Contenido

El uso de procesos de fabricación complementary metal-oxide-semiconductor (CMOS) industriales permite la integración del sensor y de la parte del proceso electrónico de la señal en un chip. También asegura una mayor fiabilidad, y una estabilidad excelente a largo plazo. Estos sensores permiten la toma de valores de temperatura y humedad del ambiente. Además, el protocolo de comunicación «serial sincrónico» los hace aptos para ser utilizados con un microcontrolador y así controlar otros dispositivos. La principal ventaja de este tipo de sensores, en virtud de su sistema de comunicación digital, consiste en la facilidad de envío de datos a un computador para su posterior almacenamiento y análisis.

Capacitive

For applications where cost, space or fragility are relevant, other types of electronic sensors are used, at the cost of lower accuracy. In capacitive hygrometers, the effect of humidity on the dielectric constant of a polymeric material or metal oxide is measured. With proper calibration, these sensors have an accuracy of ± 2% in a range between 5% and 95% relative humidity. Without calibration, the accuracy is 2 to 3 times worse. Capacitive sensors are robust to effects such as condensation and temporary high temperatures.[7]​ However, they are subject to the effects of contamination, misalignment and the effects of aging, but are suitable for many applications.

Resistive

Resistive hygrometers usually measure the change in the electrical resistance of a material (usually salts or conductive polymers) due to humidity.[7] Resistive sensors are less sensitive than capacitive sensors, as the change in the properties of the material is smaller, so they require more complex circuits. Material properties also tend to depend on both humidity and temperature, which means in practice that the sensor must be combined with a second temperature sensor. Accuracy and robustness against condensation vary depending on the resistive material chosen. There are robust, condensation-resistant sensors with an accuracy of up to ± 3% of relative humidity.

Thermal

In thermal hygrometers, the change in the thermal conductivity of air due to humidity is measured. These sensors measure absolute humidity instead of relative humidity.[7]​.

Gravimetric

A gravimetric hygrometer measures the mass of a sample of air compared to an equal volume of dry air. It is considered the most accurate primary method for determining moisture content in national air control standards,[8] being the basis of regulatory systems developed in the United States, United Kingdom, European Union, and Japan. The drawback to using these types of devices is that they are usually only used as transfer standards to calibrate less precise instruments.

Other types

Among other types of these devices, there are the following:

At a defined temperature, a balance is established between evaporation, by heating the fabric, and the absorption of water from ambient humidity by the action of a very hygroscopic chemical compound: lithium chloride: LiCl. From these data, the degree of humidity is precisely established.

Other substances have the property of changing color due to humidity. For example, cobalt chloride") (CoCl) displays blue on the integrated temperature and humidity sensor (Sensirion SHT11).

In addition to greenhouses and industrial spaces, hygrometers are used in some egg incubators, saunas, humidors, and museums. They are also used in the care of wooden musical instruments such as pianos, guitars, violins and harps, which can be damaged by inadequate humidity conditions, as well as photographic and videographic material where humidity can cause fungus to appear on the optical elements. In residential environments, hygrometers are used to assist in humidity control (when it is too low it can damage the skin and human body, while when it is too high it encourages the growth of fungi and mites). In the coatings industry they have multiple uses because the application of paint and other coatings can be very sensitive to humidity and dew point. With an increasing need for measurements, psychrometers are now being replaced by dew point meters called dewcheck. These devices make measurements much more quickly, but are often not permitted in explosive environments.

The content of this article incorporates material from the Salvat illustrated popular encyclopedic dictionary from the years 1906 to 1914 that is in the public domain..

hygroscope

A hygroscope consists of a piece of gut string that is twisted by humidity and twisted by dryness, varying in length and moving a figurine that indicates the hygrometric state of the air. It does not have a scale.

Metal-paper coil hygrometer

The metal-paper coil hygrometer is very useful in giving a linear indication of humidity changes. It is frequently used in very cheap devices, and its precision is limited, with variations of 10% or more. In these devices, water vapor is absorbed by a strip of paper impregnated with salt, attached to a metal coil, causing the metal coil to change shape due to the variation in the hardness of the paper caused by the change in humidity. These changes (analogous to those of a bimetallic thermometer) provide an indication on a dial by rotating a needle.

Hair tension hygrometers

These devices use human or animal hair under tension. Hair is hygroscopic (that is, it tends to retain moisture); Its length changes with humidity, and through a mechanical amplification system it is possible to read these changes in length on a scale dial. In the late 1700s, these devices were called hygroscopes by some scientists; This word is no longer in use today, but hygroscopic and hygroscopy, which are derived from it, are still used. The traditional devices known as time friar and time house (the latter very popular in central Europe) are based on this principle.

In 1783, Swiss physicist and geologist Horace Bénédict de Saussure (1740-1799) built the first hair tension hygrometer using human hair.

Whale baleen or other materials can be used in place of hair. In this sense, the Swiss scientist based in England Jean-André Deluc (1727–1817), published in the Philosophical Transactions the announcement of a new hygrometer similar to a mercury thermometer, with an ivory bulb that, when expanded by humidity, caused the mercury to drop.[5] Later he invented a hygrometer based on a whale's baleen, which caused the outbreak of a bitter controversy with de Saussure.[6]​.

Psychrometers (wet and dry bulb thermometers)

A psychrometer (or dry and wet bulb thermometer), consists of two thermometers, one that is dry and one that is kept moist with distilled water in a cloth case or wick. The two thermometers are called dry bulb and wet bulb. At temperatures above the freezing point of water, evaporation of water from the wick reduces the temperature, so the wet bulb thermometer usually displays a lower temperature than the dry bulb thermometer. However, when the air temperature is below freezing, the wet bulb is covered with a thin layer of ice and may be warmer than the dry bulb.

