PST Rotronic Relative Humidity Calculator
The PST Rotronic Relative Humidity Calculator is based on the Hyland and Wexler (1983) formula for measuring water vapor pressure over a range of temperatures.
It accurately represents the saturation vapor pressure of water over liquid and solid phases.
The Hyland and Wexler (1983) equation:
ln (Pvap) = A + B / (T + C)
Where:
Pvap is the water vapor pressure in Pascal (Pa).
T is the temperature in degrees celsius (°C).
A, B, and C are constants that vary depending on the water phase (liquid or solid).
The Humidity Calculator is built to focus on Relative Humidity measurement for engineers. Users can also choose between different units and parameter inputs such as dew point, wet-blub temperature, frost point, vapor concentration, and more. It can be used as a standalone tool or in combination with Rotronic humidity products.
How to use the Calculator
Using the PST Rotronic Relative Humidity Calculator is easy. 1) Choose the parameter you want to measure. 2) Enter the temperature and pressure. 3) Select the units in which you want to view your result.
Watch the quick video below demonstrating how to use the PST Rotronic Relative Humidity Calculator.
What is Relative Humidity?
Relative humidity is the measurement of how close the air (or other gas) is to being fully saturated with water vapor.
It is the ratio of water vapor pressure to saturation water vapor pressure expressed as a percentage.
%rh = (water vapor pressure/saturation water vapor pressure) * 100.0
Learn more about relative humidity and why it is measured for industries.
FAQ
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What formula does the calculator use?
The PST Rotronic Relative Humidity Calculator is built on the Hyland and Wexler (1983) Water vapor pressure formula, while the PST Michell Dew Point Calculator is built on the Sonntag (1994) Water vapor pressure formula.
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What is the difference between Hyland and Wexler (1983) and Sonntag (1994) Water vapor pressure formula?
The two formulas differ in their applicable temperature ranges. The Hyland-Wexler formula is suitable for temperatures between -100°C and 0°C, whereas the Sonntag formula is valid for a broader range of temperatures, spanning from -80°C to +50°C. This wider temperature range makes the Sonntag formula more versatile and applicable to a greater variety of situations.
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What are the differences between humidity, dew point, and relative humidity?
Humidity indicates moisture in the air, while dew point is the temperature at which moisture condenses. Relative humidity is the percentage of moisture in the air compared to its maximum capacity at a given temperature. These concepts help gauge comfort, condensation, and moisture conditions.
Learn more about these consepts
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Related Articles
Humidity Academy Theory 1 – What is Humidity?
The term “humidity” is often interchangeable with “relative humidity,” but there’s a significant difference between these two terms in the context of precise measurement.
Humidity Academy Theory 2 – Relative Humidity, Pressure and Temperature
Reviewing the laws of physics that govern water vapor in a moist gas can help you better understand the properties of what you’re measuring.
Humidity Academy Theory 3 – Humidity and Vapor Pressure
A change in the total pressure of a gas mixture, at constant composition, results in the same change in the partial pressure of each component.
Theory 4 – Definitions of Humidity: Vapor Concentration
Vapor concentration or absolute humidity of a mixture of water vapor and dry air is defined as the ratio of the mass of water vapor Mw to the volume V occupied by the mixture.
Humidity Academy Theory 5 - Effect of Temperature and Pressure on % rh
Saturation vapor pressure depends only on temperature. There is no effect of total pressure, and there is no difference between the situation in an open space and that in a closed container.
Humidity Academy Theory 6 – The Capacitive Sensor
The capacitive humidity sensor consists of a hygroscopic dielectric material placed between a pair of electrodes that forms a small capacitor.