US2331317A - Stroboscope - Google Patents

Description

SUBSTITUTE FORM-ISSING XR Od' 12, 1943 K. J. GERMESHAUSEN l 2,331,317

sTRoBoscoPE Filed May 9, 1940 2 sheets-sheet 1 Vig? Mtr/ W MW /45 T Mgg -fzaa v Oct. 12, 1943. K. J. GERMEsHAusl-:N 2,331,317

STROBOSCOPE Filed May 9, 1940 2 Sheets-Sheet 2 MSN Patented Oct. 12, 1943 UNITED STATES4 PATENT OFFICE STROBO SCOPE Kenneth Joseph Germeshausen, Cambridge, Mass.

Application May 9, 1940, Serial No. 334,123

36 Claims.

The present invention relates to stroboscopes.

In Letters Patent 2,185,189, granted January 2, 1940, and applications, Serial Nos. 129,837 and 129,838, filed March 9, 1937, which matured on May 21, 1940, into Letters Patent 2,201,166 and 2,201,167, of the former of which the present applicationis a continuation-in-part, there is disclosed a. gaseous-discharge cold-cathode tube particularly adapted for uses requiring large peak currents, with relatively small average currents.

As that tube is capable of providing very brief and intense iiashes of light, such as are necessary for stroboscopic observation, an object of the present invention is to provide a new and improved stroboscope in which the said gaseousdischarge device constitutes the lamp.

Still another object of the invention is to provide a novel method of and means for calibrating the frequency scale of the above stroboscope.

Other objects will be explained hereinafter and '.vill be particularly pointed out in the appended claims. i

For a consideration of what I believe to be novel and my invention, attention is directed to the accompanying description and the claims appended thereto.

In the accompanying drawings, Fig. 1 is a circuit diagram illustrating a preferred complete stroboscope circuit embodying the invention, with a conventional power supply to furnish direct current from alternating-current mains, a separate oscillator for driving the stroboscopic lamp so as to cause the lamp to flash at the desired frequency, means for Calibrating the oscillator, means for operating the lamp so as to cause it to flash at the frequency of the alternatingcurrent supply voltage from the line, and a contactor device for controlling the iiashing rate; Fig. 2 is an enlarged view of a plurality of scales; and Fig. 3 is a view similar to Fig. 1 of a modification illustrating a single knob for controlling all the switches.

The tube I employed in the circuits embodying the present invention may be of the coldcathode gaseous-discharge type illustrated and described in the said Letters Patent 2,185,189, 2,201,166 and 2,201,167. It may comprise an evacuated glass envelope lled with a suitable gas, such as neon, or any of the other noble gases, such as argon or helium. The pressure of the gasin the tube may vary, the usual pressure being from one to two centimeters. The tube contains several electrodes, namely, a solid cathode 2, an anode or plate 5, and one or more grids, inner and outer grids being shown at 3 and 4 between the anode 5 and the cathode 2. The grid 3 is at zero potential with respect to the cathode 2 and the grid 4 is positive with respect to the grid 3. The source oi the electrons is a bright cathode spot on the surface of the cathode. Either grid may be used as the control electrode, depending upon the polarity and the magnitude of the control voltage. Further details may be obtained by reference to the said Letters Patent.

As explained in the said Letters Patent 2,185,189 and 2,201,166, the grid 3 may, in normal us'e, be placed close to the cathode 2, say, not more than a few millimeters from the cathode. and may be of such shape that the cathode will sputter a thin surface layer or coating of a material of low work-function that does not combine chemically with the gas in the envelope, such as caesium, on the grid surface. A thin surface coating or layer of the caesium or other material of low work-function is thus maintained on the grid 3 during the normal operation of the tube. As explained in the said Letters Patent 2,201,167, however, .the grid 3 may, under certain circumstances, be precoated.

The form of the arc stream between the anode and the cathode is a column of small diameter which has high intrinsic brilliance, with substantially all the light emitted from the concentrated arc stream. This discharge is easily distinguished from a glow discharge, which occupies substantially the whole interior of the tube, with a discharge of low intrinsic brilliance, the 'greatest brilliance being at the surface of the cathode.

In the illustrated stroboscopic circuit, the anode 5 and the cathode 2 of the tube are shown connected across a condenser il, which is continuously charged, by way of conducting wires l and 8, from a suitable direct-current source of, say, 300 to 400 volts, connected through a variable current-limiting impedance l2, which may by a resistor, or a combination of resistance and inductance. The source may be constituted f thermionic or gaseous-discharge rectifiers for producing direct current from alternating current, as illustrated, or any other source of direct current. r

In the illustrative circuit', a transformer 18, a double-anode rectifier tube 'ff and a condenser 69 form a conventional power supply to give any desired direct-current voltage, say, 300 volts, from the 11G-volt alternating current mains.

` The discharge condenser Il is used for highfrequency operation of the stroboscope circuit;

for low-frequency operation, a condenser I3 is connected in parallel with the condenser II by means of a switch 66.

