A humistor is a type of

variable resistor A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat. The measuring instrume ...

whose

resistance Resistance may refer to: Arts, entertainment, and media Comics * Either of two similarly named but otherwise unrelated comic book series, both published by Wildstorm: ** ''Resistance'' (comics), based on the video game of the same title ** ''T ...

varies based on

humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity depe ...

Construction

A humistor has a ceramic composition comprising at least one component having a

spinel Spinel () is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula in the cubic crystal system. Its name comes from the Latin word , which means ''spine'' in reference to its pointed crystals. Properties S ...

type cubic symmetry selected from the group consisting

chromates Chromate salts contain the chromate anion, . Dichromate salts contain the dichromate anion, . They are oxyanions of chromium in the +6 oxidation state and are moderately strong oxidizing agents. In an aqueous solution, chromate and dichromate i ...

, stannic or titan oxides of different metals like 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. A humidity sensor has a sensing portion which usually comprises a humidity-sensitive resistor composed of an

organic polymer A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic an ...

, such as a

polyamide A polyamide is a polymer with repeating units linked by amide bonds. Polyamides occur both naturally and artificially. Examples of naturally occurring polyamides are proteins, such as wool and silk. Artificially made polyamides can be made through ...

resin, polyvinyl chloride or

polyethylene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging ( plastic bags, plastic films, geomembranes and containers including bo ...

, or a metal oxide.

Operation

A capacitive humidity sensor detects humidity based on a change of

capacitance Capacitance is the capability of a material object or device to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized are ...

between two detection electrodes provided on a

semiconductor A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...

substrate. The capacitance type humidity sensor detects humidity by measuring the change in the

electrostatic Electrostatics is a branch of physics that studies electric charges at rest (static electricity). Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for amber ...

capacity of an element corresponding to the ambient humidity. A resistive humidity sensor detects relative humidity by measuring the change in the

of an element corresponding to the ambient humidity. Most of the resistance type humidity sensors include an

electrolytic An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon dis ...

, polymeric, or metallic oxide sensor element. An impedance humidity sensor changes its

electrical impedance In electrical engineering, impedance is the opposition to alternating current presented by the combined effect of resistance and reactance in a circuit. Quantitatively, the impedance of a two-terminal circuit element is the ratio of the comp ...

as the humidity of the surrounding environment changes, and the measured impedance is converted into analog signal for humidity readings.{{Cite web , url=http://www.electronics-manufacturers.com/products/sensors-transducers-detectors/humidity-sensor/ , title=Electronics Manufacturers: Humidity sensors , access-date=2011-02-26 , archive-url=https://web.archive.org/web/20160303230915/http://www.electronics-manufacturers.com/products/sensors-transducers-detectors/humidity-sensor/ , archive-date=2016-03-03 , url-status=dead

Applications

Humidity sensors can be used not only to measure the humidity in an atmosphere but also to automatically control

humidifiers A humidifier is a device, primarily an electrical appliance, that increases humidity (moisture) in a single room or an entire building. In the home, point-of-use humidifiers are commonly used to humidify a single room, while whole-house or furnac ...

, dehumidifiers, and air conditioners for humidity adjustment.

References

Resistive components Transducers