile objects under day or night conditions. Passive and active infrared sensing modes.
This form of optical sensor uses an optical glass fiber as the sensing element. Optical fibers can be coated with materials that respond to changes in strain, temperature, or humidity. The most commonly used fiber-optic sensor types include: Strain sensing: Mechanical strain in the fiber changes the geometric properties of the fiber, which changes the refraction of the light passing through it.
Because optical sensors use light either directly or indirectly for measurements, they have a number of advantages over other forms of sensing. However, these advantages are application-specific, as are the associated disadvantages. Table presents the general advantages and disadvantages of optical sensors. Advantages and Disadvantages of Optical Sensors. Advantages Disadvantages High sensitivity Susceptible to interference from environmental effects Chemically inert Can be costly Small and lightweight Susceptible to physical damage Suitable for remote sensing Immunity to electromagnetic interference Wide dynamic range Capable of monitoring a wide range of chemical and physical parameters Reliable operation.
Semiconductor sensors have grown in popularity due to their low cost, reliability, low power consumption, long operational lifespan, and small form factor. Potentiometric Sensors This type of sensor measures differences in potential voltage between the working electrode and a reference electrode. Amperometric Sensors This form of electrochemical sensor measures changes in current. Coulometric Coulometric sensors measure the quantity of electricity in coulombs as a result of an electrochemical reaction.
Conductometric Sensors This form of sensor operates on the principle that electrical conductivity can change in the presence or absence of some chemical species. Biosensors use biochemical mechanisms to identify an analyte of interest in chemical, environmental air, soil, and water , and biological samples blood, saliva, and urine.
The sensor uses an immobilized biological material, which could be an enzyme, antibody, nucleic acid, or hormone, in a self-contained device see Figure The biological material being used in the biosensor device is immobilized in a manner that maintains its bioactivity. Methods utilized include membrane for example, electroactive polymers entrapment, physical bonding, and noncovalent or covalent binding.
The immobilization process results in contact being made between the immobilized biological material and the transducer.
When an analyte comes into contact with the immobilized biological material, the transducer produces a measurable output, such as a current, change in mass, or a change in color. Indirect methods can also be utilized, in which a biochemical reaction occurs between the analyte and sensor material, resulting in a product. During the reaction, measurable quantities such as heat, gas for example, oxygen , electrons, or hydrogen ions are produced, and can be measured.
The biosensing process. The use of biosensors has increased steadily since Yellow Springs Instruments produced the first commercially successful glucose biosensor in Setford, et al. Biosensors are now available over the counter for a large variety of consumer applications, including cholesterol measurement, fertility monitoring, ovulation status, bacterial infection or exposure such as Heliobacter pylori , allergies, and STD detection.
Biosensors have also found niches in domains outside of healthcare. The key biosensor application domains are summarized in Table Key Biosensor Application Domains.
The transduction process in a biosensor involves converting the biological activity that the sensor has measured via a bioreceptor into a quantifiable signal, such as current, an optical signal, or a change in measurable mass. The most commonly utilized transducer mechanisms are electrochemical, optical, piezoelectric, and thermometric.
In optical biosensors, an immobilized biological component on an optical fiber interacts with its target analyte, forming a complex that has distinct and measurable optical properties. Alternatively, in immunoassays, the biological component such as an antibody is immobilized in an assay tray. When the sample is added, a measureable, visible change in color or luminescence occurs. Measurement approaches include photometric and colorimetric detection. Biosensors have a unique set of characteristics, due to the use of bioreceptors that differentiate them from other sensing approaches.
Biosensors can offer superior sensitivity and specificity over other sensor types. However, they can lack robustness due to sensitivity to the operating environment. The key characteristics that affect biosensors in most applications are: Because biosensors rely on biological components, they can have stability or time-dependent degradation of performance; that is, the enzymes or antibodies can lose activity over time.
Generally, biosensors exhibit very high sensitivity and specificity. Environmental Monitoring Increased urbanization, intensive agricultural methods, industrialization, demands for power, and climate change have significantly impacted our ability to maintain a clean environment.
Many different combinations of sensors may come with an air-monitoring station. Air sensing can range from monitoring a single gas species, using a single sensor, to monitoring multiple gases, particulate matter, hydrocarbons, and metals sensing, as defined by regulatory requirements for air quality.
Regulatory monitoring utilizes expensive analytical instrumentation, including spectroscopy analysis, as in the case of sulfur dioxide monitoring by UV fluorescence, and O 3 absorption of UV light at nm EPA, As a result, only a small number of high functionality, high cost monitoring stations are deployed in any given geographical area. This low-density deployment results in less than satisfactory resolution of the data; particularly in highly urbanized areas where local effects due to specific emission sources, traffic patterns, or the types of buildings can affect local air quality.