As explained more fully in the said Letters Patent, in the operation of the circuit, the condenser I| starts to become charged from theI direct-current source through the impedance I2, the tube being non-conductive. When the voltage across the condenser I I reaches the required value, say, 110 volts, however, the voltage between the grid 4 and the cathode 2 exceeds the breakdown value and the tube 'becomes conducting. The current passes between the anode and the cathode continually but interruptedly to set up continually discharges of arc characteristic between the cathode and the anode. It is of amperage suiiiciently high to produce a potential gradient on a relatively small area only of the cathode high enough to extract electrons from the cathode while the cathode remains cold, at low average temperature, and to produce a fall of cathode potential lower than that occurring in a glow discharge. 'I'he average value of the said current is nevertheless relatively low. If a pill constituted of caesium chloride and aluminum, for example, be employed as the cathode, the action of the cathode spot causes the caesium chloride to break down, aluminum being substituted for the caesium and forming aluminum chloride. The intervals between the discharges are suiilciently large so that the average temperature of the cathode remains low enough to prevent rapid disintegration of the cathode.

Impedances 19 and 80 are shown connected between the cathode 2 and the grid 4, and between the grid 4 and the anode 5, respectively; and an impedance 8| is shown connected between the cathode 2 and the grid 3. 'I'he bias is so adjusted on the grid 4 by means of these impedances, which may be resistors, and the supply voltage is so adjusted, that it is possible to have the voltage between the anode 5 and the cathode 2 much greater than the voltage required to cause a glow discharge between the grid 4 and the grid 3, and the tube will thus stay in a non.-

conducting state when the condenser is fully` charged. The lamp. circuit comprises the said two discharge condensers I| and I3, the said current-limiting resistor I2 and the three resistors 8|, 80 and 19.

Current is also supplied from the power supply to conductors |00 and |32. 'I'he conductor |32 is connected through a resistor |24, to a switch 88, adapted to occupy two positions A and B. The conductor 00 is connected, by a contactor device 81, to a contact member with which the switch 86 is adapted to contact in position B. The circuits of the hereinafter-described multivibrator are open when the switch 86 oc cupies the position B. The switch 8B is connected-by a conductor 58, through a condenser 83, to the grid 3. The switch 88 is connected also to the source of alternating current, by way of a conductor 20, and through a resistor 84, by a switch 85. The contactor 81 may be periodically opened and closed in any desired manner;

this is not shown in order to simplify the drawings.

With the switch 86 in position B, and the switch 85 open, the lamp I can be triggered at the desired instant by means of the contactor device 81, which causes a momentary surge through the condenser 83.v When the contactor device 81 closes, therefore, the grid 3 is given av negative voltage pulse equal to the voltage existing between the conductors |00 and |32. The condenser 83 then discharges trough the resistor 8| and the grid 3 to the cathode 2, allowing the l voltage of the grid 3 to return to zero. The discharge circuit extends from one side of the condenser 83, through the resistor 8| and the grid 3 and the cathode 2, in parallel, by way of the conductors 8, and |00, and through the switches 81 and 86, the latter in the position B, to the other side of the condenser 83. Once the contactor 81 becomes closed, it may remain closed Without the stroboscope flashing on again when the condensers II and I3 build up their voltages.

The operation is independent of the length of time that the contactor 81 remains closed, the complete function being performed at the moment it rst becomes closed. The contactor 81, therefore, gives only one impulse of voltage at each closing, and the length of time the contactor 81 remains closed does not affect the operation of the tube.

The voltage applied between the grids 3 and 4 should be suicient to cause an initiating glow discharge between the grid 4 and the coating on the grid 3. The voltage at which this discharge takes place is low and substantially constant, due to the fact 'that the grids 3 and 4 shield the field between the grids from charges on the glass. To start the glow discharge between the grids may require a voltage of only about a hundred volts and a current of only a fraction of a milliam- .pere, so very little poweris required.

land a resistor.61. A filter condenser 88 is provided to remove any slight alternating-current ripple in the direct-current voltage.

The oscillator circuit comprises a pair of electron-discharge vacuum triodes 88 and 89, a pair of anode or plate resistors or other impedances |22 and |24, the grid resistors or other impedances |38 and |38 that are connected to the grids or control electrodes |4 and ||6 of the triodes 89 and 88, the grid condensers or electro-storage devices |25, |28, |21 and |28, and the condenser |29. The frequency-control circuit of the said oscillator comprises the variable, calibrating resistors or other impedances |2| and |30 and the potentiometer or other biasing source of energy or other biasing means ||8. The set of electrodes of the vacuum triode 89, comprising the filament or cathode 96, the grid or control electrode ||4 and the anode 92, and the set of electrodes of the vacuum triode 88, comprising the lament or cathode 98, the grid or control electrode ||8 and the anode 94, may be in separate envelopes, or in a single envelope. It is usually more' conven- -ient to combine the two in a single tube. The

voltage from the voltage source is applied to the potentiometer ||8 is thus connected between the calibrating resistors |2| and |30.

