The HT200 humidity sensor from SST measures relative humidity in the range of 0% to 100% and outputs its signal via a 4- 20 mA current loop. It will withstand condensing conditions and will fully recover after immersion in water, with no loss of accuracy. In addition, all electronics are protected in a watertight enclosure, making it ideal for damp or wet environments. A 20 micron porous metal filter protects the sensing element from dust, dirt and airborne particles. This filter is easily replaced in the field while the sensor is operating. A secondary logic output indicates when it is time to change the filter. This output can be connected to a PLC or other equipment to inform maintenance personnel. Not only is the filter replaceable, but so is the probe assembly. This allows the sensor to be periodically re-calibrated by simply changing the sensing element. The HT200 performs extremely well when subjected to a variety of chemical vapours including ammonia, making it the ideal choice for use in agricultural applications.