US3576462A

US3576462A - Ignition oscilloscope

Info

Publication number: US3576462A
Application number: US720583A
Authority: US
Inventors: Albert M Wanninger
Original assignee: Peerless Instrument Co Inc
Current assignee: Peerless Instrument Co Inc
Priority date: 1968-04-11
Filing date: 1968-04-11
Publication date: 1971-04-27
Anticipated expiration: 1988-04-27

Abstract

This invention is directed to ignition oscilloscope testing devices. The input circuit of the oscilloscope includes a charging capacitor which is arranged in the circuit to have a short RC time constant during the charging of the capacitor and a long RC time constant during the discharging of the capacitor. The discharging of the capacitor provides a pulse of increased time duration which is displayed on the face of the oscilloscope. The horizontal sweep circuit of the oscilloscope includes a horizontal position control and a bias control which are ganged together for movement from a common knob or shaft thereby providing means to maintain a constant focus of the trace on the face of the oscilloscope.

Description

United States Patent [72] Inventor Albert M. Wanninger Prospect Heights, 111.

[21 Appl. No. 720,583

[22] Filed Apr. 11, 1968 [45] Patented Apr. 27, 1971 [73] Assignee Peerless Instrument Co.

Chicago, Ill.

[54] IGNITION OSCILLOSCOPE 17 Claims, 9 Drawing Figs.

[52] US. Cl 315/22, 315/25, 307/267, 324/16 [51] int. Cl ..H01j 29/72,

H a G0lr 1 3/ 26 [50] Field of Search 315/22, 25; 307/26 [56] References Cited UNITED STATES PATENTS 3,510,691 5/1970 Larsen 307/267 2,431,766 12/1947 Miller et a1. 315/22 2,740,069 3/1956 Minto 315/22 3,755,414 7/1956 Snyder 315/22 2,875,402 2/1959 St. John 3 lS/22X 3,056,063 9/1962 Katzman 315/22 3,423,604 1/1969 Scholl 307/267 OTHER REFERENCES Littauer, Raphael PULSE ELECTRONICS N.Y. McGraw- Hill, 1965, pp. 306 307 TK 7835L56 c. 2

Primary ExaminerRodney D. Bennett, Jr. Assistant Examiner-T. H. Tubbesing A!t0rney-Hofgren, Wegner, Allen, Stellman & McCord ABSTRACT: This invention is directed to ignition oscilloscope testing devices. The input circuit of the oscilloscope includes a charging capacitor which is arranged'in the circuit to have a short RC time constant during the charging of the capacitor and a long RC time constant during the discharging of the capacitor. The discharging of the capacitor provides a pulse of increased time duration which is displayed on the face of the oscilloscope. The horizontal sweep circuit of the oscilloscope includes a horizontal position control and a bias control which are ganged together for movement from a common knob or shaft thereby providing means to maintain a constant focus of the trace on the face of the oscilloscope.

Patented April 27, 1971 3,576,462

5 Sheets-Sheet 2 70 G/P/D 0F [40 19% g ATTORNEYS Patented April 27, 1971 3,576,462

5 Sheets-Sheet 3 l N VENTOR.

Patented April 27, 1911 3,576,462

5 Sheets-Sheet 5 man H1 IGNITION OSCILLOSCOPE This invention relates generally to cathode-ray oscilloscopes and more particularly to a new and improved circuit arrangement for ignition Oscilloscopes for testing the performance of automobile ignition systems.

2. Description of the Prior Art During the testing of the ignition performance of automobiles the oscilloscope is connected to the ignition system of the automobile to receive therefrom electrical signal impulses indicative of the spark voltage applied across each spark plug of the automobile. This voltage is displayed on the face of a cathode-ray tube in the form of one or more sharp spikes representing a high-voltage short-duration pulse. The sharp spikes are very difficult to see on the face of the scope since the time duration of the spike is extremely small. Additionally, when the trace on the oscilloscope is arranged to display six or eight pulses for each of the six or eight spark plugs of an automobile the trace is focused to produce a sharp image. However, when the trace is expanded to display only one pulse of one of the spark plugs, the trace becomes defocused due to the unbalanced condition of the horizontal sweep circuit.

One method of improving the visual resolution of the sharp spikes; according to prior art, is to introduce a signal of proper polarity to either the grid or cathode of the oscilloscope tube to modulate the intensity of the beam during the short pulse duration thereby providing a brighter presentation of the pulse.