With the availability of low-cost sensors, there is growing interest, particularly in the research community, in using high-density sensor deployments to provide high-granularity air quality sensing. A detailed description of such applications is presented in Chapter 1 1. A variety of sensor technologies are being utilized for air quality and ambient environmental applications, including: Semiconductor sensors are used to monitor atmospheric gases CO, CO 2 , O 3 , ammonia NH 3 , CH 4 , NO 2 , as well as ambient temperature, humidity and atmospheric pressure Fine, et al.
The increasing need for clean water, driven by global demand for drinking water and industrial water requirements, has created a critical requirement for monitoring water quality. Similar to air quality, strict regulations are set out by national bodies such as the EPA and geopolitical bodies such as the EU that apply to public water systems.
These are legally enforceable and drive the need for reliable sensor technologies that can monitor different water quality parameters with the required sensitivity.
Sensor technologies need to provide real-time or near real-time readings in order to ensure that any anomalous changes in water quality will have the minimum impact on human health or manufacturing operations. The absence of such monitoring can led to incidents like the one experienced by Perrier.
Numerous parameters can be monitored in a water-quality regime. The specific mix of parameters depends on the application area, whether it be drinking water, an industrial application such as beverage manufacturing , or monitoring industrial discharges or storm drains.
There are normally three major categories of interest: physical turbidity, temperature, conductivity, chemical pH, dissolved oxygen, metals concentration, nitrates, organics , and biological biological oxygen demand, bacterial content. A number of sensor technologies are being used commercially or are currently being evaluated to measure water quality parameters, including: Electrochemical pH ISFET , ammonium, conductivity Amperometric chlorine, biochemical oxygen demand BOD , dissolved oxygen, nitrates Colorimetric organics, pesticides such as methyl parathion, Cl.
Key to the proliferation of sensors in healthcare has been the development of low-cost microsystem sensor technologies coupled, in some cases, with low-cost, low-power microcontrollers MCUs and radios. These devices have enabled the development of small form-factor, reliable, robust, accurate, low-power sensor solutions. Some key application areas of sensors in clinical healthcare are: Screening and Diagnostics: Biochemical and optical sensors are used for point-of-care monitoring and diagnostics applications, including blood and tissue analysis Yang, et al.
Wellness is generally described as maintaining a healthy balance between the mind, body, and soul in order to create an overall feeling of well-being in an individual. The National Wellness Institute definition is Institute, : Wellness is multi-dimensional and holistic, encompassing lifestyle, mental and spiritual well-being, and the environment. Range Range is a static characteristic and, as the name implies, it describes both the minimum and maximum values of the input or output.
The term range is commonly used in the following ways in datasheets: Full-scale range describes the maximum and minimum values of a measured property. The sensor offset is the output value of the sensor when no measurand is applied. In practice, very few sensors are truly linear, but they are considered to have linear characteristics if the plot of measurand versus the output values is approximately a straight line across the specified operating range.
An ideal straight line, that is a linear approximation of the transfer function, is most commonly drawn using one of the following methods see Figure : End-point method: The ideal straight line is drawn between the upper- and lower-range values of the sensor. Some transfer functions do not approximate well to linear transfer functions. Sensitivity is the change in input required to generate a unit change in output.
If the sensor response is linear, sensitivity will be constant over the range of the sensor and is equal to the slope of the straight-line plot as shown in Figure An ideal sensor will have significant and constant sensitivity. Sensor sensitivity. Interfering inputs change the straight-line intercept of a sensor. Temperature is a common example of an interfering input, as it changes the zero-bias of the sensor.
Particle sensors are common in bin and baghouse monitoring. Key specifications include transducer type, minimum detectable particle size, operating temperature range, sample volume, and response time. Particle detectors used in nuclear engineering are referred to as radiation detectors see above. More information about particle sensors may be found in our related guide All About Particle Sensors. Typical applications of motion detection are detecting the stalling of conveyors or the seizing of bearings.
Key specifications include the intended application, sensor type, sensor function, and minimum and maximum speeds. More information about motion sensors may be found in our related guide All About Motion Sensors. Metal Detectors are electronic or electro-mechanical devices used to sense the presence of metal in a variety of situations ranging from packages to people. Metal detectors can be permanent or portable and rely on a number of sensor technologies with electromagnetics being popular.
Key specifications include the intended application, maximum sensing distance, and certain feature choices like handheld and fixed systems. Metal detectors can be tailored to explicitly detect metal in specific manufacturing operations such as sawmilling or injection molding.
