What Is a Hygrometer?

Hygrometers are handheld instruments that can measure ambient humidity in the air or humidity in gas. The readings can tell operators about the moisture content in the air. For example, some hygrometers measure relative humidity, which can tell users if the area is safely within advised humidity levels or may be too moist or too dry. Other hygrometers can measure the dew point, while some measure both (as well as additional factors).

There are many different applications for hygrometers. Residential HVAC and ventilation systems can incorporate hygrometers to help homeowners maintain ideal indoor humidity levels of between 40 and 60%. Commercial businesses may use hygrometers to guarantee that cooling and refrigeration stay within safety standards. Additional applications for hygrometers include:

• Weather forecasting
• Investigating condensation and abnormal levels of moisture that can cause mold growth or even water damage
• Storing food, agricultural products, and medications
• Growing plants in greenhouses and preventing disease

How Hygrometers Work

There are four main ways hygrometers can detect and measure humidity: dew point measurement, moisture absorption, psychrometry, and thermal conductivity.

1. Dew point: The dew point is the temperature at which air can cause moisture to condense and turn into dew or fog. Higher dew points mean the air is more moist, while lower dew points signify drier air. Dew point hygrometers use a cool mirror to detect moisture and assess the dew point, and this method is very accurate.
2. Moisture absorption: Hygrometers can use specially designed hairs or films that physically react to the presence of moisture in the air by changing shape or becoming more electrically resistant. The hygrometers then analyze the degree of change and output a humidity reading on a display.
3. Psychometers use evaporative cooling to determine humidity. They use a dry thermometer and a wet thermometer, and the difference between the two temperatures translates to the relative humidity because the wet bulb cools slightly through moisture evaporation.
4. Thermal conductivity: Dry and humid air conduct heat at different rates. These hygrometers measure the difference between a thermistor exposed to the open air and one locked in dry nitrogen.

Depending on your needs, each of these methods offers different advantages in terms of cost-effectiveness, speed, accuracy, and durable hardware.

Proper Hygrometer Usage

Today's hygrometers are more accurate than ever, especially for portable and handheld devices. But there are a few best practices to keep in mind. To ensure you get the clearest and most reliable results, follow these tips:

• Use the hygrometer out of direct sunlight: Sunlight can make the temperature warmer than in the rest of the environment, interfering with results. Try to use it away from sunlight and other heat sources.
• Hold it at least five feet off the ground: This height ensures you get results with the fewest interfering variables.
• Calibrate your equipment on a regular schedule: While digital hygrometers rarely need calibration, analog tools do. Inspect your hygrometers routinely to ensure they provide consistent results.
• Store hygrometers in neutral environments: Store hygrometers away from moisture, high temperatures, and high-humidity areas. Also, clean your hygrometers after extended storage to get more accurate results.

At Schaper's Supply, we carry an extensive range of hygrometers for different residential, commercial, and industrial applications. Our team of experts can help you select the right hygrometer for your use cases and provide you with more information regarding the proper use, maintenance, and storage of your hygrometers. Contact us today to learn more about our available inventory of tools.