A Look In Various Types Hygrometers

Today hygrometers are commonly found in houses that are located in humid regions of the world. These devices give you an accurate measurement of the level of humidity indoors. High moisture level can have a damaging effect on the house as well as on the health of people living inside. Hygrometers cannot control humidity but it can tell you exact level. You can take precautionary measures to control it thereby. Hygrometers in various forms have been around since long. Let’s take a look at them.

Natural hygrometers

Plants often react to humidity. But the changes they exhibit due to presence of moisture are not always noticeable. However pinecones react explicitly to humidity. When the moisture level is high the cones close their spines tightly. But when the moisture is quite low the spines of the cone opens up. Although thy will not give an accurate data about the level of humidity, they will give you an overall idea.

Arty hygrometers

These were commonly seen in homes. These are in shape of wooden boxes in which a little woman and a little man stand in two different door ways. When it is cloudy and going to rain, the man comes out with an umbrella and when it is dry the woman is out. The mechanism that works inside the weather house is that the figures are mounted on a turntable and suspended from a piece of tightly twisted hair/ plant fiber. When the fiber is dry it tightens and twists the turntable one way. The woman is places in such position on the turntable that it comes forward in this case. When the fibre is wet, it loosens and twist the turntable other way, the man comes forward in this case.

Another such model was made by Louis Ullman of Nashville, Tennessee in 1859. It is made of a box that has twisted plant fiber inside. The plant fiber is usually of orange and others that were specified in the patent. The box is exposed to air so that moisture can get in. When there is moisture the fiber loosens and when the humidity is low it is tightens. The fiber is connected to a pointer that moves around dial. As the fiber tightens or loosens the pointer move around the dial showing the level of humidity.


All these hygrometers natural or man made only described the level of humidity in terms of high or low. But they didn’t furnish enough data about the level of humidity. Psychrometers were the first hygrometers to do so. The machine has two thermometers. One has a bulb that is exposed to air. The other has a bulb that is exposed to wet cloth. The water in the cloth causes evaporation. This results in loss of heat from the bulb which changes the temperature of the thermometer. It becomes lower compared to the thermometer exposed to air. The amount of evaporation depends on how much water vapor there is in the atmosphere. Measuring the temperature difference between the two thermometers lets you measure the relative humidity.

Electronic hygrometers

These measure the capacitance or resistance of a sample of air. The capacitance of device implies its ability to store as static electric charge. It uses this to calculate the amount of humidity. The device has two metal plates with air between them. The more water the air has, the more affected will be the plate’s capacitance. The device calculates how much charge the plate is able to store. And by doing so it also derives the amount of humidity in the air. In a resistive hygrometer, there are ceramic plates. The electricity flows by a piece of ceramic material exposed to the air. The more humid the air is the more water vapor condenses inside the ceramic. The level of condensation will change the resistance of the ceramic accordingly. Therefore measuring how much current is flowing in will also give an accurate measurement of humidity.

Hygrometer in cell phones

These days, you can even get hygrometer apps in cell phones. Basically these apps get to know your location from the GPS. They send a query to the local weather office server, which sends the humidity information that it displays.



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