A sensor (from Latin sentire , dt. "Feel" or "feel"), also called a detector , (measured variable or measuring) transducer or (measuring) sensor , is a technical component that has certain physical or chemical properties ( physically e.g. quantity of heat , temperature , humidity , pressure , sound field sizes , brightness , acceleration or chemically e.g. pH value , ionic strength , electrochemical potential ) and / or the material nature of its environment qualitatively or quantitatively as a measured variable . These variables are recorded using physical, chemical or biological effects and converted into an electrical signal that can be processed further .
With the increasing demand for fast, affordable and reliable information in today's world, single-use sensors - inexpensive and easy-to-use devices for short-term monitoring or for single measurements - have recently become increasingly important. With this class of sensors, critical analytical information can be accessed by anyone, anywhere, anytime without recalibration and without worrying about contamination.
For the measurement in is DIN 1319 -1, the term sensor (measuring sizes transducers) used and is defined as the part of a measuring device which directly responds to a measured variable. This makes the transducer the first element of a measuring chain . According to DIN 1319-2, the transducer belongs to the measuring transducers , with the same physical size at the input and output also to the measuring transducers .
The distinction between the terms sensor and measurement sensor , probe , measuring device , measuring means , etc. is fluid, since the sensor elements are further allocated in addition to the actual receiver part of the measurement chain. Related terms are also not clearly defined in the literature.
Sensors can be classified according to their size and production technology, as well as their intended use and purpose. In addition, a distinction is made between sensors according to their mode of action when converting the variables into passive and active sensors.
Passive and active sensors
Sensors can be divided into active and passive sensors based on the generation or use of electrical energy.
Active sensors generate an electrical signal based on the measuring principle , e.g. B. electrodynamic or piezoelectric . These sensors are themselves voltage generators and do not require any auxiliary electrical energy . With these sensors, however, due to the physical principles, only a change in the measured variable can often be detected, since no energy can be supplied in the static or quasi-static state. An exception is e.g. B. the thermocouple , which constantly generates voltage even with a constant temperature difference. In addition, active sensors, reversing the physical measuring principle, can also be used as actuators , e.g. B. a dynamic microphone can also be used as a loudspeaker.
Active sensors are e.g. B .:
- Thermocouple (physical basis: thermoelectric effect )
- Light sensor (physical basis: photoelectric effect )
- Pressure sensor (physical basis: piezoelectric effect )
Passive sensors contain passive components whose parameters are changed by the measured variable. These parameters are converted into electrical signals by primary electronics. An externally supplied auxiliary energy is required. With these it is possible to determine static and quasi-static measured variables. For this reason, the majority of the sensors are of a passive type.
Modern sensors often have extensive secondary electronics that are operated using externally supplied energy. However, not all of these sensors are active; the measurement process itself has to be considered.
Passive sensors are e.g. B .:
According to the measuring principle / operating principle
Sensors can be classified according to the operating principle on which the sensor is based. There are tons of applications for each active principle. Some of the operating principles and applications are listed below as examples. The list is not complete.
|Mechanically||Manometer , expansion lever , spring scale , beam scale , thermometer|
|Resistive||Strain gauges (DMS) , hot wire, semiconductor DMS, Pt100|
|Capacitive||Pressure sensor, rain sensor|
|Inductive||Inclinometer , force sensor, displacement transducer|
|Optically||CCD sensor , photocell|
|Acoustically||Level sensor, double sheet control , ultrasonic flow meter ,|
|Magnetic||Hall sensors , reed contact|
According to intended use
Furthermore, sensors differ in different types of resolution:
- Temporal resolution: the time between two recordings.
- Spectral resolution: bandwidth of the spectral channels, number of different bands.
- Radiometric resolution: Smallest difference in the amount of radiation that the sensor can distinguish.
- geometric resolution: spatial resolution, d. H. Size of a pixel.
