The amount of water vapor in the air at any given time is usually less than that required to saturate the air. The relative humidity is the percent of saturation humidity, generally calculated in relation to saturated vapor density. Relative humidity is the ratio of the current absolute humidity to the highest possible absolute humidity (which depends on the current air temperature). A reading of 100 percent relative humidity means that the air is totally saturated with water vapor and cannot hold any more, creating the possibility of rain. This doesn't mean that the relative humidity must be 100 percent in order for it to rain -- it must be 100 percent where the clouds are forming, but the relative humidity near the ground could be much less.
High Precision Field Mount Humidity and Temperature Transmitter Type 86 for EX Applications by Hygrocontrol
The 86 EX is an Excellent, Flexible and Simple Analyzer for Measuring Humidity and Temperature providing an IS supply for the probes.
Model No. Hygrocontrol 86EX
 
Hygrocontrol Type 83 by Hygrocontrol
Closed loop relative humidity and temperature meter (hygrometer) for industrial use. The drawn current (4-20mA) responds to measured humidity 0-100% RH.
 
Hygrocontrol Type 81,82 by Hygrocontrol
High-precision relative humidity and temperature meter (hygrometer) for industrial use. The following humidity units can be calculated, displayed and issued. Dew point [°C, °F], absolute humidity [g/scm], specific humidity [g/kg] and enthalpy [kJ/kg]. The temperature can be displayed as °C or °F.
 
Hygrocontrol Type 85 by Hygrocontrol
Relative humidity and temperature meter (hygrometer) for industrial use. The drawn current (4-20mA) responds to measured humidity 0-100% RH.
Model No. Hygrocontrol 86EX