psychrometer


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Related to psychrometer: Sling psychrometer

psychrometer

(sīkrŏm`ĭtər), one of many instruments used for measuring the water vapor content or relative humidityhumidity,
moisture content of the atmosphere, a primary element of climate. Humidity measurements include absolute humidity, the mass of water vapor per unit volume of natural air; relative humidity (usually meant when the term humidity
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 of the atmosphere. It consists of two identical thermometers—the wet-bulb thermometer, so called because its bulb is covered with a jacket of tight-fitting muslin cloth that can be saturated with distilled water; and the dry-bulb thermometer. When the cloth is soaked and the thermometers are properly ventilated, the wet-bulb temperature will be lower than the dry-bulb temperature (actual air temperature) because of cooling due to the evaporation of water from the cloth. The drier the air is, the greater the evaporation and thus the more the wet-bulb temperature is depressed. Psychrometric tables list various humidity variables, such as relative humidity, according to dry-bulb temperature and wet-bulb depression at equilibrium. Ventilation is provided by whirling the thermometers at the end of a chain (sling psychrometer) or by a suction fan (aspiration psychrometer). Newer psychrometers use special electronic sensors. See hygrometerhygrometer
, instrument used to measure the moisture content of a gas, as in determining the relative humidity of air. The temperature at which dew or frost forms is a measure of the absolute humidity—the weight of water vapor per unit volume of air or other gas at the
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.

Psychrometer

 

an instrument for measuring the humidity and temperature of the air. The psychrometer consists of a dry-bulb thermometer and a wet-bulb thermometer. The dry-bulb thermometer shows the temperature of the air, and the wet-bulb thermometer, whose bulb is wrapped with wet cambric, shows a temperature that is dependent on the amount of evaporation from the surface of its bulb. Because heat is used in evaporation, the drier the air whose humidity is being measured, the lower the reading of the wet-bulb thermometer.

The vapor pressure or relative humidity is determined from the readings of the dry- and wet-bulb thermometers with the aid of a psychrometric table, alignment charts, or slide rules derived from the psychrometric formula. For temperatures below — 5°C, where the moisture content of air is very low, the psychrometer does not give reliable results. Under these conditions, a hair hygrometer is preferred.

Weather-station, aspiration, and distant-recording psychrometers are the main types of psychrometers. In the weather-station

Figure 1. Aspiration psychrometer: (1) thermometers, (2) ventilating fan, and (3) radiation shields

psychrometer, the thermometers are fastened to a special frame at a weather shelter. One drawback of this type of psychrometer is the dependence of the wet-bulb thermometer reading on the velocity of the air flow at the station. In the aspiration psychrometer (Figure 1), the thermometers are placed in a special holder, which protects them against damage and the warming effect of direct solar rays; a fan is used to ventilate the wet bulb with the air being studied, at a constant rate of about 2 m/sec. At air temperatures above zero, the aspiration psychrometer is the most reliable instrument for measuring air humidity and temperature. The distant-recording psychrometer uses resistance thermometers, thermistors and thermocouples.

REFERENCE

Sternzat, M. S. Meteorologicheskie pribory i nabliudeniia. Leningrad, 1968.

psychrometer

[sī′kräm·əd·ər]
(engineering)
A device comprising two thermometers, one a dry bulb, the other a wet or wick-covered bulb, used in determining the moisture content or relative humidity of air or other gases. Also known as wet and dry bulb thermometer.

psychrometer

An instrument used to measure humidity in the atmosphere from two thermometers which are similar except that the bulb of one is kept wet, the bulb of the other being dry.

dry- and wet-bulb hygrometer

dry- and wet-bulb hygrometerclick for a larger image
An instrument to measure the dew point, relative humidity, and vapor pressure. It essentially consists of two ordinary, accurate, mercury thermometers. One has thin muslin wrapped around it and is kept wet; it is called a wetbulb thermometer. The other is a dry-bulb thermometer. The dry-bulb thermometer shows the current temperature, whereas the wet-bulb thermometer shows a somewhat lower temperature, the result of the latent heat of evaporation, which depends on the relative humidity of the air. The difference between the two thermometers is a measure of the relative humidity of the air, which is calculated by a formula. Also called a psychrometer.

sling psychrometer

An instrument used to measure the amount of water vapor or relative humidity in the air. It is a combination of wet- and dry-bulb thermometers mounted on a frame with a handle that allows it to be swung around to permit air to move across the psychrometer. See psychrometer.
References in periodicals archive ?
The air temperature and humidity were measured at a height of 0.9 m above the ground by means of an Assmann ventilated psychrometer. The average air velocity was measured for five minutes at 1.2 m above the ground by a nondirectional hot-bulb air velocity sensor (Kanomax Japan, Inc.: 6533, measurement range 0.0530.0 m/s).
The two most significant deterrents to using an aspirated psychrometer are the reduced accuracy and repeatability of the measurements in comparison to other, more expensive devices (e.g., the chilled mirror dew-point hygrometer).
The dry bulb air temperature was monitored by thermocouples (Jenway-digital psychrometer 5105, U.K.) at the centre of the cooler (I).
Similarly in the building environment, when moisture is identified on an infrared image, an exact reading can be taken by a moisture meter and psychrometer. Its readings are then transmitted to the infrared camera and recorded on the image along with other readings such as relative humidity and ambient temperature.
The dry-bulb (DB) and natural wet bulb (NWB) were measured using a "whirling psychrometer" or Sling's psychrometer that houses both dry and wet bulb thermometers in wooden grooves.
Sling psychrometer was used to measure ambient wet- and dry-bulb temperatures from which the relative humidity and air partial pressure were estimated.
N=135 Thermometer 63 yes 72 no Hygrometer 38 yes 97 no Recording hygrothermograph 84 yes 51 no Sling psychrometer 38 yes 97 no Temperature/Humidity data logger 33 yes 102 no Other 6 yes 3.
The instrument recommended for these two measurements is called a psychrometer and is readily available at a reasonable cost.
A psychrometer is an instrument used to measure the relative humidity.
These concepts are clarified via activities such as building an anemometer (to monitor the wind) and a psychrometer (to measure relative humidity).
Relative humidity and air temperature, using a sling psychrometer, and surface wind speed, using the Bufort Scale, were estimated before ignition and at the completion of each fire.
Our sports medicine staff uses a "sling psychrometer," a hand-held instrument that measures the heat stress index before every scheduled workout or practice.