A sensor is a device that produces an output signal for the purpose of detecting a physical phenomenon.
61-513: 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 in micromachinery and easy-to-use microcontroller platforms,
122-459: A central role, prefers to use the terms bias and variability instead of accuracy and precision: bias is the amount of inaccuracy and variability is the amount of imprecision. A measurement system can be accurate but not precise, precise but not accurate, neither, or both. For example, if an experiment contains a systematic error , then increasing the sample size generally increases precision but does not improve accuracy. The result would be
183-444: A certain distance, and where the metal gate is replaced by an ion -sensitive membrane , electrolyte solution and reference electrode . The ISFET is widely used in biomedical applications, such as the detection of DNA hybridization , biomarker detection from blood , antibody detection, glucose measurement, pH sensing, and genetic technology . By the mid-1980s, numerous other MOSFET sensors had been developed, including
244-459: A classification is considered correct if the correct classification falls anywhere within the top 5 predictions made by the network. Top-5 accuracy was popularized by the ImageNet challenge. It is usually higher than top-1 accuracy, as any correct predictions in the 2nd through 5th positions will not improve the top-1 score, but do improve the top-5 score. In psychometrics and psychophysics ,
305-497: A cognitive process do not always produce the same output. Cognitive accuracy (C A ) is the propensity of a cognitive process to produce the intended or desired output. Cognitive precision (C P ) is the propensity of a cognitive process to produce the same output. To measure augmented cognition in human/cog ensembles, where one or more humans work collaboratively with one or more cognitive systems (cogs), increases in cognitive accuracy and cognitive precision assist in measuring
366-450: A common mistake in evaluation of accurate models is to compare a logic simulation model to a transistor circuit simulation model . This is a comparison of differences in precision, not accuracy. Precision is measured with respect to detail and accuracy is measured with respect to reality. Information retrieval systems, such as databases and web search engines , are evaluated by many different metrics , some of which are derived from
427-739: A condition. That is, the accuracy is the proportion of correct predictions (both true positives and true negatives ) among the total number of cases examined. As such, it compares estimates of pre- and post-test probability . To make the context clear by the semantics, it is often referred to as the "Rand accuracy" or " Rand index ". It is a parameter of the test. The formula for quantifying binary accuracy is: Accuracy = T P + T N T P + T N + F P + F N {\displaystyle {\text{Accuracy}}={\frac {TP+TN}{TP+TN+FP+FN}}} where TP = True positive ; FP = False positive ; TN = True negative ; FN = False negative In this context,
488-427: A consistent yet inaccurate string of results from the flawed experiment. Eliminating the systematic error improves accuracy but does not change precision. A measurement system is considered valid if it is both accurate and precise . Related terms include bias (non- random or directed effects caused by a factor or factors unrelated to the independent variable ) and error (random variability). The terminology
549-471: A digital signal, using an analog-to-digital converter . Since sensors cannot replicate an ideal transfer function , several types of deviations can occur which limit sensor accuracy : All these deviations can be classified as systematic errors or random errors . Systematic errors can sometimes be compensated for by means of some kind of calibration strategy. Noise is a random error that can be reduced by signal processing , such as filtering, usually at
610-436: A given search. Adding a cutoff at a particular number of results takes ranking into account to some degree. The measure precision at k , for example, is a measure of precision looking only at the top ten (k=10) search results. More sophisticated metrics, such as discounted cumulative gain , take into account each individual ranking, and are more commonly used where this is important. In cognitive systems, accuracy and precision
671-410: A measurement system, related to reproducibility and repeatability , is the degree to which repeated measurements under unchanged conditions show the same results . Although the two words precision and accuracy can be synonymous in colloquial use, they are deliberately contrasted in the context of the scientific method . The field of statistics , where the interpretation of measurements plays
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#1732772106352732-557: A medical imaging modality, translating the sense of touch into a digital image is based on the tactile sensors. Tactile imaging closely mimics manual palpation, since the probe of the device with a pressure sensor array mounted on its face acts similar to human fingers during clinical examination, deforming soft tissue by the probe and detecting resulting changes in the pressure pattern. Robots designed to interact with objects requiring handling involving precision, dexterity , or interaction with unusual objects, need sensory apparatus which