SUMMARY OF THE INVENTION Briefly, the present invention is directed to improved circuitry for use in ignition oscilloscopes and includes a storage capacitor at the input of the oscilloscope which is charged to a voltage proportional to the peak voltage of a pulse applied to the input. The voltage stored on the capacitor is then applied to the vertical deflection system of the oscilloscope to display the characteristics of the input pulse on the face of the oscilloscope. The discharge rate of the storage capacitor is relatively slow, as compared to the charge rate of the capacitor, thereby causing the pulse displayed on the oscilloscope to have a substantial pulse width thereby causing the pulse to be more readily observed by the operator. Means are provided to vary the pulse width displayed on the face of the scope. Additionally, the circuit arrangement of the present invention may include circuit means connectable to the breaker points of the automobile such that the pulse display on the face of the oscilloscope not only gives spark voltage and characteristics but also gives information indicative of the dwell angle of the breaker points.

An improved horizontal sweep circuit is provided which includes horizontal position control means and bias control means connected together on a common shaft for adjustment from a signal knob to maintain a substantially uniform focus of the trace on the oscilloscope when the horizontal sweep circuit is adjusted to display one pulse of a single spark plug or eight pulses from eight spark plugs.

Accordingly, one of the objects of the present invention is to provide a new and improved ignition oscilloscope for use in testing the ignition performance of automobiles.

Another object of the present invention is to provide means to improve the display of highwoltage short time duration pulses on the face of the oscilloscope.

Another object of the present invention is to provide circuit means for maintaining substantially constant focus of the trace on the oscilloscope when varying the horizontal sweep rate through a wide range of frequencies.

Another object of the present invention is to provide an ignition oscilloscope which is relatively inexpensive to manufacture, simple in operation and reliable in performance.

Other objects, features and advantages will be more fully realized and understood from the following detailed description when taken in conjunction with the accompanying drawings wherein like reference numerals throughout the various views of the drawings are intended to designate similar elements or components.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a simplified circuit arrangement of an ignition system of an automobile;

FIG. 2 is a wavefonn representation of a spark voltage of one of the spark plugs of an automobile;

FIGS. 30 and 3b show the detailed circuit arrangement of an oscilloscope constructed in accordance with the principles of this invention;

FIG. 4 is a series of waveforms to illustrate the input voltage and display waveform presented on the face of the cathoderay oscilloscope of FIGS. 3a and 3b.

FIG. 5 is a waveform of a series of high amplitude short duration of pulses representing the firing potentials of the spark plugs of an automobile;

FIG. 6 is a single waveform representing the firing potential of a single spark plug;

FIG. 7 is a alternate input circuit arrangement for the circuit shown in FIGS. 3a and 3b.

FIG. 8 is a further alternate circuit arrangement for the input circuit of the oscilloscope of FIGS. 3a and 3b.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Seen in FIG. I is a simplified circuit diagram of an automobile ignition system and is designated generally by reference numeral 10. The ignition system 10 includes a step-up transformer II which has a primary winding 12 and a secondary winding 13. One end of the primary winding 12 is connected through a switch 14 to a battery 16 of an automobile. The other end of primary winding 12 is connected to ground potential through breaker points 17. Switch 14 is the main ignition switch located within the interior of the automobile and breaker points 17 are located within the distributor of the automobile. Closing of breaker points I7 complete the DO current path for the primary winding 12. However, when breaker points 17 open the rapid collapse of the magnetic field produced by the direct current through the primary winding 12 will induce a high-voltage short-duration pulse in the secondary 13 of transformer 11. This will develop a high-voltage firing potential to line 18 which is connected to the center plug terminal of the distributor cap of the automobile. The distributor will then distribute the high-voltage potential from line 18 to the desired spark plug in accordance with the timing of the engine. A condenser 19 is connected in parallel with breaker points 17 to substantially reduce arcing of the breaker points open during each firing of a spark plug.

The voltage waveform applied to line I8 is shown in FIG. 2 and is designated generally by reference numeral 20. The waveform 20 has at the leading edge thereof a large-amplitude short-duration pulse 21 which represents the firing voltage of the spark plug. This voltage is in the order of 5,000 to 10,000 volts on most automobiles. When the firing voltage is applied to the input of an oscilloscope, the top portion 22 of the firing voltage wave is represented by a very thin vertical line. This line is very difficult to see, especially in bright daylight, to determine the exact firing characteristics of the ignition system. Also, a diminishing oscillatory wave 23 is present on waveform 20. Therefore, when using a conventional ignition oscilloscope to display the firing voltage waveform, such as wavefonn 20, the top portion of the firing voltage wave is dis played poorly while other portions of the waveform are displayed with higher resolution.

According to the present invention, a circuit arrangement for an ignition oscilloscope is provided wherein the trace on the face of the oscilloscope produces a pulse indicative of the firing potential 21, and wherein the pulse width of the pulse is greatly increased to provide better visual resolution of the firing characteristics of the ignition system 10. Additionally, the

trace of the oscilloscope, according to the present invention, is free of extraneous information, such as the diminishing oscillatory wave 23, thereby providing visual information of the operation of the ignition system which is more easily interpreted.

