Advanced Technology for Meteorological %RH and temperature measurement - Robin Farley  

The measurement of humidity is of key importance in the field of meteorology. Weather forecasting, environmental research, pollution control, horticultural research and ice-warning systems are examples of applications that depend on accurate humidity measurement. Electronic %rh sensors are widely used, but there are many users whose understanding of the technology, its application, maintenance and calibration is often unclear. This article summarises the technology employed, and overviews current %rh sensing technology and how the user can make informed decisions about its suitability for purpose.

Sensing Humidity
There are many techniques for the measurement of humidity, and none are perfected. If you judge science and industry’s satisfaction with humidity measurement technology by the number of new research projects and proposed new measurement techniques, it is clear that this area of metrology has some way to go!

The most significant problem with humidity sensing is the need for the measurement device to be in c o n tact with the environment. With parameters such as temperature and pressure, there is the opportunity to protect the actual measurement device with mechanical protection, coatings or membranes to maintain performance over time, but with humidity this is obviously not possible. The sensor is exposed to everything that the environment presents, including chemical pollution and particulate contaminants, and this inevitably affects the long-term stability of every humidity measurement technique to some extent.