Humistor

A humistor is a type of variable resistor whose resistance varies based on humidity.

Construction

A humistor has a ceramic composition comprising at least one component having a spinel type cubic symmetry selected from the group consisting of MgCr2O4, FeCr2O4, NiCr2O4, CoCr2O4, MnCr2O4, CuCr2O4, Mg2TiO4, Zn2TiO4, Mg2SnO4 and Zn2SnO4, and, if desired, at least one component selected from the group consisting of TiO2, ZrO2, HfO2 and SnO2.[1] A humidity sensor has a sensing portion which usually comprises a humidity-sensitive resistor composed of an organic polymer, such as a polyamide resin, polyvinyl chloride or polyethylene, or a metal oxide.

Operation

A capacitive humidity sensor detects humidity based on a change of capacitance between two detection electrodes provided on a semiconductor substrate. The capacitance type humidity sensor detects humidity by measuring the change in the electrostatic capacity of an element corresponding to the ambient humidity. A resistive humidity sensor detects relative humidity by measuring the change in the resistance of an element corresponding to the ambient humidity. Most of the resistance type humidity sensors include an electrolytic, polymeric, or metallic oxide sensor element. An impedance humidity sensor changes its electrical impedance as the humidity of the surrounding environment changes, and the measured impedance is converted into humidity readings[2]

Applications

Humidity sensors can be used not only to measure the humidity in an atmosphere but also to automatically control humidifiers, dehumidifiers, and air conditioners for humidity adjustment.

References

  1. ^ U.S. Patent 4,086,556 Humidity sensitive ceramic resistor.
  2. ^ Electronics Manufacturers: Humidity sensors
Alarm sensor

In telecommunication, the term alarm sensor has the following meanings:

1. In communications systems, a device that can sense an abnormal condition within the system and provide a signal indicating the presence or nature of the abnormality to either a local or remote alarm indicator, and (b) may detect events ranging from a simple contact opening or closure to a time-phased automatic shutdown and restart cycle.

2. In a physical security system, an approved device used to indicate a change in the physical environment of a facility or a part thereof.

3. In electronic security systems, a physical device or change/presence of any electronic signal/logic which causes trigger to electronic circuit to perform application specific operation. In electronic alarm systems the use of this trigger event done by such devices is to turn on the alarm or siren producing sound and/or perform a security calling through telephone lines.

Note: Alarm sensors may also be redundant or chained, such as when one alarm sensor is used to protect the housing, cabling, or power protected by another alarm sensor.

Source: from Federal Standard 1037C and from MIL-STD-188 and from TRISHAM Software Systems

Carbon paste electrode

A carbon-paste electrode (CPE) is made from a mixture of conducting graphite powder and a pasting liquid. These electrodes are simple to make and offer an easily renewable surface for electron exchange. Carbon paste electrodes belong to a special group of heterogeneous carbon electrodes. These electrodes are widely used mainly for voltammetric measurements; however, carbon paste-based sensors are also applicable in coulometry (both amperometry and potentiometry).

Catadioptric sensor

A catadioptric sensor is a visual sensor that contains mirrors (catoptrics) and lenses (dioptrics), a combined catadioptric system. These are panoramic sensors created by pointing a camera at a curved mirror.

Catalytic bead sensor

A catalytic bead sensor is a type of sensor that is used for combustible gas detection from the family of gas sensors known as pellistors.

Displacement receiver

A displacement receiver is a device that responds to or is sensitive to directed distance (displacement).

Examples of displacement receivers include carbon microphones, strain gauges, and pressure sensors or force sensors, which, to within an appropriate scale factor, respond to distance.

In music, certain music keyboards can be considered displacement receivers in the sense that they respond to displacement, rather than velocity (as is more commonly the case).

Examples of displacement-responding sensors include the mechanical action of tracker organs, as well as the force-sensing resistors found in music keyboards that had polyphonic aftertouch capability. Polyphonic aftertouch is no longer a feature of presently manufactured keyboards, but certain older models such as the Roland A50 featured a pressure sensing resistor, similar in principle-of-operation to a carbon microphone, in each key.

Electromechanical film

Electromechanical Film is a thin membrane whose thickness is related to an electric voltage. It can be used as a pressure sensor, microphone, or a speaker. It can also convert electrical energy to vibration, functioning as an actuator.

Hook gauge evaporimeter

A Hook gauge evaporimeter is a precision instrument used to measure changes in water levels due to evaporation. It is used

to precisely measure the level of a free water surface as an evaporation pan or a tank. The main users are meteorologists and water engineers, especially in hot, arid countries where water conservation is of vital importance.

Infrared point sensor

An infrared point sensor is a point gas detector based on the nondispersive infrared sensor technology.

Intelligent sensor

An intelligent sensor is a sensor that takes some predefined action when it senses the appropriate input (light, heat, sound, motion, touch, etc.).

List of sensors

This is a list of sensors sorted by sensor type.

Pellistor

A pellistor is a solid-state device used to detect gases which are either combustible or which have a significant difference in thermal conductivity to that of air. The word "pellistor" is a combination of pellet and resistor.

