Sensor

A sensor (from the Latin sentire, "feel" or German " feel " ), detector ( measurement variables ) or pickup (measuring) sensor is a technical component, the specific physical or chemical properties (eg heat radiation, temperature, humidity, pressure, sound, brightness, or acceleration) and / or the physical condition of its environment can quantitatively or qualitatively as a benchmark. These quantities are detected by means of physical or chemical effects and converted into a processable electrical signal.

For the metrology 1319-1, the term transducer (measuring size pickup ) is used and is defined as the part of a measuring device, which immediately responds to a measured variable in DIN. Thus, the sensor is the first element of a measuring chain. According to DIN 1319-2, the pickup is one of the transmitters in the same physical size of the input and output also to the transducers.

The distinction between the terms sensor and measurement sensor, sensor, meter, etc. is blurred, because the sensor will be assigned in addition to pickup some more elements of the measuring chain. Also related terms are not clearly defined in the literature.

• 3.1 Signal processing
• 3.2 Sensor Overviews

Classification

Sensors can be classified according to size and manufacturing technology as well as on the application and purpose. A distinction sensors according to their mode of action during the forming of the variables in passive and active sensors.

Passive and active sensors

Sensors can be based on the generation or use of electric energy divided into active and passive sensors. In addition to the ambiguous definition of the term sensor here contradictory terms are even in use, - depending on whether the active transducer produces an electrical signal, or whether by external energy capture images from the activity to it.

Active transducers generate due to the measurement principle of an electrical signal, eg, electrodynamic or piezoelectric. In this case, no electrical auxiliary energy is required; in view of the use of energy is passive sensors. With these sensors is often - due to the physical principles - detectable but only a change of the measured variable, as in the static and quasi-static state, no energy can be delivered. An exception is, for example, the thermocouple, the voltage is produced continuously and at a constant temperature difference. In addition, active transducers in a reversal of the physical measuring principle can also be used as actuators, eg, a dynamic microphone can be used as a speaker.

Passive transducers contain passive components, whose parameters can be changed by the measured variable. By a primary electronics, these parameters are transformed into electrical signals. Here, a power supply supplied from the outside is required. In summary of the pickup with the reshaping stage in the term sensor can be spoken of active sensors. With these it is possible to determine both static and quasi-static measurements. For this reason, the vast number of sensors passive design. Examples are load cells or resistance thermometers.

Modern sensors often have extensive secondary electronics, which is operated by externally supplied energy. Nevertheless, all these sensors are not activated, but rather the measurement process itself should be considered.

By Use

Sensors, radiation (e.g., light, X- radiation or particles ) detected are referred to as radiation or particle. Even a normal microphone is a sensor for the sound pressure.

Furthermore, sensors are different in different resolution modes:

• Temporal resolution: time between two shots.
• Spectral resolution: bandwidth of the spectral channels, the number of different bands.
• Radiometric resolution: The smallest difference between the amount of radiation that can distinguish the sensor.
• Spatial resolution: Spatial resolution, ie size of a pixel.

According to standard

• NAMUR sensor ( Standards committee for measurement and control technology in the chemical industry)

• KTA -approved sensors for use in nuclear power plants

Virtual sensors

Virtual sensors (or soft sensors ) are not physically exist, but are implemented in software. You "measure" ( calculated ) values ​​, which are derived from the measured values ​​of real sensors using an empirically learned or physical model. Virtual sensors are used for applications in which real sensors are too expensive, or in environments where real sensors can not exist or wear out quickly.

Digital sensors

In the area of ​​automation analog systems of control engineering are increasingly replaced by digital systems. Therefore, the demand for sensors whose output signal is also digitally. A simple construction is obtained if the A / D converter is integrated into the actual sensor system. This can, for example, on the basis of delta-sigma modulation technique based and thereby offer many advantages:

• Comparing direct digital output signal ( no interference between the sensor and ADC)
• High linearity by existing feedback
• Continuous self-test without additional circuitry through use of the limit cycle of the sigma-delta technology
• High amplitude resolution and dynamic

The disadvantage is that the PWM so generated often can not be evaluated directly and must first be filtered. This can be done by an analog filter and anschliesender ADU or completely digital. In addition, the transmission path to the evaluating system is analogous and thus susceptible to failure. Therefore, Simple sensors for pressure and temperature have a real digital data output with connection via a serial or parallel bus. Widely used are here:

• I ² C
• SPI

Areas of application

The term sensor is used in the art and in the life sciences (biology and medicine), for some years now increasingly in the natural sciences. Example of the latter are applications of CCD image sensors, particle counter in astronomy, geodesy and space.

In technology, sensors play in automated processes as signal generators play an important role. The data collected from them values ​​or states are usually electrically - amplified electronically processed in the associated control that triggers the appropriate action. In recent years, this subsequent signal processing is also carried out increasingly in the sensor. Such sensors include a microprocessor or a micro system and have, so to speak, " intelligence", so they are also known as smart sensors ( engl. smart sensor ).