Bigger physical objects which might be buried within the topsoil could be
unveiled through a modification in the electrical resistance of the soil layer
at various depths. The design is about a device which may be for implementing
relative enhancements on the resistance of the soil. This particular
application can be particularly handy in archaeological excavations.
deep soil metal detector instrument includes the measuring bridge (figure 1),
the alternating voltage generator (fig 2) and the a couple of probes, sunken
inside the soil.
The resistances across the soil layers, between
the electrodes of probes are coupled to the input of the bridge arms, for
measuring the parameters.
Prior to measurement through 100 ohm resistor may be
adjusted for bridging the balance so that the dial instrument readings are
initially at the minimal.
The design of the probe represented in FIG.3
may e understood as follows:
Each of the probes signifies the insulated
rods having a diameter of around 1.5 mm. on the surface area of the bar along its
axle, these are fixed electrodes in the form of six thin-walled tube, separated
from each other.
Each electrode probe with the aid of six cable
connection is attached to the switch S1 measuring bridge, that in turn hooks up with one of
the six pairs of electrodes together with the bridge.
In this instance, each pair of
electrodes at each of the positions of the switch S1 corresponds to
the precise depth of the soil layer.
Soon after placing the probe on earth,
in accordance with FIG. 4, the electrical resistance of the subsequent layers of
soil located different depth is detected.
Evaluating the values acquired from the resistance, you are able to draw a conclusion at what depth
(which soil layer) are objects that might be changing the resistance of the
The space between the probes are pretty much decided on in each
specific scenario. Occasionally, great outcomes could be obtained with distance
that me approximately close to 2.4 m.
The variable resistor of the
bridge is 500 ohms as shown in the deep soil metal detector circuit diagram, is for controlling the sensitivity of the bridge depending on
soil type being investigated.
Courtesy: The Radio-Constructor, 1966, 8