VIT-1,VIT-2 hygrometer

Hygrometer — the measuring device for determination of humidity of air. There are several types of hygrometers which action is based on various principles: weight, hair, film and other.

The weight (absolute) hygrometer consists of system of the U - shaped tubes filled with the hygroscopic substance capable to absorb moisture from air. Through this system the pump stretch a quantity of air which humidity is defined. Knowing the mass of system before measurement, and also the volume of the passed air, find absolute humidity.

Action of a hair hygrometer is based on property of the fat - free hair to change the length at change of humidity of air that allows to measure relative humidity from 30 to 100% .

The film hygrometer has a sensitive element from an organic film which stretches at increase of humidity and contracts at decrease. Change of position of the center of a film membrane is transferred to an arrow. A hair and film hygrometer in winter time are the main devices for measurement of humidity of air. Indications of a hair and film hygrometer are periodically compared to indications of more exact device — the psychrometer which is also used to measurement of humidity of air.

In an electrolytic hygrometer the plate from electroinsulating material is covered with a hygroscopic layer of electrolyte — chloride lithium — with binding material. At change of humidity of air concentration of electrolyte and consequently, and its resistance changes.

Action of a ceramic hygrometer is based on dependence of electric resistance of firm and porous ceramic weight (mix of clay, silicon, a kaolin and some oxides of metal) on humidity of air.

The condensation hygrometer determines a dew point by temperature of the cooled metal pocket mirror at the time of emergence of the water traces on it (or ice) which is condensed from air. The condensation hygrometer consists of the device for cooling of a pocket mirror, the optical or electric device fixing the condensation moment, and the thermometer taking pocket mirror temperature. In modern condensation hygrometers for cooling of a pocket mirror use a semiconductor element which principle of action is based on Peltye effect, and temperature of a pocket mirror is taken by the wire resistance or the semiconductor microthermometer which is built in in it.

The increasing distribution is found by electrolytic hygrometers with heating which action is based on the principle of measurement of a dew point over saturated hydrochloric solution (usually chloride lithium) which for this salt is in the known dependence on humidity. The sensitive element consists of the thermometer of resistance which case the stocking from fiber glass impregnated with solution of chloride lithium, and two electrodes from a platinum wire which are reeled up over a stocking on which the alternating voltage moves is put on.