US2237101A - Keying circuit - Google Patents

Description

April 1, 1941. HAHNDdRF 2,237,101

' KEYINe,cIRcuiT Filed Dec. 8, 1959 70 {0A0 COMPENSATOR (FOR smw-Br PER/00.)

AAAAAK INVENTORAI FRITZ HAHNDORF .ATTORNEY Patented Apr. 1, 1941 that stares earner easier.

KEYING cmcm'r of Germany Applicatien December 8, 1939, Serial No. 308,229

In Germany November 15, 1938 2 Claims.

The present invention relates to a circuit arrangement in which two inductive resistances connected in parallel arrangement to the same direct voltage source are to be disconnected simultaneously. Such a circuit arrangement exists for instance in the case of relays placed in parallel and connected to a direct voltage source across a switch.

In such an arrangement it was found that after disconnecting the direct voltage source the relay contacts retain for an appreciable length of time the positions which they had at current passage so that a sufliciently rapid switching is impossible.

In accordance with the present invention this drawback is avoided in that the inductive resistance having a lower ratio between self induc- An example of construction according to the invention is shown in the figure in connection with a key relay arrangement of a telegraph transmitter. er potential and the key switch T have placed in series thereto the parallel connection of a relay coil A and a series connection of a further relay coil B and rectifier G. The rectifier which may be a dry contact rectifier for instance is inserted with a polarity such that the anode of the rectifier is toward the positive pole of the direct voltage source Q. For the normal direction of the current, therefore, the rectifier represents a negligibly low resistance.

The switch contact a actuated by the relay A serves for introducing during the switching pauses an additional load resistance. Hence, it

produces a load compensation and prevents an excessive increase of the voltage. The switch contact b actuated by the relay B serves however for the actual keying of the transmitter in that for instance the grid biasing potential of a tube of the transmitter is shifted to such a high of thick wire wound on an iron core of relativeiy large cross section and adapted to operate pow erful contact members. The self induction of the coil therefore is very high while the D. C. resistance is low. The coil of the relay B requires a smaller number of turns of thinner wire wound The direct voltage source Q of lowon an iron core of relatively small cross section, so that the self induction is substantially lower but the ohmic resistance higher than in the case of the coil A. The contacts of this relay are so designed that only a low power will be switched but with very low inertia. The relay A may be designed as a slow-acting-slow release relay and the relay B as a rapid relay.

In the absence of the rectifier G, a current induced by de-energization of the core of relay A would flow through the coils A and B at the moment in which the key T is opened. This deenergization current through the coil A has the same direction as the normal current, but in the coil 13 it would flow in the opposite direction. This is explained by the fact that the two coils form a closed circuit at all times, but during closure of the key T energy is stored in the coil of relay A having the higher reactance and is released upon opening the key T so as to discharge through the less reactive coil and in a direction opposite to that of the normal current. Obviously the absolute current variation is the smallest in the branch which has the highest self induction. On the other hand one and the same absolute current variation would even lead primarily to a reversal of the current in the branch in which at first the minor current flows, i. e., in the branch having the highest ohmic resistance. Both conditions have the result that, after disconnecting the voltage source, the current in the coil having the higher self induction and lower ohmic resistance, hence the current in the coil A, would decrease in fact but it will retain its direction, while the current in the other coil must reverse its direction.

the coil in which the ratio between the self induction and the ohmic resistance is the smaller.

Since therefore on opening of the key the current passing through the coil B reverses its direction, the contact I) would open at the most for a very brief period and the closure periods would be unduly prolonged. Hence a rapid switching of the relays and unbiased keying is not possible. But the introduced rectifier G has the effect that the de-energization current meets such a high resistance that the relay B will be unaffected thereby, and, furthermore, the relay A will de-energize more rapidly. Therefore, im-

proved keying performance is obtained.

In order that the rectifier may not be subjected to an excessive load in the direction of blocking, it is advisable to insert additionally in parallel with the relay coil A an ohmic resistance R A closer reasoning shcws that the current can be reversed only inthrough which the high potential appearing at the coil A on opening the switch T will be substantially diminished.

The invention is applicable wherever two different inductive resistances are to be connected in parallel and a rapid decrease of the current is desired on disconnecting the direct voltage. If more than two inductive resistances are employed, such rectifiers should be inserted in all parallel branches with the exception of the branch which contains the resistance having the highest ratio between self induction and ohmic resistance since in this branch the current retains its existing direction while in the other branches the direction of the current can reverse itself.

Iclaim:

1. A keying circuit having a pair of parallel connected relays, the winding of one relay being more highly reactive than the other, and means 20 including a rectifier in series with the relay winding having the lower reactance for preventing current reversals in its winding due to the gradual dissipation of energy stored in the winding of the more highly reactive relay.

2. A keying circuit having a code signal relay of relatively low reactance, a relay of relatively high reactance connected in parallel with said code signal relay, a utilization circuit under control of said high reactance relay, a key and a direct current source common to said relays for energizing the same, means including a unidirectional conductor in series with only the winding of said code signal relay for preventing the dissipation through its winding of energy stored in the relay of relatively high reactance, and a resistor in shunt with the last mentioned relay for dissipating the energy which remains stored therein after opening said key.

FRITZ HAHNDORF.

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