Sensor Termination Enclosure (P/N 202-034-05) - DESCRIPTION
For submersible pressure / level transmitters, It is important to ensure the cable and vent tube is not subject to condensation. In the daytime on a hot, humid day, the air has a high water vapor content. The submerged sensor is likely to be at a much lower temperature. At some point down the cable, both in the vent tube and the cable structure, the moist air will reach its dew point and condense. In most cases small amounts of moisture will cause no damage to a GE Sensing sensor. Water in the vent tube will not cause failure in a GE Sensing sensor but will inevitably cause a small zero offset. GE Sensing sensors have three barriers to water in the cable but a long period of exposure to quantities of water will eventually affect the sensors operation.
In order to avoid all such moisture effects the air around the electrical termination should be kept dry to a dew point below the temperature of the sensor. In many sites the heat from other devices will maintain this condition. If this is not possible then 2 methods are recommend:
The use of a termination box that contains a drying agent and is vented through a filter is recommended. A visual indicator is useful to warn when the desiccant is no longer active. Most desiccant modules can be heated either in an oven, or if made from plastic in a microwave, to drive collected moisture from them on a regular basis. The frequency of the drying period will depend upon the humidity and temperature variation encountered. Reducing the variations in temperature that the termination box is exposed to will extend the life of the desiccant modules so avoiding sites in direct sunlight is recommended.
The Use of a Barometric Sensor (in place of an STE Box)
As an alternate to the use of a desiccant box lie the STE box, an absolute pressure/level submersible sensor along with a barometer is can be used. By subtracting the barometric pressure from the submersible pressure sensor’s absolute pressure, the equivalent gauge pressure is calculated. This achieves the same result as using a desiccant box (STE) along with a vented gauge pressure submersible sensor. A common barometer used for this purpose is either the In-Situ - Level BaroTROLL - Precision Pressure Barometer or a Druck UNIK5000 Series Pressure Sensor ranged for barometric pressure.