FIGS. 30 and 3!; taken together disclose one form of an amplifier circuit 27 is a horizontal sweep circuit 28 which maybe synchronized to an external pulse, such as the firing of the one of the spark plugs of an automobile. Also connected to the oscilloscope circuit 26 is a vertical deflection circuit 29. The vertical deflection circuit 29 is connected to an input circuit 30 which, in turn, includes an input terminal 31 for receiving pulse signal information from the ignition system 10 through a voltage divider probe 33. The vertical deflection circuit 29 and the horizontal sweep circuit move the electron beam of the cathode-ray tube 426) to cause a trace of the ignition voltage waveform applied to terminal 31 to be displayed as a function of time on the cathode-ray tube screen 51. The oscilloscope circuit of F 10. 3a and 3b is operated by a power supply 32.

The cathode-ray circuit 26 includes a cathode-ray tube 40 which has a pair of vertical deflection plates 41 and 42 and a pair of

horizontal deflection plates

43 and 44. A cathode electrode 46 is positioned within the neck of the tube to emit electrons toward the area between deflection plates 4144. A filament 47 is provided to heat cathode 46.

The electrons emitted by cathode 46 are accelerated toward the deflection plates 4144 by a plurality of anodes 48, 49 and 50. After the electrons pass the deflection plates 41-44 they impinge upon a phosphor coated face 51 of the cathoderay tube 40. A control grid 52 is provided between the cathode 46 and anode 48 to provide a control potential to modulate the intensity of the electron beam from cathode 46.

Control grid 52 is connected through a resistor 53 to a filter circuit 54 associated with a rectifier 56. The filter circuit 54 filters the negative potential developed at the anode of rectifier 56. Connected to the filter circuit 54 is a voltage divider network comprising potentiometer 57, resistors 58 and 59, potentiometer 60, and

resistors

61 and 62. Resistor 62 is connected to ground potential. Also connected to ground potential is a voltage divider network comprising resistor 63, potentiometer 64 and resistor 66. Connected in parallel with resistor 66 is a capacitor 67.

The anodes 48 and 50 are connected together and to the movable contactor of potentiometer 64, and anode 49 is connected to the movable contactor of potentiometer 60. The anodes 48, 49 and 50 receive the proper potentials to accelerate and focus the electron beam toward the face 51 of the tube 40.

The rectifier 56 has a filament 68 which is connected to a secondary winding 69 of a transformer 70. A second secondary winding 71 of the transformer 70 is connected to the filament 47 of the cathode-ray tube 40. It will be understood that the filament electrodes of the associate tubes of the circuit may be operated by other suitable stepdown secondary transformer windings, not shown. Furthermore, the' power supply 32 may include other low-voltage potentials necessary for the operation of the transistor circuitry.

The filament winding 69 of the transformer 70 is associated with a step-up winding 72 which develops the high voltage for the rectifier tube 56 and additional voltage for the operation of other tubes. The winding 72 is connected thereto a diode 73 and a resistor capacitor filter network 74 to develop a negative 150 volts at the line 76. The diode 73 and filter network 74 form a conventional half-wave rectifier circuit.

Another secondary winding 77 has one end thereof connected to a pair of diodes 78 and 79 and the other end thereof connected to a pair of capacitors 80 and 81. The diodes 78 and 79 together with capacitors and 81 form a full-wave voltage doubler rectifier circuit. This rectifier'circuit applies approximately 700 volts to a line 82'which is applied to the plate electrodes of the tubes within the horizontal sweep amplifier circuit 27 and the vertical circuit 29. Connected between the output of the full-wave voltage doubler rectifier circuit and the line 82 is a resistor 83. Connected between one end of resistor 83 and ground potential is a pair of

resistors

84 and 85 which are shunted by capacitors 86 and 87.

Transformer 70 includes a primary winding 88 which has a neon lamp 89 connected in parallel therewith. The neon lamp 89 gives a visual indication that power is applied to the circuit of FIGS. 3a and 3b. The primary winding 88 has one end thereof connected to a capacitor 90 and the other end thereof connected to a capacitor 91. Capacitors 90 and 91 provide suitable isolation between the primary winding 88 and the chassis for mounting the circuitry of FIGS. 3a and 3b. A pushbutton switch 92 is provided for applying power to the primary winding 88, and the alternating current voltage applied thereto is fused by a fuse 93.