Relative humidity is calculated from the ambient temperature (marked by the dry bulb thermometer) and the temperature difference (between the wet bulb and dry bulb thermometers). Relative humidity can also be determined by locating the intersection of the graphs of the two temperatures on a psychrometric chart. When the two thermometers coincide, then the air is completely saturated; and the greater the difference, the drier the air. Psychrometers are commonly used in meteorology, and in the HVAC industry to determine the proper refrigerant charge in residential and commercial air conditioning systems.

Digital electronic versions of this type of device are also used, in which the dry and wet temperatures are taken using thermistors, with the necessary calculations being carried out automatically to present the humidity value on a numerical display.

The rotating psychrometer, where thermometers are attached to a handle or length of string and centrifuged in air for a few minutes, is sometimes used for field measurements, but is being replaced by more user-friendly electronic sensors. Alternatively, there are other types of rotary psychrometer that use the same principle, but in which the two thermometers are mounted on a device that resembles a ratchet, with a handle and a ball joint.

Dew point hygrometer

The dew point is the temperature at which a sample of humid air (or any other water vapor) at constant pressure reaches water vapor saturation. At this saturation temperature, additional cooling results in condensation of water. Chilled mirror dew point hygrometers are some of the most accurate instruments commonly available. They use a cooled mirror and an optoelectronic mechanism to detect condensation on the mirror surface. The mirror temperature is controlled by electronic feedback to maintain a dynamic balance between evaporation and condensation on the mirror, therefore the measurement remains close to the dew point temperature. An accuracy of 0.2°C can be achieved with these devices, which correlates in typical office environments with a relative humidity accuracy of approximately ±1.2%. These devices require frequent cleaning, a skilled operator, and periodic calibration to achieve these levels of accuracy. Even so, they are prone to dirt buildup in environments where smoke or impure air may be present.

Contenido

El uso de procesos de fabricación complementary metal-oxide-semiconductor (CMOS) industriales permite la integración del sensor y de la parte del proceso electrónico de la señal en un chip. También asegura una mayor fiabilidad, y una estabilidad excelente a largo plazo. Estos sensores permiten la toma de valores de temperatura y humedad del ambiente. Además, el protocolo de comunicación «serial sincrónico» los hace aptos para ser utilizados con un microcontrolador y así controlar otros dispositivos. La principal ventaja de este tipo de sensores, en virtud de su sistema de comunicación digital, consiste en la facilidad de envío de datos a un computador para su posterior almacenamiento y análisis.

Capacitive

For applications where cost, space or fragility are relevant, other types of electronic sensors are used, at the cost of lower accuracy. In capacitive hygrometers, the effect of humidity on the dielectric constant of a polymeric material or metal oxide is measured. With proper calibration, these sensors have an accuracy of ± 2% in a range between 5% and 95% relative humidity. Without calibration, the accuracy is 2 to 3 times worse. Capacitive sensors are robust to effects such as condensation and temporary high temperatures.[7]​ However, they are subject to the effects of contamination, misalignment and the effects of aging, but are suitable for many applications.

Resistive

Resistive hygrometers usually measure the change in the electrical resistance of a material (usually salts or conductive polymers) due to humidity.[7] Resistive sensors are less sensitive than capacitive sensors, as the change in the properties of the material is smaller, so they require more complex circuits. Material properties also tend to depend on both humidity and temperature, which means in practice that the sensor must be combined with a second temperature sensor. Accuracy and robustness against condensation vary depending on the resistive material chosen. There are robust, condensation-resistant sensors with an accuracy of up to ± 3% of relative humidity.

Thermal

In thermal hygrometers, the change in the thermal conductivity of air due to humidity is measured. These sensors measure absolute humidity instead of relative humidity.[7]​.

Gravimetric

A gravimetric hygrometer measures the mass of a sample of air compared to an equal volume of dry air. It is considered the most accurate primary method for determining moisture content in national air control standards,[8] being the basis of regulatory systems developed in the United States, United Kingdom, European Union, and Japan. The drawback to using these types of devices is that they are usually only used as transfer standards to calibrate less precise instruments.

Other types

Among other types of these devices, there are the following:

At a defined temperature, a balance is established between evaporation, by heating the fabric, and the absorption of water from ambient humidity by the action of a very hygroscopic chemical compound: lithium chloride: LiCl. From these data, the degree of humidity is precisely established.

Other substances have the property of changing color due to humidity. For example, cobalt chloride") (CoCl) displays blue on the integrated temperature and humidity sensor (Sensirion SHT11).

In addition to greenhouses and industrial spaces, hygrometers are used in some egg incubators, saunas, humidors, and museums. They are also used in the care of wooden musical instruments such as pianos, guitars, violins and harps, which can be damaged by inadequate humidity conditions, as well as photographic and videographic material where humidity can cause fungus to appear on the optical elements. In residential environments, hygrometers are used to assist in humidity control (when it is too low it can damage the skin and human body, while when it is too high it encourages the growth of fungi and mites). In the coatings industry they have multiple uses because the application of paint and other coatings can be very sensitive to humidity and dew point. With an increasing need for measurements, psychrometers are now being replaced by dew point meters called dewcheck. These devices make measurements much more quickly, but are often not permitted in explosive environments.

The content of this article incorporates material from the Salvat illustrated popular encyclopedic dictionary from the years 1906 to 1914 that is in the public domain..