We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

What Is Humidity Calibration?

By Jerry Morrison
Updated May 21, 2024
Our promise to you
All The Science is dedicated to creating trustworthy, high-quality content that always prioritizes transparency, integrity, and inclusivity above all else. Our ensure that our content creation and review process includes rigorous fact-checking, evidence-based, and continual updates to ensure accuracy and reliability.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

Editorial Standards

At All The Science, we are committed to creating content that you can trust. Our editorial process is designed to ensure that every piece of content we publish is accurate, reliable, and informative.

Our team of experienced writers and editors follows a strict set of guidelines to ensure the highest quality content. We conduct thorough research, fact-check all information, and rely on credible sources to back up our claims. Our content is reviewed by subject-matter experts to ensure accuracy and clarity.

We believe in transparency and maintain editorial independence from our advertisers. Our team does not receive direct compensation from advertisers, allowing us to create unbiased content that prioritizes your interests.

Humidity calibration involves checking the accuracy of and making the proper adjustment to sensors that measure moisture content in the air. Such measurements are critically important in many laboratory and manufacturing processes. Accurate calibration for relative humidity (RH), the amount of moisture in the air compared to the maximum it can hold at a particular temperature, is particularly difficult. A small change in ambient temperature can alter the value even when the moisture content remains the same. Proper humidity calibration of monitoring devices helps ensure that environmental conditions will remain within required specifications for a reliable length of time.

Hygrometers are devices used to measure humidity. Most of these measure a quantity such as temperature, atmospheric pressure or changes in electrical properties that are sensitive to change in humidity. Typically, these measurements indicate a humidity value by comparison with a standard reference. One difficulty in calibration is the generation of an accurate and stable relative humidity outside a special lab.

A convenient and widely used method of humidity calibration involves saturated salt solutions. Data has been compiled on the properties of 28 different salt solutions that cover the entire range of RH values. In this process, the bottom of an airtight box is covered with a saturated salt solution that generates a relative humidity in the space above it with reasonable accuracy. The RH value depends on the salt used and is largely independent of temperature. Uniformity of temperature within the box is necessary, however.

Non-saturated salt solutions can also be used to generate a certain relative humidity. In this case, the RH values produced depend on careful management of the salt concentration and ambient temperature. Just as in the above method, the measuring device is supported in the space above the solution for humidity calibration. Once the desired RH value has been generated, the device's reading can be noted and adjustments made.

In another method, a stream of dry air at 0% RH is directed into two flows. One is saturated with water vapor up to 100% RH. The relative humidity in the measuring chamber can then be adjusted by mixing the two flows with a mass flow controller (MFC), an instrument used to control the flow of gasses. While this method allows for humidity calibration at a range of levels, it is itself dependent on the proper calibration of the MFC.

Implementations of the saturated salt method are often sold in kit form to companies without the resources to set up an in-house lab or contract with an instrument calibration firm. Pharmaceutical companies, microelectronic manufacturers and research labs depend on closely regulated environments, however. In these sites, professional humidity calibration is a standard and regularly implemented procedure.

All The Science is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Discussion Comments
All The Science, in your inbox

Our latest articles, guides, and more, delivered daily.

All The Science, in your inbox

Our latest articles, guides, and more, delivered daily.