7792

• UCREFRP Catalog Number: 7792
• Author: Kolz, A. L.
• Title: In-water Electrical Measurements for Evaluating Electrofishing Systems.
• USFW Year: 1993.
• USFW - Doc Type: \
• Copyright Material: NO

IN -WATER ELECTRICAL MEASUREMENTS 19
Fig. 21. Profiles of voltage gradient (E)
and the squared value of voltage gra-
dient (E) for Wisconsin arrays with
four and six rods suspended from a
30.5-cm supporting ring.
101
14
q
d
goo 10'
d
m
10°
b
910-1
5
410-2
10-3
0
10-4
Wisconsin array with 30.5-cm ring
E -six rods, 2.54 an
?'??_ E - four rods, 0.64 om
??? E1-six rode, 2.64 cm
E1- four rods, 0.64 cm
0 50 100
150 200
Distance (centimeters)
Fig. 22. Profiles of voltage gradient (E)
and the squared value of voltage gra-
dient (E) for Wisconsin arrays with
four and six rods suspended from a
58-cm supporting ring.
Wisconsin array with 58-cm ring
E -six rods, 2.54 cm
E - four rode, 0.64 cm
E1-sixrods, 2.54 cm
E2 - four rods, 0.64 cm
50 100 150 200
Distance (centimeters)
several radial transects in a common horizontal
plane. Figure 24 illustrates an example for esti-
mating the vertical components of voltage gradient
for a 27.7-cm sphere with profiles recorded at
depths of 2, 5, 10, 20, 40, and 80 cm. Note how the
three profiles plotted at depths of 2, 5, and 10 cm
generate a common profile, and this uniformity
indicates that there is no vertical gradient in this
region of the electrical field. However, the graph
shows an initial difference of about 35 volts be-
tween the profiles taken at depths 40 and 80 cm.
101
a?
101
t
to
10°
b
9
910-1

q
410-2
a
10-3
0
10-4
If it is assumed that this voltage is linearly applied
over the 40 cm separating the two profiles (it is
actually nonlinear), then the component of vertical
gradient would be estimated at 35 V/40 cm =
0.88 V/cm. This magnitude of voltage gradient can
be significant when electrofishing (Kolz and
Reynolds 1989).
The voltage gradient probe (method 2) is well
suited to measuring the horizontal components of
voltage gradient. However, the probe illustrated
in Fig. 11 cannot measure the components of ver-