US2252084A

US2252084A - Signal responsive relay system

Info

Publication number: US2252084A
Application number: US327046A
Authority: US
Inventors: John S Leigh
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1940-03-30
Filing date: 1940-03-30
Publication date: 1941-08-12
Anticipated expiration: 1958-08-12

Description

Aug. 1941- J. s. LEIGH 2,252,084

SIGNAL RESRONSIVE RELAY SYSTEM Filed March 30, 1940 Snventor Jab azag meg Patented Aug. 12, 1941 SIGNAL RESPONSIVE RELAY SYSTEM John S. Leigh, Pennsauken, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application March 30, 1940, Serial No. 327,046

4 Claims.

This invention relates to signal responsive relay systems for actuating control apparatus in re sponse to applied signals, and has for its primary object to provide a relay system of the character referred to which is highly sensitive and which may be connected with a signal supply circuit without causing distortion of signals therein.

It is also an object of the present invention to provide a signal responsive relay system for radio signal circuits and the like, which is of simplified and low cost construction and which imposes a negligible load on the system in operation.

A relay system embodying the invention is particularly adapted for use in connection with audio frequency signal transmission circuits providing for muting or silencing the output therefrom, in the absence of received signals. However, the system may be employed for the control of any circuit and includes a highly sensitive rectifier device providing a uniform and substantially negligible load on the signal supply circuit and a relay device having suitable control contacts.

ihe invention will, however, be better understood from the following description, when considered in connection with the accompanying drawing, and its scope is pointed out in the appended claims.

In the drawing,

Figure 1 is a schematic circuit diagram of a signal amplifier and control means therefor embodying, the invention, and

Figures 2 and 3 are graphs showing curves illustrating operating features of the circuit of Fig. 1.

Referring to Fig. l, 5 and low potential leads of a signal conveying channel 1 comprising suitable amplifying

apparatus

8 and 9 and a signal output device, such as a loudspeaker l0. The

amplifiers

8 and 9 may be connected by a suitable circuit indicated by leads and I2 corresponding to leads 5 and 6, and providing a continuation of the signal channel through the two amplifying

portions

8 and 9.

The amplifying portion 9, representing any suitable portion of the signal channel which may be controlled, is provided with a circuit comprising leads I3 for modifying the signal output of the channel in any suitable manner, such as by muting or cutting off the signal output entirely or reducing it to a sub-normal value when the circuit I3 is closed or opened. In the present example, it may be assumed that when the circuit I3 is closed, as by means of relay contacts indicated at [4 and E5, the signal channel is normally operative to convey signals from the leads 5 and 6 are the high and 6 through to the loudspeaker device l0, and that when the circuit I3 is open, as by opening the contacts l4 and I5, the signal channel is inoperative, or reduced in effectiveness, to produce signals at the loudspeaker I0.

The relay contacts M and I5 are controlled by a relay coil l6 connected in the output circuit I! of a detector or signal rectifier I8, which receives signal energy from the signal channel I at any suitable point, such as between the amplifier sections 8 and S in connection with the leads I and i2. This signal energy is applied to the tube l8 through a step-up audio frequency transformer 20 providing a relatively high step-up ratio between the primary winding 2| and the secondary winding 22.

The primary winding 2| is connected through leads 23 with the signal channel across the circuit at H and I2 and may include a filter device or other control element 25, hereinafter referred to, between the primary winding 2| and the leads I ||2.

The detector I8 may be of any suitable type comprising a cathode 26, a signal input grid 21, and an output anode 28 connected with the output circuit H. The transformer secondary 22 is connected between the cathode and the grid 21 through a grid leak resistor 29 and a grid capacitor 30, whereby grid rectification takes place in response to signals and providing a negative bias on the grid 21 proportional to the signal strength.

The resulting anode current supplied from suitable terminals 32 connected between the relay l6 and a cathode lead 33, varies in accordance with the curve 35 shown in Fig. 2, assuming a maximum value in the absence of signals and falling to a lower Value as the signal strength is increased. It will be noted that this change in anode current requires a relatively wide change in signal strength and the anode current change is relatively low.

By applying an initial positive bias to the grid 21 from the positive B supply circuit through a controlling resistor 36 which is preferably variable as shown, a. higher degree of sensitivity may be obtained without effecting the loading of the primary 2| and the signal conveying circuit. The variation in anode current of the detector |8 with a predetermined positive bias applied to the grid 21 is indicated by the curve 31 in Fig. 2 and, as will be noted, the anode current varies over a relatively wide range with a relatively small change in input signal amplitude, making the system highly sensitive and providing a change in operating current through the relay coil 15, which actuates the contacts [4, i5 in response to a slight signal.

However, this is made possible by the fact that the step-up ratio of the transformer 28 from the primary 2| to the secondary 22 and the grid circuit of the tube is such that with a very low amplitude signal in the channel at H-l2 corresponding to a slight signal voltage at 5-5, sufficient voltage is applied to the signal grid 21 to bias the tube 21 substantially to cut-off as ind cated by the curve 31,

The step-up ratio of the transformer, therefore, is dependent upon the operating characteristics of the tube employed and the amplification in the signal channel preceding the circuit I [-1 2, and the arrangement is such that, in any case, a relatively small change in signal amplitude at the input circuit 5-5 is sufficient to cause the anode current of the tube to fall from a relatively high value established by the control resistor and the biasing potential applied therethrough, and substantially zero anode current.

