DESCRIPTION: The electrical time fuze has been worked on in Germany for about 15 years and has been in standard service in bombs with the armed services for some time. All electrical time and influence fuzes have fundamentally the same firing circuit, and this has been standarzied. (See fig. 597B.) The triggering voltage may then come from either the outpost of the influence device or from the charging of a condensor network in the case of the electrical time fuze. Electrical firing is also used in some contact fuzes. This section will deal only with the electrical time fuze for projectiles.

Before firing, the fuze is hand or machine charged by puttin 300 or 500 volts across the shell and an isulated contact, which puts voltage on the annular storage condenser. This may also be accomplished by allowing the feeler wire, see figure 597A, to contact a muzzle charging ring as the projectile leaves the gun. This muzzle charging ring will be described at the end of this section. In various types of fuzes this condenser varies from 0.2 to 2.0 mfd. It may be charged as long as 30 minutes before firing. At set-back, by means of a switch, this energy is leaked onto the actual firing condenser through a charging resistor (rang 0.25 to 3.0 meg). The usual values for the firing condenser vary from 0.2 to 0.5 mfd. Condensor values are kept fairly high to insure firing of the primer with a minimum pf delay. The sketch shows the position of the set-back switch before and during set-back, also its position during flight. The electrical connections to the set-back switch are the same before and during set-back. On set-back the spring is depres-sed and a 4- to 5-mm ball is allowing to spin out, which, after the set-back forces are over and the projectile is out of the muzzle, allows the switch to come back up 4 or 5 mm further than before, thus making new connections. This set-back switch, RC safe-ty, and a spin operated plug under the squib are the only safety features except for the booster which is separate.

Figure 597A – El.Zt.Z. S/30

Figure 597B – Wiring Diagram

The squib itself has a restistance of 5 to 10 ohms and is of bridge wire construc-tion. It is packaged into a small capsule with explosive around it and sealed up. Formley, they had used squibs with resistance of 1,000-5,000 ohms but the newer type had been much more reliable. The squibs can be fired 100 percent from an 0.35-mfd. condenser charged to 42-50 volts.

Molded plastic blocks hold all the partys securely in individual holes, and are further pot-ted in place with pitch, wax, or putty. The number and size of parts varies only slightly between models so standard molds may be used for all types of electrical fuzes. The out-side metal parts used in influence fuzes also use stan-dard electrical time fuze parts.

Electrical time fuzes usually receive an initial charge of, about 500 volts (on C2) some time before firing and a "vernier" charge from about +120 to -90 volts (on C5), giving a range of about 3-30 seconds. If no vernier charge is applied the time to burst is 16.0 se-conds. This "vernier" charge is either applied before firing with the time interval to the gun very accurately controlled, or by use of a "feeler wire" from the nose contacting a metal charging ring at the muzzle of the gun and picking up the charge as it is fired.

The control tube is of the cold cathode arc discharge type. Various types are used any-where from 2 to 4 elements. In the general types used, one has a 160-volt break-down and the other 19-volt for bomb and shell respectively. Two element tube are used in electrical time fuzes and the 3- and 4-element types are used in the influence types. The 2-element tube is used with 10- to 15-volt control. The initial charge on the storage condensor determines the sensitivity. The correct initial voltage has to be applied so that when this storage condensor voltage is leaked througha resistor onto the firing con-densor a margin of safety is left, say 187 volts for a 190-volt tube. The remaining 3 volts to trigger the fuze then comes from the control device. The control element is sometime centertapped on a 10,000-megohm voltage divider in parallel with the firing condenser and the glow tube. This is done to give the control element the correct initial voltage.

Some of the tubes are externally coated with graphite or a similar material to leak off any stray charges. The glow tubes generally have iron or steel electrodes, nickel plated and then potassium or barium coated. They are argon or krypton filled to a 20- to 30-mm pressure. In manufacture the striking voltage cannot be held close enough by the spac-ing of the elements alone, so the gas pressure is controlled as well (over the above ran-ge), being regulated for each tube when it is made to get the striking voltage exact. When the tubes are finished they are supported to stand 12,000 g.

Figure 597C – Muzzle Charging Ring

MUZZLE CHARGING RING: The muzzle-loading device consists of a cylinder which fits around the barrel of the gun just behind the muzzle and the charging ring which is held out in front of the muzzle by means of three arms located 120° apart. (See fig. 597C.) The cylinder is connected by means of a cable to the battery and voltage-control me-chanism, at the breech end of the gun. Dircet connection is made between the cylinder and the charging ring via the three arms welded to the charging ring.

The hand charging device consists of a truncated cone so designed that is will fit snug on the fuze. The charging point inside the cone that contacts the insulated charging point on the fuze is connected to the switch on the handle. This enables the operator to charge the storage condenser and govern the charging time to the excat second as-sembly.