Patent GB-319674-A (GB)
Title: Improvements in or relating to automatic current limiting and regulating devices for use in electrical signalling
IPC: H03G3/22
Filed: 1928-05-22
Abstract: 319,674. Mathieu, G. A. May 22, 1928. Addition to 288,371. Thermionic amplifiers.-In order to increase the range of regulation provided in the regulating apparatus described in, the parent Specification wherein signal intensity reducing means are controlled by a plurality of relays to vary the attenuation, automatic means are provided for controlling the input to the apparatus in a plurality of steps, and the arrangement is such that for each step of input the regulating apparatus gives its own range of control. Fig. 1 (Provisional) shows automatic apparatus for controlling the input supplied by the high frequency amplifying valves VI, V2 to the regulating apparatus (not shown) described in the parent Specification. The first and last relays of the group in that regulator respectively control the circuits 7, 7a and 8, 8a of stepping magnets M2, M1. When one or other of the circuits is closed in response to currents which lie outside the range of the regulating apparatus, the shaft S is stepped in one or other direction by the appropriate ratchet wheel 3 or 4 to move the contact arms 5g, 6g over contact groups 5a - - 5c, 6a - - 6e associated with resistances R1, R2 to vary the input to the valves V1, V2 in such a manner that the output current is again brought within the range of the regulating apparatus and the stepping circuit is opened. Automatic stepping of the shaft during closure of either circuit 7, 7a or 8, 8a is accomplished by interrupter contacts 3b, 4b operated by the ratchet pawls 3a, 4a. The stepping magnet circuits are completed through slip rings 1c, 2c and stepping of the shaft S beyond the limits of movement is prevented by insulating segments 1d, 2d on the slip rings. In order to prevent momentary paralysis of the low frequency amplifying valves supplying the regulator due to incorrect balance in the respective high and low frequency amplifiers at a transition period of increasing regulation by the apparatus shown, a resistance network is switched into circuit between the detector and the low frequency amplifier by a relay connected in parallel with the stepping magnet M2. In the modification shown in Fig. 1 (Comp.) the circuits of the stepping magnets are independent of the relays of the regulator and are respectively controlled by relays B2, B3 which are under the control of a polarized relay B1 fed from the valves VI, V2. When the output of the valves varies above or below predetermined values, the relay B1 is operated in one or other direction in bringing into operation one cr other of the relays B2, B3 through the intermediary of corresponding valves V3, V4. Assuming the armature 12<c> is moved into engagement with its upper contact, negative bias is supplied to the grid V3 from battery Eg3 over contacts 4<c>, 5<c> of the relay B2 and condenser K1 is charged. The negative bias prevents current flow in the anode circuit containing the relay B2, so that the relay de-energizes and opens, at the contacts 4<c>, 5<c>, the battery circuit. The condenser K<1> discharges and when the negative potential on the grid of the valve V3 falls to a predetermined value, the anode current rises sufficiently to energize the relay B2 to again apply negative bias from the battery Eg3 and recharge the condenser. This cycle of operations is repeated to vibrate the armature of the relay B2 to so long as relay B1 maintains engagement with its upper contact. The armature of the relay B2 impulses, at the contact 7d, the circuit of the stepping magnet M2 to rotate the regulating shaft in the appropriate direction. The stepping magnet M1 is operated by the relay B3 in circuit with the valve V4 in a similar manner when relay B1 engages its lower contact. The stepping magnets are prevented from simultaneous operation by arranging that each circuit is completed over the contacts of the relay associated with the other magnet. In a further modification the relays B2, B3 control auxiliary relays for operating the stepping magnets. The relays of the regulator described in the parent Specification may be controlled by an additional modulation frequency lying outside the signal frequency band or the control frequency may lie within the range of signal frequencies, the same frequency in the signals being suppresed.