793-399: A multiple of the basic measurement unit: 8.0 km is equivalent to 8.0 × 10 m. It indicates a margin of 0.05 km (50 m). However, reliance on this convention can lead to false precision errors when accepting data from sources that do not obey it. For example, a source reporting a number like 153,753 with precision +/- 5,000 looks like it has precision +/- 0.5. Under
854-411: A related measure: trueness , "the closeness of agreement between the arithmetic mean of a large number of test results and the true or accepted reference value." While precision is a description of random errors (a measure of statistical variability ), accuracy has two different definitions: In simpler terms, given a statistical sample or set of data points from repeated measurements of
915-479: A sharp distinction between a biosensor and a standard chemical sensor is superfluous. Typical biomimetic materials used in sensor development are molecularly imprinted polymers and aptamers . In biomedicine and biotechnology , sensors which detect analytes thanks to a biological component, such as cells, protein, nucleic acid or biomimetic polymers , are called biosensors . Whereas a non-biological sensor, even organic (carbon chemistry), for biological analytes
976-402: A small effect on what is measured; making the sensor smaller often improves this and may introduce other advantages. Tactile sensors can be used to test the performance of all types of applications. For example, these sensors have been used in the manufacturing of automobiles (brakes, clutches, door seals, gasket ), battery lamination, bolted joints, fuel cells etc. Tactile imaging , as
1037-420: A thermometer moves 1 cm when the temperature changes by 1 °C, its sensitivity is 1 cm/°C (it is basically the slope dy/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
1098-400: 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
1159-887: Is a 'tactile element'. Each tactel is capable of detecting normal forces. Tactel-based sensors provide a high resolution 'image' of the contact surface. Alongside spatial resolution and force sensitivity, systems-integration questions such as wiring and signal routing are important. Pressure sensor arrays are available in thin-film form. They are primarily used as analytical tools used in the manufacturing and R&D processes by engineers and technicians, and have been adapted for use in robots. Examples of such sensors available to consumers include arrays built from conductive rubber , lead zirconate titanate (PZT), polyvinylidene fluoride (PVDF), PVDF-TrFE, FET , and metallic capacitive sensing elements. Several kinds of tactile sensors have been developed that take advantage of camera-like technology to provide high-resolution data. A key exemplar
1220-473: Is a device that measures information arising from physical interaction with its environment. Tactile sensors are generally modeled after the biological sense of cutaneous touch which is capable of detecting stimuli resulting from mechanical stimulation, temperature, and pain (although pain sensing is not common in artificial tactile sensors). Tactile sensors are used in robotics , computer hardware and security systems . A common application of tactile sensors
1281-436: Is a self-contained analytical device that can provide information about the chemical composition of its environment, that is, a liquid or a gas phase . The information is provided in the form of a measurable physical signal that is correlated with the concentration of a certain chemical species (termed as analyte ). Two main steps are involved in the functioning of a chemical sensor, namely, recognition and transduction . In
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#17327721063521342-429: Is also applied to indirect measurements—that is, values obtained by a computational procedure from observed data. In addition to accuracy and precision, measurements may also have a measurement resolution , which is the smallest change in the underlying physical quantity that produces a response in the measurement. In numerical analysis , accuracy is also the nearness of a calculation to the true value; while precision
1403-499: Is also reflected in the 2008 issue of the BIPM International Vocabulary of Metrology (VIM), items 2.13 and 2.14. According to ISO 5725-1, the general term "accuracy" is used to describe the closeness of a measurement to the true value. When the term is applied to sets of measurements of the same measurand , it involves a component of random error and a component of systematic error. In this case trueness
1464-403: Is ambiguous; the trailing zeros may or may not be intended as significant figures. To avoid this ambiguity, the number could be represented in scientific notation: 8.0 × 10 m indicates that the first zero is significant (hence a margin of 50 m) while 8.000 × 10 m indicates that all three zeros are significant, giving a margin of 0.5 m. Similarly, one can use
