US2533251A - Time base circuit for cathode-ray oscillographs - Google Patents

Description

Dec. 12, 1950 s. s. HILL 2,533,251

TIME BASE CIRCUIT FOR CATHODE-RAY OSCILLOGRAPHS Filed Sept. 25. 1947 INVENTOR STUART 5- HILL ATTORNEY Patented Dec. 12, 1950 TIME BASE CIRCUIT FOR CATHODE-RAY OSCILLOGRAPHS Stuart Seymour Hill, London, England, assignor to International Standard Electric Corporation, New York, N. Y., a. corporation of Delaware Application September 25, 1947, Serial No. 775,993 In Great Britain September 25, 1946 4 Claims.

The present invention relates to electric timebase circuits for cathode ray 'oscillographs, and is concerned with a circuit which provides either a recurrent or a single-stroke time-base.

Time-base generators which operate by charging or discharging a condenser through a resistance are well known in the art. In some cases, there is a need for a circuit which by switching means can be made to produce either a train of recurrent saw-tooth waves, or else a single deflecting stroke in response to a pulse produced in any manner. A very simple circuit of this kind results when the arrangements are such that the single deflecting stroke is in the opposite direction to the recurrent strokes. When, necessary, conventional means for inverting the single strokes, for example, may obviously be provided as will be understood by those skilled in the art.

The invention accordingly provides a time base circuit for a cathode ray oscillograph comprising means for producing periodically recurrent deflections of the cathode ray in a given direction, and means for producing single non-recurgent deflections of the ray in the opposite direcion.

The invention will be explained with reference to the accompanying drawing, in which Fig. 1 shows a schematic circuit diagram of an embodiment of the inv ntion, and Fig. 2 shows a minor modification of Fig. l.

The time base deflecting voltages are produced in Fig. l by an adjustable condenser I which is charged through an adjustable resistance 2 from a high voltage source, not shown. the negative terminal of which is intended to be connected to the grounded terminal 3, and the positive terminal to terminal 4. A protective resistance such as a lamp 5 is provided in series with terminal 4;.

Two two-way switches 6 and I, which are represented schematically for purposes of illustration and which are adapted to be simultaneously operated from a single control, are provided to set up the circuit for producing either recurrent or single-stroke deflecting voltages as desired. In the position shown, the circuit is set up for recurrent voltages and generates the usual saw tooth wave. A grid-controlled gas-filled valve 8 is connected across the condenser I and operates periodically to discharge it through a small current limiting resistance 9 in the well known way. The control grid of the valve 8 is connected through a resistance Ill and switch I to the movable contact of a potentiometer I I which is connected between terminal 3 and a terminal I2 to which is connected a negative grid biassing source IZa, not shown. This arrangement provides a'variable grid bias for the valve 8. by

" means of which the voltage at which the valve fires may be adjusted.

is applied at terminals I6 and I1.

1 does not fire.

The saw-tooth voltage output is taken from terminal I3 which is connected to'the junction point of two resistances l4 and I5 connected across the condenser I, and may be applied to the deflecting elements of the oscillograph after amplification if necessary.

With this well-known arrangement the condenser I charges comparatively slowly through the resistance 2, thus producing the sloping or deflecting portions of the wave, and is discharged rapidly through the valve 8, so producing the fly-back strokes. If the maximum potential of the condenser is small compared with that of the high voltage source, the increase across voltage of the condenser will be substantially proportional to time.

If it is desired to synchronise the saw-tooth waves, a train of pulses or other periodic wave The pulses are amplified by an ordinary valve I8 provided with a grid resistance, I9, cathode bias resistance 29 and anode resistance 2I. A relay 22 controlling contacts 23 is also connected in series with the anode of the valve I8 for a purpose to be explained later.

The pulses should be applied in negative sense to the control grid of the valve l8, so that positive amplified pulses are obtained at the anode and are applied through the blocking condenser 24 and switch 6 to the control grid of the valve 8,

thus synchronising the generated saw-tooth waves in the known manner.

When it is desired to produce single operating deflections, the switches 6 and I are set in the other position. The control grid of the valve 8 is now negatively biassed to the maximum degree. and the voltage of the source connected to terminal I2 should be such that the valve 8 does not fire with the maximum voltage of the high voltage source applied to its anode. The condenser I therefore charges up to nearly the voltage of the high voltage source, provided resistances l4 and I5 are large compared with resistance 2.

The operation of the switch 6 to the lower position connects the blocking condenser 24 to the control grid of a second grid-controlled gasfilled valve 25 instead of to that of the valve 8. This valve has its anode connected directly to the protective lamp 5 and its cathode through the contacts 23 of the relay 22 to the earth terminal 3. The control grid is connected to terminal I2 through a resistance 26, and is thus negatively biassed so that the valve normally The relay 22 will be operated by the anode current of the valve I8, so that the contacts 23 will normally be closed. 1

The single stroke may be initiated by the closing of a pair of contacts IBa, not shown, which will be connected between terminals I6 ance 25.

and 27. The latter terminal is connected to terminal 52. When the contacts are closed, the bias of the control grid of the valve I8 is suddenly increased negatively, so that a positive pulse is produced at the anode of this valve. This positive pulse should be of sufficient amplitude to overcome the negative bias on the con trol grid of the valve 25 so that this valve is fired, thereby practically short circuiting the charging source for the condenser I which therefore discharges through the resistance 2 producing the desired single stroke. It will be noted that this stroke consists of a decrease of the condenser potential, while in the case of the recurrent saw-tooth waves, the operating strokes consisted of increases of the condenser potential. The deflections of the cathode ray produced will therefore be in opposite directions in the two cases.

