     a sensor is a device that detects events or changes in quantities and provides a corresponding output, generally as an electrical or optical signal; for example, a thermocouple converts temperature to an output voltage. but a mercury-in-glass thermometer is also a sensor; it converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated glass tube. sensors are used in everyday objects such as touch-sensitive elevator buttons (tactile sensor) and lamps which dim or brighten by touching the base, besides innumerable applications of which most people are never aware. with advances in micromachinery and easy-to-use microcontroller platforms, the uses of sensors have expanded beyond the more traditional fields of temperature, pressure or flow measurement, for example into marg sensors. moreover, analog sensors such as potentiometers and force-sensing resistors are still widely used. applications include manufacturing and machinery, airplanes and aerospace, cars, medicine and robotics. a sensor's sensitivity indicates how much the sensor's output changes when the input quantity being measured changes. for instance, if the mercury in a thermometer moves 1&nbsp;cm when the temperature changes by 1&nbsp;Â°c, the sensitivity is 1&nbsp;cm/Â°c (it is basically the slope dy/dx assuming a linear characteristic). some sensors can 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 . ==classification of measurement errors== thumb|an infrared sensor a good sensor obeys the following rules : * is sensitive to the measured property on
Measuring_instruments Sensors Transducers