List of sensor terms
A Labautopedia compendium of words and terms related to Sensors. Click on linked terms for more detail. Refer to the Contributing section for author information.
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- Absolute Humidity - the mass of water vapor in a unit volume of gas mixture
- Absolute Pressure - the pressure exerted on a vacuum
- Acceleration - the time rate of change of velocity
- Accuracy - The accuracy of the sensor is the maximum difference that will exist between the actual value (which must be measured by a primary or good secondary standard) and the indicated value at the output of the sensor. Again, the accuracy can be expressed either as a percentage of full scale or in absolute terms.
- Adiabatic - a process which takes place without any exchange of heat between a system and its surrounding
- Ambient - surrounding or prevailing conditions
- Ampere or Amp - the metric unit for electric current
- Amp-Hour - a quantity of electricity equal to the integral of the current with time.
- Anemoclinometer - a device for measuring the inclination of the wind to a horizontal plane
- Anemometer - a device for measuring wind speed
- Ängstrom - a unit of length defined as 1/6438.4696 of the wavelength of Cadmium red line, very close to 10-10 meter
- Aspiration - using a partial vacuum to draw up gas
- Backlash - similar to hysterisis but more commonly applied to mechanical systems
- Bandwidth – Bandwidth is the frequency range in which the MEMS sensor operates. Such sensors respond from DC to a user-defineable upper cutoff frequency. The maximum bandwidth is determined by the mechanical resonant frequency (-3dB) of the sensor.
- Barometer - an absolute pressure gauge for measuring atmospheric pressure
- Baseline - a reference set of data against which operating data is compared
- Bathometer - a device for measuring depth in water
- Blackbody - an object that absorbs all incident radiation regardless of spectral or directional composition. A black body will also radiate energy at a rate expressed by the Stefan-Boltzmann Law with a spectral distribution expressed by Planck's radiation equation
- Bolometer - an infrared detector that functions by measuring the heating effect of the incident radiation
- Bourdon Tube - a pressure sensing element constructed from a flattened tube, seal at one end, twisted or curved. Applied pressure untwists the tube
- Bridge - an electronic network that effectively provides zero offsetting
- Buckley Gauge - a device that measures very low pressures by sensing the ionization current flow
- Calibrate - to ascertain the relationship between the input and output of a sensor or measuring device
- Calorie - a Unit of heat equal to that required to raise the temperature of 1 gm of water 1°C and is equivalent to 4.184 joules. Some confusion exists when used in the context of food where the kilocalorie is used and termed the "large calorie" but more commonly just "Calorie"
- Candela - unit for luminous intensity as related to human eye spectral response
- Ceilometer - a device for measuring the height of the base of clouds
- Celsius - scale of temperature measurement
- Centigrade - obsolete term for Celsius temperature scale
- Cerenkov Radiation - visible light produced when charged particles pass through a transparent medium at a speed exceeding the speed of light in that medium
- Color Code - a coding system for identifying a specific type of object within a class of object.
- Conductivity (electrical) - the property of a water sample to transmit electric current under a set of standard conditions. It is the inverse of resistance and expressed in units of Siemens
- Cryogenic - any process carried out at very low temperature - say below -50°C
- Cryometer - a low temperature thermometer
- Curie Point - the temperature at which a magnetic material losses its magnetic properties
- Dalton's Law - the total pressure exerted by a mixture of gases equals the sum of the pressures that would be exerted if each of the individual gases present were to occupy the same volume by itself
- DAQ - Data Acquisition device.
- Dark Current - the current that flows in a photo sensor when there is no incident radiation. Often temperature dependent
- Decibel - a logarithmic unit for measuring relative strength of a signal
- Dew Point - the temperature at which condensation from the vapor phase occurs
- Diffraction Grating - an array of fine, equally spaced reflecting or transmitting lines, which diffracts light in a direction characteristic of the wavelength of the light
- Doppler Shift - a phenomenon that causes waves to have a longer wavelength if the source and observer are moving apart and conversely becomes shorter if they are moving together. Very useful effect for flow and speed measurement
- Drift - an undesired change in output over a period of time that is unrelated to input. Can be due to aging, temperature effects, sensor contamination etc
- Drosomenter - a device for determining the amount of dew that condenses on a given surface
- Dry Bulb Temperature - the temperature of the air. Used in conjunction with the wet bulb temperature to measure humidity.
