The illustration, Fig. 10, represents the automatic re-regulator - C.E.L. Brown's patent. Motion is imparted to the cores of two electro-magnets at the ends by the pulleys, W W. The cores have a projection opposite to the spindle, a b, which latter is screw-threaded. By a relay one or other electro-magnet is put in action, and the rotating core, which is magnetized, causes rotation of the spindle by attraction, resulting in the movement of the contact along the resistance stops. The relay is acted upon directly by the potential of the dynamo, and the variable resistance is included in the shunt field of the machine, so that changes in the potential, resulting from changes in load or speed, are compensated for.
The arrangements of the lamp circuits and the lamp itself may now be described. The lamps are all run in parallel circuit, but are divided into groups of five, each group being controlled by a separate switch on the board - Figs. 11 and 11a. These switches are not in direct communication with the dynamo, but make that connection through a large central switch, S, which therefore carries the whole current. The returns from each group are brought to the connections seen between the two resistances, where the circuits may be disconnected if desired, and the main current then passes through the ammeter, A, to the other terminal of the machine. One of the smaller switches at the top, Fig. 11a, is directly connected with one terminal of the 20 horse power dynamo before mentioned, and the other side of the switch to the motor in the machine tool exhibit. Also one of the switches in connection with the central switch, S, is connected to the same motor, and therefore the latter may be run by either machine, or, in fact, any combination of machines, lamps, and motor be made as required.Fig. 11a
The form of switch made by the Oerlikon Works is illustrated in Fig. 7. Two thick semicircular bands of copper are screwed at one end to opposite sides of a square block which is turned round by the switch handle. The block has a projection at each corner, and two strong, flat, stationary springs are attached to the framework of the switch and press on opposite sides of the block. The ends of the springs engage in the projections and prevent the switch being turned round the wrong way, while the pressure of the springs on opposite sides forces the copper bands to take up a position exactly in line with the terminal contacts when the switch is closed, or at right angles to them when it is opened.Fig. 4A
Further, each lamp has its own separate adjustable resistance, fuse, and switch. These are of special construction, combined in one, and are illustrated in Figs. 4 and 4a; the other figures, 4b and 4c, showing some of the details of the same. The wires, W W, lead from and to one lamp. The current enters at one wire, passes through the fuse, f - Figs. 4c and 4a - down the center of the cylinder to a divided contact, into which a switch arm can be shot. When this is so, a connection is made to the upright brass rod, T, which serves to grip the band, R, passing round the body of the cylinder. The current then passes through all the turns of wire above the band, and out at the other terminal. The resistance can be varied by raising or lowering the band. Fig. 4b shows the manner of tightening the band against the wires on the cylinder. The upright rod, T, is seen in section, and is fixed in one position to the frame of the apparatus. Abutting against this, and working in the block to which the two ends of the band are screwed, is a thumb screw, S, by turning which the band may be loosened for adjusting, and tightened when the right position is found. The cylinder is covered with asbestos sheet, and the wire, which is of nickel, and measures altogether from 3 to 4 ohms, is wound helically round this. The switch arm, to which the handle is attached below, does not itself make and break the circuit, but carries a spring, as shown, which, when the arm is at the end of its movement, pulls over the contact lever with a rapid action, shooting the same between the divided contact piece, and making a perfect contact.
The switchboard forms one side of a closed wooden case or cupboard, with sufficient room for a man to enter and adjust the resistances or switches for each lamp. These are screwed to the inside of the case in rows, to the number of twenty-five. The greatest care has been taken in the fixing of the connections to the inside of this case, and no leading wires of different potential are allowed to cross each other.Figs. 4, 4B and 4C
The Oerlikon lamp, which is designed to work with constant potential, is shown partly in section in Fig. 8. There is only one solenoid, A, through which all the current passes, and whose action is to strike the arc and maintain the current constant. The soft iron core, C, is suspended from the inside of the tube, T, in which it has an up and down movement checked by an air piston in the tube. An end elevation of the brake wheels and solenoid is given in Fig. 9, where it will be seen that the spindle carrying these wheels also carries between them a pinion engaging with the rack rod, R. The top carbon attached to the rack rod falls by its own weight, and is therefore in contact with the lower carbon before the lamp is switched in circuit. When this is done the core is instantly magnetized, and attracted to the soft iron brake wheels, which it holds firmly. The air cushion in the tube prevents the core being drawn up until it has fairly gripped the sides of the wheels. The subsequent raising of the core therefore turns the wheels, raises the rack rod, and strikes the arc. The feed is operated by the weakening of the magnetic field of the coil, which causes the core to lose its grip of the wheels, and allows the top carbon to descend.