1525-821: Is functionally equivalent to a human's tactile ability. Tactile sensors have been developed for use with robots. Tactile sensors can complement visual systems by providing added information when the robot begins to grip an object. At this time vision is no longer sufficient, as the mechanical properties of the object cannot be determined by vision alone. Determining weight, texture, stiffness , center of mass , coefficient of friction , and thermal conductivity require object interaction and some sort of tactile sensing. Several classes of tactile sensors are used in robots of different kinds, for tasks spanning collision avoidance and manipulation. Some methods for simultaneous localization and mapping are based on tactile sensors. Pressure sensor arrays are large grids of tactels. A "tactel"
1586-540: Is in touchscreen devices on mobile phones and computing . Tactile sensors may be of different types including piezoresistive , piezoelectric , optical, capacitive and elastoresistive sensors. Tactile sensors appear in everyday life such as elevator buttons and lamps which dim or brighten by touching the base. There are also innumerable other applications for tactile sensors of which most people are never aware. Sensors that measure very small changes must have very high sensitivities. Sensors need to be designed to have
1647-736: Is measured; making the sensor smaller often improves this and may introduce other advantages. Technological progress allows more and more sensors to be manufactured on a microscopic scale as microsensors using MEMS technology. In most cases, a microsensor reaches a significantly faster measurement time and higher sensitivity compared with macroscopic approaches. 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
1708-403: Is referred to as sensor or nanosensor . This terminology applies for both in-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 a semipermeable barrier , such as a dialysis membrane or a hydrogel , or a 3D polymer matrix, which either physically constrains
1769-412: Is simply the fraction of correct classifications: Accuracy = correct classifications all classifications {\displaystyle {\text{Accuracy}}={\frac {\text{correct classifications}}{\text{all classifications}}}} This is usually expressed as a percentage. For example, if a classifier makes ten predictions and nine of them are correct, the accuracy is 90%. Accuracy
1830-431: Is sometimes also viewed as a micro metric , to underline that it tends to be greatly affected by the particular class prevalence in a dataset and the classifier's biases. Furthermore, it is also called top-1 accuracy to distinguish it from top-5 accuracy, common in convolutional neural network evaluation. To evaluate top-5 accuracy, the classifier must provide relative likelihoods for each class. When these are sorted,
1891-469: Is the Gelsight technology first developed at MIT which uses a camera behind an opaque gel layer to achieve high-resolution tactile feedback. The Samsung ``See-through-your-skin (STS) sensor uses a semi-transparent gel to produce combined tactile and optical imaging. Strain gauges rosettes are constructed from multiple strain gauges , with each gauge detecting the force in a particular direction. When
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1952-569: Is the basis for modern image sensors , including the charge-coupled device (CCD) and the CMOS active-pixel sensor (CMOS sensor), used in digital imaging and digital cameras . Willard Boyle and George 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
2013-509: Is the closeness of the mean of a set of measurement results to the actual (true) value, that is the systematic error, and precision is the closeness of agreement among a set of results, that is the random error. ISO 5725-1 and VIM also avoid the use of the term " bias ", previously specified in BS 5497-1, because it has different connotations outside the fields of science and engineering, as in medicine and law. In industrial instrumentation, accuracy
2074-471: Is the measurement tolerance, or transmission of the instrument and defines the limits of the errors made when the instrument is used in normal operating conditions. Ideally a measurement device is both accurate and precise, with measurements all close to and tightly clustered around the true value. The accuracy and precision of a measurement process is usually established by repeatedly measuring some traceable reference standard . Such standards are defined in
2135-476: Is the resolution of the representation, typically defined by the number of decimal or binary digits. In military terms, accuracy refers primarily to the accuracy of fire ( justesse de tir ), the precision of fire expressed by the closeness of a grouping of shots at and around the centre of the target. A shift in the meaning of these terms appeared with the publication of the ISO 5725 series of standards in 1994, which
2196-415: Is used to characterize and measure results of a cognitive process performed by biological or artificial entities where a cognitive process is a transformation of data, information, knowledge, or wisdom to a higher-valued form. ( DIKW Pyramid ) Sometimes, a cognitive process produces exactly the intended or desired output but sometimes produces output far from the intended or desired. Furthermore, repetitions of
2257-603: The International System of Units (abbreviated SI from French: Système international d'unités ) and maintained by national standards organizations such as the National Institute of Standards and Technology in the United States. This also applies when measurements are repeated and averaged. In that case, the term standard error is properly applied: the precision of the average is equal to
