Figure 4. — Velocity control structure at upstream end of main exi)erimuut;il canal. 



The electrodes were wired to make a total of 

 five groups (fig. 7) ; when energized, each grouiD 

 produced an electrical field. The applied voltage 

 to all of the electrodes was the same; hence, the 

 voltage gradient created by the eleci^rode arrange- 

 ment and wiring pattern was higher on the down- 

 stream side than on the upstream side of the array. 

 Figure 8 is an analog gradient plot of an electrical 

 field created by one pulse at one specific location 

 on the left side of the electrode array. The plotting 

 interval is 10 percent of the applied voltage. Only 

 one pulse of the five-pulse cycle is illustrated, but 

 it is representative of the electrical fields produced 

 with each pulse, because the wiring pattern was 

 uniform with respect to electrode spacing. 



Tlie electrodes were energized with d.c, square- 

 wave pulses, supplied by interrupting the output 

 of a d.c. generator with sequential switching equip- 

 ment ( Volz, 1962) . Figure 9 shows a block diagram 

 of this equipment. The pulse amplitude was 125 



volts, the duration 20 milliseconds, and the fre- 

 quency 15 pulses per second. Because the electrodes 

 were wired in five groups and the groups pulsed 

 sequentially, each group was actually energized 

 only three times per second (total pulse frequency 

 divided by number of electrode groups). These 

 electrical conditions had been tested in previous 

 guiding experiments and had proved to be non- 

 injurious to fish (Pugh, 1962). 



Table 1 shows the pulsing sequence of the elec- 

 trode array. When the first pulse was delivered, the 

 electrodes connected to pulse supply cable 1 became 

 positively energized and all the electrodes in the 

 downstream row (pulse supply cable 6) became 

 negati^•ely energized. On the second pulse, the elec- 

 trodes connected to pulse supply cable 2 became 

 positively energized and the electrodes in the down- 

 stream row became negatively energized. This suc- 

 cession of pulses continued through pulse supply 

 cables 3, 4, and 5. "WTien the fifth pulse had been 



FISH-GUIDING EFFICIENCY OF AN ELECTRICAL GUIDING SYSTEM 



311 



