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, all sensors need to be calibrated against known standards.
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 or stimulus.Here,the term "stimulus" means a property or a quantity that needs to be converted into electrical form.Hence,sensor can be defined as a device which receives a signal and converts it into electrical form which can be further used for electronic devices.A sensor differs from a transducer in the way that a transducer converts one form of energy into other form whereas a sensor converts the received signal into electrical form only.
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. 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.
A good sensor obeys the following rules:
Ideal sensors are designed to be linear. The output signal of such a sensor is linearly proportional to the value 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.
If the sensor is not ideal, several types of deviations can be observed:
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.
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.
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:
Artificial sensors that mimic biological sensors by using a biological sensitive component, are called biosensors.
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 thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated glass tube.
There are a lot of different types of sensors. Sensors are used in everyday objects.
A sensor that detects temperature. Thermal sensors are found in many laptops and computers in order to sound an alarm when a certain temperature has been exceeded.
An electronic device used to measure a physical quantity such as pressure or loudness and convert it into an electronic signal of some kind (e.g a voltage).
A motion sensor detects physical movement in a given area.
Because of certain disadvantages of physical contact sensors, newer technology non-contact sensors have become prevalent in industry, performing well in many applications. The recent style of non-contact sensors shows that “Thin(g) is In”. Market trends show that form and size are important. Users are looking for smaller and more accurate sensors. New technologies for the sensing chips are breaking application barriers. For the future, the trend will be to continue to provide smaller, more affordable sensors that have the flexbility to fit even more applications in both industrial and commercial environments.