US2193093A

US2193093A - Alarm system

Info

Publication number: US2193093A
Application number: US126414A
Authority: US
Inventors: Leland A Gardner
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1937-02-18
Filing date: 1937-02-18
Publication date: 1940-03-12
Anticipated expiration: 1957-03-12

Description

Filed Feb. 18, 1937 FIG/ . INVENmR LA. GARDNER 7 WJW A 7' TOP/VEV Patented Mar. 12, 1940 UNITED STATES ALARM SYSTEM Leland A. Gardner, Maplewood, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application February 18, 1937, Serial No. 126,414

9 Claims.

This invention relates to alarm systems and particularly'to hit indicators for electrical circuits such as telegraph systems.

Line hits are defined as short open pulses or other forms of line interference which impair transmission over the line. Since these hits produce errors in the messages received, they must be detected and the fault must be eliminated as promptly as possible. A number of alarm sys-.

10 terms for this purpose have been proposed heretofore and when such systems are used at repeater stations of a telegraph system, they are efiective to indicate line trouble when the line is idle or when signals are being transmitted from the repeater to the line under test. However, when the direction of transmission reverses the alarm is operated even when there is no line trouble as the system is incapable of discriminating between line interference and signals being received from the line.

The object of this invention is an efiicient and reliable hit indicator circuit by means of which an attendant may distinguish readily between line interference and a reversal in the direction of transmission over the line being tested.

According to the invention, as applied to a tele I graph system, a gas-filled trigger tube is asso-' ciated with the line in such a way as to be flashed upon the occurrence of a line hit or an incoming signal pulse thereby completing a circuit including a recording device or an indicating device such as a lamp. In one embodiment of the invention a key is provided for resetting the tube, extinguishing the lamp and preparing an alter- 5 nate control circuit for the lamp of such a nature as to produce a flashing of the lamp at 'a predetermined frequency if signals are being received from the line. When the lamp is lighted the attendant operates the key and if the lamp flashes 40 he does not regard the first operation as an indication of trouble unless the signal is repeated after the incoming signals cease.

In another embodiment of the invention the first flash of the gas-filled tube lights the hit 45. lamp and automatically prepares a control circuit for a second lamp which flashes as long as signals are being received. When transmission ceases, the attendant resets the tube and disregards the first hit indication unless the hit lamp only is relighted.

The invention and the manner in which it may be utilized in systems of various types will be more clearly understood from the following detail description and the accompanying drawing in which Fig. 1 shows. an alarm system or hit indicator according to the invention which has only a single indicating device and which is adapted for use with telegraph repeaters wired for test board answering; 1 i 5 Fig. 2 shows a similar system adaptedto be connected as a loop leak or armature leak circuit:

Fig. 3 shOWS an alternate alarm system having separate hit and transmission indicators and adapted for use with test board answering repeaters; and

Fig. 4 shows the lternate system of Fig. 3 adapted foruseas a loop leak or armature leak circuit.

In Fig. 1' the hit indicator circuit is shown associated with a telegraph repeater and the line L. The repeater comprises the usual receiving relay R, the armature of which cooperates with the marking contact 111. and the spacing contact 5, and the sending relay S together with the other apparatus (not shown) which is usually associated therewith. The repeater shown is also provided with a jack H and a cord l2 whereby the repeater circuit is extended to a jack l3 at the test board where the hit indicator circuit is located so as to be readily available for use on any one of a number of such repeater circuits.

The indicator comprises a gas-filled tube I4 having in its output circuit a relay I5 for controlling the lamp E6 or other indicating or recording 30 device. When the line is idle or when signals are being sent out from this station, the armature of the relay R is normally'at rest on its marking contact m as shown. The potential dropin the resistor 9 maintains a steady current in the primary of the transformer 89 and the grid ll of the tube is negatively biased by the battery l8 so that under this condition the tube is blocked and no current flows in the plate circuit.

The transformer Ii! is connected to the repeater with the proper polarity so that for changes in the line current which would tend .to make the armature of the relay R leave its marking contact m, the potential induced in the transformer secondary reduces the bias onthe grid l1 and permits a current to flow in the plate circuit of the tube. This current operates the relay 15 which lights the lamp l6 and completes a holding circuit for the relay extending from the grounded battery 20 through the key 2! conductor 22, the holding winding on the relay conductor 23, key 2 l, the contacts of the relay to ground at the lamp it. While the change in potential across the resistor 9 when a hit occurs on the linewill ordinarily be only a few volts the trans- 55 relay at jack 33.

the winding and contact 45 of former I9 is preferably selected so that the voltage induced in the secondary is relatively large. Under this condition the system is very sensitive and may be adjusted to detect even line disturbances which are not of sufiicient magnitude to produce a false operation of the receiving relay.

The attendant observing that the lamp is lighted operates and holds the key 2|. The breaking of the normally closed

contacts

24 and 25 breaks holding circuit of the relay and the plate circuit of the tube thereby releasing the relay, resetting the tube, and extinguishing the lamp. The making of

contacts

26 and 21 prepares the plate circuit through the two windings and contact 28 of the relay but if the lamp was lighted by a line hit the relay does not reoperate since the tube has been reset. If, however, the direction of transmission has reversed and signals are coming in, the next space impulse again flashes the tube, operates the relay and opens contact 28 so that the plate current is diverted through the resistor 29 and the condenser 30 and is gradually reduced to zero as the condenser is charged. This delays the resetting or deionization of the tube and the release of the relay but when the current reaches some lower value the relay releases, extinguishing the lamp and closing contact 28 to discharge the condenser through the resistor 29. After the tube has reset the next space impulse repeats this cycle and the lamp I 6 flashes at a frequency determined by the values of the resistor 29 and the condenser 30. Due to the thermal lag of the filament, the lamp cannot flash at the frequency of the line signals and in the absence of the condenser and resistance would remain either lighted or out, but with a suitable circuit of the type shown it may be made to flash at a lower frequency to produce a characteristic indication of reversed transmission.