The cathodes of the oscillator tubes 88 and B9 are connected to the conductor |00. The anodes of the oscillator tubes are'connected to the conductor |32 and the resistor |2| through the resistors |22 and |24. The pair of resistances |22 and |24 thus connect the anodes 92 and 94, respectively, to the upper end of the potentiometer |.|8, which is positive with respect to the cathconnected by the conductor 64, through the resistor 61, to that terminal of the rectifier 11 that is positive with respect to their cathodes. The resistors |22 and |24, therefore, maintain the anodes 92 and 94 positive with respect to the cathodes. The switch 86 is connected, in position A, to the anode 94 of the triode 88. The anodcs 92 and 94 are thus connected to one sideV of the source of voltage by the conductor |32, through the resistances |22 and |24. The cathodes 96 and 98 of these respective triodes are connected to the other side of the voltage source by the conductor |00. The slider |34 of tlie potentiometer ||8 is connected to the two resistors cr other impedances |36 and |38 by a conductor |33.

The input circuit of the triode 89 may be traced from the filament 96, by way of the conductor |00, through the Calibrating resistor |30, the lower portion of the potentiometer H8, and the adjustable arm |34, and by way of the conductor |33, through the resistor |38, to the grid |4. The .input circuit of the triode 88 may similarly be traced from the filament 98, by way of the conductor |00, through the Calibrating resistor |30, the lower portion of the potentiometer ||8, and the adjustable arm |34, and by way of the conductor |33, through the resistor |38, to the grid H6. One of the ends of each of the respective resistances |36 and |38 is thus connected to one of the respective control electrodes ||4 and ||6 of the respective tubes 89 and 88. Their other ends are connected to a potential positive i with respect to the cathodes 96 and 98, by way of the conductor |33, to the adjustable arm |34 of the potentiometer ||8. The said other ends of the resistors |36 and |38 are thus maintained positive with respect to the cathodes 96 and 98. The output circuit of the triode 89 may be traced from the filament 96, by way of the conductor |00, through the Calibrating resistor |30, the potentiometer ||8, and the Calibrating resistor |2| and, by way of the conductor |32, through the resistor |22, to the anode 92. The output circuit of the triode 88 may similarly be traced from the filament 98, by way of the conductor |00, through the Calibrating resistor |30, the potentiometer ||8 and the calibrating resistor |2| and, by way of the conductor |32, through the resistor |24, to the anode 94. The condenser |25 is connected between the grid ||6 of the electrondischarge device 88 and the anode 92 of the electron-discharge device 89, and the condenser |26 may be connected in parallel therewith. The condenser |21 is similarly connected between the grid ||4 of the electron-discharge device 89 and the anode 94 of the electron-discharge device 88, and the condenser |28 may be connected in parallel therewith.

With the switch 86 in the position A, the output of the oscillator, taken from the plate of one of the triodes, is connected to the stroboscopic lamp through the coupling condenser 83 and the conductor 58.

The principles of operation of the oscillator and odes 96 and 98 by reason of the fact that it is its production of a saw-tooth wave form are well understood in the art and hence will not be gone into here. In the usual oscillator, the conductor |33, joining the ends of the grid resistors |36 and |38, is connected to the cathode circuit of the triodes, represented by the conductor |00. The

frequency of the oscillator is then varied by vary- .A ing the resistors |36 and |38. Since the resistors |38 and |38 are of considerable magnitude (say 1 megohni) they are not conveniently procurable in the Variable form and, furthermore, varying these resistors gives a non-linear frequency scale of the exponential-type- According to the invention illustrated and described herein and in Letters Patent 2,302,690, issued November 24, 1942, the frequency of the multivibrator is controlled linearly by adjusting the slider |34 back and forth on the potentiometer I8 to vary the positive bias on the grids of the triodes 88 and 89 in alinear fashion. This yields not only a linear frequency scale, but also a wide frequency rangee-as much as six to one. The potentiometer ||8 is calibrated in flashes per minute of the stroboscope lamp, as hereinafter more fully described, with the aid of a vibrating reed |40 and the Calibrating resistors |2| and |30. It has a direct-reading scale of frequency against resistor setting, instead of an exponential scale, as formerly obtained. A somewhat greater frequency range occurs, moreover, with reasonable values of resistance in the po tentiometer ||8.

The potentiometer ||8 is provided with two linearly calibrated or uniformly divided scales |52 and |54, with a four-to-one factor between them. The frequency of the oscillator is shifted by this factor by means of the condens'ers |26 and |28. Connecting these condensers in the circuit by means of their accompanying respective switches |56 and |58 reduces the frequency of the oscillator and shifts the whole frequency scale in linear fashion, the amount of the shift depending on the values of the condensers. The stroboscope may have a flashing range extending to over 15,000 flashes per minute.

To insure an absolutely linear scale, it is important that the time constant of the resistor |22 with condenser |25, and the time constant of resistor |24 with condenser |21, be appreciably less than the shortest interval between oscillatlons at the high-frequency end of the scale. The condenser |29 may be connected across the conductors |00 and |32, in parallel with the resistors |2| and |30 and the potentiometer IIB, to correct a slight curvature at the lower end of the scale.

There is a tendency for the scale or scales |52 and |54 to have a further slight curvature in the region of operation of the oscillator with the bias voltage on the grids at the lower end, near the zero, of the scale. This may be corrected for -by having the minimum value of the resistor |30 not less about ten per cent of the potentiometer ||8. The stability of the oscillator, furthermore, is improved when it is operating with some positive bias on the grids.