According to the present invention, a new and improved horizontal sweep amplifier circuit is provided and is designated by reference numeral 27. The horizontal sweep amplifier, circuit 27 includes a pair of

tubes

96 and 97 which may be a duotriode. However, it will be understood that the

tubes

96 and 97 may be separate tubes rather than two tubes contained in a single glass envelope. The cathodes of

tubes

96 and 97 are connected together and to a resistor 98 which, in turn, is connected to a potentiometer 99. The potentiometer 99 is connected to a second potentiometer 100 which, in turn, is connected to a negative volts of power supply 32. The plate electrode of tube 96 is connected to a .-l-700 volts through a resistor 101, and the plate electrode of tube 97 is connected to a +700 volts through a resistor 102. The signal potential developed by the

tubes

96 and 97 is applied to a pair of

lines

103 and 104 which, in turn, are connected to

deflection plates

43 and 44 respectively of the cathode-ray tube 40. The signal potential developed across

lines

103 and 104 is a sawtooth wave form which produces a horizontal sweep of the electron beam thereby causing a horizontal trace on the face 51 of the cathode-ray tube 40. The plate electrode of tube 96 is also connected to the control grid 52 of the cathode-ray tube 40 through a

capacitor

106 and 107. The signals applied to control grid 52 through capacitor 106 and line 107 provide a blanking voltage which prevents electrons from reaching the face of the cathode-ray tube 40 during the retrace of the sweep. This prevents extraneous lines from appearing on the face 51.

The grid electrode of tube 97 is connected to ground potential through a capacitor 108 and to the movable contactor of the potentiometer 109. The potentiometer is connected between the ground potential and the negative 150 volts through a resistor 110.

According to the present invention, potentiometerllll) and potentiometer 109 are arranged for common adjustment. This may be accomplished in the usual manner of mounting both potentiometers on a single shaft for adjustment from a single knob. It has been found through experimentation that by ganging of the

potentiometers

100 and 109 the focus of the sweep on the face 51 of cathode-ray tube 40 is substantially constant when changing the sweep rate from displaying six or eight firing potentials of the six or eight spark plugs to displaying a single firing potential of a spark plug. Furthermore, improved focusing also can be obtained by ganging together the horizontal position controls with either the focus or the astigmatism control.

Connected to the horizontal sweep amplifier circuit 27 is a sawtooth generator circuit 28 which is synchronized in accordance with external pulse signals. The sawtooth generator circuit 28 includes a trigger input 112 which includes a pickup transformer 113. The transformer 113 is connected between the base and emitter of a transistor 114. The transistor 114 has the emitter thereof connected to ground potential through a resistor 116 and to the base electrode of a transistor 117. The collector electrode of transistor 117 is connected to a l0- volt power supply through a coil 118. Transistor 117 and coil 118 are shunted by a capacitor 119. The output of transistor 117 is delivered to the control grid of a tube 120 through a coil 121 and a capacitor 122. The movable contact of potentiometer 123 is connected to a resistor 123a which, in turn, is connected to the control grid of tube 120.

Tube 120 is a thyratron connected in a grounded-plate triangular wave generator circuit. The cathode of tube 120 is connected to the plate electrode of a tube 124 which, in turn, has its cathode connected to the negative 150 volts of the power supply 32. Connected between the control grid and the cathode of tube 124 is the capacitor 126. Also connected to the control grid of tube 124 is a resistor 127, which, in turn, is connected to the junction of the resistor 128 and the diode 129. The diode 129 has the cathode thereof connected to the anode of the diode 130 which, in turn, has the cathode thereof connected to the movable contactor of the potentiometer 131. The plate electrode of tube 124 is connected to thejunction of

diodes

129 and 130 through a capacitor 132.

A capacitor 133 is connected between the plate and cathode of the tube 120 and is paralleled by a resistor 134 and a potentiometer 136. The movable contactor of potentiometer 136 is connected to the control grid of tube 96, of the horizontal sweep amplifier circuit 27. Output signals from tube 120 provide the drive for the horizontal sweep amplifier circuit 27. Potentiometer 123 adjusts the level of synchronization signal applied to the grid of thyratron 120 to give a horizontal sweep circuit rate in agreement with the time rate of the ignition voltage applied to input 112.

The vertical deflection circuit 29 includes a pair of tubes 140 and 141 which have their cathodes connected together to a resistor 142 which, in turn, is connected to a potentiometer 143. The potentiometer 143 is connected to the negative I50- volt line of power supply 32. The plate electrode of tube 140 is connected to the positive 700-volt line of the power supply 32 through a resistor 144, and the plate electrode of tube 141 is connected to the positive 700volt source through a resistor 1 146. The plate electrodes of tubes 140 and 141 are connected to

lines

150 and 151 respectively which, in turn, are connected to the deflection plates 42 and 41 respectively. The signal information to be displayed on the face 51 of cathoderay tube 40 is applied to the vertical deflection circuit 29 to deflect the electron beam of cathode-ray tube 40 in a vertical direction and thereby produce a trace on the face 51 indicative of the wave shape of the electrical signal information applied to the input 31 of the circuit.

input signal information applied to the input terminal 31 is delivered to the input circuit 30 via a line 156. The line 156 is connected to a switch 157 and therefrom to an attenuator circuit 160. The attenuator circuit 160 includes a capacitor 161, a potentiometer 162 and a capacitor 163. The output of the attenuator circuit 160 is applied to the grid electrode of a tube 140 through a switch 164. The switches 157 and 164 are ganged together for operation from a common push button. By using the external voltage divider probe 33, the attenuator circuit 160 is dimensioned to receive input signals of approximately 30,000 volts. The probe 33 may, for example, have a 300:1 attenuator.

