Basic Systems. There were three basic sonic systems:

1. Systems where the maximum rate-of-change of sound level was limited: A 1, A 2, A 3, A 104.

2. Systems were both maximum and minimum rate of change of sound level were imit-ed: A 4, A 105.

3. System were both maximum and minimum rate of change of sound level were limited and determined from a reference point equal to the average background sound level: A 7, A 107.

System 1. In the first system, when the initiating level was reached, the rate of sound level increase did not exceed that shown in figures 173a, b, c; the unit fired 1 1/2 seconds after the sound reached the firing level in figure 173a and when the firing level was reached in figure 173b. If the rate exceeded that shown, the unit would be rendered passive for a period dependet upon the anti-counter-mining circuit.

System 2. In the seond system, after the initiating level was reached, the rate of sound level increase had to be between the two points indicated in figure 173c, if the mine was fire when the firing level was reached. Otherwise, the unit would be rendered passive for a period depending on the anti-counter-mining circuit.

System 3. In the third system the circuit was capable of determining average sound background level. This level was used as a reference point, and operation from this point was the same as in system 2.

Figure 173a – System 1 – Initiating Level

Figure 173b – System 1 – Initiating Level

Figure 173c – System 2 – Initiating Level