Though the potentiometer ||8 has a uniform tion in frequency per unit adjustment of the slider 34 may be slightly greater or less than that indicated on the scale. 'I'he before-mentioned variable resistors |2| and |30, however, serve to adjust the calibration of the frequency vscale by matching the oscillator to the scale. The resistor |2| adjusts the frequency of the oscillator at the high end of the scale to corre'- spond to the scale markings, without appreciably affecting the lower end of the scale, and the resistor |30 similarly adjusts the lower end of the scale, without affecting the higher end. Both resistors |2| and |30, at their respective ends of the scale, serve to adjust the rate at which the frequency of the multivibrator changes in response to changes in the applied bias voltage. By means of these resistors it is possible so to calibrate the oscillator as exactly to match the frequency to the. linearly calibrated scale provided, regardless of slight variations in the oscillator circuit due to manufacturing errors or aging of the parts.

It is further desirable to check the calibration of the oscillator, not only at a single frequency but throughout the length of the scale. This may be effected in the same way as the original calibration of the oscillator. According to the specific embodiment of the invention that is illustrated and described herein, the checking apparatus comprises the vibrating reed |40, driven by means of a solenoid |42 in exact synchronism with the alternating current of the line. To this end, the solenoid |42 is connected in circuit with a switch |44 and conductors |46 and |48 across the alternating-current supply. At most localities, the frequency of the alternating mains is controlled with suillcient accuracy to enable the vibrating reed |40 to serve as a standard. The reed is placed so that the light from the flashing lamp falls upon it so that, when the flashing rate of the lamp is the same as the frequency of the reed, the reed appears to stand still. When this occurs, the slider |34 of the potentiometer 8 should be at a marked Calibrating point. If it is not, it may be brought to the proper point by adjustments of the Calibrating resistors |2| and |30. The check is easily and quickly made and serves to compensate for factors that may impair the calibration.

With the reed |40 operating at 7200 vibrations per minute, for example, a stand-still pattern of the reed may be obtained not only at 3600 vibrations, but also at many multiples and fractional sub-multiples of 120 cycles per second, the reed frequency. The scale may thus be readily checked, for example, at 3600, 2400, 1800, 1440, 1080, 900, 800, 720 and 600 vibrations per minute. These may afford many calibration points of the scale. It usually suillces, in actual practice, to effect the check at two points only, say. 3600 and 900 or 600 vibrations per minute. 'I'he resistors |2| and |30, as before explained, en-

able setting of frequency of the oscillator in terms of the 60-cycle reed |40 to correspond to the scale markings at both ends of the scale, without disturbing the linear variation of frequency with adjustment of the slider |34 over the potentiometer H8. The resistors |2| and |30 may be said to serve the function of so tipping the whole frequency scale that the value, say, 3600, checked at one frequency by means of the reed |40 shall correspond to all frequencies throughout the length of the scale. Uniform rate f Change of frequency corresponding to the adjustment of the slider |34A is thus preserved throughout the length of the scale.

Analternative method of vchecking the calibration is shown by a glow lamp |50 and a resistor |49, connected in series to thealternatingcurrent supply at one anode of the rectifier 11 and to the anode 5 of the stroboscope lamp. The glow-lamp |50 will indicate the difference in frequency between the frequency of the alternatingcurrent-supply source and the flashing frequency of the stroboscope. When the frequency of the alternating-current supply and the stroboscope are the same and in phase, the glow lamp will be extinguished. When the frequency is slightly different, the glow lamp will go on and off at a rate equal to the difference in frequency. This is the familiar beat method of matching frequencies.

To elaborate further upon the method of calibration, the slider element |34 is flrst adjusted to a desired reading of the scale, say, the 3600 reading at the high end of the scale. The corresponding adjustment of the potentiometer ||8 will not, however, necessarily be such as to cause the multivibrator to oscillate at the desired 3600 -frequency. The resistor |2| will therefore be adjusted until the multivibrator does oscillate at the 3600 frequency. The operator will be guided in his adjustment of the resistor |2| by observing the relation between the flashes of the tube and the vibrations of the reed.| 40 or the` flashes of the glow-tube |50. When the flashing frequency of the tube coincides with the frequency of the brating reed |40 or the glow-tube |50, the fla the 3600 reading at the high end of the scale.

The slider |34 will then be set to another reading of the scale, say, the 600 or the 900 reading of the low end of the scale. The resistor |30 will now be adjusted to vary the frequency of the oscillations of the multivibrator, until the flashing frequency of the intermittently flashing tube I again coincides with the frequency of the known source of frequency, namely, the vibrating reed |40 or the glow-lamp |50. The flashing frequencywill now be matched also against the 600 or the 900 reading at the low end of the scale.

The slider |34 may, in this manner, be set to occupy as many different positions with respect to the scale as desired, and the frequency of the multivibrator may be adjusted at each of these settings in the same way. To each predetermined setting of the slider |34, there will be found to correspond a flashing frequency of the tube I, the value of which may be obtained by adjustment of one or the other of the resistors |2| and |30. It will be found that two such settings are, in practice, all that are needed. Owing to the fact that the resistor |2| effects adjustment at the high end of the scalewithout affecting the low end of the scale and without disturbing the linearity, and that the resistor |30 effects ad- .J'ustment at the low end of the scale withoutafing frequency will be matched against synchronism therewith. This is useful in certain applications of the stroboscope.

