SVK Test Model 3

Unit Construction. This model was similar to the second, except that it employed only the A cell. The current from the A cell was amplified and fed to the I relay over a con-denser (in series) so that when slow changes in light intensity occurred the current flow-ing to the relay was too weak to operate it. On the other hand, when rapid changes oc-currend the relay was operated. Thus the unit depended not only on the change in light intensity, but also on the ratio of light intensity change per time unit. This change was occasioned by the fact that, since the light intensity variations caused by sea motion could not be prevented, it appeared fuitle to attempt to suppress the effects of all other variations in light by means of complicated differential circuits.

Test Results. Trials of the third model revealed that it would also fire under conditions of heavy seas and sunshine due to the cylindrical lens effect of wave crests. However, it was contemplated that this difficulty could be overcome by using an acoustic unit to trigger the opticla one. In the course of further trials with this unit, it was found that the depth effect of the optical unit had much less significance than the translucence of the water and the water depth, since the translucence of a layer of water is a logarithmic function of its thickness.