Humidity is an indication of the amount of water in the atmosphere.
According to the technical specifications of the World Meteorological Organization (WMO), there are six ways of expressing humidity, namely, water-vapor mixing ratio, specific humidity, water-vapor pressure, absolute humidity, relative humidity and dew point. The history of humidity observation instruments is as follows:
15th century A.D.: German Nicolaus de Cusa invented the hygrometer.
1650: Ferdinand II, Grand Marquis of Tuscana, invented the condensation hygrometer. 1769: Lambert, a German, made the hygrometer.
1783: Swiss H.B. Saussure invented the hair hygrometer.
1799: Leslie, a Frenchman, was the first to use the DifferentialThermometer to measure humidity.
1815: Frenchman Gay-Lussac found the formula for measuring humidity by DifferentialThermometer.
1819: Frenchman Henri Victor Regnault manufactures a condensation hygrometer.
1854: Frenchman H.V. Regnault produces a dew-point meter.
1887: German R. Assmann invented the ventilation hygrometer.
1938: Dumore, an American, began research on motorized hygrometers.
The development of humidity observation instruments can be summarized as hygrometer method, hair method, resistance method, and dew point or frost point method. The introduction of humidity observation instruments is as follows:
(1)Hair hygrometer
Use time: Since the station has been set up to date
Use: Measurement of atmospheric humidity
Construction and principle:
Take a bunch of degreased hair, the upper end of the hair is fixed in the metal frame, the lower end of the lever and the pointer connected to the rod, there is a small retractable copper hammer on the rod, so that the hair is straight, and there is a small screw at the top, for the hair to be straightened. There is a small screw at the top of the lever to adjust the position of the pointer, and to reduce the oscillation of the pointer axis, a hairspring can be installed to control it. Hair has a lot of holes, when the humidity in the atmosphere increases, the holes absorb moisture and elongation, when the humidity decreases, the holes release water vapor and contraction, the variables drive the pointer, that is, you can know the humidity.
Some hair hygrometer scale plate has three rows, the upper row for the number of wet, the lower row for the relative humidity, the air temperature minus the number of wet is the dew point temperature. Thermometer also has two scales, the right scale for the left side of the temperature equivalent to the maximum water vapor tension, the maximum water vapor tension multiplied by the relative humidity that is the absolute humidity.
(2)Lithium chloride dew point meter
This instrument is made of nickel light temperature measurement resistor body, sealed into the stainless steel protection tube, the protection of the outside of the tube wrapped with Teflon insulating sheet, the surface of the surface and then wrapped up with fiberglass tape. One of the 2 conductors into a spiral winding, the use of 3.8% of the lithium chloride liquid coated on the wire, the wire on the 25VAC voltage, lithium chloride liquid and the external environment, humidity balance, the platinum resistance temperature measurement of nickel temperature is the dew point temperature. In the humidity laboratory, ventilation speed control at 1 ± 0.4m / s, slightly smaller than the actual normal operation, temperature control in the range of 25 ℃, measurement results shown in Figure VI. The principle is the same as the single-tube thermometer, the structure is slightly different, that is, the use of capillary tube connected to the circular induction section, the capillary tube is then fixed to the scale plate. Sensor connected to the outer casing, the outer casing filled with dry air, so that not due to hot and cold and water vapor condensation on the wall, affecting the readings, the upper end of the outer casing and then closed to. The advantage of the double tube thermometer is that the scale plate is not in contact with the outside moist air, so the scale will not be blurred, and the dry air inside can also be isolated from the effects of radiant heat.