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Sensors and Transducers

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 thermometerthermocouple converts temperature to an output voltage which can be read by a voltmeter. For accuracy, most sensors are calibrated against known standards. converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated glass tube. A


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.

List of sensors

Acoustic, sound, vibration
Lace Sensor a guitar pickup
Automotive, transportation
Curb feeler, used to warn driver of curbs
Defect detector, used on railroads to detect axle and signal problems in passing trains
MAP sensor, Manifold Absolute Pressure, used in regulating fuel metering.
Parking sensors, used to alert the driver of unseen obstacles during parking manoeuvres
Radar gun, used to detect the speed of other objects
Speedometer, used measure the instantaneous speed of a land vehicle
Speed sensor, used to detect the speed of an object
Throttle position sensor, used to monitor the position of the throttle in an internal combustion engine
Variable reluctance sensor, used to measure position and speed of moving metal components
Water sensor or water-in-fuel sensor, used to indicate the presence of water in fuel
Wheel speed sensor, used for reading the speed of a vehicle's wheel rotation
Electric current, electric potential, magnetic, radio
Environment, weather, moisture, humidity
Flow, fluid velocity
Ionising radiation, subatomic particles
Navigation instruments
Position, angle, displacement, distance, speed, acceleration
Optical, light, imaging
Infra-red sensor
Fiber optic sensors
Force, density, level
Thermal, heat, temperature
Proximity, presence
Sensor technology


This article is about transducers in physics. For transducers in computer science, see Finite state transducer

A transducer is a device that converts one type of energy to another. The conversion can be to/from electrical, electro-mechanical, electromagnetic, photonic, photovoltaic, or any other form of energy. While the term transducer commonly implies use as a sensor/detector, any device which converts energy can be considered a transducer.


Transducers may be categorized by application: sensor, actuator, or combination.

A sensor is used to detect a parameter in one form and report it in another form of energy (usually an electrical and/or digital signal). For example, a pressure sensor might detect pressure (a mechanical form of energy) and convert it to electricity for display at a remote gauge.

An actuator accepts energy and produces movement (action). The energy supplied to an actuator might be electrical or mechanical (pneumatic, hydraulic, etc.). An electric motor and a loudspeaker are both actuators, converting electrical energy into motion for different purposes.

Combination transducers have both functions; they both detect and create action. For example, a typical ultrasonic transducer switches back and forth many times a second between acting as an actuator to produce ultrasonic waves, and acting as a sensor to detect ultrasonic waves.