2318-428: The confusion matrix , which divides results into true positives (documents correctly retrieved), true negatives (documents correctly not retrieved), false positives (documents incorrectly retrieved), and false negatives (documents incorrectly not retrieved). Commonly used metrics include the notions of precision and recall . In this context, precision is defined as the fraction of documents correctly retrieved compared to
2379-532: The gas sensor FET (GASFET), surface accessible FET (SAFET), charge flow transistor (CFT), pressure sensor FET (PRESSFET), chemical field-effect transistor (ChemFET), reference ISFET (REFET), biosensor FET (BioFET), enzyme-modified FET (ENFET) and immunologically modified FET (IMFET). By the early 2000s, BioFET types such as the DNA field-effect transistor (DNAFET), gene-modified FET (GenFET) and cell-potential BioFET (CPFET) had been developed. MOS technology
2440-477: The advent of cheap optical cameras, novel sensors have been proposed which can be built easily and cheaply with a 3D printer. Accuracy and precision Accuracy and precision are two measures of observational error . Accuracy is how close a given set of measurements ( observations or readings) are to their true value . Precision is how close the measurements are to each other. The International Organization for Standardization (ISO) defines
2501-511: The concepts of trueness and precision as defined by ISO 5725-1 are not applicable. One reason is that there is not a single “true value” of a quantity, but rather two possible true values for every case, while accuracy is an average across all cases and therefore takes into account both values. However, the term precision is used in this context to mean a different metric originating from the field of information retrieval ( see below ). When computing accuracy in multiclass classification, accuracy
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2562-408: The convention it would have been rounded to 150,000. Alternatively, in a scientific context, if it is desired to indicate the margin of error with more precision, one can use a notation such as 7.54398(23) × 10 m, meaning a range of between 7.54375 and 7.54421 × 10 m. Precision includes: In engineering, precision is often taken as three times Standard Deviation of measurements taken, representing
2623-414: The distribution of pressures, and the pattern of forces that would come from pressure sensor arrays and strain gauge rosettes, allowing two-point discrimination and force sensing, with human-like ability. Advanced versions of biologically designed tactile sensors include vibration sensing which has been determined to be important for understanding interactions between the tactile sensor and objects where
2684-444: The documents (true positives plus true negatives divided by true positives plus true negatives plus false positives plus false negatives). None of these metrics take into account the ranking of results. Ranking is very important for web search engines because readers seldom go past the first page of results, and there are too many documents on the web to manually classify all of them as to whether they should be included or excluded from
2745-442: The documents retrieved (true positives divided by true positives plus false positives), using a set of ground truth relevant results selected by humans. Recall is defined as the fraction of documents correctly retrieved compared to the relevant documents (true positives divided by true positives plus false negatives). Less commonly, the metric of accuracy is used, is defined as the fraction of documents correctly classified compared to
2806-499: The expense of the dynamic behavior of the sensor. The sensor resolution or measurement 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 the numerical resolution of the digital output. The resolution is related to the precision with which the measurement is made, but they are not the same thing. A sensor's accuracy may be considerably worse than its resolution. A chemical sensor
2867-500: The information from each strain gauge is combined, the information allows determination of a pattern of forces or torques. A variety of biologically inspired designs have been suggested ranging from simple whisker-like sensors which measure only one point at a time through more advanced fingertip-like sensors, to complete skin-like sensors as on the latest iCub . Biologically inspired tactile sensors often incorporate more than one sensing strategy. For example, they might detect both
2928-506: The known standard deviation of the process divided by the square root of the number of measurements averaged. Further, the central limit theorem shows that the probability distribution of the averaged measurements will be closer to a normal distribution than that of individual measurements. With regard to accuracy we can distinguish: A common convention in science and engineering is to express accuracy and/or precision implicitly by means of significant figures . Where not explicitly stated,
