US2479954A

US2479954A - Pulse delay system

Info

Publication number: US2479954A
Application number: US533385A
Authority: US
Inventors: Robert C Moore
Original assignee: Philco Ford Corp
Current assignee: Space Systems Loral LLC
Priority date: 1944-04-29
Filing date: 1944-04-29
Publication date: 1949-08-23
Anticipated expiration: 1966-08-23
Also published as: GB614550A

Description

Aug. 23, 1949.

' R. C. MOORE PULSE DELAY SYSTEM Filed April 29, .1944

Evie/j 6. 17007 his AW .5

Patented Aug. 23, 1949 PULSE DELAY SYSTEM Robert C. Moore, Philadelphia, Pa., mesne assignments, to Philco assignor, by Corporation,

Philadelphia, Pa, a corporation of Pennsylvania Application April 29, 1944, Serial No. 533,385

7 Glaims.

This invention relates to pulse delay systems and particularly to pulse delay systems in which the interval between the applied pulse and the output pulse is adjustable.

There are numerous occasions in the art of electronics when it is desired to utilize the eifect of a pulse at some predetermined time after the occurrence of the pulse. Furthermore, it is often desirable that the interval between the initial pulse and the delayed pulse be adjustable over a wide range.

It is therefore an object of the present invention to provide by means of a novel circuit, a sy--- tem in which the interval between the applied pulse and the output pulse may be easily and effectively varied over a wide range.

This and other objects and features of the invention will be understood from the following description and the accompanying drawings, in which:

Fig. 1 illustrates schematically the preferred embodiment of the circuit of the present invention;

Fig. 2 is an explanatory diagram showing the wave forms ofcurrent and voltage at various points of the system for a cycle of operation; and a 1 Fig. 3 shows an alternative portion of the circuit of Fig. 1.

Referring now to Fig. 1, there is shown schematically the preferred circuit arrangement of this invention. This circuit may be considered as a modified form of a conventional cathodeloaded multivibrator in which T1 and T2 represent the two electron discharge devices. While T1 and T2 are shown as separate vacuum tubes, and as triodes, it is evident that both sets of electrodes may be enclosed in a single envelope, and that multi-electrocle tubes other than triodes may be used in the circuit with the conventional circuit modifications. The cathodes of tubes T1 and T2 are connected together and grounded through the common cathode resistors II] and II, resistor II being shunted by an inductance I2 to form a differentiating circuit whose function will be described hereinafter. The anode potential for tube T1 is obtained from a suitable direct current source B+ and is applied through resistor I3 and the resistance of potentiometer I4. Resistor I 3 may be a separate element as shown, or it may be included in potentiometer I4, depending upon the desired operating conditions. Vacuum tube T2 derives its anode potential from the source 3+ through the current limiting resistance I5. A by-pass condenser I6 is connected embodiment of a between the anode of tube T2 and ground. To the grid of tube T1 there is connected a conventional input circuit, comprising coupling condenser I1 and grid resistor I8. The grid of vacuum tube T2 is coupled to the plate of tube T1 through two serially connected resistance-capacitance networks [9 and 20. Network I9 is composed of a'condenser 2i shunted by the total resistance of a resistor 22 in series with that portion of potentiometer resistance I4 between the movable contact arm 23 and the plate of tube T1. The resistance-capacitance network 20 comprises a condenser 24 in shuntwith resistor 25. The input and output terminals of the system are shown at 26 and 27 respectively.

The multivibrator utilized for the present invention diifers from the more conventional multivibrator oscillators in that it is constructed and. arranged to produce only one cycle of oscillation in response to a given input pulse. Such single-cycle operation is not new, per se, but this mode ofoperation is utilized in the practice of the present invention. 7

The operation of the system will now be described with particular reference to Fig. 1, and to the voltage and current wave forms shown in Fig. 2.

In the absence of an input signal tube T2 is conducting, since a small positive potential is applied to its control grid from the plate circult of tube T1 through resistors 22 and 25. These two resistors are of sufliciently high value to develop a large voltage drop across them due to the slight amount of grid current flowing in tube T2. The. space current of tube Tzflowing through the common cathode load IIJ-III2 develops sufiicient voltage across resistor It] to bias the grid of tube T1 below its plate-current cut-01f value, the bias voltage being applied through grid resistor I3. With no signal input, tube T1 is then not conducting.

