A dewpoint instrument or a relative humidity instrument?

“Dewpoint” and “relative humidity” are commonly used water vapor parameters. Each refers to a specific way of quantifying water vapor, and each can be used over a broad range of conditions. Because the range of possible water vapor concentrations is so wide, there is no single measurement instrument that is suitable for measuring water vapor in all possible concentrations. Vaisala has developed several technologies to address this challenge. By convention, Vaisala “dewpoint” instruments are used to measure conditions that are drier than normal atmospheric conditions (RH less than 10% at a temperature of 20°C). Vaisala “relative humidity” instruments are used to measure typical atmospheric conditions and higher levels of water vapor. Both types of instruments are capable of expressing water vapor concentration in a number of different parameters (e.g., relative humidity, dewpoint temperature, parts per million by volume, mixing ratio, etc.). If you are uncertain as to which type of instrument to select, contact Vaisala for guidance.