Sensor

2011-04-25T02:36:00.000-07:00

Sensor

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For other uses, see Sensor (disambiguation).

"Sensors" redirects here. For other uses, see Sensors (disambiguation).

"Detector" redirects here. For other uses, see Detector (disambiguation).

Thermocouple sensor for high temperature measurement

A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated glass tube. A thermocouple converts temperature to an output voltage which can be read by a voltmeter. For accuracy, most sensors are calibrated against known standards.

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[edit] Use

Sensors are used in everyday objects such as touch-sensitive elevator buttons (tactile sensor) and lamps which dim or brighten by touching the base. There are also innumerable applications for sensors of which most people are never aware. Applications include cars, machines, aerospace, medicine, manufacturing and robotics.
A sensor is a device which receives and responds to a signal. A sensor's sensitivity indicates how much the sensor's output changes when the measured quantity changes. For instance, if the mercury in a thermometer moves 1 cm when the temperature changes by 1 °C, the sensitivity is 1 cm/°C (it is basically the slope Dy/Dx assuming a linear characteristic). Sensors that measure very small changes must have very high sensitivities. Sensors also have an impact on 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 need to be designed to have a small effect on what 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 higher speed and sensitivity compared with macroscopic approaches.

[edit] Classification of measurement errors

A good sensor obeys the following rules:

Is sensitive to the measured property
Is insensitive to any other property likely to be encountered in its application
Does not influence the measured property

Ideal sensors are designed to be linear or linear to some simple mathematical function of the measurement, typically logarithmic. The output signal of such a sensor is linearly proportional to the value or simple function of the measured property. The sensitivity is then defined as the ratio between output signal and measured property. For example, if a sensor measures temperature and has a voltage output, the sensitivity is a constant with the unit [V/K]; this sensor is linear because the ratio is constant at all points of measurement.

[edit] Sensor deviations

If the sensor is not ideal, several types of deviations can be observed:

The sensitivity may in practice differ from the value specified. This is called a sensitivity error, but the sensor is still linear.
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. The full scale range defines the maximum and minimum values of the measured property.
If the output signal is not zero when the measured property is zero, the sensor has an offset or bias. This is defined as the output of the sensor at zero input.
If the sensitivity is not constant over the range of the sensor, this is called nonlinearity. 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.
If the deviation is caused by a rapid change of the measured property over time, there is a dynamic error. Often, this behaviour is described with a bode plot showing sensitivity error and phase shift as function of the frequency of a periodic input signal.
If the output signal slowly changes independent of the measured property, this is defined as drift (telecommunication).
Long term drift usually indicates a slow degradation of sensor properties over a long period of time.
Noise is a random deviation of the signal that varies in time.
Hysteresis is an error caused by when the measured property reverses direction, but there is some finite lag in time for the sensor to respond, creating a different offset error in one direction than in the other.
If the sensor has a digital output, the output is essentially an approximation of the measured property. The approximation error is also called digitization error.
If the signal is monitored digitally, limitation of the sampling frequency also can cause a dynamic error, or if the variable or added noise noise changes periodically at a frequency near a multiple of the sampling rate may induce aliasing errors.
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 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 the expense of the dynamic behaviour of the sensor.

[edit] Resolution

The resolution of a sensor is the smallest change it can detect in the quantity that it is measuring. Often in a digital display, the least significant digit will fluctuate, indicating that changes of that magnitude are only just resolved. The resolution is related to the precision with which the measurement is made. For example, a scanning tunneling probe (a fine tip near a surface collects an electron tunnelling current) can resolve atoms and molecules.

[edit] Types

Main article: List of sensors

[edit] Sensors in Nature

Further information: Sense

All living organisms contain biological sensors with functions similar to those of the mechanical devices described. Most of these are specialized cells that are sensitive to:

Light, motion, temperature, magnetic fields, gravity, humidity, vibration, pressure, electrical fields, sound, and other physical aspects of the external environment
Physical aspects of the internal environment, such as stretch, motion of the organism, and position of appendages (proprioception)
Environmental molecules, including toxins, nutrients, and pheromones
Estimation of biomolecules interaction and some kinetics parameters
Internal metabolic milieu, such as glucose level, oxygen level, or osmolality
Internal signal molecules, such as hormones, neurotransmitters, and cytokines
Differences between proteins of the organism itself and of the environment or alien creatures.