In the present example, therefore, the relay i6 is arranged to permit the contacts l4l5 to be held open in the absence of signals and to close in the presence of even a slight signal, thereby placing the channel in operation.

In a preferred application of the invention, the element 25 in the input circuit of the transformer is a band pass or low pass filter permitting voice currents in a predetermined range to actuate the relay, thereby permitting speech to be transmitted through the channel l, 22 from the terminals 5, 6 and to exclude all other signals and to render the system immune from noise by muting the output in the absence of the desired signals. It is obvious, however, that the contacts I i, I5 may be utilized to control any suitable circuit and that the element in the input circuit may be omitted or may be utilized to control the response of the system in any suitable manner.

The operation of the tube l8 in response to sig nals and the control of the positive bias may be understood more clearly from a consideration of Fig. 3, wherein the curve 33 is the grid current curve of the tube and the curve 38 is the plate current curve, drawn to different scales, the normal zero signal plate current being indicated at the point to on the curve 39, while the zero -signal plate current with positive bias, is indicated at the point M on the curve 39.

It has been found that this system and mode of operation of the rectifier provides a highly responsive control; that is, it is quickly responsive to apply signals and causes no appreciable distortion of the signals through the channel H, 2 for the reason that it provides substantially light and constant load over the signal cycle. Fiuthermore, it is relatively simple in arrangement and involves circuit elements which are of relatively low cost, including the transformer 20 which may be of small size, since it is not utilized to convey any appreciable power, but is required only to provide a high voltage step-up between the signal channel and the rectifier IS.

A visual indication of the change in anode current as an indication of the strength of the applied signals may be provided by a suitable current responsive device in the anode circuit i? such as an indicating meter 45, a by-pass capacitor 46 being provided to shunt the said meter, and the potential supply source 32, as indicated.

The regulation of the resistor 36 is relatively poor in operation, causing a drop in potential as the grid current tends to increase and with a triode detector, as shown, may have a value of 220,000 ohms. A suitable grid leak and capacitor for audio frequency currents comprises a resistor of substantially 5.4 megohms at 29 and a capacitor of .1 mid. at 30.

I claim as my invention:

1. A signal responsive control system compris ing, in combination, a signal supply circuit including a step-up transformer having a relatively high step-up ratio, a rectifier device having a signal input grid-cathode circuit including the secondary of said transformer, means providing a negative bias source for said last named circuit in response to signals and through said transformer a load on said supply circuit which is relatively low and substantially uniform over each signal cycle, an output anode circuit for said rectifier device including a control device responsive to changes in anode current, and means for applying a positive bias potential across said input circuit, the relation of said biasing potential and the step-up ratio of said transformer being such that a relatively wide range of variation in the anode current is effected by a relatively small change in signal amplitude applied to said input circuit.

2. The combination with a signal amplifying channel, of a step-up transformer having a primary winding and a secondary winding providing a relatively high step-up ratio, means for applying signals to said primary winding from said channel, a control tube having a grid circuit connected with said secondary winding and a source of negative biasing potential responsive to applied signals, said circuit providing a relatively light and substantially constant load on said signal channel with said relatively high step-up ratio for said transformer, means including a series regulating resistor for applying a predetermined initial positive bias potential to said grid circuit, and means providing an output anode circuit responsive to variations in anode current.

3. The combination with a signal amplifying channel, of a step-up transformer having a primary winding and a secondary winding providing a relatively high step-up ratio, means for applying signals to said primary winding from said channel, a control tube having a grid circuit connected with said secondary winding including a grid leak and a grid capacitor providing a negative bias potential source therein in response to signals, said circuit impedance providing a relatively light and substantially constant load on said signal channel with said relatively high stepup ratio for said transformer, means including a series regulating resistor for applying a predetermined initial positive biasing potential to said grid circuit, means providing an output anode circuit for said control tube responsive to variations in anode current, and means controlled by said current variations for impairing the signal transmission through said channel.

4. The combination with a signal transmission channel, of a transformer having a primary winding connected with said channel to receive amplified signals therefrom, a detector having a grid, a cathode and an output anode, an output anode circuit connected between said anode and said cathode, means for supplying anode current to said circuit, a secondary for said transformer connected between said grid and cathode, a grid leak and a shunt grid capacitor therefor serially included in circuit between said secondary and the grid of said tube, a bias supply circuit including a series resistor connected with said grid for applying thereto a positive potential with normal value, and said transformer having a step-up ratio providing a signal voltage from said channel of an amplitude to reduce said anode current substantially to zero in response to sigrespect to the cathode whereby the zero signal 5 nals of a predetermined low amplitude.

anode current of said tube is increased above a JOHN S. LEIGH.