Rotronic solutions for measuring humidity and moisture

products-servicesRotronic AG
November 10th 2020

Measurement of environmental humidity and moisture levels play key roles in ensuring ideal conditions in pharmaceutical production facilities, clean rooms and storage areas and across the whole value chain from manufacturing to pharmacy distribution and retail.

Rotronic is part of the PST Group (Process Sensing Technologies) and one of the world’s longest-established and most respected providers of solutions for humidity measurement as well as assessing moisture levels.

Relative humidity vs. specific humidity

Relative and specific humidity measurement and monitoring is often a key concern, particularly in heating, ventilation and air-conditioning (HVAC) systems, drying processes and storage. However, effects of humidity also vary with temperature, which is why Rotronic measuring and monitoring instruments usually combine temperature and humidity measurement capabilities.

Since humidity is affected by both air density and ambient temperature, it can be measured in different ways.

  • Relative humidity is the ratio of the partial pressure of water vapor to the equilibrium vapor pressure of water at the same temperature. Thus relative humidity depends on temperature and the pressure within the system of interest.
  • Specific humidity, sometimes referred to as the humidity ratio, is the ratio between water vapor mass (mv) to the total volume (parcel) of air enclosed. This “mixing ratio” can be defined as the ratio of the mass of water vapor in an air parcel to the mass of dry air for the same parcel.
  • Absolute humidity is the total mass of water vapor present in a given volume of air, ranging from near zero to roughly 30 grams per cubic meter when the air is saturated at 30 °C.

Measurement of humidity must often take account of a further variable, the dew temperature or dew point: the temperature at water vapor reaches saturation and condenses into liquid dew.

Rotronic offers a free online calculator for dew point, specific humidity and relative humidity.

Role of the Hygrometer

A hygrometer can also be thought of as a humidity meter – a device used to measure all the key variables concerning humidity, including air temperature, relative humidity, dew point temperature and wet bulb temperature (the global standard description for heat stress). A hygrometer that measures both humidity and temperature can also be called a  a thermo-hygrometer.

An exceptionally accurate hygrometer, combined with humidity generator,  such as Rotronic’s HygroGen2 HGS-2  can also be used as a calibration station for remotely mounted or handheld humidity meters, humidity probes, and humidity sensors.

RMS integration of humidity measurement

Rotronic provides a wide range of temperature and humidity instruments and systems. These can act as stand-alone solutions or can be connected into RMS, the Rotronic Continuous Monitoring System, which provides a fully integrated and comprehensive environmental monitoring solution to integrate otherwise fragmented and complex systems working in isolation.

RMS is an end-to-end solution that can interface with the full range of Rotronic components, including humidity probes, humidity sensors, humidity testers, humidity transmitters, moisture meters, and moisture sensors to measure and record all the key parameters in environmental monitoring, including relative humidity, temperature, CO2 and differential pressure, as well as other applications such as monitoring light (lux) and oxygen.

Rotronic humidity and moisture instruments

Rotronic humidity and moisture measurement components include ranges of data loggers, measuring probes, wall-mounted transmitters and monitors  and handheld instruments:

Wall-mounted transmitters/monitors

HygroFlex3 – HF3: measures relative humidity and temperature and calculates the dew/frost point. Available n R-Type or S-Type variants for interior use where elegant aesthetics are also a consideration or in W-Type / D-Type variants for HVAC applications focused on reliability and repeatability.

HygroFlex5 – HF5: The HygroFlex5-series marked a significant development in transmitters for humidity, temperature and dew point, with their capability  to output any psychrometric calculation as an analogue signal.

HygroFlex5 – EX – The HygroFlex5-EX series incorporate all the advanced features of the HF5 for the exact measurement of humidity and temperature but is designed for use in explosive atmospheres. This device conforms to the latest ATEX international standards.

HygroFlex8 – HF8: A multi-function wall-mounted transmitter that displays relative humidity, temperature and all calculated (psychrometric) parameters  that is designed to meet the requirements of HVAC, industrial and pharma applications requiring multiple measurements within one self-contained instrument. The HF8 has an extensive set of optional functions and settings that can be configured and enabled with HW4 software after connecting to a PC.

Handheld instruments and portable calibrators

HygroGen2 HG2-S Humidity Generator – Portable humidity and temperature generator to calibrate humidity and temperature measuring instruments for multi-point calibration

HygroGen2 HG2-XL: Humidity Calibrator – A high capacity humidity and temperature calibration tool that can simultaneously calibrate multiple humidity and temperature measuring instruments across a site.

HygroPalm HP31/32  Part of a range of  high-end handheld instruments than can measure humidity and temperature, while also calculating all psychrometric parameters and offering various additional functions, either with their own probes or by connecting to any Rotronic probe or sensor. All the Rotronic Airchip 3000 series transmitters can be adjusted via a service cable for calibration of low dew point, CO2, differential pressure and airflow.

Data loggers

HygroLog HL-1D – A compact, dependable and inexpensive data logger ideal for extensive networked installations.

HygroLog BL-1D – A range of compact, dependable and inexpensive Data Loggers for barometric pressure, humidity temperature and dew point, equipped with FDA 21 CFR Part 11 / GAMP 5-compliant HW4 software.

RMS-LOG Data Logger: This series of wall-mounted monitoring stations can store up to 44,000 pairs of measured values from interchangeable humidity, temperature, CO2, differential pressure, or low dew point probes, and transmit them to the RMS database via LAN link. They also work autonomously to display current readings as well as visual and audible alarms even if the power supply and communication should fail temporarily.

RMS-MLOG Wireless Mini-Data Loggers: The RMS-MLOG-Series is a protfolio of low-cost discrete data loggers with small housings and wireless interfaces that make them flexible tools for buidinbg up a highly distributed RMS monitoring network. These mini loggersa are available in various sensor variants to measure vartious combinations of temperature, humidity, light, etc.  .


HC2A-S Probe: The HC2-S or HC2-S3 are the most versatile probes from Rotronic and form the basic building blocks of the overall temperature and humidity measuring range.  They measure humidity and temperature and calculate dew or frost point. They are equipped with  UART Digital interface and scalable analog outputs.

HC2A-S3 Standard meteo probe – a variation of the HC2A designed for meteorological measurements and designed for exterior mounting.


Click on Rotronic Measurement and Monitoring of Relative Humidity for further information and video.
Click on Products for more information on Rotronic measurement solutions.

Rotronic solutions for measuring humidity and moisture

RMS temperature and humidity monitoring embraces a wide choice of modules and input devices

Rotronic solutions for measuring humidity and moisture

HygroFlex3 – HF3 – Wall-mounted transmitter for interior use

Rotronic solutions for measuring humidity and moisture

HygroGen2 – HG2-S – Humidity Generator

Rotronic solutions for measuring humidity and moisture

Handheld Humidity Meters – Rotronic Hygropalm HP-Series