Fig. 3 illustrates a complete stroboscope circuit in which all of the switches are operated by a single controlling knob 302. 'I'he circuit is similar to that shown in Fig. 2 and performs the same function. i

' An output jack 200 is provided in the discharge circuit of the condenser Il so that the discharge surge of the condenser may be used to operate a larger stroboscope.

The switches 303, 304, 305, 306 and 20| are arranged to be operated by an insulating shaft 30| which may be turned by means of the knob 302. With the switch in the position C, the toggle switch 20| is off. With the switch in any of the positions D, E, F, G and H, the toggle switch is on, thus supplying alternating current through -the wires 202, 203, 204 and 205 to the primary of the power transformer 18. With the switch in position D, the condensers |26 and |28 are connected into the oscillator circuit by switches 30| and 304 and the oscillator operates on the low scale |52. Switch 305 connects the output of the oscillator from the plate 34 to the grid 3 of the tube I by means of conductor 301, condenser 83 and conductor 58. The switch 306 connects the discharge condenser I3 in parallel with the condenser II. The stroboscope is thus adapted to run on the low scale. y

With the switch in position E, condensers |23 and |28 are disconnected, switch 305 connects the oscillator to the grid 3 and condenser I3 is disconnected. The stroboscope is thus adapted to run on lthe high scale.

With the switch in the position F, some 60- cycle current is supplied to the grid of the os'- cillator tube 88, from the secondary of the transformer 18, through resistor 84, through switch 303, and by the conductor 309. The switch 304 connects the condenser |28 in parallel with the condenser |21, switch 305 connects the output of the oscillator to the grid of the tube I, and switch 300 connects the condenser I3 in parallel with the condenser I I. The stroboscope is thus adapted to operate ln synchronism with the alternating supply voltage.

With the switch in position G, the switch 305 disconnects the grid 3 from the oscillator and connects it to the contactor element 81. The circuit is then adapted to be operated by means of the contactor 01 as described in connection with Fig. 2. Switch 306 connects the condenser I3 in parallel with condenser I I, making the operation suitable for low frequencies. For high-frequency contactor operation the switch is turned to position H, which disconnects the condenser I3.

Connecting al1 the switches to a single control knob greatly simplies the operation of the stroboscope and makes it a more practical and useful instrument.

In Fig. 3, calibration is effected by means oi the resistors IIO and |30.

The light produced by this stroboscope, obtained from a ll-volt, 60-cycle alternating-currcntsource, is sufficient to permit good stroboscopic observation of mechanisms, particularly when the light is concentrated by means of a' parabolic reflector. Because of the calibrated requency scale, the stroboscope is particularly useful in measuring the speed of rotating or vibrating mechanisms.

Modifications will occurto persons skilled in the art, and all such are considered to fall within the scope and spirit of the invention.

What is claimed is:

1. A stroboscope having, in combination, a luminescent-discharge device, means for causing intermittent flashing of the discharge device, a linearly calibrated scale, and means for adjusting the dashing frequency to correspond substantially linearly to the scale throughout substantially the length of the scale.

2. A stroboscope having, in combination, a luminescent-discharge device, an oscillator for causing intermittent flashing of the discharge device, a linearly calibrated scale and means for adjusting the frequency of the oscillator to correspond substantially linearly to the scale throughout substantially the length of the scale, thereby to effect linear calibration of the flashing frequency. 1

3. A stroboscope having, in combination, a luminescent-discharge device comprising an anode and a cathode of a material that will break down under the action of a cathode spot and form a surface coating thereon of a material of low work-function, a condenser, a charging circuit for connecting the condenser to a source of energy, means ior periodically discharging the condenser through the discharge device to subject the cathode and the anode to energy suiiicient in character and amount to form cathode spots on the cathodebut Without supplying suffi cient heat to the cathode to cause destruction of the cathode by heat, thereby to cause intermittent fiashing of the discharge device, a linearly calibrated scale, and means for adjusting the flashing frequency to correspond substantially linearly to the scale throughout substantially the length to the scale.

4. A stroboscope. having, in combination, a luminescent-discharge device comprising an envelope containing gas and having therein electrodes comprising an anode, a solid cold cathode and a control electrode, a condenser, means connecting the condenser to the anode and the cathode, a source of energy, means for charging the condenser from the source, an oscillator, means for impressing the oscillations of the oscillator upon the control electrode to cause electrical discharges to be passed from the condenser periodically between the cathode and the anode through the gas in the envelope to cause intermittent flashing of the discharge device, a linearly calibrated scale, and means for adjusting the frequency of the oscillator to correspond substantially linearly to the scale throughoutsubstantially the length of the scale, thereby to eiect linear calibration of the dashing frequency.

5. A stroboscope having, in combination, a luminescent-discharge device comprising an envelope containing gas and having electrodes cornprising an anode, a solid cold cathode and a control electrode, the cathode being constituted of a material having a relatively low work-function and that does not combine chemically with the gas in the envelope, means for applying a voltage between the anode and the cathode, an oscillator, means for impressing the oscillations of the oscillator upon the control electrode to cause electrical discharges to be passed periodically between the anode and the cathode through the gas in the envelope to cause intermittent flashing of the discharge device, a linearly calibrated scale, and means for adjusting the frequency of the oscillator to correspond substantially linearly to the scale throughout substantially the length of the scale, thereby to effect linear calibration of the dashing frequency.

