Types of Hygrometers – Different Hygrometer Options

One of the most effective ways to monitor the humidity in an area is with one of the many different hygrometer options available on the market. There are many different types of hygrometers and each excels in specific applications.

In this article, we will take a closer look at what hygrometers are, the different types and their uses.

What Is A Hygrometer?

digital thermometer hygrometer

A hygrometer is a measuring device. It is used to measure the amount of water vapor in the atmosphere. In other words, a hygrometer tells you in simple terms the relative humidity as it relates to the current temperature and air pressure in a given location.

Types of Hygrometers

There are a number of different types of hygrometers. Here we look at the various types of hygrometer options with an explanation on how each one operates in order to record and display the humidity level for observation.

Electrical Hygrometers

Resistance or capacitance is used to measure humidity with an electrical hygrometer.

The capacitive type uses two metal plates with air between them. As the air becomes moist, it impacts the static electric charge storage capacity of the plates. This is how the humidity is recorded.

In resistive electrical hygrometers, a ceramic substance is used to pass electricity through. The ceramic material is exposed to the air and as water vapor condenses inside of it, the higher the humidity level which results in an alteration in the level of resistance.

Psychrometers

This thermohygrometer utilizes two bulbs in two different thermometers. There is a dry bulb and a wet bulb and when the wet bulb experiences evaporation, the temperature drops below that of the dry bulb. The difference between them is how humidity is calculated.

Dew Point Hygrometers

Considered the most precise of all the different types of humidity gauge instruments, a dew point hygrometer measures the amount of moist air in a gas. They are the best devices when the smallest amount of moisture needs to be identified and measured.

Hair-Tension Hygrometers

A human or animal hair is used for this type of humidity monitor. The hair is held under pressure and will retain moisture. As a result, when the humidity changes, so does the length of the hair in the device which indicates either an increase or decrease of moisture content.

Metal-Paper Coil Hygrometers

This is the most common method used in inexpensive hygrometers. The device has a salt-impregnated strip that is attached to a metal coil. Water vapor is absorbed by the strip which makes the coil change shape which is recorded on a dial with a needle that gives you a reading.

Chilled Mirror Hygrometers

The chilled mirror hygrometer is a variation on the dew point style and as such, is one of the most accurate digital hygrometer devices. This one employs a chilled mirror and an optoelectronic mechanism that records the condensation on the surface of the mirror.

Electronics control the mirror temperature in order to maintain equilibrium between evaporation and condensation levels. In other words, it closely monitors and measures the dew point temperature. Smokey air will hamper the otherwise extreme precision of this device.

Gravimetric Hygrometers

This method of measuring humidity is considered to be the most accurate. What a gravimetric hygrometer does is it will measure the mass of an air sample and compare that to an equal volume of dry air. Many countries in the world have established standards using this method.

Thermal Hygrometer

This type of device monitors the change in thermal conductivity of air resulting from a change in humidity. It employs built-in sensors to provide a level reading. It is important to note that this type of hygrometer actually reads absolute humidity rather than relative humidity.

Optical Hygrometer

A light emitter and a light detector are arranged in such a manner that air is located between them. The moisture in the air is measured through the recording of light absorption levels of the water in the air. Humidity is indicated by the attenuation of the light as viewed by the detector.

Humidity Cards

A humidity indicator card contains moisture-sensitive chemicals that are impregnated on a piece of card stock. When the humidity level is reached, the chemical changes color which will indicate a specific humidity level. These are inexpensive and not all that accurate.

Hygrometer Calibration

The most common method used to calibrate a hygrometer is known as saturated salt calibration. As the name suggests, a mixture of salt and water are used to determine the humidity and is then used to calibrate the device. Here are the steps required to calibrate digital or analog devices.

Digital Hygrometer Calibration

You will need to following items to perform the calibration. They include:

  • Your digital thermometer hygrometer
  • ½ cup of salt
  • ¼ cup of water
  • A cup
  • A releasable plastic bag

Prepare the salt solution by mixing the water and salt in the cup. Stir thoroughly. With the cup containing the salt solution, place it in the plastic bag with the hygrometer. Leave the bag with these items inside a cabinet in a room with constant temperature making sure the salt solution and hygrometer do not touch.

After no more than 12 hours, check the reading on the hygrometer. It should say 75% relative humidity. There may be a slightly different reading of two or three percentage points above or below the desired 75%. If this happens, remove the hygrometer and press the calibration button or reset button and wait for it to read 75%.

If there is no reset or calibration button, make note of the difference in the reading from 75%. For example, if your device reads 73%, the difference is 2%. Make a note of this so that when you use this hygrometer in the future, you will know to add 2% in order to know the correct humidity level.

