Sensors based on the measuring principle

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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:

Resistive sensors

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).

Potentiometric sensors work like a potentiometer . Wire (wire potentiometer) or conductive plastic is used as the resistance material.

Strain gauges are based on the effect of the change in electrical resistance due to mechanical expansion:

  • Semiconductor strain gauges
  • Metal strain gauges
    • Wire strain gauges
    • Foil strain gauges
    • Thin film strain gauges

Torque transducers , pressure sensors , force transducers and load cells can be built according to the DMS principle .

Inductive sensors

Inductive sensors are based on electromagnetic induction , damping or the change in frequency of an oscillating circuit or a coil.

Scanning systems for records and some vibration sensors work on the electrodynamic or electromagnetic principle.

Differential transformer

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

Magnetic field sensors are based on the effects of the magnetic field in hard or soft magnetic materials , semiconductors, ultra-thin layers, light guides, liquids or their surfaces:

Magnetoelastic sensors

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.

Capacitive sensors

Capacitive sensors are used, among other things, to measure distances. Capacitive distance sensors are based on a change in the capacitance of a capacitor

They can be designed as differential sensors (distance or angle), pressure sensors , fill level sensors or capacitive proximity switches . Another example is the condenser microphone .

Piezoelectric sensors

Piezoelectric sensors are based on the piezoelectric effect . They are used as force transducers , pressure sensors , acceleration transducers ( e.g. structure-borne sound transducers, pickups ).

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 in digital photo and video cameras ( CMOS and CCD sensors ) and in pattern recognition (e.g. barcode scanners ) are often referred to as image sensors .

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 .

Electrochemical sensors

You use z. B. catalytic effect , ionization and partial pressure differences .

The lambda probe is based on the ionic conductivity of zirconium oxide .

Temperature sensors

Temperature sensors are used to measure temperature, which can be done either in contact with the object, such as a thermometer , or based on the radiation emission of the object.

Resistance thermometers are based on a change in resistance, for example a platinum resistance ( PT100 ).

Temperature sensor circuits are semiconductor temperature sensors that supply an analog or digital signal proportional to the temperature .

Thermocouples are based on the thermoelectric effect . They supply an electrical voltage that is largely proportional to temperature.

Fiber optic temperature sensors measure the temperature profile along a glass fiber . The principle is the Raman effect .

NTC thermistors and PTC thermistors usually have a non-linear temperature profile of their electrical resistance .

Pyrometers measure the temperature of distant objects based on their thermal radiation . A distinction is made between total radiation pyrometers, ribbon radiation pyrometers and ratio pyrometers.

The temperature sensors also include motion detectors and thermography devices based on the pyroelectric effect .

Web links

Wikibooks: Linearization of Resistive Sensors  - Learning and Teaching Materials

Individual evidence

  1. ↑ A. Schwersenz, P. Cörlin, C. Leiser, T. Kitzler, T. Senkbeil: P3.5 - Contact-free electro-magnetic reactance based mechanical tension sensors . In: Proceedings Sensor 2017 . May 30, 2017, doi : 10.5162 / sensor2017 / P3.5 ( ama-science.org [accessed January 23, 2018]).