(a) 



"off 



JLfUUL 



_1 I I I L 



.^LLfl 



"dist- 1 



_l I I I L. 



"dist' 



•< — 



"dist"^ 



Load #1 



JULXJL 



n ,, = 6 

 off 



J I I I L. 



(b) 



J I I I \ I I ] 1 1 I I I'll 



dist 



Set 1 



_] I I I I I I I 1 L. 



Set 2 



I I I 1_1 L. 



n = 6 

 off 



JUL 



J I I I I L. 



_l I I I ■ 



Load #2 



Set 1 



Set 2 



Note: Each division corresponds to the 8 msec basic control cycle. 



Figure 5. — Examples of Freshwater Fish Electro-Motivator (FFEM) pulse patterns: (a) one load, Son = 2, 

 Soff = 3, Ndist = 1 and (b) two loads, Son = 2, Soff = 3, Njist = 2. 



point 9 (anode) to point 10 (cathode) via the 

 water path surrounding the two electrodes. 



For multiple loads having a common anode, 

 the switching arrangement is shown in Figure 

 6b. If we use point 9 as the anode and points 4, 

 5, 6, and 7 as the cathodes, then current will 

 flow in the electrode load whenever any of the 

 switches e, f, g, or h is closed and switch i is 

 closed. Current can only flow when the timing 

 switch is closed. 



For multiple loads, where a given electrode 

 may be used as an anode and at a different time 

 be used as a cathode, such as in the phased 

 array, the switching arrangements Eire shown in 

 Figure 6c. If electrodes are attached to points 7, 

 1, 2, 3, and 8 with points 1 and 4, 2 and 5, and 

 3 and 6 jumpered, then when a single pair of 

 swatches (a-e loading i; b-f loading i), current will 

 flow between a pair of electrodes. For example, 

 if only routing switches b and f are closed, then 

 current will flow between the anode electrode 

 (point 2) and the cathode electrode (point 1 or 

 4) when switch i is closed. Now if routing switch 

 c and g are closed, then current flows between 



the anode electrode, point 3 and the cathode 

 electrode (point 2 or 5) when the switching SCR 

 is closed. In the first case, the electrode at point 

 2 served as the anode, and in the second case, it 

 became a cathode. To achieve the greatest 

 versatility, the arrangement shown in Figure 6c 

 is used, and a subset of the switches are used for 

 the other alternatives. 



In reality SCR are used in place of the 

 switches. An SCR is basically an on-off switch 

 which can be turned on by momentary 

 application of current to the gate which causes 

 current to flow from anode to cathode only. 

 Once turned on, the gate cannot be used to turn 

 off the SCR. Thus, for turning off the SCR in 

 the load distribution and switching logic, a 

 reverse voltage is applied across the anode and 

 cathode of the SCR. To accomplish the turn-off 

 we use a self -commutation circuit. 



The commutation circuit consists of three 

 SCR, a capacitor (C2), and inductor (L2) 

 (Figure 7). The commutation is performed as 

 follows: assume that there is no current flowing 

 in the circuit and that C2 is discharged. Now, if 



