| C1-2 HOLDS: | AND | C1-1 HOLDS: |
| 0 | 1 | |
| 1 | 0 |
A circuit that will do this is the one shown in [Fig. 7]. In [Fig. 8] is a circuit that will do all the desired things together: give the right information to the C5 relay coils if and only if the C4 relays hold 01.
Fig. 8. Negation circuit.
Let us check this circuit. First, if there is any operation other than 01 stored in the C4 relays, then no current will be able to get through the C4 contacts shown and into the C5 relay coils, and the result is blank. Second, if we have the operation 01 stored in the C4 relays, then the C4-2 contacts will not be energized—a condition which passes current—and the C4-1 contacts will be energized—another condition which passes current—and:
| If the number in C1 is: | then C1-1: | and C1-2: | and the C5 relays energized are: |
| 0 | does not close | does not close | neither |
| 1 | closes | does not close | C5-2, C5-1 |
| 2 | does not close | closes | C5-2 only |
| 3 | closes | closes | C5-1 only |
Thus we have shown that this circuit is correct.
We see that this circuit uses more than one set of contacts for several relays (C1-2, C4-1, C4-2); relays are regularly made with 4, 6, or 12 sets of contacts arranged side by side, all controlled by the same pickup coil. These are called 4-, 6-, or 12-pole relays.
Fig. 9. Addition circuit.