6. A stroboscope having, in combination, a lu.-

mnescent-discharge device comprising an en,- velope containing gas and having an anode, :a cathode, a grid disposed between the anode and the cathode, a grid disposed between the cathode and the first-named grid, an impedance connected between the anode and the first-named grid,

'an impedance connected between the cathode and the first-named grid, a source of voltage, means connecting the source to the anode and the cathode in parallel to the impedances connected in series, an impedance connected between the cathode and the second-named grid, an oscillator, means for impressing the oscillations of the oscillator upon the second-named grid to cause electrical discharges to be passed periodically between the grids and, therefore, between the cathode and the anode to cause intermittent flashing of the discharge device, a linearly calibrated scale, and means for adjusting the frequency of the oscillator to correspond substantially linearly to the scale throughout substantially the length of the scale, thereby to eiect linear calibration of the ashing frequency.

7. A stroboscope having, in combination, a luminescent-discharge device, a multivibrator for causing intermittent flashing of the discharge device, the multivibrator comprising two sets of electrodes, each comprising a cathode, a control electrode and an anode, an input circuit connected between the cathode and the control electrode of each set, an output circuit connected between the cathode and the anode of each set, an impedance connected in the output circuit of one of the sets of electrodes, Yan impedance connected in the output circuit of the other set of electrodes, two

condensers connected, respectively, between the control electrode of each of the sets and the imtween the cathode and the anode of each set, an impedance connected in the output circuit of one of the sets of electrodes, an impedance connected in the output circuit of the other set of electrodes, two condensers connected, respectively, between the control electrode of each of the sets and the impedance of the other set, a source of energy connected in both output circuits, means for applying an adjustable voltage in substantially linear fashion to the input circuits, and an impedance connected between the source of energy and one of the multivibrator electrodes. I

10. A stroboscope having, in combination, a luminescent-discharge device, a multivibrator for causing intermittent flashing of the dis- 1 charge device, the multivibrator comprising two pedance of the other set, and means for energizing the output circuits and for applying an adjustable voltage bias on the control electrodes in substantially linear fashion in order to control the` frequency of the multivibrator substantially linearly.

8. A stroboscope having, in combination, a luminescent-discharge device, a multivibrator for causing intermittent flashing of the discharge device, the multivibrator comprising two sets of electrodes, each comprising a cathode, a control electrode and an anode, an input circuit connected between the cathode and the control electrode of each set, an output circuit connected between the cathode and the anode of each set, an impedance connected in the output circuit of one of the sets of electrodes, an impedance connected in the output circuit of the other set of electrodes, two condensers connected, respectively, between thel control electrode of each of the sets and the impedance of the other set, means for energizing the output circuits and for applying an adjustable voltage bias on the con.- trol electrodes in substantially linear fashion in order to control the frequency of the multivibrator substantially linearly, an impedance, and means for varying the impedance to adjust the rate at which the said frequency changes in response to changes in the applied bias voltage.

9. A stroboscope having, in combination, a luminescent-discharge device, a multivibrator for causing intermittent flashing of the discharge device, the multivibrator comprising two sets of electrodes, each comprising a cathode, a control electrode and an anode, an input circuit connected between the cathode and the control electrode of each set, an output circuit connected besets of electrodes, each comprising a cathode, a control electrode and an anode, an input circuit connected between the cathode and the control electrode of each set, an output circuit connected between the cathode and the anode of each set, an impedance connected in the output circuit of one of the sets of electrodes, an impedance connected in the output circuit of the other set of electrodes, means for selectively connecting two pairs of condensers, the condensers of each pair, respectively, between the control electrode of each of the sets and the impedance of the other set, and means for energizing the output circuits and for applying an adjustable voltage bias on the control electrodes in substantially linear fashion in order to control the frequency of the multivibrator substantially linearly.

l1. A stroboscope having, in combination, a stroboscopic tube comprising a luminescent-discharge device having an anode and a cathode, a condenser, a source of alternating energy, means for rectifying the energy, means for periodically chargingthe condenser from the rectied energy, means for connecting the condenser to the anode and the cathode, a multivibrator comprising two sets of electrodes, each comprising a cathode, a control electrode and an anode, an input circuit connected between the cathode and the control electrode of each set, an output circuit connected between the cathode and the anode of each set, an impedance connected in the output circuit of one of the sets of electrodes, an impedance connected in the output circuit of the other set of electrodes, means connected in both output circuits for biasing the control electrodes positively, two condensers connected, respectively, between the control electrodes of each of the setsv and the impedance of the other set, and means for comparing the frequency of the multivibrator with that of the source of alternating energy connected in both output circuits comprising a glow lamp connected between the said source and the anode of the luminous-discharge device.

l2. A stroboscope comprising a luminescentdischarge device, 'an oscillator for causing intermittent flashing of said discharge device, means for adjusting the frequency of the said oscillator, a vibrating member energized to vibrate at a predetermined frequency positioned to be i1- luminated by intermittent flashing of said discharge device, and additional means for adjusting the output frequency of said oscillator to synchronize the intermittent hashing of said discharge device and the vibration of said vibrating member.

