Humidity Measurement & Monitoring Relative Humidity

Humidity levels affect materials of all kinds, as well as the health and well-being of individuals. Humidity measurement is important in production processes throughout industry, in the packaging and storage of products; it is crucial for ensuring product quality. In the highly regulated pharmaceutical and food industries, it is a key requirement and must be fully documented. In museums and galleries, humidity must be controlled to protect artifacts. Meteorological reports necessarily include the measurement of humidity as well as temperature and other parameters. It is vitally important to measure temperature along with humidity because a small temperature variation has a large effect.

To measure relative humidity (RH) accurately, it is essential to measure temperature accurately and take air pressure into account. Relative humidity is highly dependent on temperature because warm air can hold more moisture than cold air, which is why humidity sensors are often combined with temperature sensors. In addition, air pressure affects the moisture capacity of the air: higher pressure increases the saturation limit, while low pressure decreases it. In applications where pressure varies (e.g. at high altitudes), humidity measurements must be corrected accordingly to ensure accurate results.

The accuracy of humidity meters depends to a large extent on the installation location. The location should be chosen so that there are no local sources of interference such as radiators, air conditioners, humidity generators or open water surfaces nearby, as these can falsify temperature and humidity conditions. Direct sunlight or poor ventilation also lead to inaccurate results. A neutral, representative location with stable ambient conditions is crucial to ensure precise measurements. The accuracy of humidity meters is influenced by various factors. One of the most important is temperature, since relative humidity is temperature-dependent and inaccuracies or fluctuations in temperature measurement can falsify the results. The aging of sensors also plays a role: Over time, contamination, chemical influences or material fatigue can affect accuracy. Environmental conditions such as condensation, dust or extreme humidity can also disrupt the sensor or reduce its precision. Regular calibration is essential, as missing adjustments lead to deviations from the actual humidity value. Fluctuating air pressure, such as at high altitudes, affects the calculation of relative humidity if it is not taken into account. Electronic interference such as electromagnetic interference or unstable power supply can also distort the results. In addition, slow sensor response time to changing conditions can lead to inaccurate or delayed readings.

A good humidity and temperature probe is characterized by high accuracy, stability and reliability. Ideally, it offers a humidity accuracy of ±1–2 % RH and a temperature accuracy of ±0.1 °C to ensure precise measurements. It should be able to cover a wide measurement range, for example 0–100% RH for humidity and -50°C to 100/200°C for temperature. A long lifespan and minimal drift, such as < 1% RH per year, ensure stable readings over time. A high-quality sensor responds quickly to fluctuations, with short response times of less than 15 seconds. It is also important to have integrated temperature compensation to minimize errors caused by temperature fluctuations. Robust construction with protection against condensation, dust and chemicals, or special coatings, increases durability. Its compact design allows for use in confined spaces, while easy calibration and low energy consumption improve maintenance and efficiency. Modern sensors also offer interfaces such as Modbus RTU for easy integration into control or monitoring systems. Overall, a good humidity and temperature sensor should offer an optimal price-performance ratio and be tailored to the specific requirements of the application.

The sensor technology of the HC2A generation has a high long-term stability and all probes are adjusted before delivery ex works. The long-term stability is better than 1% RH per year. Depending on the application, it is recommended to calibrate the probe every 6 to 12 months. Calibration or adjustment can be carried out using the HygroSoft software or the devices of the HC2(A) generation (hand-held meters, transmitters, data loggers). Depending on the application, we recommend recalibration after one year of use. We offer a calibration and adjustment service, but you can also do it yourself on site using the Rotronic SCS humidity standards or our HG2-S humidity generators.

Rotronic is one of the world's leading manufacturers of humidity sensors, with over 40 years' experience in developing high-precision measuring equipment. Rotronic sensors offer exceptional accuracy, durability and reliability, even under extreme conditions. Thanks to innovative technology and high-quality materials, the humidity sensors are particularly resistant to variations in temperature and humidity, as well as to chemical influences. This makes them ideal for demanding applications in fields such as industry, meteorology and pharmaceuticals. Continuous research and development and strict quality controls ensure that Rotronic sensors always meet the highest standards and deliver long-lasting performance.

Rotronic HygroClips are highly accurate humidity and temperature probes based on capacitive humidity sensing. A hygroscopic film between two electrodes absorbs moisture from the air, which changes the capacitance, which is then measured and converted into humidity values. The integrated temperature sensor measures the air temperature, which is required to calculate the relative humidity accurately. The digital signals are processed and forwarded to systems via interfaces such as Modbus or I²C. The HC2-A-S is characterized by high accuracy, resistance to extreme conditions and a long service life, making it ideal for demanding applications in industry and research.

Rotronic has created several help documents to assist in finding the right product for your application. The following documents are available: Right Humidity Probe Critical for your application Right Humidity Probe Industrial Applications Choose Humidity Transmitter