Xylem H-3521 - Manual (Page 19)

H-3521
Installation 2-9
2.11 Testing
Before installing the H-3521 in your field location, you may wish to first test the sensor and data
logger in your shop or lab. This allows you to become familiar with H-3521 and the data logger
in a controlled environment. The H-3521 can be tested with a pressure standard or water filled
standpipe. However, for this test to work correctly, the standpipe must be connected to the
chassis ground of the data recorder. The wire establishes a ground connection between the water
and the data logger. Water and other conductive objects isolated by a plastic bucket or table
surface pick up AC noise from nearby lighting and power lines. The AC noise is coupled by the
water to the stainless diaphragm in the pressure sensor. If a plastic or non-conductive tube is
used to connect to the pressure source to the H-3521, the sensor will be electrically isolated from
the water media. The AC noise may affect the pressure measurement due to large voltages
between the water media and the sensor (data logger) ground. This precaution is not necessary
for field installations because surface water and ground water are not isolated from earth ground.