The voltages and currents at various parts of the circuit for no signal input are shown in Fig. 2 for an interval of time represented between the vertical lines I and m. Referring to Fig. 2, we have then for Zero signal input (see curve a), zero plate current in tube T1 as indicated by curve IpTl, a steady currentin the plate circuit of tube T2 shown at IpTZ, a small positive potential on the grid of tub'e'Tz as indicated by curve QgTZ, a steady current through inductance I2 represented by IL, and zero output as indicated by the output curve I). 7

During this period of no input signal the condensers 2| and 24 of Fig. 1 are charged to the voltages impressed on their terminals by the voltage drops developed across resistors 22 and 25 respectively. The total voltage across the two resistance-capacitance networks is then approximately equal to the anode supply voltage 13+, since the voltage across the common cathode load circuit is just sufficient to bias tube T1 to cut-off.

Now when a positive pulse (seecu-rve a, Fig. 2) is applied to the input terminal 26, tube'Ti cone ducts and the potential on the plate of tube T1 quickly drops by an amount equal to the voltage drop developed across the plate load resistance comprising resistor l3 and potentiometer M. This fall of potential is applied to the grid of tube T2 through condensers 2! and 24 thereby biasing the tube T2 to a potential well "below its plate- =current cut-off value. At this point then tube T1 is conducting and tube T2 is not conducting.

The potential on the grid of tube T2 remains below the plate-current cut-off value until the condensers 2i and 24 have sufficiently discharged through their respective shunting resistances '22 and 25 to bring th potential on the grid of tube T2 up .to its cut-on value.

The length of time that the grid of tube T2 remains below its cut-ofi value is determined by the time constants of the RC networks l9 and 20 and by the setting ,of contact arm 23 of potentiorneter I 4 the position of .arm 23 determining the .eiTective time constant of the coupling networks. The adjustment of the time interval willbedescribedlater.

When the grid .of tube T2 reaches its cut-off value (indicated in curv .512 y the dashed line "0. the system regenerates; that is, tube 1'2 becomes conducting and tube'Ti is again cut-.off by the large negative bias developed across the cathode circuit resistance by thespace current of tube T2. When the plate .current .of tube T; is cut .01? its plate potential immediately rises to substantially that of the supply potential 113+. This increase in potential is also applied to "the grid of tube T2 through the coupling network condensers 2| and 24 causing a sudden increase .in the plate .Current of tube T2. This high positive potential on the grid of T2soon ialls to .the original small positive potential 'by virtue of the grid current of tube T2.

However, during the instant the plate current of tube T2 suddenly increases from .zero .to the large value due to the high positive potential .on its grid there is generated in the differentiating circuit 'li-I-Z a high voltage of short duration. The magnitude of this voltage is, of course, proportional to the rate of change of space current in T2. This voltage developed across inductance l2 at this particular instantap earsas a positive pulse at output terminal 21. There ,is then enerated in inductance 12 a voltage at the time the conduction changes ,from one tube to the other; however when the conduction changes ,from tube T2 to tube T1 there vis only a relatively small change in current through inductor 1.2 and .001 seguently only a very small negative pulse is then developedat the output terminal .21.

The voltage ,and current conditjonsjin the various parts of .the circuit from the time of the applied pulse at the input terminal '26 to the time when the circuit returns to its steady psi-signalinput state are given in Fig. 2 between the vertical lines 112 and n. In this portion of Fig.2, the position of the input pulse is shown on some a. and the changes that occur in those parts of the circuit, previously described for the interval lto m, are shown from the time of application .015

plication of apulse 1 stan't of network 4 the pulse until the grid of tube T2 returns to its steady small positive potential.

Curve e T2 clearly illustrates the drop of potential on the grid of tube T2 at the instant the positive pulse occurs. The resultant change in conduction of tubes T1 and T2 is given at IpTl and IpTZ respectively, while at It the change in current through inductance =12 is indicated, the very small negative pulse resulting from the decrease in current in coil l2 being shown in curve I). During the interval represented between lines m and n of Fig. 2, the gradual rise of the grid potential of tube T2 from the large negative potential to the .cut-off .value c. 0. (due to the discharge of condensers 2| and 24 of Fig. 1) is illustrated 'Zt GgTZ. This curve also shows the sudden rise in grid potential at the instant the grid of tube T2 reaches the plate-current cut-off value.

The resulting rise in plate current of tube T2 is given by curve IpTZ. Curve IL shows the sudden increase of current through inductance l2, and the position of the positive output pulse is given in .curve b at the instant n.

