# Joni Partanen

Product Manager

Vaisala

###### Industrial Measurements

The first step on the journey to mastering humidity parameters is to understand partial pressures. We’ll begin our journey by the sea, with a one-meter square drawn in the sand. Now, imagine that there is an air column going up through the atmosphere and into space, with an air weight of about 10,300 kg. This air mass generates hydrostatic pressure with a force of 101,325 Newtons per square meter.

This defines a pressure unit called Pascal [Pa]: Newtons per square meter. That is the total pressure. The air we breathe is a mixture of gases, where the main components are nitrogen (N2), oxygen (O2), water vapor (H2O), argon (Ar), and carbon dioxide (CO2). These components can be expressed using Dalton’s law of partial pressures:

The component with the concentration that varies the most is water vapor, and it plays an important role in affecting weather and climate, as well as numerous industrial processes and other aspects of our everyday lives.

On earth, water exists in three different forms: ice, water, and gas. The maximum amount of gaseous water is dictated by the temperature: the higher the temperature, the higher the partial pressure of water vapor, i.e. there is more dissolved water in the air. The maximum water vapor pressure at a specific temperature is called water vapor saturation pressure. Water vapor pressure cannot exceed this limit, and a simple way to prove this fact is to look at the clouds in the sky. Clouds are formed when the water vapor saturation pressure has been reached and the environment can no longer hold the water in its vaporous phase, meaning some of it condenses into tiny droplets that may eventually fall on us as rain.

Relative humidity (%RH) is a concept that defines what percentage of water vapor is present at that temperature relative to the saturation point. When it’s raining, it’s obviously 100 %RH up there in the clouds where the droplets are forming. While the instruments and technologies available to us have greatly improved over the years, the weather can still sometimes surprise us. We humans tend to try to control our environment, and this has led to great strides forward in technological and industrial development. We can create controlled environments depending on our need, whether it’s for laundry drying or manufacturing cutting-edge technology from highly sensitive materials.

What do a wet cotton shirt, conducting salts used for lithium battery manufacturing, and a HUMICAP® thin-film polymer sensor have in common? The answer is they are all hygroscopic materials, which means that they attract water molecules from their surrounding environment until they reach an equilibrium state. Here, relative humidity (RH) plays an important role because the equilibrium moisture content of a material is closely related to the relative humidity level. Luckily, I can trust that the battery in my mobile phone has been manufactured in a controlled environment and protected in a way that it tolerates occasional splashes. What about the cotton shirt that got wet in the rain? It doesn’t dry that well outdoors while it’s raining – even if I protect it from the rain. However, I can greatly enhance the shirt’s drying rate by putting it into a clothes dryer. Why does the shirt dry faster at a high temperature? Is there less humidity in the drying cabinet? The short answer is that the air is relatively drier at elevated temperatures. This means that the relative humidity (RH) inside the dryer is lower and the cotton shirt therefore seeks to achieve equilibrium with its surroundings and eventually becomes drier.

Relative humidity (RH) is the ratio of the water vapor pressure to the saturation vapor pressure at a given temperature. If you want to deepen your knowledge of how to calculate relative humidity, related quantities, and many other humidity parameters, download our Conversion Formulas technical eBook.

### Joni Partanen

Product Manager

Vaisala

Joni Partanen is a Product Manager at Vaisala. He is responsible for the development of humidity and vaporized hydrogen peroxide measuring products. He has over 16 years of experience in process industry measurement technology, industrial engineering, and instrumentation. Joni holds a Bachelor of Engineering degree in Automation Technology.

## Vaisala humidity calculator

Relative humidity, absolute humidity, wet-bulb temperature, enthalpy, water concentration, and many more. Humidity calculations and conversions made easy.

