7792 - Laserfiche WebLink

Home Browse Search

12 BIoLoGICAL REPORT 11 simply moved horizontally along the beam while recording the voltmeter and distance readings. The voltage profiles for the cylinders were measured at a separation of 2.7 m. This distance was increased to 4 in for the spheres, loops, Wis- consin arrays, and vertical plates. The effect of close electrode spacing is to possibly cause the middle portion of the S-curve to display an exag- gerated slope because mutual coupling may exist between the two electric fields. The middle of the S-curve should display a minimal slope when the two electrodes are not interacting. In retrospect, it would have been better to measure all of the electrodes with a separation of 4 in, but this incon- sistency is not judged detrimental in the following experimental results. Presentation of In-water Electrode Measurements Data are presented for 18 electrode configura- tions in a generalized format that can apply to a variety of electrofishing requirements. The follow- ing includes a table listing the empirical resistance values, a table comparing the spatial electric fields generated by each type of electrode, a set of voltage profiles, a graphic summary displaying calcula- tions of voltage gradient and the squared values of voltage gradients, and a discussion regarding the voltage gradient vector. Values of Electrode Resistance The calculated resistance values for the 18 elec- trode configurations are presented in Table 1. Adequate spatial separation was provided be- tween the electrodes to ensure minimal coupling between the electric fields; therefore, the resis- tance values are representative of a single, iso- lated electrode. All values of electrode resistance have been normalized for water having an electri- cal conductivity of 100 pS/cm, but these resis- tances can readily be converted for actual field applications to any value of water conductivity by applying equation 3. The resistances presented in Table 1 and Fig. 3 are directly applicable to any electrofishing system using these particular elec- trode configurations. Boat hulls are often wired as cathodes when electrofishing with direct current or pulsed direct current, and it would have been desirable to pre- sent resistance measurements for various sizes of hulls in this report. However, the dimensions of the indoor test facility precluded this opportunity. Cer- tainly, boat hulls can be measured by the proce- dures already described, but the awkward logistics of having to interwire between two boats (each boat being an electrode) may be avoided by considering the following interactive solution. First, determine the electrical resistance of the anodes by the pro- cedures already described. The metal-to-water in- terface of a boat hull is large in comparison to that of the anodes, so most of the electrode resistance is associated with the anodes. Approximate electri- cal calculations may be performed by assuming that the hull's resistance is one-tenth that of the anode resistance. Based on these initial calcula- tions, the equipment may be operated and the estimated value of the hull resistance corrected by using the actual voltage and current readings dis- played at the control panel. Table 1. Electrical resistance of various electrode configurations.' Electrical resistance Electrode configuration (ohms) Spheres 15.2 cm 89 27.7 cm 55 Cylinders (60-cm length) 0.64 cm 142 1.27 cm 117 2.54 cm 99 5.08 cm 81 Horizontal loops 0.64 X 36 cm 86 1.27X61 cm 46 Wisconsin array (60-cm rods, 30.5-cm ring) four rods at 0.64 cm 57 six rods at 0.64 cm 50 four rods at 2.54 cm 46 six rods at 2.54 cm 43 Wisconsin array (60-cm rods, 58-cm ring) four rods at 0.64 cm 45 four rods at 2.54 cm 37 six rods at 2.54 cm 31 Vertical plates (0.32 cm thick x 122 cm wide) 15.2 cm immersion 54 30.5 cm immersion 39 45.7 cm immersion 30 'All electrodes constructed with aluminum materials. bMeasurements are for diameters unless stated otherwise. e Single electrode in 100-pS/cm water.