The hit indicator portion of the circuit of Fig. 2 is quite similar to that of Fig. 1 except that the transformer I9 is replaced by a coupling resistor 3!, which is connected to the repeater by means of a single conductor cord 32. This type of hit indicator input circuit is particularly applicable for connection to points in the system where the change in voltage when a hit occurs is large enough to flash the tube without the use of a transformer. This is true, for example, when the indicator is used in a subscribers loop by plugging the cord 32 into the jack ill or when it is connected to the armature of the receiving In either case when a hit occurs the normal bias on the grid ll of the tube will be reduced, the tube will flash and the indicator will function in the same manner as already described in connection with Fig. 1.

The indicator of Fig. 3 has an input circuit of the type shown in Fig. l and the indicator of Fig. 4 has an input circuit of the type shown in Fig. 2. In the circuits of both Figs. 3 and 4, a hit or an initial space impulse flashes the tube l4 and operates the relay l5 over a circuit extending from the battery 26 to key 47, the operating winding of the relay, relay contact 4! to the plate of the tube. The operation of the relay closes contact 42 to lock in the relay and the hit lamp 43 and opens contact 4! to reset the tube and closes contact 44 thereby transferring the plate circuit of the tube to the battery 20 through the relay 46. If the foregoing operations were caused by a line hit, nothing further occurs, the attendant records the hit and momentarily opens the key 4'! to release the relay l5 and extinguish the lamp. If,

' ly operating. said indicating means means for conditioning the tube to reset however, the lamp 43 was lighted by a reversal of transmission, the relay 46 will be operated by succeeding space impulses and will flash the transmitting lamp 48 at a predetermined irequency determined by the valves of the resistor 49 and the condenser 50 as in the circuit of Fig. 1. It will be observed that the hit indicator of Figs. 3 and 4 distinguishes between line hits and transmission without any action on the part of the attendant. This is a material advantage in that the attendant, when busy on some other work at a distance from the indicator, may ignore the hit lamp 43 as long as the lamp #8 is flashing. When transmission from the line ceases, he momentarily opens the key 41 to extinguish the lamp 43 and condition the indicator to respond to any subsequent hits.

While the invention has been disclosed with reference to its application to a telegraph repeater, it will be understood that it may be used an indicating device, of a relay controlling the device and having normally closed contacts, an output-circuit for the tube extending through the Winding and the closed contacts of the relay,

and means comprising a condenser shunting said contacts efiective upon the opening of the con tacts to delay the resetting of the tube.

2..In a hit indicator for telegraph circuits, the combination with a normally blocked, gas-filled tube adapted to be flashed by-an impulse from a telegraph circuit and indicating in a first manner by the flashing of the tube in response to a hit .or a reversal in the direction of the transmission of signal pulses, of means for conditioning the tube to reset automatically after a predetermined delay and means for subsequentin a second manner, in response to a reversal in the direction of transmission of said pulses.

3. The combination with a normally blocked gas-filled tube, means for flashing the tube and an indicating device operated by the tube, of means for resetting the tube and the device, automatically ata first rate, and means comprising a condenser temporarily eiiectively in series between the anode of said tube and positive battery operative when the tube is so conditioned for changing said rate of resetting of the tube.

4. The combination with a normally blocked gas-filled tube, means for flashing the tube, an

tween the anode of said tube and positive battery when said contacts are open.

5. The combination with a normally blocked gas-filled tube, means for flashing the tube and two indicating devices, of a first relay controlling one of the devices and adapted to operate when the tube is flashed, a second relay controlling the other device and adapted to operate when the tube is flashed while the first relay is operated, and means associated with'the second and output circuit for the tube completed by the operation of said one relay and extending through the winding and closed contacts of the other relay.

7. A telegraph circuit, a hit indicator connected to said circuit, means comprising a normally blocked gas-filled tube and an indicating device in said indicator for indicating both a circuit disturbance and a change in the direction of the transmission of telegraph signals in said circuit, means'also in said indicator comprising a condenser effectively in series between the anode of said tube and positive battery for discriminating between said disturbance and said reversal.

8. In a telegraph circuit hit indicator, means for discriminating between a circuit disturbance and a reversal in the direction of telegraph signal transmission, said means comprising a gasfilled tube having two different anode circuits, one of which contains a condenserin serieswith the anode and positive battery, said condenser being switched into said anode circuit intermittently.

I 9. In a hit indicator, a normally blocked gasfilled tube, an output circuit for said tube extend ing through the winding of a relay, a device controlled by said relay for indicating that said tube has flashed due to either of two conditions, means for maintaining said device in the indicating con- ,dition, means in said hitindicator comprising a condenser effectively in series between the anode of said tube and positive battery for resetting said tube and said device so as to discriminate between the said two conditions.

LELAND, A. GARDNER.