Xylem H-3521 - Manual (Page 12)

2-2 Installation
H-3521
2.3 General Installation Recommendations
The H-3521 pressure transducer is not recommended for use in applications where silt and mud
are problematic. In addition, if the sensor is used in a shallow water application and happens to
dry out with mud coating the sensor diaphragm, the diaphragm compliance will be altered and
the factory calibration spoiled.
The H-3521 sensor will be permanently damaged if it is frozen. Transducers which are installed
in geographical areas with harsh winters should be removed for the winter unless they are
installed in a heated shelter or are used with ethylene glycol or other antifreeze media.
2.4 Instrument Shelter
The sensor should be installed in a protected, dry, location such as an instrument shelter. The
installation should provide easy access and facilitate regular inspection and maintenance. Care
should be taken to place it where it will not be jarred or dropped, the H-3521 is a precision
instrument. Normally the H-3521 is mounted with the 4-corner feet on a level surface. Normally
the H-3521 is used to measure the hydrostatic head of a water source. The instrument should be
fastened to a gauge station shelf or fixed such that the elevation cannot accidently change.
Because the surface of the water being measured is exposed to atmospheric pressure, the pressure
sensor must provide correction for changes in barometric air pressure. To provide the best
accuracy possible, the H-3521 uses an atmospheric referenced pressure sensor design. The
internal pressure sensor in the H-3521 has a vent tube connected to the back side its pressure
diaphragm. The vent tube is routed to a sintered bronze filter next to the pressure port. Make
certain the gauge station enclosure is open to the atmosphere. If the sensor is placed in a cabinet
or sealed enclosure, the cabinet must have a screened vent or other opening to the atmosphere.