Piezometer

A piezometer is either a device used to measure liquid pressure in a system by measuring the height to which a column of the liquid rises against gravity, or a device which measures the pressure (more precisely, the piezometric head) of groundwater at a specific point. A piezometer is designed to measure static pressures, and thus differs from a pitot tube by not being pointed into the fluid flow.

Observation wells give some information on the water level in a formation, but must be read manually. Electrical pressure transducers of several types can be read automatically, making data acquisition more convenient.

Position sensor

A position sensor is any device that permits position measurement. It can either be an absolute position sensor or a relative one (displacement sensor). Position sensors can be linear, angular, or multi-axis.

Some position sensors available today:

Capacitive transducer

Capacitive displacement sensor

Eddy-current sensor

Ultrasonic sensor

Grating sensor

Hall effect sensor

Inductive non-contact position sensors

Laser Doppler vibrometer (optical)

Linear variable differential transformer (LVDT)

Multi-axis displacement transducer

Photodiode array

Piezo-electric transducer (piezo-electric)

Potentiometer

Proximity sensor (optical)

Rotary encoder (angular)

Seismic displacement pick-up

String potentiometer (also known as string pot., string encoder, cable position transducer)

Confocal chromatic sensor

Potentiometric sensor

A potentiometric sensor is a type of chemical sensor that may be used to determine the analytical concentration of some components of the analyte gas or solution. These sensors measure the electrical potential of an electrode when no current is present.

Quartz thermometer

The quartz thermometer is a high-precision, high accuracy temperature sensor. It measures temperature by measuring the frequency of a quartz crystal oscillator. The oscillator contains a specially cut crystal that results in a linear temperature coefficient of frequency, so the measurement of the temperature is essentially reduced to measurement of the oscillator frequency. Resolutions of .0001 °C, and accuracy of .02 °C from 0-100 °C are achievable. The high linearity makes it possible to achieve high accuracy over an important temperature range that contains only one convenient temperature reference point for calibration, the triple point of water.

Introduced by Hewlett-Packard in 1965, the successor company, Agilent, has discontinued the Model 2804A Quartz Thermometer.

Other manufacturers make nearly linear-in-temperature quartz crystals that may be used to construct thermometers of similar performance.

Velocity receiver

A velocity receiver (velocity sensor) is a sensor that responds to velocity rather than absolute position. For example, dynamic microphones are velocity receivers. Likewise, many electronic keyboards used for music are velocity sensitive, and may be said to possess a velocity receiver in each key. Most of these function by measuring the time difference between switch closures at two different positions along the travel of each key.

There are two types of velocity receivers, moving coil and piezoelectric. The former contains a coil supported by springs and a permanently fixed magnet and require no output signal amplifiers. Movement causes the coil to move relative to the magnet, which in turn generates a voltage that is proportional to the velocity of that movement.

Piezoelectric sensor velocity receivers are similar to a piezoelectric accelerometer, except that the output of the device is proportional to the velocity of the transducer. Unlike the moving coil variety, piezoelectric sensors will likely require an amplifier due to the small generated signal.

Water sensor

The Water in Fuel Sensor or WiF sensor indicates the presence of water in the fuel. It is installed in the fuel filter and when the water level in the water separator reaches the warning level, the Wif sends an electrical signal to the ECU or to dashboard (lamp).

The WiF is used especially in the Common Rail engines to avoid the Fuel injector damage.

The WiF sensor uses the difference of electric conductivity through water and diesel fuel by 2 electrodes.

First generation WiF sensors use a potting resin to isolate the electronic circuit, while the latest generation of Wif sensors (the WS3 sensor in Surface-mount technology) are made totally without leakage using an innovative co-moulding process.

The latest generation of WiF sensors have a high resistance to vibrations and to thermal excursion cycles.

The main automotive WiF designer and producer is SMP Poland.

Wavefront sensor

A wavefront sensor is a device for measuring the aberrations of an optical wavefront. Although an amplitude splitting interferometer such as the Michelson interferometer could be called a wavefront sensor, the term is normally applied to instruments that do not require an unaberrated reference beam to interfere with. They are commonly used in adaptive optics systems, lens testing and increasingly in ophthalmology.

There are several types of wavefront sensors, including:

Shack–Hartmann wavefront sensor

Phase-shifting Schlieren technique

Wavefront curvature sensor

Pyramid wavefront sensor

Common-path interferometer

Foucault knife-edge test

Multilateral shearing interferometer

Ronchi tester

Shearing interferometer

Yaw-rate sensor

A yaw-rate sensor is a gyroscopic device that measures a vehicle’s angular velocity around its vertical axis. The angle between the vehicle's heading and vehicle actual movement direction is called slip angle, which is related to the yaw rate.

Acoustic, sound, vibration
Automotive, transportation
Chemical
Electric, magnetic, radio
Environment, weather,
moisture
Flow, fluid velocity
Ionising radiation,
subatomic particles
Navigation instruments
Position, angle,
displacement
Optical, light, imaging
Pressure
Force, density, level
Thermal, heat,
temperature
Proximity, presence
Sensor technology
Related

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.