- Dynamic Range - The dynamic range is the total range of the sensor from minimum to maximum.
- Dynamic Linearity - The dynamic linearity of the sensor is a measure of its ability to follow rapid changes in the input parameter. Amplitude distortion characteristics, phase distortion characteristics, and response time are important in determining dynamic linearity. Given a system of low hysteresis (always desirable), the amplitude response is represented by:
- F(X) = aX + bX2 + cX3 + dX4 + ••• + K
- In this equation, the term F(X) is the output signal, while the X terms represent the input parameter and its harmonics, and K is an offset constant (if any). The harmonics become especially important when the error harmonics generated by the sensor action fall into the same frequency bands as the natural harmonics produced by the dynamic action of the input parameter. All continuous waveforms are represented :by a Fourier series of a fundamental sinewave and its harmonics. In any nonsinusoidal waveform (including time-varying changes of a :physical parameter). Harmonics present will be that can be affected by the action of the sensor.
- The nature of the nonlinearity of the calibration curves above tell something about which harmonics are present. In the left figure, the :calibration curve (shown as a dotted line) is asymmetrical, so only odd harmonic terms exist. Assuming a form for the ideal curve of F(x) = :mx + K, the response equation becomes for the symmetrical case:
- F(X) = aX + bX2 + cX4 + ••• + K
- In the other type of calibration curve (right figure), the indicated values are symmetrical about the ideal mx + K curve. In this case, F(X) = -F(-X), and the form of the response equation is:
- F(X) = aX + bX3 + cX5 + ••• + K
- F(X) = aX + bX3 + cX5 + ••• + K
- Eddy Current - an AC current setup near the surface of a conductor exposed to an electromagnetic field
- Electrolevel - a sensor for detecting inclination changes. Consists of a conductive fluid and an air bubble in a seal chamber with three or more electrodes. Used in a bridge circuit with AC excitation. Can be very sensitive although can be prone to drift
- EMC - ElectroMagnetic Conformance - standards associated with the emission of undesired radio frequency energy by devices and the level of susceptibility of a device to similar energy
- Encoder (sensor) - a device that converts a linear or rotary displacement into digital representation
- Erg - unit of energy in the CGS system of units. 1 erg = 10-7 joules
- ESD Tolerance — The device will continue to meet specifications after an electrostatic shock that is less than or equal to the ESD tolerance. Some sensors are specced to the Human Body Model (HBM), where an ESD pulse is similar to that produced by a person who is electrically charged.
- Eudiometer - a device for measuring electric current by measuring the volume of gas produced at electrodes during electrolysis
- Evaporimeter - and instrument for measuring evaporation rates, particularly of water into the atmosphere
- Excitation - power applied to a sensor to enable it to function
- Extensometer - a device for measuring small changes in length. Used in geotechnical and materials science areas.
- Fahrenheit - a temperature scale still in use in USA
- Ferrography - the science of sampling lubricants from machines and analyzing the size distribution of wear particles
- Fiber Optic Sensors - a sensor based on some optical property that can be detected by light reflected back through an optical fiber. While expensive, these sensor are safe in hazardous environments
- Filter - a circuit or a software program that is able to reduce unwanted noise, thus improving the signal to noise ratio
- Fixed Point - or defining point - a reproducible standard value, usually derived from a physical property of a pure substance. For example the triple point of pure water defines a temperature of 0.010°C
- Floating - a condition where the voltage on a line relative to a reference point is not defined due to the lack of an electrical connection or due to very high source impedance
- Flow Meter - an instrument to measure volume or mass flow of a fluid in a pipe or channel
- F/T - Force and Torque.
- Fxy - The resultant force vector comprised of components Fx and Fy.
