Asensor is often defined as a device that receives and responds to a signal or stimulus. The stimulus is the quantity, property, or condition that is sensed and converted into electrical signal.[1]
In the broadest definition, a sensor is a device, module, machine, or subsystem that detects events or changes in its environment and sends the information to other electronics, frequently a computer processor.
Sensors are used in everyday objects such as touch-sensitive elevator buttons (tactile sensor) and lamps which dim or brighten by touching the base, and in innumerable applications of which most people are never aware. With advances inmicromachinery and easy-to-usemicrocontroller platforms, the uses of sensors have expanded beyond the traditional fields of temperature, pressure and flow measurement,[2] for example intoMARG sensors.
Analog sensors such aspotentiometers andforce-sensing resistors are still widely used. Their applications include manufacturing and machinery, airplanes and aerospace, cars, medicine,robotics and many other aspects of our day-to-day life. There is a wide range of other sensors that measure chemical and physical properties of materials, including optical sensors for refractive index measurement, vibrational sensors for fluid viscosity measurement, and electro-chemical sensors for monitoring pH of fluids.
A sensor's sensitivity indicates how much its output changes when the input quantity it measures changes. For instance, if the mercury in a thermometer moves 1 cm when the temperature changes by 1 °C, its sensitivity is 1 cm/°C (it is basically the slopedy/dx assuming a linear characteristic). Some sensors can also affect what they measure; for instance, a room temperature thermometer inserted into a hot cup of liquid cools the liquid while the liquid heats the thermometer. Sensors are usually designed to have a small effect on what is measured; making the sensor smaller often improves this and may introduce other advantages.[3]
Technological progress allows more and more sensors to be manufactured on amicroscopic scale as microsensors usingMEMS technology. In most cases, a microsensor reaches a significantly faster measurement time and higher sensitivity compared withmacroscopic approaches.[3][4] Due to the increasing demand for rapid, affordable and reliable information in today's world, disposable sensors—low-cost and easy‐to‐use devices for short‐term monitoring or single‐shot measurements—have recently gained growing importance. Using this class of sensors, critical analytical information can be obtained by anyone, anywhere and at any time, without the need for recalibration and worrying about contamination.[5]
it is insensitive to any other property likely to be encountered in its application, and
it does not influence the measured property.
Most sensors have alineartransfer function. Thesensitivity is then defined as the ratio between the output signal and measured property. For example, if a sensor measures temperature and has a voltage output, the sensitivity is constant with the units [V/K]. The sensitivity is the slope of the transfer function. Converting the sensor's electrical output (for example V) to the measured units (for example K) requires dividing the electrical output by the slope (or multiplying by its reciprocal). In addition, an offset is frequently added or subtracted. For example, −40 must be added to the output if 0 V output corresponds to −40 C input.
For an analog sensor signal to be processed or used in digital equipment, it needs to be converted to a digital signal, using ananalog-to-digital converter.
Since sensors cannot replicate an idealtransfer function, several types of deviations can occur which limit sensoraccuracy:
Since the range of the output signal is always limited, the output signal will eventually reach a minimum or maximum when the measured property exceeds the limits. Thefull scale range defines the maximum and minimum values of the measured property.[citation needed]
Thesensitivity may in practice differ from the value specified. This is called a sensitivity error. This is an error in the slope of a linear transfer function.
If the output signal differs from the correct value by a constant, the sensor has an offset error orbias. This is an error in they-intercept of a linear transfer function.
Nonlinearity is deviation of a sensor's transfer function from a straight line transfer function. Usually, this is defined by the amount the output differs from ideal behavior over the full range of the sensor, often noted as a percentage of the full range.
Deviation caused by rapid changes of the measured property over time is adynamic error. Often, this behavior is described with abode plot showing sensitivity error and phase shift as a function of the frequency of a periodic input signal.
If the output signal slowly changes independent of the measured property, this is defined asdrift. Long term drift over months or years is caused by physical changes in the sensor.
Noise is a random deviation of the signal that varies in time.
Ahysteresis error causes the output value to vary depending on the previous input values. If a sensor's output is different depending on whether a specific input value was reached by increasing vs. decreasing the input, then the sensor has a hysteresis error.
If the sensor has a digital output, the output is essentially an approximation of the measured property. This error is also calledquantization error.
If the signal is monitored digitally, thesampling frequency can cause a dynamic error, or if the input variable or added noise changes periodically at a frequency near a multiple of the sampling rate,aliasing errors may occur.
The sensor may to some extent be sensitive to properties other than the property being measured. For example, most sensors are influenced by the temperature of their environment.
All these deviations can be classified assystematic errors orrandom errors. Systematic errors can sometimes be compensated for by means of some kind ofcalibration strategy. Noise is a random error that can be reduced bysignal processing, such as filtering, usually at the expense of the dynamic behavior of the sensor.
Thesensor resolution ormeasurement resolution is the smallest change that can be detected in the quantity that is being measured. The resolution of a sensor with a digital output is usually thenumerical resolution of the digital output. The resolution is related to theprecision with which the measurement is made, but they are not the same thing. A sensor's accuracy may be considerably worse than its resolution.
