What is an analog hygrometer?
Hygrometer is a tool that measures relative humidity. The analog hygrometer measures continuous changes in relative humidity, but because it is analogue, its resolution limits its accuracy. For comparison, the digital hygrometer measures discrete changes in relative humidity. The psychrometer is the most common type of analog hygrometer. It calculates the relative humidity by comparing the difference between wet and dry temperatures.
The psychrometer consists of two thermometers, one with a wet bulb and the other with a dry bulb. The psychrometer has a handle that allows the operator to spin it in the air before the deductions. The water around the wet bulb is evaporated when the temperature is above frost, which generally reduces the temperature of this thermometer. The water forms an insulating layer of ice when the temperature is under freezing, which generally causes the thermometer of the wet bulb in the analog hydrometer to have a higher temperature than the dry thermometer for the bulb.
Analog hygrometer requires a psychrometric graph to provide relative humidity. ThisThe graph type generally consists of a series of dry bulb temperatures and a column of temperature of the wet bulb. Relative humidity can be obtained by cross reference of the temperature of wet and dry bulb.
Assmann's psychrometer is one of the most accurate types of analog hygometers. Adolph Richard Assmann invented this facility at the end of the 19th century. Every thermometer in Assmann's psychrometer is suspended inside the polished metal tube, which is suspended inside another metal tube. This arrangement insulates thermometers from radiant heat. The fan attracts air through the thermometer bulbs to maximize the evaporation of the water from the bulbs.
The accuracy of the analog hygrometer is highly dependent on the thermometer insulation from the radiant heat and adequate air withdrawal through the thermometer bulbs. These factors are particularly critical in low humidity conditions when the temperature of the wet bulb is close to the dry bulb temperature. The most accurate analog hygroThe meters used by the thermometers of wet bulbs can have an error rate of up to 5 percent for low humidity.
Analog hygrometer can use the electric heater to improve its accuracy when the temperature is under freezing. The heater heats up the air before it reaches thermometers without affecting the moisture content. This function eliminates the need to maintain a wet bulb in freezing conditions.