- Gage Pressure - a measure of pressure relative to prevailing atmospheric pressure
- Galvanometer - an instrument for measuring small electric currents the movement of a current carrying coil in a magnetic field
- Gauss Meter - an instrument for measuring the intensity magnetic fields
- Geiger-Muller Counter - a radiation measuring instrument based on a high voltage (200V to 1000V) gas filled tube that detects charged particles using amplification by an avalanche process
- Grey Code - a generic term for a family of binary codes that have the characteristic of changing only one bit in the code where incrementing or decrementing a single number in the code. This is done to overcome the potential ambiguity caused by uncertainty about the precise point when individual bits in a non-Grey code flip due to a change of input
- Ground - a neutral reference for electrical potential, generally the potential of the Earths crust
- Hall Effect - a voltage developed as a result of current flow in the presence of a magnetic field. The voltage is at right angles to both the current and the magnetic field. The effect is strongest when the speed of the current carriers is greatest as is some semi-conducting materials
- Hertz - the unit of frequency - cycles per second
- Humidity - an absolute (by mass or volume) or relative measure of the amount of water vapor in air
- HVAC - Heating, Ventilating and Air Conditioning. An acronym used in building and control industries
- Hydrometer - a device for indicating the the specific gravity of a fluid
- Hygrometer - a device for indicating humidity
- Hysteresis - A characteristic of materials, sensors and sometimes instruments to make their behavior dependent on the immediate history to which they have been subjected. Typically the final settling point is different when approached from above to when it is approached from below
- IFPS - InterFace/Power Supply box.
- Impedance - the complex ratio of a force like parameter to a related velocity like parameter. For example temperature to heat flow, voltage to current, pressure to flow
- Impulse Excitation - A method of measuring the response of a system by applying a short, sharp pulse
- Inclinometer - a device for measuring the change of angle relative to the direction of gravitational pull
- Indicator - a device to display the value of a parameter
- Infrared - any electromagnetic wave whose wavelength is between 0.78 and 300 µM
- Instrument - a device for measuring the value of an observable parameter. The device may display, record or otherwise process the measurement
- Integrator - a device that mathematically integrates and input. For example and integrator connected to a flow meter will output the volume pasted since last reset
- Intrinsic Safety - A protection method for use in potentially explosive atmospheres that limits the energy available to create a spark or heat surfaces
- Ionization Gauge - a pressure sensor based on conduction of electric current through ionized gas Useful below 100 Pa
- IP Code - a coding system to describe the level of protection against the penetration by solids and liquids provided by an enclosure or case for equipment.
- IP60 - Ingress Protection Rating "60" designates protection against dust
- IP65 - Ingress Protection Rating "65" designates protection against water spray
- IP68 - Ingress Protection Rating "68" designates submergibility in fresh water, in this case, to a depth of 10 meters
- IRGA - Infra Red Gas Analyzer - an instrument able to measure some types of gas in a gas mixture by measuring their characteristic infrared absorption
- Johnson Noise - thermally induced electrical noise in resistive elements
- Joule - a unit of energy in the MKS units system
- Kalman Filter - a process for estimating the value of parameters in the presence of noise and time delays.
- Kelvin - an absolute temperature scale.
- Konimeter - a device for measuring dust concentration in air by collecting dust on a glass slide ready for counting under a microscope
- Leakage - an undesired electric current path from signal wires to ground or other destination. Leakage can introduce significant errors with high impedance sensors
- Linearity - The linearity of the transducer is an expression of the extent to which the actual measured curve of a sensor departs from the ideal curve. The figure below shows a somewhat exaggerated relationship between the ideal, or least squares fit, line and the actual measured or calibration line (Note in most cases, the static curve is used to determine linearity, and this may deviate somewhat from a dynamic linearity) Linearity is often specified in terms of percentage of nonlinearity, which is defined as where
- Nonlinearity (%) is the percentage of nonlinearity
- Din(max) is the maximum input deviation
- INf.s. is the maximum, full-scale input
- The static nonlinearity defined by the equation above is often subject to environmental factors, including temperature, vibration, acoustic noise level, and humidity. It is important to know under what conditions the specification is valid and departures from those conditions may not yield linear changes of linearity.
