Íslenskar landbúnaðarrannsóknir - 01.09.1978, Qupperneq 60

58 ÍSLENZKAR LANDBÚNAÐARRANNSÓKNIR
Fig. 1. Sensor mat made offive steel cables, held apart and supported by tubings. Photojón Kristjánsson.
nected that an increase in conductivity of
the lowest electrode adds to the upper
main electrode, and vice versa. The effect
of wave motion is very strong and the
auxiliary electrodes are operated at lower
potential than the main electrodes.
In Fig. 3 the equipotential lines around
the electrodes, measured in a model, are
shown with 1-volt potential on the main
electrodes and 0.5-volt potential on the
auxiliary electrodes, all with reference to
the center electrode spacing. Although the
lines between the main electrodes and the
center electrode run almost parallel, the
field is rather weak at the top so less sen-
sitivity is to be expected here.
Figure 4 displays results of model
measurements showing sensitivity as a
function ofdepth for a fish of ,,full spacing
size“ and the other for a fish of ,,half
spacing size.“ This diagram indicates that
the amplitude of the signal is inversely
related to the distance of the fish from the
electrodes and proprtionally to the size of
the fish.
Electronic unit.
The electronic unit is depicted in some
detail in the block diagram (Fig. 2). The
mats are energized by an oscillator and
driver circuit. The mat circuitry is ad-
justed for optimum compensation and
balance leading to approximately no in-