Line 156 is also connected to

additional switches

158 and 159. Switch 158 is connected to an attenuator circuit 166 which includes a capacitor 167, a potentiometer 168- and a capacitor 169. The output of attenuator circuit 166 is connected to the grid electrode of tube 140 through a switch 170.

Switch

158 and 170 are ganged together for operation from a common pushbutton. By using the external voltage divider 33. the attenuator circuit 166 is dimensioned so as to receive input voltages having a peak voltage of approximately 15,000 volts.

According to the present invention, the input signals ap plied to input terminal 31 may be delivered to a pulse stretching circuit 171 through the switch 159. Pulse stretching circuit 171 includes a transistor 172 which has the base elec trode thereof connected to a resistor 173 and a capacitor 174. The collector electrode of transistor 172 is connected to negative l5-volt source of power supply 32. The emitter electrode of transistor 172 is connected to ground potential through a resistor 176. Also connected to the emitter electrode of transistor 172 is a diode 177 which is forward biased by transistor 172 to charge a capacitor 178 in response to the input signals applied to input terminal 31. The RC time constant of capacitor 178, during the forward bias of diode 177 is relatively short thereby causing substantially a full charge to be impressed across the capacitor 178. After the pulse has been charged on the capacitor 178, diode 177 is reverse biased to prevent the capacitor 178 from discharging through resistor 176. Connected in parallel with the capacitor 178 is a resistor 179 and a potentiometer 180. The resistor 179 and potentiometer 180 offer a relatively high equivalent resistance across capacitor 178 to provide a long discharge time for the capacitor. The output of capacitor 178 is delivered to the grid electrode of tube through a switch 181. The potentiometer controls the amplitude of the signal voltage supplied to tube 140.

Switches

159 and 181 are ganged together for operation from a common pushbutton. By using the external voltage divider 33, the input circuit 171 is dimensioned so as to receive 15,000 volts input signals.

As seen in FIG. 4 the input signals are represented by the wave shape and it is seen that the input signals are high-amplitude short-duration pulses or spikes. The amplitude of wave shape 183 is proportional to the amplitude of wave shape 182. It will be understood that the time duration of wave shape 183 may be determined independently of the amplitude of wave shape 182, as will be more fully understood from the following description. Furthermore, one advantage obtained by using the input circuit 171 of the present invention is that the cathode-ray tube 40 may be provided with electromagnetic deflection means rather than the electrostatic plates 41--44.

Accordingly, the ignition oscilloscope of the present invention provides a new and improved input circuit for extending the duration of time for which the pulse signal information is displayed on the face 51 of the cathode-ray tube 40. Additionally, the present invention provides a unique horizontal sweep amplifier circuit 27 which maintains a substantially constant focus of the electron beam within the tube 40 during adjustment of the beam from a display of eight pulses to one pulse. For example, FIG. 5 shows the display of a conventional ignition oscilloscope indicating eight pulses for each of the eight spark plugs of an eight-cylinder automobile. As in common practice, the sweep of the horizontal circuit 27 is increased so as to stretch the sweep to display only one firing voltage of a signal spark plug, as illustrated in FlG. 6. In conventional circuits, this operation usually causes the electron beam to become defocused and blur the image, as illustrated, whenever the pattern is positioned to view the last cylinder in the firing order. However, it has been found that by ganging together the

potentiometers

100 and 109 this defocusing affect is substantially eliminated.

Seen in FIG. 7 is an alternate arrangement of an input circuit constructed in accordance with the principles of this invention and is designated generally by reference numeral 200. The input circuit 200 includes a line 201 which may be connected to switch 159, FIG. 3A. Line 201 is connected to a capacitor 202 which, in turn, is connected to a capacitor 203 and a resistor 204. Connected at the junction of capacitor 203 and resistor 204 is a resistor 206 which has the other end thereof connected to a +40-volt source of power supply 32. The input signal applied to capacitor 203 and resistor 204 is impressed in the grid electrode of a tube 207. The plate electrode of 207 is connected to the 300-volt source of power supply 32 through a resistor 208. The output signal of tube 207 is delivered to a monostable multivibrator 209 through a capacitor 210. The monostable multivibrator includes a pair of

tubes

211 and 212 which have their cathodes connected together and to a resistor 213. The resistor 213 has its other end connected to ground potential. Also connected to the grid electrode of the tube 211 is a diode 214 and a resistor 216. The plate electrode of tube 211 is connected to +300 volts through a resistor 217. Similarly, the plate electrode of tube 212 is connected to +300 volts through a resistor 218. The cross-coupling signal of the multivibrator 209 is delivered through a capacitor 219 which has one end thereof connected to the plate electrode of tube 211 and the other end thereof connected to the grid electrode of tube 212. Also connected to the grid electrode of tube 212 is a resistor 220 and a potentiometer 221. Potentiometer 221 provides means for adjusting the pulse width or time duration of the square wave or pulse developed by the multivibrator 209.