- Load Cell - a transducer for the measurement of force or weight, usually based on a strain gauge bridge or vibrating wire sensor
- Loudness Level - A measure of sound intensity. Expressed in decibels relative to a pressure of 20 µPa at 1 kHz
- Lumen - a unit of light flux visible to the human eye
- Luminance - the luminous intensity of a surface in a given direction per unit of projected area in a plane perpendicular to that direction
- Lux - metric unit of illuminance
- Magnetometer - an instrument for measuring the strength of a magnetic field
- Manpower - in the physical world a unit of power equivalent to 74.60 watts. Obsolete
- Mass - the amount of matter in a object, not to be confused with weight which is the result of gravity acting on a mass.
- Maximum Single-Axis Overload - The largest amount of pure load (not compound loading) that the transducer can withstand without damage.
- Measurement Uncertainty - The maximum expected error in measurements, as specified on the calibration certificate.
- Mechanical Shock — The maximum mechanical shock applied in any direction at which the part will not be damaged when nominal Vdd is applied to the device.
- Noise - The generally unwanted component of a signal that tends to interfere with the measuring process. The noise can be random or periodic, and often varies in intensity
- Non-linearity — Sensors do not demonstrate a perfectly linear relationship between input and. This non-linearity is the maximum deviation of output from the “best fit line”, the straight line defined by sensitivity, expressed in percentage of Full-Scale Output (FSO). See "Linearity"
- Odometer - a device that displays the distance traveled by a motor vehicle
- Ohm - a unit of electrical resistance
- Oleometer - a device for measuring the specific gravity of oil as a means of determining purity.
- Olfactometer - and instrument for measuring the sense of smell by issuing know concentrations of odorous materials.
- Offset - The offset error of a transducer is defined as the output that will exist when it should be zero or, alternatively, the difference between the actual output value and the specified output value under some particular set of conditions. An example of the first situation in terms of Figure 1 would exist if the characteristic curve had the same sensitivity slope as the ideal but crossed the Y-axis (output) at b instead of zero. An example of the other form of offset is seen in the characteristic curve of a pH electrode shown in Figure 2. The ideal curve will exist only at one temperature (usually 25°C), while the actual curve will be between the minimum temperature and maximum temperature limits depending on the temperature of the sample and electrode.
- Overload - The condition where more load is applied to the transducer than it can measure. This will result in saturation.
- Pachymeter - an instrument for measuring the thickness of material, particularly paper
- Parameter - in the context of sensors, the thing that is being measured
- Pedometer - a device for measuring to distance walked
- Penetrometer - an instrument for determining the strength of semi-solids such as grease, wax and soil
- Peltier Effect - the observable effect of a voltage generated by a temperature gradient in two wires of dissimilar metals joined at one end. See
- pH - logarithmic measure of the hydrogen ion concentration in water. It is measured with a pH electrode
- Phytometer - a device or system for measuring the transpiration of plants
- PID - Proportional-Integral-Deriverative - refers to a control method where the controlling signal is a function of the error, the error's history and the error's rate of change
- PIN Photo-diode - a semiconductor light detecting diode with a particularly fast response time
- Pirani Gauge - a sensor for low pressures (<100 kPa) that utilizes the pressure dependent effect of thermal conductivity between air and a heated wire
- Pitot Tube - a sensor to measure fluid velocity by generating a pressure that is the difference between the total static pressure and the dynamic pressure
- Piezoelectric Effect - the generation of electric charge by certain materials when a force is applied, or conversely the deformation of the material when a potential is applied. Usually electrodes are deposited or attached to the material to facilitate electrical coupling
- Plank's Equation - an equation defining the radiation emitted by a blackbody.
- Point of Origin - The point on the transducer from which all forces and torques are measured.
- Precision - The concept of precision refers to the degree of reproducibility of a measurement. In other words, if exactly the same value were measured a number of times, an ideal sensor would output exactly the same value every time. But real sensors output a range of values distributed in some manner relative to the actual correct value. For example, suppose a pressure of exactly 150 mm Hg is applied to a sensor. Even if the applied pressure never changes, the output values from the sensor will vary considerably. Some subtle problems arise in the matter of precision when the true value and the sensor's mean value are not within a certain distance of each other.
