What is Humidity?

Condensation of water vapour

Humidity is the presence of water vapour in air (water in a gaseous form) which is not visible to the human eye. Humidity measurement taken by a hygrometer are used to predict condensation or frost and is used in psychrometric calculations to get a dew point, Dry Bulb Temperature or Wet Bulb Temperature, Enthalpy etc..

Humidity effects many things in our day to day lives.

The presence of humidity will effect the perceived temperature and a higher humidity does make the average person feel hotter. The Humidex was created to describe a comfort level by calculating temperature and humidity together to give a scale of  comfort.

Electronics are effected by humidity levels with most electronic devices having a minimum and maximum temperature and humidity specified, but despite these  figures there are extensive .  Electro mechanical devices will have extended lifespan if humidity is controlled within a specific range.

Food and pharmaceutical industry are very reliant on a controlled humidity environment. Due to higher humidity being advantageous for bacterial, mold and mildew growth.

Measurement of humidity can be perceived with a few techniques:

Absolute humidity:

Is the water content in air and measured in grams per cubic meter. An easy way to explain this measurement is as if  you were able to extract all the moisture from air in cubic meter into a liquid form and then weight it.

Relative humidity:

Measured as a percentage 0% to 100% of the current absolute humidity relative to the highest point for a specific temperature At 100% the air would often be referred to as saturated. In essence water vapour is at equilibrium and no more evaporation would occur when water in liquid form is exposed to this air that has 100% relative Humidity. It is in this state that dew,  fog or frost is likely to form.

Specific humidity:

 The ratio of the mass of water vapour to the total mass of the moist air parcel.

How do we measure Humidity? With a Hygrometer?

OEM SeEnsor Humidity and Temperature

There are various methods to measure Humidity, and are commonly referred to as Hygrometers. These include wet and dry bulb Hygrometers, dew point hygrometers, hair tension hygrometers, captivate of resistive relative humidity sensors. As a distributor of Rotronic who predominantly focus on Relative Humidity through captive sensors. These humidity sensors consist of a substrate on which a film of polymer is deposited between electrodes, which forms a capacitor. The sensor will absorb water vapour from the air and will find and equilibrium between sensor and air. The result is that the capacitance change as humidity increases or decreases.

Selection of Hygrometer Products

  • Humidity Data Logger – HygroLog – HL-1D


    Economical Humidity Data Logger

    The HL1D is a compact, low cost humidity data logger. Capable of ±3.0 %RH and ±0.3°C measurement accuracy. Memory can store up to 32,000 data points. HW4-Lite software key included in the purchase (software downloaded from internet).

    Humidity Data Logger Features

    • Accurate humidity and temperature measurement±3.0 %RH and ±0.3 °C
    • Compact design with a high IP67 protection
    • FDA 21 CFR Part 11 / GAMP 5 conform software HW4
    • Large storage capacity: 32,000 lines
    • Programmable start and stop time for data logger with the HW4 software
    • Long battery life (up to 3 years)
    • MIN/MAX/AVG Humidity and temperature statistical function
    • Includes HW4-lite software key for programmable and analytical software
    • Clear LCD with visual alerts
  • Temperature and Humidity Display HD1


    Temperature and Humidity Display Clock

    This is a compact temperature and humidity display,  ideal for displaying temperature, relative humidity and dew point in rooms, labs cabinets, storage or your work environment. Easily mounted on the wall, thanks to its integrated fastening points or set it up freestanding on a flat surface. Clear and visible display for easy reading, even from a few meters. With clock, time and date functionality.

    Temperature and Humidity Display Features

    • Bench-top & wall display for humidity, temperature and dew point
    • Time & Date Display
    • Industrial accuracy
    • MAX/MIN/AVG function
    • Audible & visual HI/Lo Alarm
    • Great value for money
    • Easy use
    Included in Temperature and Humidity Display
    • Factory certificate
    • 4 AA batteries
    • Short instruction manual
  • Handheld Air Velocity, Humidity and Temperature Meter AFP1


    The intelligent AFP1 multi-parameter measuring instrument is ideal for spot measurements in HVAC systems. Thanks to easy operation via a smartphone, it is possible not only to take random measurements, but also to record, export and display data as wanted.

    Operation with “ROTRONIC” App
    The AFP1 sensor is operated via Bluetooth communication with the ROTRONIC smartphone app, which can be obtained free-of charge from the App Store (iOS) or Play Store (Android).
    The app offers functions to display, log and send the required measured values by e-mail. It is also possible, among others, to define parameter-specific settings and options for the measurement.


    • Intelligent multi-parameter measuring instrument for air velocity, humidity and temperature
    • Small vane anemometer for in-tube measurements
    • Smartphone connection via Bluetooth®
    • Easy data logging via iOS or Android app
    • Direct volume flow calculation
    • Numeric or graphic display
    • Simple data export for evaluation on a PC

    Delivery package

    • Factory certificate
    • Short instruction manual
    • APP (online)
    • Batteries 2 x 3 V (CR2032)
    • Soft case
  • CO2 Display


    This CO2 display is the latest development that simultaneously measures and records CO2, humidity and temperature and can be wall-mounted or sit on a bench-top. Configurable directly via buttons and stored data can be exported to a USB memory stick for analysis with the free ROTRONIC software package SW21. This instrument offers unbeatable value for money, equipped with a stable ROTRONIC HYGROMER® IN-1 humidity sensor.

    Indoor Air Quality for: Open-Plan Offices, Classrooms, Meeting Rooms, Shopping Centers, Fitness Studios...


    • Adjustable, visual CO2 indicator
    • Measures and records CO2, relative humidity and temperature
    • Accuracy ±2.5 %RH / ±0.3 K / ±30 ppm + 5% of measured value
    • Humidity sensor HYGROMER® IN-1
    • 18,000 data point memory for CO2, humidity and temperature values
    • Display of date and time
    • Large, easy-to-read display
    • USB access for data download
  • HYGROPALM - HP21 - Humidity and Temperature HANDHELD



    The HP21 is a highly accurate handheld indicator that displays relative humidity, temperature and dew or frost point temperature. The HP21 is perfect for spot checking HVAC installations, manufacturing or storage areas and any ambient air measurement within the temperature range of -10 to 60°C (14 to 140 °F). The HP21 is designed to meet a wide range of user requirements from the most basic applications to the most demanding applications.

    The HP21 indicator offers an extensive set of settings and functions that can be configured and enabled by the user with the ROTRONIC HW4 software. In spite of its high end design, the HP21 is ideal even as a simple humidity and temperature indicator.