Typical level sensors use ultrasonic, capacitance, vibratory, or mechanical means to determine product height. Key specifications include sensor type, sensor function, and maximum sensing distance. More information about level sensors may be found in our related guide All About Level Sensors. Some leak detectors rely on ultrasonic means to detect air leaks, for example.
Other leak detectors rely on simple foaming agents to measure the soundness of pipe joints. Still, other leak detectors are used to measure the effectiveness of the seals in vacuum packages.
More information about leak sensors may be found in our related guide All About Leak Sensors. Key specifications include maximum response time and minimum and maximum operating temperatures. More information about humidity sensors may be found in our related guide All About Humidity Sensors.
More information about gas and chemical sensors may be found in our related guide All About Gas and Chemical Sensors. A force sensor typically relies on a load cell, a piezoelectric device whose resistance changes under deforming loads. Other methods exist for measuring torque and strain. Key specifications include sensor function, number of axes, minimum and maximum loads or torques , minimum and maximum operating temperature, as well as the dimensions of the sensor itself. Force sensors are used in load measuring applications of all kinds, from truck scales to bolt tensioning devices.
More information about force sensors may be found in our related guide All About Force Sensors. A flow sensor can be all electronic—using ultrasonic detection from outside a pipeline, say—or partially mechanical—a paddlewheel, for instance, that sits and spins directly in the flow stream itself.
Flow sensors are used extensively in the processing industries. Some designs for panel mounting allow quick indication of flow conditions to process operators. More information about flow sensors may be found in our related guide All About Flow Sensors.
Flaw detectors use ultrasonic, acoustic, or other means to identify defects in materials and can be portable or fixed installations. Key specifications include sensor type, detectable defect or thickness range, and intended application.
More information about flaw sensors may be found in our related guide All About Flaw Sensors. Flame Detectors are optoelectronic devices used to sense the presence and quality of fire and provide signals to the inputs of control devices. The tachometer once again uses electromotive force generated in a coil rotating in a constant magnetic field. The structure is shown in figure 2. The emf generated is proportional to the angular velocity of the rotor.
Accelerometers are very common in on-line control of machinery to detect runaway components fault detection. Since inertial force is proportional to acceleration, spring loaded potentiometer heads can be used to measure acceleration linear. Jerk is the third derivative w. High jerk can cause extreme conditions of wear in moving parts of machinery.
It can be detected by taking derivatives automatically of other motion detectors. An interesting application is found in some of the earlier switches that activated the seat-belt clamp in automobiles they used a mercury switch.
The most common proximity sensors are used to detect the presence of approaching magnetic materials mostly iron and its alloys. A simple way to implement proximity sensors is by using a movable coil which has a low DC current flowing through it. The current makes the coil to act like a magnet, and any approaching magnetic material due to induced magnetic poles exerts an attractive force on the coil, which triggers a switch internally.
More commonly, proximity sensors are designed to electronically detect presence of conducting materials. These operate by generating a high frequency electromagnetic field that induces eddy currents in nearby metal targets.
The sensor inductance is part of an oscillator circuit. When the target nears the sensor, the oscillations are damped, and the resulting change in oscillator current is made to actuate a solid-state switch. In more sophisticated applications, vision-based sensors may be used to detect proximity.
Another common presence sensing method is the use of optical sensors. Some common ones are described here:. Also called photoresistors, these are made of semiconductor materials whose conductivity increases with the intensity of incident light or in general, electromagnetic radiations. Photoresistive cells use materials like cadmium selenide, cadmium sulfide etc.
If the presence of a non-transparent object blocks off some of the incident light on a photoresistive sensor, the voltage across it decreases, thus sensing presence. These are made of materials in which a voltage is generated when they are exposed to electromagnetic radiation. They are most commonly used in solar cells. Optical sensors for presence or position sensing are composed of two separate units: an optical transmitter, which is usually an LED light emitting diode , and a receiver, which is either photoresistive, or photovoltaic.
Three common configurations are found in practice shown in figure 2. In practice, the choice of configuration depends on space factors and reflectivity of the material whose presence is to be sensed. The diffuse arrangement in figure 2.
Applications: machine tools -clash avoidance, assembly conveyor operations where contact is to be avoided. The simplest method is to introduce a small paddle wheel in the path of the flow.
And sensing technology, simply put, is a technology that uses sensors to acquire information by detecting the physical, chemical, or biological property quantities and convert them into readable signal. Yokogawa is a leading company in the field of process automation sensors. With its wide and amazing range of sensor products and analyzers, catering to diverse industrial applications, Yokogawa is a name associated with accuracy, reliability, stability, and world-class services.
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