Specifications

CIRCUIT IDEAS
S.C. DWIVEDI
WATER-TANK LEVEL METER
CIRCUIT IDEAS
M.K. CHANDRA MOULEESWARAN
T
he water-tank level meter de-
scribed here is very simple and
useful for monitoring the water
level in an overhead tank (OHT). The wa-
ter level at 30cm intervals is monitored
and continuously indicated by LEDs ar-
ranged in a meter-format. When all the
LEDs are ‘off’, it indicates that the OHT is
empty. When the water level reaches the
top limit, the whole LED-meter begins to
flash.
The height at which the level-sensing
electrodes are fitted is adjustable. Thus,
the minimum and maximum level settings
may be varied as desired. The range of the
meter can also
be enlarged to
cater to any
level.
No special
or critical com-
ponents are
used. CMOS
ICs are used to
limit the idle
current to a
minimum level.
Even when
all the LEDs
are ‘on’, i.e. wa-
ter reaches the
top level, the
demand on the
power supply is
reasonably low.
Further, the ex-
tremely high in-
put resistance
of the Schmitt
inverter gates
reduces the in-
put current and
thus minimises
the erosion of
electrodes.
The princi-
pal part of the
device is its wa-
ter-level sensor
assembly. By
using easily
available material, it can be fabricated to
meet one’s own specific requirements.
The common ground reference elec-
trode ‘X’ is an aluminium conduit of 15mm
outer diameter and 3-metre length, to ca-
ter to a 3-metre deep overhead tank. Insu-
lating spacer rings ‘Y’ (10mm length,
15mm dia.) are fabricated from electrical
wiring conduits of 15mm inner diameter.
These are pushed tightly over the alumi-
num conduit at preferred places, say 30cm
apart. If the pieces are too tight, they can
be heated in boiling water for softening
and then pushed over ‘X’.
The sensor electrodes ‘Z’ are made out
of copper or brass strips (6mm wide and
1mm thick) which are shaped into rings
that can tightly slip over the ‘Y’ pieces.
The ends of these strips are folded firmly
and formed into solder tags S1 to S10 and
SG. The wall-mounting brackets, made of
aluminium die-cast, are screwed directly
on ‘X’ at two suitable places. The sensor
cable ‘WC’ wires are soldered to solder
tags, and some epoxy cement is applied
around the joints and tags to avoid corro-
sion by water. The common ground refer-
ence wire ‘SG’ is taken from tag ‘T’. The
cable’s individual wires from S1 to S10
and SG are cut and matched in length for
a neat layout. The other ends of the cable
are connected to the PCB terminal points
S1 to S10 and SG respectively. No sepa-
rate ground is needed.
The electronics portion is simple and
straightforward. A long piece of veroboard
can hold all the parts including the power
supply section. For easy installation, the
LEDs can be set at the track side of the
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