A humistor is a type of variable resistor whose resistance 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 (meteorology), precipitation, dew, or fog t ...

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 , a diminutive form of ''spine,'' in reference to its pointed crystals. Prop ...

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 ...

, 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 () is a substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeating subunits derived from one or more species of monomers. Due to their broad spectrum of properties, bot ...

, 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 throug ...

resin,

polyvinyl chloride Polyvinyl chloride (alternatively: poly(vinyl chloride), colloquial: vinyl or polyvinyl; abbreviated: PVC) is the world's third-most widely produced synthetic polymer of plastic (after polyethylene and polypropylene). About 40 million tons of ...

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 bott ...

, or a

metal oxide An oxide () is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of −2) of oxygen, an O2− ion with oxygen in the oxidation state o ...

Operation

A capacitive humidity sensor detects humidity based on a change of

capacitance Capacitance is the ability of an object 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 two closely related ...

between two detection electrodes provided on a

semiconductor A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...

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

electrostatic Electrostatics is a branch of physics that studies slow-moving or stationary electric charges. Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word (), mean ...

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 In electrical engineering, impedance is the opposition to alternating current presented by the combined effect of Electrical_resistance, resistance and Electrical_reactance, reactance in a electrical circuit, circuit. Quantitatively, the impedan ...

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, dehumidifiers, and air conditioners for humidity adjustment.

References

Resistive components Transducers