Sensor Termination Enclosure (P/N: 202-034-05) - DESCRIPTION

Sensor Termination Enclosure (P/N:  202-034-05) - DESCRIPTION
by Druck

It is important to ensure that the cable and vent tube are not subject to condensation in submersible pressure / level transmitters. In the daytime on a hot, humid day, the air has a high water vapor content, hence, the submerged sensor is likely to be at a much lower temperature than normal. 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 not cause damage to a Druck Sensing sensor.  Water in the vent tube will not cause failure in a Druck Sensing sensor, but will inevitably cause a small zero offset.  Druck 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 recommended.

Desiccant Box:
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   A visual indicator is useful to warn when the desiccant is no longer active.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 out on a regular basis.  The frequency of the drying period will depend upon the humidity and temperature variations encountered.  Reducing the variations in temperature to which the termination box is exposed will extend the life of the desiccant modules. Avoiding sites in direct sunlight is highly recommended. 

Barometric Sensor (in place of an STE Box):
As an alternative to using a desiccant box, like the STE box, an absolute pressure/level submersible sensor, along with a barometer, 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.