Sensors based on the measuring principle
This list of sensors based on the measuring principle is intended to provide an overview of various types of sensors.
Sensors based on the measuring principle
Examples of sensors categorized according to measured variables:
The operating principle of resistive sensors is that the ohmic resistance of the sensor changes depending on the measured variables (length, temperature, ...). This change in resistance leads to a changed voltage drop at the sensor, which can then be recorded, for example, with a simple voltage divider or a bridge circuit (higher measurement accuracy).
- Semiconductor strain gauges
- Metal strain gauges
- Wire strain gauges
- Foil strain gauges
- Thin film strain gauges
The differential transformer is based on a variable coupling with a movable iron core. The two halves of the output coil are located in front of and behind an excitation coil. The output voltage is tapped at their connection. If an iron core, which is located between the two coils, is moved, the alternating voltage ratio between the two output coil halves changes. If it is moved beyond the middle position, the polarity changes at the output voltage tap.
Inductive displacement transducers
Inductive displacement transducers with an armature can also work with just one coil. This can be subdivided as part of an AC measuring bridge.
- One coil + longitudinal anchor
- Differential coil + longitudinal armature
- Differential coil + cross armature
The movable armature can consist of ferromagnetic material or a non-magnetic, highly conductive metal. In the latter case, the change in inductance is caused by field displacement by eddy currents . See also coil (electrical engineering) # Variable inductances .
Inductive distance sensor
The inductive distance sensor and eddy current sensor is based on a change in the magnetic field in the vicinity of a coil caused by a conductive or ferromagnetic object, i.e. In other words, they work without contact and only react to metals.
Inductive proximity switches and eddy current initiators have a threshold switch inside and trigger a switching signal when a conductive object is approached.
Eddy current sensor
Eddy current sensors detect the change in phase position of an alternating voltage excited coil located near an electrically conductive surface. They are used to measure sheet metal thickness, but mostly to measure the distance to a conductive object ( layer thickness measurement , micrometer-accurate distance measurement ) but also to test materials .
Magnetic field sensors
- Galvanomagnetic Effects:
- Magneto-resistive (MR) effects
- Thomson effect in field plates
- macroscopic magnetic Barkhausen effect in Wiegand sensors
- Anisotropic MR effect : change in resistance in metallic and semi-conductors, e.g. B. in AMR sensors
- Gigantic MR effect : change in resistance in thin-film conductors, e.g. B. in GMR sensors
- Colossal MR effect
- Tunnel MR effect : change in resistance in thin-film insulators, e.g. B. in TMR sensors
- Voigt effect : magnetic birefringence in gases
- Cotton-Mouton effect magnetic birefringence in liquids, e.g. B. in magnetic field polarimeters
- Magneto-optical Kerr effect : change in polarization on ferromagnetic surfaces
- Faraday effect : change in polarization in transparent media, e.g. B. MagView
- Zeeman effect : Magnetic splitting of spectral lines, e.g. B. in nuclear magnetic resonance, Mössbauer, atomic absorption spectroscopy and magnetic resonance tomography (MRT)
They are based on the effect of the change in magnetic permeability (magnetic conductivity, is a measure of how well a material allows magnetic fields to pass through) when there is a change in length (reverse magnetostriction ). Pressduktor is also a name . They are used, for example, to measure torque or force. There are both passive magnetoelastic sensors and active ones. The passive magnetoelastic sensors are based on a premagnetization of the measuring point and the measurement of a change in the magnetic field due to an applied load. The active magnetoelastic sensors couple a magnetic field into a measuring point via an inductance and measure the resulting magnetic field via secondary inductances.
Photoelectric sensors (optical sensors)
Photoelectric sensors have the task of converting optical information into signals that can be evaluated electrically. In doing so, the focus is primarily on visible light, as well as infrared radiation and ultraviolet light. The basis of optical sensors is the conversion of signals through quantum mechanical effects of light ( photo effect ).
For example, photocells use the external photoelectric effect . Optical sensors can also be based on the internal photoelectric effect ; they then consist of semiconductors in which, when exposed to light, charge carriers are created that change the electrical properties of the material. The incident light therefore either causes a change in electrical conductivity ( photoresistance ) or a photovoltage ( photodiode or photo element). A variant of the internal photo effect is the barrier layer photo effect, it is used in phototransistors and also photodiodes.
Optical sensors are used primarily in automation technology. There they are, in addition to simple recognition tasks, etc. a. used for position measurements (e.g. light barrier ), speed and angle measurement (e.g. incremental encoder ) and for distance measurement .