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

6 BIOLOGICAL REPORT 11
Lne A
8.6
ohms
23 23 34 VA
ohms ohms ohms
AA ?3
OA I+
`2
1A
.
Power 3 .
Source V g V s 24.6
? o>?a
(voltage)
v
16 v
ohms B
\ 16
1 i ehms
8.1A
Line B
Fig. 5. Progression of a circuit analysis for an
electrofishing system having three electrodes on line
A and,one electrode on line B: (a) Complete electrical
circuit with resistance values shown for each
electrode. (b) Circuit with the three electrodes on line
A replaced by a single equivalent resistance
(8.6 ohms). (c) Single value of resistance (24.6 ohms)
calculated for the electrofishing system.
and
VB = (8)
01e,N/ Rr) x Vs = (16/ 24.6) x V. = 0.65 Vs.
Therefore, the three electrodes connected to line
A will each receive 35% of the applied voltage
(paralleled electrodes always have the same ap-
plied voltage even if their resistance values are
different), while the single electrode on line B will
dissipate 65%. Note that the sum of the two elec-
trode voltages must always equal the applied volt-
age. That is,
VS = VA + VB. (9)
To continue this analysis, assume that the
power supply is adjusted to an applied voltage of
200 volts. The electrode voltages VA and VB are
calculated by equations 7 and 8 to be 70 and
130 volts, respectively. All of the voltages and re-
sistances for the four-electrode system are now
determined, and Ohm's Law (I = V / R) can be
applied to calculate the current conducted by each
electrode (Fig. 5) or the total current conducted by
the system (200 volts / 24.6 ohms = 8.1 amps).
Power Analysis
The circuit analysis is completed by calculating
the electrical power dissipated in the electric fields
surrounding each of the four electrodes. Three
expressions for power are available, and the most
convenient can be chosen:
Power = VI = V2/R = 12R watts. (10)
For this example, the wattages are 210 W
(3.0 amps x 70 volts) dissipated around each of the
1.27-cm cylinders, 147 W (2.1 amps x 70 volts) for
the 2.54-cm electrode, and 1,053 W (8.1 amps x
130 volts) for the single 5.08-cm electrode. The
total power delivered into the water is 1,620 W.
These wattage values are valid only for water
conductivity of 500 pS/cm.
Comments on Power Supply
Instrumentation
Electrofishing equipment is usually instru-
mented to measure some combination of voltage,
current, and power at the generator or equipment
control panel. For the preceding example, the volt-
meter, ammeter, and wattmeter at the generator
would read 200 volts, 8.1 amps, and 1,620 watts.
However, the individual electrode voltages, cur-
rents, or power (as calculated in the example) could
not be determined with this metering without
knowing the resistance values for the electrodes.
It is unsettling to realize that the metering on
eectrofishing equipment is basically a monitor of
the power supply, and that this metering does not
provide comparative information regarding the
electric fields generated in the water. The on-board
metering serves as a placebo for the equipment
operators. Equipment operators should never ex-
pect two eectrofishing units that are connected to
dissimilar electrode arrays to function alike just
because the voltage, current, or power meters read
the same. Consistent operational procedures and
equipment standardization can only be developed
based on comparative in-water measurements
with known electrode configurations.
Voltage Measurements in a
Volume of Water
The engineering approach to electrical field the-
ory involves complex equations and electrical pa-
rameters that are often difficult for the fishery
biologist to apply. Most field practitioners would
prefer to forego these mathematical complexities;
they simply desire comparative information for an
educated selection of an electrode system. For elec-
trofishing applications, it is fortunate that any