Xylem WL550 OIL WATER INTERFACE METERS - Manual (Page 4)

Global Water
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II. Principle of Operation
The instrument detects the presence of water with the two stainless steel pins and
electronic circuit that measures current flowing through water which is not distilled.
The instrument detects oil with the prism assembly. An infrared light beam is emitted
from the sensor. This beam strikes the prism at a 45 degree angle and is refracted
internally as a result of Snell’s Principle. If the prism is immersed in a liquid with an
optical index similar to that of the prism, the light beam will not be refracted internally
and will escape from the prism assembly. A missing pulse detector indicates the
prism is in a liquid. A microprocessor, determines that if the prism assembly is in a
conductive fluid it must be water.
III. Battery Installation & First-Time Use
Only change the battery in a safe area. Make certain to follow the polarity for the
correct placement of the battery in the drawer. Although quite difficult, it is possible to
put some batteries in backwards, so if you have any difficulty placing the battery in
the holder, VERIFY the polarity. The battery drawer cannot be inserted backwards.