The square wave pulse developed at the output of multivibrator 209 is delivered to a capacitor 222 and a diode 223. Connected in parallel with the diode 223 is a resistor 224. Connected at the junction of diode 223 and resistor 224 is a resistor 226 which has its other end connected to the +150 volts supply of power supply 32. The signal coupled through capacitor 222 is applied to the grid electrode of a tube 227. The cathode of tube 227 is connected to ground potential through a resistor 228. Tube 227 operates as a cathode follower.

The output of tube 207 is also delivered to a capacitor 231 and diode resistor network including diode 233 and a resistor 234. The signal coupled through capacitor 231 is applied to the grid electrode of a tube 232. The cathode electrode of tube 232 is connected to ground potential through a resistor 236, and the plate electrode of tube 232 is connected to a +300-volt potential of power supply 32. Tube 232 forward biases a diode 237 which, in turn, causes a pulse to be charged on a charging capacitor 238. However, capacitor 238 is discharged at a predetermined time in response to the output of tube 227. Also connected to line 239 and diode 240 is a pair of

resistors

241 and 242. Therefore, capacitor 238 is charged in response to the input pulse applied through capacitor 202 and discharged in response to the output signalof tube 227. This causes a square wave pulse to be generated at the junction of diodes 237 and 240 and capacitor 238. This square wave pulse is applied to a line 243, which in turn, is connected to switch 181, FIG. 3a.

As seen in FIG. 4, the wave shape 244 is represents the square wave output applied to line 243. Wave shape 244 is reproduced on the face 51 of the cathode-ray tube 40. The width of the wave shape 244 is substantially greater than the width of wave shape 182 and therefore, it is much easier to see.

FIG. 8 illustrates a further embodiment of an input circuit constructed in accordance with the principles of this invention and is designated generally by reference numeral 300. The input to circuit 300 includes a line 301 which is connectable to the switch 159, of FIG. 3A. Line 301 is connected to a capacitor 302 which, in turn, is connected to a base electrode of a transistor 303. Also connected to the base electrode of transistor 303 is a capacitor 304 and a resistor 306. The emitter electrode of transistor 303 is connected to ground potential through a resistor 307 and, the collector electrode of transistor 303 is connected to a negative voltage source.

The output of transistor 303 forward biases a diode 308 which, in turn, charges a charging capacitor 309. The charging voltage on capacitor 309 is applied to an output line 310 which is connectable to switch 181, of FIG. 3a.

A discharging circuit is provided an is connectable to the ignition points of the automobile. The discharging circuit includes a resistor 311, a capacitor 312, and resistor 313, a capacitor 314 and a resistor 315. Resistor 315 is connected to the base electrode of a transistor 316. The collector electrode of transistor 316 is connected to a positive voltage source through a resistor 317. The emitter electrode of transistor 316 is connected to ground potential. The output of transistor 316 is delivered through a capacitor 318 and impressed across a resistor 319 and a diode 320. Resistor 319 and diode 320 each end of capacitor 321 is connected to a resistor 322, a diode 323, and a resistor 324. The

resistors

319 and 322 together with the

diodes

320 and 323 and capacitor 321 form a waveshaping network to convert the square. wave output of transistor 316 into a positive discharge pulse which is applied to the charging capacitor 309. Therefore,the pulse applied to charging capacitor 309 is discharged in response to the switching of the ignition points of the automobile. Accordingly, the space between pulses, as seen on the face 51 of the cathode-ray tube 40, is indicative of the dwell angle of the automobile distributor.

In FIG. 4, the wave shape 330 represents the wave shape displayed on the face 51 when in the input circuit 300 is incorporated in the oscilloscope circuit. The distance between the trailing edge of the first pulse and the leading edge of the second pulse represents the dwell angle of the automobile distributor.

Accordingly, the present invention discloses new and improved input circuit arrangements for displaying a pulse on the face of an ignition oscilloscope with increased time duration to enable the operator of the oscilloscope to better interpret the pulse signal information. Additionally, the present invention provides a new and improved horizontal sweep circuit for maintaining a substantially constant focus of the electron beam within the cathode-ray tube 40.

The external voltage divide probe 33 includes a connector at one end thereof for connection-a coil tower and a connector at the other end thereof for connection to the high voltage wire from the coil. A capacitor pickup 34 provides the proper attenuation for the probe.