Analog Hygrometer Calibration

analog hygrometer humidity meter

Before you attempt to calibrate your analog device, examine it beforehand to identify whether or not it has a small screw in the back. If it does, this is your calibration screw. If the hygrometer does not have one, it likely cannot be manually calibrated.

You can test to see if your analog hygrometer is working by performing the following test. Wrap it in a slightly wet towel or blanket. After letting it sit for about 30-minutes, check the reading. The dial should say 95%. If it does not, turn the calibration screw until it does.

In this next step, you will need a few items including:

  • Your analog hygrometer
  • Distilled water
  • 1 tablespoon salt
  • A small plastic container
  • A small and clean bottle cap or jar lid

Prepare the salt solution by putting salt into the cap and dripping distilled water into it until the salt is completely moistened. Do not put in so much water that the salt begins to dissolve. Then place the cap of salt and analog hygrometer into the container so that they are not touching and seal the container.

Leave the sealed container in a location where it will not be disturbed and will not be in direct sunlight. After 6 hours, open the container and read the hygrometer. It should say 75% and if it is off slightly, simply turn the screw in the back until you get a 75% reading.

Styles of Hygrometers

There are many different types of hygrometers. Here is a look at each with a small description.

Analog

An analog hygrometer is simply a humidity measuring device that has a dial with numbers and steps on it. A needle or pointer is used to identify the humidity level for ease of reading.

See some of our picks of the best analog hygrometers here.

Digital

A digital humidity meter is a measuring device that provides an easy-to-read LED or LCD screen with large digits to indicate the humidity level. Temperature, daily records and more can be displayed on a digital hygrometer depending on the exact style and design.

To have a look at a variety of digital hygrometers, click here.

Indoor

Designed for use indoors, these hygrometers can be quite stylish in cabinet shapes, wall-mountable and related variations.

See more information on indoor hygrometers here.

Outdoor

Outdoor hygrometers are designed to be easy to see from a distance so dials and digital readouts tend to be rather large. Also, these devices are designed to withstand all weather conditions and are typically wall mountable.

Click here for more information on the best outdoor hygrometers.

Remote Monitoring/Sensor

A remote monitoring hygrometer is a device that measures humidity, and often temperature and other weather-related data. The difference here is that you can monitor the data remotely through an app that you download to your smartphone.

Depending on the actual hygrometer, some have sensors that will send an alert to your phone notifying you of any changes in humidity that may fall out of a selected zone. Some of these devices permit you to change conditions right from your phone.

Wifi Connected

A wifi connected hygrometer allows you to monitor the data just like you would with a remote monitoring device. Instead, the data is sent through your home wifi system. You can still change settings and conditions remotely with wifi connectivity.

Hygrometer Combined With Other Instruments

It is not uncommon to find ‘combination’ devices that include a digital or analog hygrometer. The most popular of these is a weather station configuration that contains several devices that measure wind speed, humidity, temperature, air pressure, hours of sunlight, rainfall and also provide local weather forecasts.

Hygrometer Usage And Applications

Just as there are many different types and styles of hygrometers, there are a number of ways to use them. Some hygrometers are task-specific while others can be used in more than one application. Here is a general look at the most common hygrometer usage applications.

Residential Personal Monitoring

These are the hygrometers that would be used for indoor and outdoor humidity level monitoring. Home use is one of the most common applications of hygrometers.

Small Enclosed Specific Usage Circumstances

Hobbyists and collectors use hygrometers in instrument cases, humidors, greenhouses, terrariums and similar small spaces to monitor changes in moisture content.

Residential, Commercial, Industrial Humidity Control

These applications often include a hygrometer as part of a complete humidity control and air quality system. In addition to a hygrometer, a fan, humidifier, and dehumidifier would all be used to regulate humidity in large structures where climate control is required.

Some examples would be in saunas, museums to keep delicate collections in the correct condition, incubators, refrigerators, warehouses that require controlled environments and precision factories where humidity impacts the product being manufactured.

Smart home applications are also becoming more common with hygrometers installed to monitor the humidity levels in bathrooms, laundry rooms, and kitchens where moisture in the air is most frequent. When levels are too high or low, the system kicks in to correct it.

Weather Stations/Meteorological

Probably the most widely recognized application of hygrometers is in the field of weather studies. Ranging from official weather departments in radio and television to airports and other navigational operations, an accurate hygrometer is the most useful tool.

Conclusion

As you can see, there are many types of hygrometers available to suit many different applications. Hygrometers are important devices to have if you live in a climate where humidity – too much or too little – is an issue. They perform a valuable task in identifying the relative humidity and always gives you a means of monitoring it.

To protect valuables, stay healthy and to keep your home or building in good condition, being able to monitor and regulate the humidity is vital. Without one of the many hygrometer options available, the moisture content in the air around you could potentially be harmful if it is not regulated.

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