SVK Test Model 1

Unit Construction. This model consisted of a lens made of plexi-glass mounted in the center of the upper cover of a sheet-brass cylinder closed on all sides. Directly under the lens two identically constructed photo-cells were installed. The inner ring surface of the cylinder was coated with silver and ploished to form a mirror. The individual parts were measured and fitted so that the beams of light were directed in the following man-ner:

The leight from area A was projected on cell A by the lens.

The light from area B was projected on cell B by the lens and mirror surfaces.

The output current from the photo-cells A and B at any intensity of 1000 lux (measu-red from the lens) is equalized by the use of auxiliary voltages and resistors, so that nor-mally the differential current is zero. When the light area over one of the cells is darke-ned by the passage of a ship, a differential current is caused, which, after being ampli-fied, operates a neon-tube firing relay.

Unit Batteries. The following dry-cell batteries were necessary for operating the unit:

Two batteries of 80 volts each for the A and B cells

One battery of 120 volts for the neon tube relay

One battery of 120 volts for the amplifier switch

One battery of four volts for heating the amplifier tubes

Difficulties with Units. The first model presented the following difficulties:

1. Battery drain was high; and because of the large number of batteries involved, considerable space was necessary to house them. It was difficult to maintain a constant voltage at the neon tube. This was found to be necessary, since with a small reduction of voltage the differential-current was insufficient to increase the primary potential of the neon relay to a firing level. It was found that a dry-cell battery changes approximately 1/200 volts per cell for each degree of Celsius tem-perature. To obviate the variations of voltage in transferring the unit from air to water, the primary voltage was, in the intial tests, controlled from shore.

2. Since the sensitivity of the photo-cells varied, the differential-current could be ad-justed to zero only at certain intensities. Consequently, at all other intensities a differential current of sufficient strength to fire the mine was created by conditions other than the passage of a ship.

3. The sensitivity of the photo-electric of the photo-elecritc cells proved to be too low under water. The cells used were a standard type made by the Infram Firm, Leipzig, which were more senetivity to the red-yellow band of the spectrum than to the blue-green band, which has a greater intensitity in water. Since part of the light received by the B cell was transmitted by reflection, an unavoidable loss of energy resulted. Area B was too small in comparison to area A, and insufficient im-portance was palces on the fact that the surface brightness of the water, the length of the path through the water, the light absorption of the water, and the surface intensity on the lens surface and on the photo-electric cell surfaces are all functions of the cosine of the angle of entry. Additional difficulties were experien-ced with reflection losses in the air-water areas which increase with greater angles of entry, and with the fact that, when the sun shone directly onto the photo-cells, their outputs became unequal, so that the unit would operate properly only under an overcast sky.

Figure 260 – Optical Mine-Firing Mechansims