- Pyroelectric Effect - the generation of electric charge by certain materials when heat is applied by conduction or radiation
- Quantization - the sub-division of the range of a reading into a finite number of steps, not necessary equal, each of which is assigned a value. The concept is particularly applicable to analog to digital and digital to analog conversion processes
- Quantum noise - noise due to the discrete or particular nature of light and other short wavelength electromagnetic radiation
- Quartz - a transparent crystalline mineral of silica that finds application in sensors due to its optical and piezoelectric characteristics
- Radiation Shield - in air temperature measurement a vented and reflective enclosure to shield a sensor from incident infrared radiation. See the Temperature page. In the nuclear field a heavy shield to absorb high energy subatomic particles
- Range - Every sensor is designed to work over a specified range. The design ranges are usually fixed, and if exceeded, result in permanent damage to or destruction of a sensor. It is customary to use transducing elements over only the part of their range where they provide predictable performance and often enhanced linearity.
- Raoult's Law - a dissolved substance will lower the partial pressure of the solvent proportionally to the mole fraction of the dissolved substance. Useful phenomena for the calibration of humidity sensors.
- Resolution - The smallest change in load that can be measured. This is usually much smaller than accuracy.
- Response - The time taken by a sensor to approach its true output when subjected to a step input is sometimes referred to as its response time. It is more usual, however, to quote a sensor as having a flat response between specified limits of frequency. This is known as the frequency response, and it indicates that if the sensor is subjected to sinusoidally oscillating input of constant amplitude, the output will faithfully reproduce a signal proportional to the input.
- Response Time - Sensors do not change output state immediately when an input parameter change occurs. Rather, it will change to the new state over a period of time, called the response time (Tr in Figure below). The response time can be defined as the time required for a sensor output to change from its previous state to a final settled value within a tolerance band of the correct new value. This concept is somewhat different from the notion of the time constant (T) of the system. This term can be defined in a manner similar to that for a capacitor charging through a resistance and is usually less than the response time.The curves in the figure below show two types of response time. In the first figure the curve represents the response time following an abrupt positive going step-function change of the input parameter. The form shown in the second figure is a decay time (Td to distinguish from Tr, for they are not always the same) in response to a negative going step-function change of the input parameter.
- Reynolds Number - an important dimensionless number associated with fluid flow and used in scaling fluid systems and in determining the transition point from laminar to turbulent flow. It represents the ratio of the momentum forces to the viscous forces in the fluid flow
- RTU - Remote Transmitter Unit - a device accepts data from a range of sensors and telemeters the information to a distant destination for recording and processing. RTUs can also receive instructions and act on them as part of a control loop
- Scale factor - a constant multiplier which converts an instrument reading to a measured value in standard units for the parameter being measured
- Scanner - a switching device that enable a single measuring instrument to sequentially sample multiple sensors
- Self Heating - a generally undesirable characteristic of some types of sensors, particularly temperature sensors, to be heated by the excitation power required to obtain a reading.
- Sensitivity - the smallest change in a physical quantity or parameter that can be detected by a measuring system. Determined by signal to noise ratio, system amplification and / or quantizing limit
- Sensitivity Error - The sensitivity error is a departure from the ideal slope of the characteristic curve.
- Sensor - a device that detects the value or the change of value of a physical quantity or parameter and converts the value into a signal for an indicating or recording instrument. Also see Transducer
- Sensor System - The entire assembly consisting of parts from transducer to data acquisition card.
- Six-axis Force/Torque Sensor- Transducer measuring and outputting forces and torques from all three Cartesian coordinates (x, y and z). A six-axis force/torque transducer is also known as multi-axis force/torque transducer, a multi-axis load cell, F/T sensor, six-axis load cell.
- Stevenson Screen - a radiation shield used to house outdoor meteorological instruments
- Strain Gauge - a device that responds to mechanical strain. Metal foil gauges are the most common type, responding to strain with a small change in resistance. Also vibrating wire types
- Saturation - The condition where the transducer or data acquisition hardware has a load or signal outside of its sensing range.
- Tachometer - an instrument for measuring the speed of rotation
- TAP - Tool AdaptorPlate. The TAP part of the transducer is attached to the load that is to be measured.