The sensor may to some extent be sensitive to properties other than the property being measured. For example, most sensors are influenced by the temperature of their environment.
A chemical sensor is a self-contained analytical device that can provide information about the chemical composition of its environment, that is, aliquid or agas phase.[6][7] The information is provided in the form of a measurable physical signal that is correlated with theconcentration of a certain chemical species (termed asanalyte). Two main steps are involved in the functioning of a chemical sensor, namely, recognition andtransduction. In the recognition step, analyte molecules interact selectively withreceptor molecules or sites included in the structure of the recognition element of the sensor. Consequently, a characteristic physical parameter varies and this variation is reported by means of an integratedtransducer that generates the output signal.A chemical sensor based on recognition material of biological nature is abiosensor. However, as syntheticbiomimetic materials are going to substitute to some extent recognition biomaterials, a sharp distinction between a biosensor and a standard chemical sensor is superfluous. Typical biomimetic materials used in sensor development aremolecularly imprinted polymers andaptamers.[8]
Achemical sensor array is a sensor architecture with multiple sensor components that create a pattern for analyte detection from the additive responses of individual sensor components. There exist several types of chemical sensor arrays including electronic, optical, acoustic wave, and potentiometric devices. These chemical sensor arrays can employ multiple sensor types that are cross-reactive or tuned to sense specific analytes.[9][10][11][12]
Inbiomedicine andbiotechnology, sensors which detectanalytes thanks to a biological component, such as cells, protein, nucleic acid orbiomimetic polymers, are calledbiosensors.Whereas a non-biological sensor, even organic (carbon chemistry), for biological analytes is referred to as sensor ornanosensor. This terminology applies for bothin-vitro and in vivo applications.The encapsulation of the biological component in biosensors, presents a slightly different problem that ordinary sensors; this can either be done by means of asemipermeable barrier, such as adialysis membrane or ahydrogel, or a 3D polymer matrix, which either physically constrains the sensingmacromolecule or chemically constrains the macromolecule by bounding it to the scaffold.
Neuromorphic sensors are sensors that physically mimic structures and functions of biological neural entities.[13] One example of this is theevent camera.
MOS technology is the basis for modernimage sensors, including thecharge-coupled device (CCD) and theCMOSactive-pixel sensor (CMOS sensor), used indigital imaging anddigital cameras.[23]Willard Boyle andGeorge E. Smith developed the CCD in 1969. While researching the MOS process, they realized that an electric charge was the analogy of the magnetic bubble and that it could be stored on a tiny MOS capacitor. As it was fairly straightforward to fabricate a series of MOS capacitors in a row, they connected a suitable voltage to them so that the charge could be stepped along from one to the next.[23] The CCD is a semiconductor circuit that was later used in the firstdigital video cameras fortelevision broadcasting.[24]
The MOSactive-pixel sensor (APS) was developed by Tsutomu Nakamura atOlympus in 1985.[25] The CMOS active-pixel sensor was later developed byEric Fossum and his team in the early 1990s.[26]
MOS image sensors are widely used inoptical mouse technology. The first optical mouse, invented byRichard F. Lyon atXerox in 1980, used a5μmNMOS sensor chip.[27][28] Since the first commercial optical mouse, theIntelliMouse introduced in 1999, most optical mouse devices use CMOS sensors.[29]
^FRADEN, JACOB (2004).HANDBOOK OF MODERN SENSORS (3rd ed.). New York: Springer. p. 1.ISBN0-387-00750-4.
^Bennett, S. (1993).A History of Control Engineering 1930–1955. London: Peter Peregrinus Ltd. on behalf of the Institution of Electrical Engineers.ISBN978-0-86341-280-6The source states "controls" rather than "sensors", so its applicability is assumed. Many units are derived from the basic measurements to which it refers, such as a liquid's level measured by a differential pressure sensor.{{cite book}}: CS1 maint: postscript (link)
^Bǎnicǎ, Florinel-Gabriel (2012).Chemical Sensors and Biosensors:Fundamentals and Applications. Chichester, UK: John Wiley & Sons. p. 576.ISBN978-1-118-35423-0.
^Svigelj, Rossella; Dossi, Nicolo; Pizzolato, Stefania; Toniolo, Rosanna; Miranda-Castro, Rebeca; de-los-Santos-Álvarez, Noemí; Lobo-Castañón, María Jesús (1 October 2020). "Truncated aptamers as selective receptors in a gluten sensor supporting direct measurement in a deep eutectic solvent".Biosensors and Bioelectronics.165 112339.doi:10.1016/j.bios.2020.112339.hdl:10651/57640.PMID32729482.S2CID219902328.
^Eric R. Fossum (1993), "Active Pixel Sensors: Are CCD's Dinosaurs?" Proc. SPIE Vol. 1900, p. 2–14,Charge-Coupled Devices and Solid State Optical Sensors III, Morley M. Blouke; Ed.
M. Kretschmar and S. Welsby (2005), Capacitive and Inductive Displacement Sensors, in Sensor Technology Handbook, J. Wilson editor, Newnes: Burlington, MA.
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