The single stroke alternatively may be initiated by applying to terminal It a negative pulse derived from any type of source.

The firing of the valve '25 also substantially removes the anode potential for the valve 18, and

so also removes the operating current for the relay 22. This relay should be a slow release relay, so that after a short period, such as half a second, it opens the contacts 23 and extinguishes the valve 25. .Anode potential for the valve is is thus restored, the relay 22 operates again and recloses the contacts 23. The circuit is thus automatically reset so that it is ready to produce another single stroke.

It will be evident that when the valve 25 is fired, a negative voltage pulse will be generated in the protective lamp 5. This pulse may if desired be obtained from terminal 23 connected to the junction point of the resistance 2 and the lamp 5 and may be applied in known manner to the cathode of the oscillograph to release the cathode ray during the period of the single stroke, this ray being normally suppressed.

Since the valves 8 and 25 are not employed at the same time, by the slight modification of the arrangement shown in Fig. 2, one valve may be used to serve the purpose of both. In Fig. '2, the valve 25 and resistance 25 and also the switch 6 are omitted, and the blocking condenser 24 is connected permanently to the control grid of the valve 3. The contacts 23 of the relay 22 are connected in series with the cathode of the valve B, and switch 23, which operates simultaneously with the switch l, is arranged to connect the anode of the valve 8 either to the resistance 9, or to the lamp 5 through conductor as indicated. The other elements of Fig. 2 are arranged in the same way as in Fig. 1.

It will be seen that when the switches 1 and 29 are in the position shown, the circuit of Fig. 2

is the same as that of Fig. l with the switches 6 and i on the position shown, it being remembered that the contacts 23 will be closed. When the switches i and 28 of Fig. 2 are set in the other position, the circuit is the same as that of Fig. l with the switches 6 and I in the other position, except that the valve 8 and resistance iii are being used instead of the valve 25 and resist- The operation of Fig. 2 will therefore be the same as that of Fig. 1 for both positions of the switches.

The condenser E and resistance 2 may if desired be calibrated to indicate the velocity with which the cathode ray spot is deflected-across the screen. In this case, of course, if an amplifier is used between the time base circuit and the oscillograph, its characteristic must be known.

It may be mentioned that the switch I in Figs. 1 or 2 could be omitted if desired, a permanent connection being made from the resistance IE! to the movable *contact of the potentiometer H. When it is desired to switch over to the single stroke time base, then switch 6 will be operated to the other position and the potentiometer II will be adjusted to produce the maximum negative bias for the valve 8.

The contacts 2'3 need not be in series with the cathode of the valve 8 or 25. They could for example be connected instead in series with the anode of the valve 2-5 in Fig. l or in series with conductor 30 in Fig, 2.

It is also not essential to connect the relay 2 2 in series with the anode of the valve it. Alternatively, it could be connected in afse'parate circuit between terminal 3 and the lamp 5, a suitable resistance being connected in series with it, if

necessary. I

Other variations of the arrangements are also possible. For example, the variable resistance could be provided by the anode-cathode circuit of a thermionic valve, and the output resistances i i and I5 could be replaced by a valve arranged as a cathode follower with the control grid connected to the junction point of elementsl and 2, and the cathode connected to terminal 13.

What is claimed is:

1. A time-base circuit for a cathode ray oscillograph comprising a first gas-filled valve, a second gas-filled valve, means for applying a nonperiodic pulse .to said second valve, a direct current source, a resistance, a condenser connected to said direct current source through said resistance, switching means for normally coupling said first valve to said condenser through an electrical path excluding said resistance to periodically and rapidly discharge said condenser, said switching means being operative to connect said second gas-filled valve to said condenser through an electrical oath including said resistance to discharge the said [condenser once through said resistance upon the application of .said nonperiodic pulse to said second valve, and means for electrically coupling the voltage variations of said condenser to the deflecting elements of the oscillograph.

2. A circuit according to claim 1, further comprising means for extinguishing the valve which discharges the said condenser once for the purpose of resetting the circuit,

3. A circuit according to claim 2 in which the said means comprises a normally operated slow release relay adapted to be released by the firing of the said valve and on release to interrupt the cathode circuit of the valve.

4. A circuit according to claim 3 in which an amplifier valve is provided for the pulse which fires the said second valve, the said relay being connected in series with the anode circuit of the said amplifier valve.

STUART SEYMOUR REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATE- 3 PATENTS Number Name Date 2,144,779 Schlesinger Jan. 24, 1939 2,359,969 Schrader et al. May 30, 1944 2,363,810 Schrader et a1. a- Nov. 28, 1944

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