2989-443: The margin of error is understood to be one-half the value of the last significant place. For instance, a recording of 843.6 m, or 843.0 m, or 800.0 m would imply a margin of 0.05 m (the last significant place is the tenths place), while a recording of 843 m would imply a margin of error of 0.5 m (the last significant digits are the units). A reading of 8,000 m, with trailing zeros and no decimal point,
3050-407: The need for recalibration and worrying about contamination. A good sensor obeys the following rules: Most sensors have a linear transfer function . The sensitivity 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
3111-403: The open-gate field-effect transistor (OGFET) introduced by Johannessen in 1970, the ion-sensitive field-effect transistor (ISFET) invented by Piet Bergveld in 1970, the adsorption FET (ADFET) patented by P.F. Cox in 1974, and a hydrogen -sensitive MOSFET demonstrated by I. Lundstrom, M.S. Shivaraman, C.S. Svenson and L. Lundkvist in 1975. The ISFET is a special type of MOSFET with a gate at
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#17327721063523172-466: The range that 99.73% of measurements can occur within. For example, an ergonomist measuring the human body can be confident that 99.73% of their extracted measurements fall within ± 0.7 cm - if using the GRYPHON processing system - or ± 13 cm - if using unprocessed data. Accuracy is also used as a statistical measure of how well a binary classification test correctly identifies or excludes
3233-521: The recognition step, analyte molecules interact selectively with receptor 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 integrated transducer that generates the output signal. A chemical sensor based on recognition material of biological nature is a biosensor . However, as synthetic biomimetic materials are going to substitute to some extent recognition biomaterials,
3294-433: The same quantity, the sample or set can be said to be accurate if their average is close to the true value of the quantity being measured, while the set can be said to be precise if their standard deviation is relatively small. In the fields of science and engineering , the accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantity's true value . The precision of
3355-656: The sensing macromolecule 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. One example of this is the event camera . The MOSFET invented at Bell Labs between 1955 and 1960, MOSFET sensors (MOS sensors) were later developed, and they have since been widely used to measure physical , chemical , biological and environmental parameters. A number of MOSFET sensors have been developed, for measuring physical , chemical , biological , and environmental parameters. The earliest MOSFET sensors include
3416-414: The sensor slides over the object. Such interactions are now understood to be important for human tool use and judging the texture of an object. One such sensor combines force sensing, vibration sensing, and heat transfer sensing. Recently, a sophisticated tactile sensor has been made open-hardware , enabling enthusiasts and hobbyists to experiment with an otherwise expensive technology. Furthermore, with
3477-588: The term accuracy is interchangeably used with validity and constant error . Precision is a synonym for reliability and variable error . The validity of a measurement instrument or psychological test is established through experiment or correlation with behavior. Reliability is established with a variety of statistical techniques, classically through an internal consistency test like Cronbach's alpha to ensure sets of related questions have related responses, and then comparison of those related question between reference and target population. In logic simulation ,
3538-459: 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
3599-400: The uses of sensors have expanded beyond the traditional fields of temperature, pressure and flow measurement, for example into MARG sensors . Analog sensors such as potentiometers and force-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
3660-428: 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. The CCD is a semiconductor circuit that was later used in the first digital video cameras for television broadcasting . The MOS active-pixel sensor (APS) was developed by Tsutomu Nakamura at Olympus in 1985. The CMOS active-pixel sensor
3721-1109: Was later developed by Eric Fossum and his team in the early 1990s. MOS image sensors are widely used in optical mouse technology. The first optical mouse, invented by Richard F. Lyon at Xerox in 1980, used a 5 μm NMOS sensor chip. Since the first commercial optical mouse, the IntelliMouse introduced in 1999, most optical mouse devices use CMOS sensors. MOS monitoring sensors are used for house monitoring , office and agriculture monitoring, traffic monitoring (including car speed , traffic jams , and traffic accidents ), weather monitoring (such as for rain , wind , lightning and storms ), defense monitoring, and monitoring temperature , humidity , air pollution , fire , health , security and lighting . MOS gas detector sensors are used to detect carbon monoxide , sulfur dioxide , hydrogen sulfide , ammonia , and other gas substances. Other MOS sensors include intelligent sensors and wireless sensor network (WSN) technology. Tactile sensor A tactile sensor
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