[edit] Biosensor

Main article: biosensor

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 is referred to as sensor or nanosensor (such a microcantilevers). This terminology applies for both in vitro and in vivo applications. The encapsulation of the biological component in biosensors, presents with 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, a 3D polymer matrix, which either physically constrains the sensing macromolecule or chemically (macromolecule is bound to the scaffold).^[1]

[edit] See also

[edit] References

^ Wolfbeis, O. S. (2000). "Fiber-optic chemical sensors and biosensors." Anal Chem 72(12): 81R-89R

[edit] External links

Wikimedia Commons has media related to: Sensors

Look up sensor in Wiktionary, the free dictionary.

Tutorial on Various type of sensors
Capacitive Position/Displacement Sensor Theory/Tutorial
Capacitive Position/Displacement Overview
Comparing Capacitive and Eddy-Current Sensors
M. Kretschmar and S. Welsby (2005), Capacitive and Inductive Displacement Sensors, in Sensor Technology Handbook, J. Wilson editor, Newnes: Burlington, MA.
C. A. Grimes, E. C. Dickey, and M. V. Pishko (2006), Encyclopedia of Sensors (10-Volume Set), American Scientific Publishers. ISBN 1-58883-056-X
Sensors - Open access journal of MDPI
M. Pohanka, O. Pavlis, and P. Skladal. Rapid Characterization of Monoclonal Antibodies using the Piezoelectric Immunosensor. Sensors 2007, 7, 341-353
SensEdu; how sensors work
Clifford K. Ho, Alex Robinson, David R. Miller and Mary J. Davis. Overview of Sensors and Needs for Environmental Monitoring. Sensors 2005, 5, 4-37
Wireless hydrogen sensor
Sensors and Actuators A: Physical - Elsevier journal
Sensors and Actuators B: Chemical - Elsevier journal
Automated Deformation Monitoring system
Droid's Sensors -adware for droidsensors

Sensor for Android

2011-04-25T02:26:00.000-07:00

from Android App Market Place ::
http://www.androidfreeware.net/tag-sensor.html

List of various Menufacturers

2011-04-25T02:21:00.000-07:00

Web Address :: http://www.sensorsportal.com/HTML/SENSORS/Other_Manufacturers.htm

List of Sensors Manufacturers
		HD 2013.2 - rain sensor, frequency output 1 500 … 6 000 Hz (rain … dry sensor)
		Low Frequency B-DOT Sensor The PRODYN Model B-27(A) is a small, free-field low frequency sensor, which was designed to measure the first time derivative of B fields in a plasma environment
		7000 SWN - selfcleaning turbidity and suspended solids sensor with frequency output
		Series F410 Frequency Sensor
	ESIS PTY LTD	A wide range of smart sensors, weather stations, water quality and gas monitoring equipment from Monitor Sensors
		SBE 4 - Frequency output (3000 to 12000 Hz) conductivity sensors SBE49 FastCAT CTD - integrated conductivity, temperature, pressure sensor
SOCLAIRELECTRONIC		Transducers with Frequency Output
		DRN-FP / DRX-FP - Frequency / Pulse Signal Conditioner
		kW and kwh Transducer XD303F - High Accuracy kW transducer with isolated frequency output proportional to true power
		MPS-D3 - digital-output multiparameter sensor for simultaneous measurement of water level, temperature and electric conductivity / salinity and TDS. MPS-D8 - multiparameter sensor for 13 parameters: water level, °C, conductivity, salinity, O2, pH, ORP, NH3, NO3-, Cl-, NH4+, Na+, Ca2+, F-, K+ and turbidity.
		A100L2, A100M, A100K - frequency output anemometers (wind speed sensors)
		CTD Smart Sensor - low cost, high accuracy conductivity, temperature and pressure sensor, RS-232 communications, optional half duplex addressable RS-485 or TTL
		Smart Power Measuring Sensor (SPMS) with digital output (RS232 or RS485 interface)
		ADIS16250 - programmable MEMS Gyroscope
		AS2702 - a new generation AS-Interface slave device, which supports AS-Interface bus systems with up to 62 slave modules

About Sensor

Sensor

Sensor

Contents

[edit] Use

[edit] Classification of measurement errors

[edit] Sensor deviations

[edit] Resolution

[edit] Types

[edit] Sensors in Nature

[edit] Biosensor

[edit] See also

[edit] References

[edit] External links

Sensor for Android

List of various Menufacturers