it is apparent then from Fig. 2 that the time taken for the grid of tube T2-to rise from its'highly negative value to its cut-off value determines the time interval between the applied pulse and the output pulse of the circuit of the present invention. ,As previously stated, the time that the grid of tube T2 remains below its cut-off value is determined by the time constants of the coupling networks l9 and 20, and by the position of adjustable contact arm 23 of potentiometer M. The variation of the time interval between apto the input terminal 26 and the generation of the output pulse at -'termin al 21 is accomplished by means of the arrangement of the resistance-capacitance networks 1'9 and 2-11. In the preferred arrangement of these networks the time constant of network I9 is much less than that of network 20. .In addition, r esistor "22 is much smaller than resistor 25. Thus when potentiometer arm 23 is at the plate end of potentiometer 14, no voltage is applied to network 19 from the potentiometer and the time constant of network 20 predominates, for the network I9 has little efiect upon the rate of voltage built-up on the grid of tube T2 since the voltage across condenser 21 is small relative to that across condenser 24. When the contact arm .23 is at the opposite end of potentiometer 14 the voltage across the potentiometer resistance is applied to network 9. and consequently the voltage cross condenser 21 is large and the time con- 19 practically co trols the interval between the applied pulse and the output pulse. Intermediate positions of arm '23 will then vary the duration of the interval'betweena short e delay time govern d primarily by the network I15, and a lo er elay ime n e ime co stant of network 2.1) prevails.

"By the prop r sel n o e time c n t nt of networks 19 and 2D and a su table ratio of potentiometer l4 resistance to the total resistance of the plate circuit of tube T1 the interval between the app ed p se and the e ayed o pu pulselm y'be eas y a ju ted by a ioe e ontrol over ,a wide ran e.

'Whilethe invention h e n d scr bed for one par icular embod ment accordin to Eli 1, it will appa n to hose skil ed in thea t tha rnodifications of the circuit may be made without devia ing f om t e general pr nciples-of the invention. For in ance Fi .3, which illustrates a l ernative arrangement of a portion of the circuit of (switch 28 in right-hand position) or through a suitable potential source (switch 28 in left-hand position).

In practicing this invention in 'accordancewith the embodiment illustrated in Fig. 1, a pulse delay from approximately 4 to 400 microseconds. values of the circuit elements were approximately as follows:

section of a type 7N7 tube Although this invention has been described with particular reference to the embodiments of disclosure but only by the scope of the appended claims.

I claim: 1. A pulse vibrator circuit of the type 2. A pulse vibrator circuit employing first and second tubes and the grid of said second tube, the first of said networks comprising fixed resistance and fixed capacitance, the second of said networks comprising a condenser and an adjustable resistor.

3. A pulse delay system, comprising a singlecycle multivibrator of the type employing a pair of inter-coupled vacuum tubes having at least the grid of the second tube, and means for applying a voltage of variable said networks so as to provide a substantial range of adjustment of the time interval between said pulses.

5. A pulse delay system, comprising a multivibrator circuit employing first and second tubes having triode elements regeneratively interfor efiecting a delay between said input pulse and said output pulse, said delay-efiecting means time delay network having a relatively small time constant and a second time 6. A pulse delay system, comprising a multivibrator circuit of the type employing a first and a second tube regeneratively intercoupled to proond tube for the grid circuit of sa1d second tube, network comprising resistance and capacitance elements and having a relatively large time constant, and means for applying a variable v.portion of the anode voltage change of said firstitiibe :to said ifirstne'tworik .so as to vary the relative effectiveness of said networks and thus vary the "time delay'between saidinputpulse and said'voltage ,pulse. a

"Z. In a system of the type described, .a first electron tube "having at least .triode elements, a source of anode voltage, aresistorconnected between Ithe anode .o'f said tube .and said source, va second electron tube having at least triocle elements, a pair or condensers serially connedted between "the anode of said first tube and the grid of said second tube, a resistor connected between the junction of said condensers and an adjustable tap :on said first-mentioned resistor so as to provide afirst delay network, the values of said elements of said network being such as to impart to said "network a relatively small Ztimc constant, and a resistor connected in shunt with the second condenser 'so as to provide a second time :delay network, the values of "thela'tter elements' be'ingsuch as .to impart to said secondntwork 'arelative'ly large time constant.

8 REFERENCES orzrsn The following reierenees'are of record in the file of this =pa'tent:

5 UNIT-ED S'IlATE'S PATENTS Number Name Date 2,050,059 K0611 Aug. 4, 1936 2,118,626 iSmith May 24, 1938 2,193,850 -i-mdrieu Mar.19, 1940 10 .2,22s;n0s Cawe'in Dec. 31, 1940 2262,8138 Delorai'me eti'a1.- .Nov. 1 -8, 1931 2,266,401 Reeves Dec. '16, 1941 :2;266;668 :Uubbs iDec. 16,1941 2,212,070 Reeves Feb. 3, 1-942 15 2294368 Hadfield S'ept. 1,:1942 12,366,076 Wilbur .Dec. 26, 1944 2,373,145 :Sensiper et :al Apr. 710, 1945 2502,9 15 Schroeder June 25, 1946 20 FOREIGN PATENTS Number Country Date 356,111 Grea'tBfitain AugfQA, I931