It will be understood that variations and modifications may be effected without departing from the spirit and scope of the novel concepts of this invention.

I claim:

1. In an oscilloscope apparatus for displaying a representation of a relatively short duration pulse having a cathode-ray tube for displaying electrical signal information on the face thereof and including horizontal and vertical deflection means, a horizontal sweep circuit connected to said horizontal deflection means to produce a horizontal trace on said face, a vertical deflection circuit connected to said vertical deflection means to give vertical deflection of said horizontal trace for displaying a representation of the pulse on said face, an input circuit connected to said vertical deflection circuit and receiving the pulse to be displayed on said face, said input circuit comprising: a capacitor; means for applying said pulse to the capacitor to charge the capacitor to a voltage corresponding directly to the amplitude of the pulse; resistance means connected across the capacitor defining with said capacitor an RC circuit providing a time delay discharge of said capacitor only through said resistance means to produce an output relatively long duration signal corresponding accurately in amplitude to the'amplitude of said short duration pulse; and means connecting said RC circuit to said deflection plate of the cathoderay tube to cause display of said output signal on said face.

2. A cathode-ray oscilloscope apparatus according to claim 1 wherein said input circuit further comprises a transistor having emitter, collector and base electrodes, said base electrode arranged for receiving said signal information, a source of potential connected to said collector electrode, and a diode connected to the emitter electrode of said transistor, whereby signal information causes said transistor to forward bias said diode to charge said capacitor.

3. A cathode-ray oscilloscope apparatus according to claim 1 wherein said input circuit comprises a monostable multivibrator having the input thereof arranged for receiving said signal information and further having an output, and an electronic switch having the input thereof arranged for receiving said signal information, and a diode connected to said electronic switch to charge said capacitor in response thereto, said output of said multivibrator being connected to said storage capacitor to selectively discharge said storage capacitor at a predetermined time after the charging of said storage capacitor thereby applying a pulse to said vertical deflection circuit having a pulse width greater than the pulse width of said signal information.

' 4. A cathode-ray oscilloscope apparatus according to claim 1 further comprising electronic switch means connected to said capacitor to discharge said capacitor at a predetermined time after the charging of said capacitor from said signal information.

5. A cathode-ray oscilloscope apparatus according to claim 1 wherein said input circuit further comprises a transistor having emitter, collector and base electrodes, said base electrode arranged for receiving said signal information, a source of potential connected to said collector electrode, and a diode connected to the emitter electrode of said transistor, and further including switch means connected to said capacitor to discharge said capacitor at a predetermined time after the charging of said capacitor.

6. A cathode-ray oscilloscope apparatus according to claim 1 wherein said horizontal sweep circuit comprises electromagnetic deflection means.

7. A cathode-ray oscilloscope apparatus according to claim 1 wherein said vertical deflection circuit comprises electromagnetic deflection means.

8. A cathode-ray oscilloscope for testing the ignition performance of an automobile, comprising: a cathode-ray tube for displaying electrical signal information on the face thereof, said cathode-ray tube including horizontal and vertical deflection means, a horizontal sweep circuit connected to said horizontal deflection means to produce a horizontal trace on said face, said horizontal sweep circuit including a horizontal position control means to position the trace on said face, bias means, and mechanical means connecting said horizontal position control means for common operation, thereby providing means maintaining a constant focus of trace on said face; a vertical deflection circuit connected to said vertical deflection means to give vertical deflection of said horizontal trace thereby displaying the electrical signal information on said face; and input circuit means connected to said vertical deflection circuit and receiving the signal information to be displayed on said face, said input circuit including a storage capacitor and a diode, said storage capacitor and said diode having a short RC time constant during the charging of said capacitor and having a long RC time constant during the discharging of said capacitor, said input circuit means arranged for connection to a portion of the ignition circuit of an automobile; whereby, signal information indicative of the firing potential of the spark plugs of the automobile will be displayed on said face for a longer time duration.

9. In a cathode-ray oscilloscope for testing the ignition performance of an automobile according to claim 8 wherein said input circuit means further includes a transistor having emitter, collector and base electrodes, said base electrode arranged for receiving said signal information, a source of potential connected to said collector electrode, and said diode connected to the emitter electrode of said transistor, whereby, signal information causes said transistor to forward bias said diode to charge said capacitor.

10. A cathode-ray oscilloscope for testing ignition per- I formance of an automobile according to claim 8 wherein said input circuit includes a monostable multivibrator having the input thereof arranged for receiving said signal information, and further having an output; an electronic switch having the input thereof arranged for receiving said signal information, said diode connected to said electronic switch to charge said capacitor in response thereto, said output of said multivibrator connected to said capacitor to selectively discharge said capacitor at a predetermined time after the charging of said capacitor thereby applying a pulse to said vertical deflection circuit having a pulse width greater than the pulse width of said signal information.

