The chilled mirror hygrometer is a primary dew point measurement device which utilizes a set of photo optics observing a reflective mirrored surface which is heated and cooled with a thermal electric cooler. Upon cooling of the mirror, dew or frost will form scattering the light beam thus resulting in a change of light intensity. A precision temperature sensor embedded in the mirror tracks the exact dew or frost point temperature.

Polymer relative humidity sensors vary in the capacity between two electrically conductive layers, separated by an isolating layer of specially selected polymer. Changes in water vapor pressure of the surrounding gases result in variations in the electrical output of the sensor due to the interaction of water molecules with the sensor’s polymer layer.

The moisture concentration of a gas is measured as it passes across platinum electrodes coated with phosphorus pentoxide. The phosphorus pentoxide absorbs water molecules from the gas. Voltage is applied to the electrodes decomposing the water molecules into hydrogen and oxygen. Using Faraday’s Law, the measured current is used to calculate the number of water molecules electrolyzed.