Humidity, dewpoint and temperature measurement 

Well established internationally

Vaisala's relative humidity products incorporate a capacitive thin-film polymer sensor, Vaisala HUMICAP® Sensor. The HUMICAP® sensor features high accuracy, excellent long-term stability and negligible hysteresis. It is insensitive to dust, particulate dirt and most chemicals.

Operating principle

The thin-film polymer either absorbs or releases water vapor as the relative humidity of the ambient air rises or drops. The dielectric properties of the polymer film depend on the amount of water contained in it: as the relative humidity changes, the dielectric properties of the film change, and so the capacitance of the sensor changes. The electronics of the instrument measure the capacitance of the sensor and convert it into a humidity reading.

History of the Vaisala HUMICAP®

In 1973 Vaisala presented a completely new way of measuring humidity. Vaisala HUMICAP® Sensor, the world's first thin-film capacitive humidity sensor was brought into markets. Due to the success of the Vaisala HUMICAP® Sensor and products, Vaisala has reached the position as world's market leader in relative humidity measurement instruments. Throughout its 30-years history, the Vaisala HUMICAP® technology has been under continuous development in order to ensure all time high-tech sensors and instruments. The latest member of Vaisala HUMICAP® product family is the Vaisala HUMICAP® Humidity and Temperature Transmitter Series HMT330.

The Vaisala Humidity Transmitter HMT330

The HMT337 has been developed for demanding meteorological measurement in very humid or chemically harsh conditions. It comes with a non-warmed probe for conditions of moderate humidity and with an unique warmed probe to maintain measurement reliability in extreme conditions of humidity. As the probe head is warmed, the humidity level inside the head stays below the ambient level. Ambient dewpoint can be calculated precisely, due to accurate temperature measurement. The HMT330 MIK (Meteorological Installation Kit) is available for the installation of the HMT337 outdoors.

Vaisala HUMICAP® Humidity and Temperature Probes HMP45A/D

Vaisala HUMICAP® Humidity and Temperature Probes HMP45A/D provide a conventional way to measure relative humidity and temperature in meteorological applications. They can be used together with radiation shield DTR503A and incorporate the Vaisala HUMICAP® Sensor providing excellent accuracy and good long-term stability being also resistant to dust and most chemicals. The Vaisala HUMICAP® Humidity and Temperature Probes HMP45A/D provide measurements up to 100 % RH with high accuracy. They are easily calibrated in the field, and are also NIST traceable (certificate included).

For further information contact metinstruments@vaisala.com