11. A cathode-ray oscilloscope for testing ignition performance of automobiles according to claim 8 further including electronic switch means connected to said capacitor to discharge said capacitor after a predetermined time after the charging of said capacitor.

12. A cathode-ray oscilloscope for testing ignition performance of automobiles according to claim 8 wherein said input circuit means further includes a transistor having emitter, collector and base electrodes, said base electrode arranged for receiving said signal information indicative of ignition performance of an automobile; a source of potential connected to said collector electrode; and said diode connected to the emitter electrode of said transistor to forward bias said diode to charge said capacitor in response to said signal information; and electronic switch means connected to said capacitor to discharge said capacitor at a predetermined time after the charging of said capacitor.

13. A cathode-ray oscilloscope for testing the ignition performance of an automobile according to claim 8 wherein said horizontal position control means and said bias control means are potentiometers connected together for operation from a common control shaft.

14. A cathode-ray oscilloscope comprising: a cathode-ray tube for displaying electrical signal information on the face thereof, said cathode-ray tube including horizontal and vertical deflection means; a horizontal sweep circuit connected to said horizontal deflection means to produce a horizontal trace on said face; a vertical deflection circuit connected to said vertical deflection means to give vertical deflection of said horizontal trace thereby displaying the electrical signal information on said face; horizontal position control means in circuit with said horizontal sweep circuit; bias control means in circuit with said horizontal position means and said bias means together for common control thereby providing means for constant focus of the trace on said face.

15. A cathode'ray oscilloscope according to claim 14 wherein said horizontal position means and said base control means are potentiometers connected together for operation from a common shaft.

16. A cathode-ray oscilloscope, comprising: cathode-ray tube for displaying electrical information on the face thereof, said cathode-ray tube including horizontal and vertical deflection means; a horizontal sweep circuit connected to said horizontal deflection means to produce a horizontal trace on said face, said horizontal sweep circuit including a horizontal position control, a bias control, and mechanical means connecting said horizontal position control to said bias control for common adjustment, thereby providing means to maintain constant focus of the display on said face of said cathode-ray tube; a vertical deflection circuit connected to said vertical deflection means to give vertical deflection of said horizontal trace thereby displaying the electrical signal information on said face; and input circuit means connected to said deflection circuit and receiving the signal information to be displayed on said face, said input circuit including a storage capacitor and a diode, said storage capacitor and diode having a short RC time constant during the charging of said capacitor and having a long RC constant during the discharging of said capacitor; whereby, signal information of short time duration is stored in said capacitor and then applied to said vertical deflection circuit to produce a vertical pulse display on the face of said cathode-ray tube which has a time duration greater than the time duration of the signal information applied to said input circuit means.

17. A cathode-ray oscilloscope according to claim 16 wherein said horizontal position control and said bias control are potentiometers mounted for operation on a common shaft.

Claims

1. In an oscilloscope apparatus for displaying a representation of a relatively short duration pulse having a cathode-ray tube for displaying electrical signal information on the face thereof and including horizontal and vertical deflection means, a horizontal sweep circuit connected to said horizontal deflection means to produce a horizontal trace on said face, a vertical deflection circuit connected to said vertical deflection means to give vertical deflection of said horizontal trace for displaying a representation of the pulse on said face, an input circuit connected to said vertical deflection circuit and receiving the pulse to be displayed on said face, said input circuit comprising: a capacitor; means for applying said pulse to the capacitor to charge the capacitor to a voltage corresponding directly to the amplitude of the pulse; resistance means connected across the capacitor defining with said capacitor an RC circuit providing a time delay discharge of said capacitor only through said resistance means to produce an output relatively long duration signal corresponding accurately in amplitude to the amplitude of said short duration pulse; and means connecting said RC circuit to said deflection plate of the cathode-ray tube to cause display of said output signal on said face.

4. A cathode-ray oscilloscope apparatus according to claim 1 further comprising electronic switch means connected to said capacitor to discharge said capacitor at a predetermined time after the charging of said capacitor from said signal information.

10. A cathode-ray oscilloscope for testing ignition performance of an automobile according to claim 8 wherein said input circuit includes a monostable multivibrator having the input thereof arranged for receiving said signal information, and further having an output; an electronic switch having the input thereof arranged for receiving said signal information, said diode connected to said electronic switch to charge said capacitor in response thereto, said output of said multivibrator connected to said capacitor to selectively discharge said capacitor at a predetermined time after the charging of said capacitor thereby applying a pulse to said vertical deflection circuit having a pulse width greater than the pulse width of said signal information.

15. A cathode-ray oscilloscope according to claim 14 wherein said horizontal position means and said base control means are potentiometers connected together for operation from a common shaft.