## Relative humidity related products

### Humidity and Temperature Transmitter Series HMDW110

Vaisala HUMICAP® Humidity and Temperature Transmitter Series HMDW110 is suitable for relative humidity, dew-point, enthalpy, wet-bulb temperature and temperature measurement in demanding HVAC applications

### Humidity and Temperature Transmitter Series HMDW80

The HMDW80 series is versatile with transmitters for wall and duct mounting for measuring relative humidity and temperature in various building automation applications.

### Moisture and Temperature Meter Series MMT310

Vaisala HUMICAP® Moisture and Temperature Transmitter Series MMT310 is a fast and reliable on-line detector for moisture in oil.

### Hand-Held Humidity and Temperature Meter HM40

Compact, portable, and easy-to-use Vaisala HUMICAP® HM40 handheld humidity meter is designed for spot-checking in a wide variety of environments

### Handheld Humidity and Temperature Meter HM70

Vaisala HUMICAP® HM70 Handheld is designed for demanding humidity measurement in spot-checking applications. It is also ideal for field checking and calibration of Vaisala's fixed humidity instruments.

### Humidity and Temperature Transmitters HMT120/130

The Vaisala HUMICAP® HMT120 and HMT130 transmitters are suitable for cleanrooms, museums, laboratories and data centers.

### Turbine Mounting Kit HMT300TMK

Note that the HMT300TMK is being discontinued. HMT330TMK monitors the air intake of gas and liquid fueled power turbines and is used together with HMT337 Temperature and Humidity Transmitter.

### Humidity and Temperature Probe HMP110

The Vaisala HUMICAP® Humidity and Temperature Probe HMP110 is a trouble-free and cost-effective humidity transmitter with high accuracy and good stability. The power consumption is low and it has fast startup for battery-powered applications.

### HUMICAP® Humidity and Temperature Probe HMP113

The Vaisala HUMICAP® Humidity and Temperature Probe HMP113 is a highly accurate and cost-effective humidity probe with a plastic enclosure.

### Digital Open Frame Humidity Module HMM105

An open frame module for integration into environmental chambers and incubators. The module incorporates the Vaisala HUMICAP® 180R sensor which ensures excellent measurement accuracy. A reliable choice for OEM use.

### Humidity Module HMM100

The Vaisala HUMICAP® Humidity Module HMM100 is an open frame module for integration into environmental chambers. The modules provide a single analog output channel for relative humidity (RH) or dew point (Td).

### HMP60 Humidity and Temperature Probe

HMP60 is a simple, durable and cost-effective humidity probe suitable for volume applications, integration into other manufacturers' equipment, incubators, glove boxes, greenhouses, fermentation chambers and data loggers.

### INTERCAP® Humidity and Temperature Probe HMP63

The Vaisala INTERCAP® Humidity and Temperature Probe HMP63 is a cost-effective humidity probe with plastic enclosure.

### Relative Humidity and Temperature Probe HMP7

Vaisala HUMICAP® Humidity and Temperature Probe HMP7 is designed for applications which involve constant high humidity or rapid changes in humidity

### Relative Humidity and Temperature Probe HMP4

Vaisala HUMICAP® Humidity and Temperature Probe HMP4 is designed for high-pressure applications such as compressed air systems in maritime, breathing air, and industrial applications, where measurement performance and chemical tolerance are essential.

### Relative Humidity and Temperature Probe HMP5

Vaisala HUMICAP® Humidity and Temperature Probe HMP5 is designed for high temperature applications such as baking ovens, pasta dryers, ceramics and industrial drying kilns where measurement performance and chemical tolerance are essential.

### Relative Humidity and Temperature Probe HMP8

Vaisala HUMICAP® Humidity and Temperature Probe HMP8 is designed for pressurized applications in compressed air systems, refrigerant dryers, and other pressurized industrial applications where easy insertion and removal of the probe and adjustable installation depth into the pipeline are needed.

### Compact Humidity and Temperature Probe HMP9

The Vaisala HUMICAP® Humidity and Temperature Probe HMP9 is designed for easy installation in rapidly changing environments where a fast response time, measurement performance, and chemical tolerance are essential.