User manual

Released 03/2008 Rights reserv ed f or change in technical data! HYGROSENS INSTRUMENTS GmbH Postf ach 1054 D-79839 Löf f ingen Tel: [phone] Fax: [phone]
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LEVEL CONTROLLER FOR
CONDUCTING LIQUIDS
5.6 Construction of sensor
The sensor can be constructed in various ways:
 In plastic containers, the electrodes can be fitted in pairs on the container wall.
Each pair always consists of a reference electrode and a sensing electrode, which
are placed at a distance of approx. 5-15 cm from each other. For liquids of high
conductivity, just one electrode at the bottom of the container is also good
enough. The reference electrodes are connected together to the terminal COM.
Due to contamination deposits on the container walls with time, such
constructions are probably not maintenance free. The wall area between the
electrodes should be periodically cleaned.
 Electrodes of stainless steel rods, hanged from top into the medium, are ideally
suited for this purpose. The reference electrode is in the middle of the 4
diagonally arranged sensing electrodes which are placed in a span of approx. 1-5
cm. The spacing should be wide enough so that no drop of liquid sticks back to
the rods when the level falls down. These electrodes are practically maintenance
free.
 Cable probes are very simple to manufacture. For this purpose, multi-core silicon
cable can be stripped at the end and joined to stainless steel balls which act as
weight and also contact surface. The individual weights are lowered in the
container up to the desired switching point and then the cable is tied up. For
reference electrode, a bare stainless steel rope with weight can be used, which
goes up to the bottom of the container. Cable sensing elements are also very
reliable and practically maintenance free.
 For applications in condensate tubs and for low liquid levels, the sensing system
can be constructed as a PCB which is mounted on the tank wall. Such sensing
elements should also be periodically cleaned if the medium is polluted.