- Telemetry - The process by which measured quantities from a remote site are transmitted to a data collection point for recording and processing
- Temperature - a measure of the amount of heat in an object expressed in degrees on one of the established temperature scales
- Thermistor - a temperature sensor based on the high temperature coefficient of resistance of certain semi-conducing materials.
- Thermocouple - a temperature sensor based on voltage produced by a temperature gradient in two wires of dissimilar metal joined at one end.
- Thermopile - an array of usually series connected thermocouples designed to increase to signal level and or provide a degree of spatial temperature averaging.
- Time Constant - The time required to complete 63.2% of the total rise or decay after a step change of input. It is derived from the exponential response e-t/T where t is time and T is the time constant
- Time Series - a sequence of data assigned specific moments in time. It is the history of the object of interest
- Tool Transformation - Mathematically changing the measurement coordinate system by translating the origin and/or rotating the axes.
- Torque - a rotary force
- Transducer - a device that converts an input signal of one form into an output signal of another form. Often used interchangeably but not necessarily correctly with sensor. In this work, "sensor" generally refers to the "raw" sensing element which is strictly speaking a transducer, and the term "transducer" is used to describe a sensor with some signal conditioning within the package
- Turbidity - the optical opacity of water containing suspended matter. Measured with a nephelometer
- Tyndall Effect - the side ways scattering of light passing through a transparent fluid containing suspended material
- Txy - The resultant torque vector comprised of components Tx and Ty.
- Ultrasonics - the technology associated with the use of sound above 15 kHz. Applied to thickness, density, flow and level sensing. Also used for imaging
- U-Tube Manometer - a sensitive means of measuring low pressures by use of a partially fluid filled U shaped tube. Suitable for gauage and Differential pressure measurement
- Vapor Pressure - the pressure (at a given temperature) at which a liquid is in equilibrium with is vapor
- Venturi Meter - a flow meter that measures flow rate by determining the pressure drop through a venturi constriction
- Vibrating Plate Electrometer - a means for measuring high impedance voltage source using a capacitor with a vibrating electrode to rapidly change the capacitance. The resulting small current flow can then be measured via series resistor
- Vibrating Wire Strain Gauge - a device that responds to strain by changing its natural resonant frequency. The wire is electrically plucked and the frequency measured. Alternatively wire can be maintained in continual vibration with appropriated circuits
- Viscosity - a measure of internal friction of a fluid. Metric units of viscosity are poise, however there are a number of other units used in industry, particularly for lubricants and sugar.
- Volt - a unit of electromotive force or potential difference
- Vortex Flow Meter - a sensor that detects the frequency of vortex shedding behind an obstacle in flowing fluid by small pressure variations
- Warm-up Period - the time it takes a circuit to stabilize after the application of power.
- Watt - the metric unit of power
- Wet-Bulb Temperature - the lowest temperature a wetted body will attain when exposed to an air current. It is the temperature of adiabatic saturation.
- Wheatstone Bridge - a four arm resistance bridge having 1, 2 or 4 variable resistances. It is commonly used with resistance based sensors, especially strain gauges and RTDs. It is effective in suppressing to zero point thus allowing higher amplification and for temperature compensation
- Wien Bridge - a type of AC bridge, now rarely deployed
- Wind Chill Factor - a factor applied to temperature that attempts to better represent the feel of low temperature, wind and humidity on people
- Wollaston Wire - a fine platinum wire used in hot wire anemometers. It is made by drawing a silver sheathed platinum wire and dissolving the silver with acid. Is being replaced with micro-machining methods
- Zero - When making a measurement it is necessary to start at a known datum, and it is often convenient to adjust the output of the instrument to zero at the datum. It, therefore, is a value ascribed to some defined point in the measured range.
- Zero Drift - The signal level may vary from its set zero value when the sensor works. This introduces an error into the measurement equal to the amount of variation, or drift as it is usually termed. Zero drift may result from changes of temperature, electronics stabilizing, or aging of the transducer or electronic components.
- Zero Suppression - a process used to increase system sensitivity of sensors with a large output offset. By suppressing the zero, higher amplification may be applied. The bridge circuit is an example
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