- Operating
principle
Electrode controls used for the automatic control of pumps or
electromagnetic valves as well as overflow or run-dry protection
in wells or tanks with conductive liquids. The liquid levels are
monitored by electrodes which give switching commands to the electronic
relay if they come into contact with the liquid. For a two-point
control system, you require two control electrodes and one earth
electrode will suffice. You can also us a metallic, conductive tank
wall as an earth connection in place of the earth electrode.
However,
we recommend the use of a separate earth electrode in all cases.
- Recommendations
for the design of the electrode
a)
Highly conductive liquids: if there is sufficent space, we
advice you to use several single electrodes at a spacing
of approx. 100 mm instead of a multiple electrode.
b) Poorly conductive liquids: if electrodes are used
in poorly conductive liquids, the electrode rods should be mounted
as close as possible to one another. For these applications, we
recommend the use of a multiple electrode in place of several
single electrodes.
c) All liquids: wherever possible, we recommend the use of
an electrode with plastic threaded nipple, as the plastic
acts as an insulator and therefore increases the insulation distance
between the electrode rod and the conductive tank. If you use an
electrode with
metallic threaded nipple, this electrode will take same tank potential
(= earth electrode E0). The insulation distance between electrode
rod(s) and tank will then be limited to the insulators used in the
electrode.
- Recommendations
for special cases - the uses of electrode controls in electrolysis
baths:
When installing electrodes in electrolysis baths, it is always
necessary to mount the electrodes across the voltage path.
They must not be mounted along the voltage path.
It
should be noted that in the case of movable poles (the object to
be galvanised itself constitutes a pole) the voltage path can change
and therefore cause false alarms.
- Electrode
controls can or should not be used:
a) in non-conductive liquids /e.g. in mineral oils);
b) in liquids with a tendency to foam (e.g. possibly beer, washing
sodas etc.);
c) in liquids with a high level of steam generation and condensate
(e.g. at higher
temperatures);
d) in liquids with a tendency to form deposits (e.g. in limonestone
milk, oily waste etc.)
- Electrical
connection
For the connection of electrode to electrode relay, we recommend
the use of standard installation cables (e.g. NYM 2 x 1.5 mm²
or 3 x 1.5 mm²). Telephone cables or heavily twisted bell wires
should not be used.
- Emptying
and filling of a tank via an electrode control
Before you connect up the electrode relay, you must check whether
the mains voltage to be connected with the mains terminals is the
same as that specified on the rating plate. The built-in transformer
steps down the mains voltage to a safe low voltage and forwards
it to electronics of the relay via the connected electrodes. As
soon as the upper electrode E1 comes into contact with the liquid,
the energising current flows through the liquid between E1 and E0,
and the relay type ES 5/G or drops off with the electrode relay
types NR 5,
NR 3 or NR 5/G. At the same time, the electrode current between
the electrode mounted at the bottom (E2) and the earth electrode
(E0) ensures that the switching status is retained until the falling
liquid level releases the electrode E2.
The relay is therefore switched on by E1 at the maximum liquid level
and switched off by E2 at the minimum level. The potential-free
output contact is suitable for controlling pumps etc. It is designed
for max. AC 4 V. The maximum voltage must not exceed AC 250 V and
the permanent load of the contacts must not exceed 500 VA (ohmic
load).
For
the "pumping empty" function, in which the pump pumps
a full tank empty, the contactor for the pump motor should be connected
in accordance with the diagrams "pumping empty".
In these cases, control is effected by the normally open contact
of the electrode relay ES 5/G or by the normally closed contact
of the types NR 5, NR 3 or
NR 5/G. The pump is switched on when the tank is full and switched
off when the tank is empty.
For the "pumping full" function, in which
the pump pumps a empty tank full, the contactor for the pump motor
should be connected in accordance with the diagrams "pumping
full ". In these cases, control is effected by the normally
closed contact of the electrode relay ES 5/G or by the normally
open contact of the types NR 5, NR 3 or
NR 5/G. The pump is switched
on when the tank is at the minimum liquid level and the electrode
are not in contact with the liquid and switched off when the top
electrode comes into contact with the liquid and causes the relay
to attract in the type ES 5/G or the drop off with the types NR
5, NR 3 or NR 5/G.
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