US2218659A

US2218659A - Impulse repeater

Info

Publication number: US2218659A
Application number: US212885A
Authority: US
Inventors: Saville Willie
Original assignee: Associated Telephone and Telegraph Co
Current assignee: Associated Telephone and Telegraph Co
Priority date: 1937-07-05
Filing date: 1938-06-10
Publication date: 1940-10-22
Anticipated expiration: 1957-10-22
Also published as: GB498310A

Description

Patented Oct. 22, 1940 rarer was IMPULSE REPEATEB Willie Saville, Huyton, Liverpool, England, as-

signor to Associated Telephone 85 -'Ielegraph Company, Chicago, Ill., a corporation of Delaware ' Application June 10, 1938, Serial No. 212,885

- In Great Britain July 5, 1937 3 Claims; (01. 179-16) ductors, relay D being polarised so that super- 15 vision can be effected over the junction by reversal of current in well-known manner. During each train of repeatedimpulses these relays are short-circuited. to improve the impulsing conditions to the'distant exchange equipment, and at 20 the end of each train they are introduced'into the loop circuit of the distant impulse accepting relay. Due to their high impedance there is then a momentary drop in the loop current beyond that corresponding to their ordinary direct our- 25 rent resistance, and unless the impulsing relay has been energised over a very short junction so that its core is well saturated, it may release momentarily and give a false impulse to its associated switch.

30 In one method suggested for overcoming this trouble so that the junction impulsing limits could be extended it was arranged to decrease the initial impedance of the bridge relays by means of a second winding which was short-cir- 35 cuited over their normally closed armatures. This and similar schemes cannot however be easily applied to existing impulse repeating ar-- rangements, and furthermore they require extra contacts and windings on the bridge relays. It 40 is the object of the invention to provide a simple and cheap arrangement for overcoming the above mentioned trouble which can be readily applied to existing equipments without the necessity for appreciable modifications thereto. 45 According to the invention in an impulse repeater for use in telephone or like systems arranged so that an impedance bridged across the outgoing circuit is shunted during the transmission of a train of impulses, at the same time the 50 shunt is removed a'unit of non-linear resistance material connected across the impedance serves to absorb the inductive kick otherwise produced. By the term non-linear resistance material is meant material the resistance of which is sub- 55 stantially the same for both directions of current flow but which decreases with increase of voltage.

The invention will be better understood from the following description of one method of carrying it into effect, reference being had to the accompanying drawing. This shows a circuit dia- 5 gram of an outgoing impulse repeater AR of wellknown type which is connected by way of a junction J to a final selector FS at a distant exchange. It will be understood that the diagram shows only suflicient detail to enable the inventicn to be properly understood.

Considering the general circuit operations, when the repeater is taken into use, relays A and B operate, and incoming trains of impulses subsequently received are repeated by the armature a2 to the distant impulse accepting relay lA. Relay 0 holds operated during each train and at armature cl short-circuits relays D and I to improve the impulse repeating conditions.

At the end of each train, relay C releases after its slow period and at armature cl removes the short-circuit from relays D and I and the unit of non-linear resistance material NLR thereby introducing them into the loop circuit including relay lA. The transient conditions which now obtain are difficult to describe with any degree of precision but it may be said broadly that a back E. M. F. of considerable value is generated in the highly inductive windings of relay IA due to the fall of the loop current and this E. M. F. causes a rapid drop to occur in the resistance of the material NLR. As the voltage applied across this material decreases so will its resistance increasebut during this time the initial impedance of the bridge relays gradually falls towards the D. C. resistance value. As a result the loop current is prevented from falling as far as it otherwise would do Without the provision of the non-linear resistance shunt path and relay IA is thereby en-' abled to remain operated even when long junc- 40 tion lines are in use. When steady conditions are reestablished, the voltage applied to the material will be small and will only be equal to the voltage drop across the D and I relays so that its resistance will be of high value and it will therefore offer a negligible leakage path during any subsequent transmission of tones or speech currents over the line conductors.

In a preferred form of carrying the invention into effect, the non-linear resistance material takes the form of silicon carbide mixed with carbon and/or tungsten or molybdenum which is agglomerated under pressure and subsequently baked, the resulting mass having a resistancecurrent characteristic which is substantially hyperbolic. The resistance material may be made into various shapes, for instance, it may be made in the form of a disc or Washer and the surface metal-sprayed at appropriate points as described in my United States application Ser. No. 198,182, filed March 26, 1938.

I claim:

1. In an impulse repeater, an incoming and an outgoing line, an impedance bridged across the outgoing line, a non-linear resistance connected in shunt with said impedance, means responsive to impulses received over the incoming line for transmitting impulses over the outgoing line, and means effective to short-circuit said impedance only during the transmission of impulses.

2. In combination, a series circuit including a source of current, a relay, and a short-circuited impedance, said relay operated in said circuit, means for disconnecting the short circuit from said impedance, and a non-linear resistance permanently connected in shunt with said impedance to prevent the relay from being restored by the disconnection of said short circuit.

3. In combination, a series circuit including a source of current, a relay, and a short-circuited impedance, said relay operated in said circuit, means for disconnecting the short circuit'from said impedance, a resistor permanently bridging said impedance and having a resistance value controlled by the voltage across said impedance, said resistor having, upon the disconnection of said short circuit, a low resistance due to the back electromotive force generated in the impedance and effective to increase in resistance as the current flow through the impedance increases to a steady value, said resistor thereby assisting in maintaining said relay operated during the transient conditions following the disconnection of said short circuit and comprising substantially an insulator when the flow of current through the impedance becomes steady.

WILLIE SAVILLE.