13. A stroboscope having, in combination, a stroboscopic tube comprising a luminescentdischarge device having an anode and a cathode, a condenser, a source of alternating energy,

means for rectifying the energy, means for periodically charging the condenser from the rectihed energy, means for connecting the condenser to the anode and the cathode, an oscillator for controlling the discharge of the condenser between the anode and the cathode, and means for comparing the frequency of the oscillator with that of the source of alternating energy comprising a glow lamp connected between the said source and the anode.

14. A stroboscope having, in combination, a luminescent-discharge device, a multivibrator for causing intermittent hashing of the discharge device, the multivibrator comprising two sets of electrodes, each comprising a cathode, a control electrode and an anode, an input circuit connected between the cathode and the control electrode of each set, an output circuit connected between the cathode and the anode of each set, means for applying an adjustable voltage in substantially linear fashion to the input circuits, thereby to adjust the hashing frequency substantially linearly, and means for adjusting the rate at which the said frequency changes in response to changes in the applied voltage.

15. A stroboscope having, 'n combination, a luminescent-discharge device, means for causing intermittent hashing of the discharge device, a linearly calibrated scale, a periodically movable member arranged to be illuminated by intermit-V tent hashing of the discharge device, and means for adjusting the hashing frequency to correspond substantially linearly to the scale and in synchronism with the movements of the periodically movable member.

16. A stroboscope having, in combination, a luminescent-discharge device, means for causing intermittent hashing of the discharge device, a linearly calibrated scale, a vibrating member arranged to be illuminated by intermittent hashing of the discharge device, and means for adjusting the hashing frequency to correspond substantially linearly to the scale and in synchronism with the vibrations of the vibrating member.

17. A stroboscope having, in lcombination, a luminescent-discharge device, means comprising an oscillator for causing intermittent hashing of the discharge device, a linearly calibrated scale, a vibrating member arranged to be illuminated by intermittent hashing of the discharge device, and means for adjusting the oscillator to adjust the hashing frequency to correspond substantially linearly to the scale and in synchronism with the vibrations of the vibrating member.

18. A stroboscope having, in combination, a scale having an indicator, the scale and the indicator being adapted to be set relative to each other to correspond to predetermined values of the hashing frequency, and means for matching 'the hashing frequencies of the stroboscope with the scale comprising means for adjusting the hashing frequency to the predetermined values corresponding to the relative settings of the scale and the indicator.

19. A method of matching the hashing frequencies of a stroboscope with a scale having an indicator that comprises setting the scale and the indicator relative to each other to correspond to predetermined values of the hashing frequency, and matching the hashing frequencies of the stroboscope with the scale by adjusting the hashing frequency to the predetermined values corscale comprising means for adjusting the hashing frequency to the values corresponding to the positions of the slider; A

21. A stroboscope having, in combination, means adjustable to vary the hashing frequency of the stroboscope, a scale having an indicator adapted to occupy different positions relative to the scale corresponding to different adjustments of the varying means, the scale and the indicator being adapted to be set relative to each other to correspond to predetermined values of the hashingfrequency, and means for matching the hashing frequencies of the stroboscope with the scale comprising means for adjusting the hashing frequency to the values corresponding to the relative settings of the scale and the indicator.

22. A `stroboscope having, in combination,

means adjustable to vary the hashing frequency of the stroboscope, a linearly calibrated scale having an indicator adapted to occupy different positions lrelative to the scale corresponding to different adjustments of the varying means, the scale and the indicator being adapted to be set relative,to each other to correspond to predetermined values of the hashing frequency, and means for matching the hashing frequencies of the stroboscope with the scale comprising two adjustable resistors for adjusting the hashing frequency to the values corresponding to the relative settings of the scale and the indicator, adjustment of one of the resistors controlling the linear correspondence at one end of the scale, andy adjustment of the other resistor controlling the linear correspondence at the other end of the scale.

23. A stroboscope having, in combination, a

luminescent-discharge device, means for causing intermittent hashing of the discharge device, means adjustable to vary the hashing frequency, a scale having an indicator adapted to occupy different positions relative to the scale corresponding to different adjustments of the varying means, the scale and the indicator being adapted to be set relative to each other to correspond to predetermined values of the hashing frequency, and means for matching the frequencies of the stroboscope with the scale comprising means for adjusting the hashing frequency to the values corresponding to the relative settings of the scale and the indicator.

24. A stroboscope having, in combination, an oscillator for varying the hashing frequency of the stroboscope, means adjustable to vary the f requency of the oscillator to vary the hashing fre quency, a scale having an indicator adapted to occupy different positions relative to the scale corresponding to different adjustments of the varying means, the scale and the indicator being i scale having an indicator, the scale and the indiv the scale and the indicator.

25. A stroboscope having, in combination, a

cator being adapted to be set relativey to each f other to correspond to predetermined values of the flashing frequency, a source of known frequency, and means for matching the flashing frequencies of the stroboscope with the scale comprising means for adjusting the flashing fre-4 quency into correspondence With the frequency of the source to obtain the values of the flashing frequency corresponding to the relative settings of the scale and the indicator.

