FIGURE 17: OPERATION OF AN ELECTRODE PROBES SYSTEM
When water level goes below electrode n°1, there is no contact between COM and any other electrodes. The relay understands that the tank is getting empty, and starts the pump. Then the water level increases in the tank, until water touches the electrode n°2. This makes contact between COM and electrode n°2, the relay understands that the tank is full and stops the pump. Electrode 1
Electrode 2
Electrode COM
Output cables to be connected to the relay (1 cable per electrode)
It is possible to face electrode probes because some pump controllers use this type of probe as standard. They are much
more reliable over time than floating sensors. When installing them, make sure to attach them to a support because the
electrodes are suspended from cables, and will be subject to the swirl of water into the tank created during refills. They must
be fixed to a weighted cable or placed in a HDPE tube which is itself fixed to a wall, so they do not start to spin with the
tank water filling.
POTENTIOMETRIC PROBES (OR « 4/20 MA ») Magnetic float sensors This type of sensor is especially used on metal and plastic tanks because
they are screwed onto the tank. It is very rare to see them on concrete
tanks unless you have made a metal plate with screw connections.
A float with magnetic ring inside will slide along a rigid rod (See figure 18 for
illustration). Depending on the position of the float on the rod, the current
that the probe passes will vary between 4 mA (minimum level) and 20 mA
(maximum level). This current is then interpreted by a remote display (see
the displays below). This type of probe is very reliable and can display a
level with 1 cm of precision.
