Difference Between A Hygrometer And Psychrometer

Many people are confused between these two devices, leaving them unsure as to what they should get when planning to buy one.

What is the difference between a hygrometer and psychrometer, then? The truth is that there is no difference between these two because a psychrometer is, in fact, a hygrometer.

A hygrometer is a type of device used for measuring the air’s moisture content, which basically refers to the dew point and relative humidity. This is something that can be done in several different ways. The oldest and probably most common is by using a wet bulb and a dry bulb thermometer, which is what is referred to as a psychrometer.

How to Measure Humidity

Before you learn how you can measure something, you need to know first what you are measuring in the first place and what the measurements are going to mean. Most things are being measured in scientific units of a certain type or another, like meters, seconds, or kilograms. However, it is slightly different when it comes to humidity and this is typically measured in two different ways.

The so-called specific humidity is one potential measurement. This refers to the water vapor mass found in one kilogram mass of air, with water included, written in units like grams per kilogram. There is another similar measurement referred to as mixing ratio. This is the water vapor mass in kilogram mass of dry air, written in units like grams per kilogram.

Relative humidity is a more common measurement, which is the water vapor amount in the air in contrast the maximum amount that there can possibly be at the said temperature. This is written as percentage with no units.

During an extremely soggy and wet day, it is likely that the relative humidity is around 90 to 100 percent. During dry days when dry wind blows with no or little chance of rain, the possible relative humidity is 60 to 75 percent. When referring to humidity as percentage, this pertains to relative humidity.

Since specific humidities are somewhat meaningless to many people, relative humidities are often quoted in weather forecasts. User-friendly hygrometers are being calibrated this way as well, marked with the measurement on the displays or dials.

What is a Hygrometer?

If you ever experienced a rainforest’s drenched steamy heat or the dryness of a desert, this is something you will surely never forget. The humidity of such extreme environments is the one thing that makes them different from each other.

When you speak of humidity, this is the water vapor amount found in the atmosphere. Obviously, a desert has little or no water at all. On the other hand, walking in the midst of a rainforest will make you feel like you are stepping into a shower.

Humidity measurement is a crucial aspect of weather forecasting and also proves to be extremely helpful for sauna owners and gardeners using glasshouses. Measuring humidity is something you can do efficiently and simply using a cunning instrument like a hygrometer.

Make Your Own Homemade Hygrometer

Many plants react to humidity changes. The spines of pine cones open when it is dry in order to release the seeds, but they close tight when it is wet. As you know, this is the reason why it is common to use fallen pine cones to determine the humidity outside.

However, pine cones are not the most accurate type of hygrometers you can find because it can take some time for them to open or close.

There are several devices for measuring humidity that are not more sophisticated compared to pine cones. For instance, a weather house can use a little woman and a little man standing in two doors of a closed box made from wood.

If rain will pour, the main will come out of his own door carrying an umbrella. If it is dry, the man will go inside and the woman will pop out of her own door instead.

In the weather house, these two figures are actually mounted on the turntable then suspended from one piece of tightly twisted plant fiber or hair. If it is dry, the hair will tighten up and twist the turntable in one way.

During wet conditions, the hair will loosen and the turntable will rotate the other way. Just as how you can use a pine cone as your home hygrometer, you can also do the same thing using a chunk of your hair or even the hair of a friend!

What is a Psychrometer?

Weather houses and pine cones give a somewhat unclear indication of humidity at its best. So, how will you put numbers to the humidity then measure it in a more accurate way?

One way is by using an instrument known as a psychrometer or also called a dry and wet bulb thermometer. This makes use of a pair of thermometers that stand side by side.

One thermometer has its bulb open up to the air while the bulb of the other one is covered using a wet cloth. The cloth’s water content causes heat loss and evaporation from the bulb that makes its reading lower compared to the reading of the dry bulb thermometer.

The evaporation amount and lowering of temperature will depend on the amount of water vapor that already exists in the atmosphere. Measuring the difference in temperature between these two thermometers will let you measure relative humidity.

Which One Should You Use?

The next obvious question is which is the ideal option to measure the air’s moisture content? Well, it depends on your specific needs. For meteorologists or for those who consider accuracy as the most important factor, it is better to use a psychrometer.

There are some people who have to determine the air’s moisture content such as HVAC technicians and in certain instances, painters will also appreciate convenience instead of complete accuracy.

Usually, an electronic hygrometer is their best option because it is easier to read and works fast. For many users, you will not really need accuracy to the tent of a degree, and for this, an electronic version will be fine.

If you are someone who is just interested in weather, your best choice is either a psychrometer or a hygrometer.