According to standard
- NAMUR sensor (standards working group for measurement and control technology in the chemical industry)
Virtual sensors (or soft sensors ) do not exist physically, but are implemented in software. They “measure” (calculate) values which are derived from the measured values of real sensors with the help of an empirically learned or physical model. Virtual sensors are used for applications where real sensors are too expensive or in environments where real sensors cannot survive or wear out quickly. Further use cases are processes in which the desired values cannot be measured because there are no hardware sensors that can be used in the process or when the process cannot be stopped for calibration and maintenance of classic sensors. Virtual sensors are already used in the chemical industry and are increasingly being used in other branches of industry such as B. the plastics industry.
In the field of automation, analog control engineering systems are increasingly being replaced by digital systems. Therefore, the need for sensors whose output signal is also digital is increasing. A simple structure results when the A / D converter is integrated into the actual sensor system. This can, for example, be based on the delta-sigma modulation technique and thus offer many advantages:
- directly determined digital output signal (no interference between sensor and ADU)
- high linearity through existing feedback
- Constant self-test without additional circuitry using the limit cycle of the sigma-delta technology
- high amplitude resolution and dynamics
The disadvantage is that the PWM generated in this way often cannot be evaluated directly and must first be filtered. This can be done through an analog filter and subsequent ADC or completely digital. In addition, the transmission path to the evaluating system is analog and therefore prone to failure. Simple sensors for pressure and temperature therefore have a real digital data output with connection via a serial or parallel bus. The following are widespread here:
Molecular sensors are based on a single molecule which, after binding another molecule or after being exposed to photons, has different properties that can then be read out. With fluorescence-marked sensors, more than two states can be detected by changing the emission spectrum . This means that such a sensor can also be used as a molecular locking system .
The term sensor is used in technology and in the life sciences ( biology and medicine ), and for some years now more and more in the natural sciences . Example of the latter are applications of CCD - image sensors and particle counters in astronomy , geodesy and aerospace .
In technology, sensors play an important role as signal transmitters in automated processes . The values or states recorded by them are processed, usually electrically - electronically amplified , in the associated control system , which triggers the corresponding further steps. In recent years, this subsequent signal processing has also increasingly been carried out in the sensor. Such sensors include a microprocessor or a micro system and have, so to speak "intelligence" so they are as smart sensors (Engl. Smart sensors ), respectively.
- Temperature sensor
- Distance sensor
- Pressure sensor
- Gas sensor
- Field device
- Sensor network
- BiSS interface
- Sensor particles
Typical amplifiers for signal processing:
- Edmund Schiessle: Sensor technology and recording of measured values . Vogel, Würzburg 1992, ISBN 3-8023-0470-5 .
- Jörg Hoffmann: Pocket book of measurement technology . 5th edition. Hanser Verlag, Leipzig 2007, ISBN 978-3-446-40993-4 .
- Wolf-Dieter Schmidt: Sensor circuit technology . 3. Edition. Vogel, Würzburg 2007, ISBN 978-3-8342-3111-6 .
- Günter Spanner: "Sensor Technology" learning package . Franzis, Poing 2009, ISBN 978-3-7723-5547-9 .
- T. Hochrein, I. Alig: Process measurement technology in plastics processing . Vogel, Würzburg 2011, ISBN 978-3-8343-3117-5 .
- Can Dincer, Richard Bruch, Estefanía Costa-Rama, Maria Teresa Fernández-Abedul, Arben Merkoçi: Disposable Sensors in Diagnostics, Food, and Environmental Monitoring . In: Advanced Materials . May 15, 2019, ISSN 0935-9648 , p. 1806739 , doi : 10.1002 / adma.201806739 .
- C. Kugler, T. Hochrein, M. Bastian, T. Froese: Hidden treasures in data graves. In: QZ quality and reliability. 3, 2014, pp. 38-41.
- Bhimsen Rout, Linor Unger, Gad Armony, Mark A. Iron, David Margulies: Medication Detection by a Combinatorial Fluorescent Molecular Sensor. In: Angewandte Chemie. 124, 2012, pp. 12645–12649, doi: 10.1002 / anie.201206374 .
- Bhimsen Rout, Petr Milko, Mark A. Iron, Leila Motiei, David Margulies: Authorizing Multiple Chemical Passwords by a Combinatorial Molecular Keypad Lock. In: Journal of the American Chemical Society. 135, 2013, pp. 15330-15333, doi: 10.1021 / ja4081748 .