26. A method of matching the flashing frequencies of a stroboscope with a scale having an indicator that comprises setting the scale and the indicator relative to each other to correspond to predetermined values of the flashing frequency, and matching the flashing frequencies of the stroboscope with the scale by adjusting the flashing frequency, following upon each setl ting, into correspondence with the frequency of luminescent-discharge device, an oscillator for` a source of known frequency to obtain the values of the flashing frequency corresponding to the relative settings of the scale and the indicator.

27. A stroboscope having, in combination, a

causing intermittent dashing of the discharge device, means adjustable to vary the frequency of the oscillator to Vary the flashing frequency, a scale having an indicator adapted to occupy different positions relative to the scale corresponding to different adjustments ofthe varying means, the scale and the indicator being adapted to be set relative to each other to correspond to predetermined values of the flashing frequency, and means for matching the frequencies of the stroboscope with the scale comprising means for adjusting the frequency of the oscillator to adjust the flashing frequency to the values corresponding to the relative settings of the scale and the indicator.

28. A stroboscope having, in combination, a luminescent-discharge device, an oscillator for causing intermittent flashing of the discharge device, the oscillator comprising control-electrode means and a source of energy, means for connecting the source of energy to the control-electrode means. the connecting means being adjustable to adjust the frequency of the oscillator to vary the flashing frequency, a scale having an indicator adapted to occupy different positions relative to the scale corresponding to different adjustments of the connecting means, the scale and the indicator being adapted to be set relative to each other to correspond to predetermined values of the flashing frequency, and means for matching the frequencies of the stroboscope with the scale comprising means for adjusting the frequency of the oscillator to adjust the flashing frequency to the values corresponding to the' relative settings of the scale and the indicator.

29. A stroboscope having, in combination, a luminescent-discharge device, a source of alternating energy, means for connecting lthe discharge device to the source, means-for causing intermittent flashing of the discharge device, means adjustable to vary the flashing frequency, a scale having an indicator adapted to occupy different positions relative to thev scale corresponding to different adjustments of the varying means, the scale and the indicator being adapted to be set relative to each other to correspond to predetermined values of the flashing frequency, a glow-lamp connected between the source and the discharge device for indicating the difference in frequency between the frequency of the source and the flashing frequency, and means for matching the flashing frequencies of the stroboscope and the scale comprising means for adjusting the Iflashing frequency to correspond to the relative settings of the scale and the indicator.

30. A stroboscope having, in combination, a luminescent-discharge device, a source of alterhating energy, means for connecting the discharge device to the source, means for causing intermittent flashing of the discharge device, means adjustable to vary the flashing frequency, a scale having an indicator adapted to occupy different positions relative to the scale corresponding to different adjustments of the varying means, the scale and the indicator being adapted to be set relative to each other to correspond to predetermined values of the flashing frequency, a vibratory member positioned to be illuminated by the flashes from the discharge device, means connected to the source for vibratingthe vibratory member, and means for matching the flashing frequencies of the stroboscope and the scale comprising means for adjusting the flashing frequency into correspondence with the frequency of vibration of the vibratory member to obtain the values of the flashing frequency corresponding to the relative settings of the scale and the indicator.

31. A stroboscope having, in combination, a luminescent-discharge device, a condenser, a charging circuit for connecting the condenser to a source of energy, means for discharging the condenser through the discharge device to cause intermittent flashing of the discharge device, means adjustable to vary the flashing frequency, a scale having an indicator adapted to occupy different positions relative to the scale corresponding to different adjustments of the varying means, the scale and the indicator being adapted to be set relative to each other to correspond to predetermined values of the flashing frequency, and means for matching the flashing frequencies of the stroboscope with the scale comprising means for adjusting the flashing frequency to the values corresponding to the relative settings of the scale and the indicator.

32. A stroboscope having, in combination, a luminescent-discharge device, an oscillator for causing intermittent flashing of the discharge device, the oscillator having electrodes comprising cathode means, control-electrode means and anode means, an input circuit connected between the cathode means and the control-electrode means, an output circuit connected between the cathode means and the anode. means, means for applying an adjustable voltage to the input circuit to vary the flashing frequency, means forl adjusting the flashing frequency, a scale having an indicator adapted to occupy different positions relative to the scale corresponding to different adjustments of the voltage-applying means, the scale and the indicator being adapted to be set relative to each other to correspond to predetermined values of the flashing frequency, and means for matching the frequencies of the stroboscope with the scale comprising means for adjusting the frequency of the oscillator to adjust the flashing frequency to the values corresponding to the relative settings of the scale and the indicator.

33. A stroboscope having, in combination, a

(la t luminescent-discharge device, a source of alternating energy, meansfor connecting the discharge device to the source, means for causing lnternnttent flashing of the discharge device, means adjustable to vary the flashing frequency,

a scale having an indicator adapted to occupy different positions relative to the scale corre- A spending to different adjustments of the varying means, the scale and the indicator being adapted to be set relative to each other to correspond to predetermined values of the flashing frequency, and means for matching the flashing frequencies of the stroboscope with the scale comprising means for adjusting the flashing frequency into correspondence with the frequencies of the source to obtain the values of the flashing frequency corresponding to the relative settings of the scale and the indicator.

34. A stroboscope having, in combination, a luminescent-discharge device, a multivibrator for causing intermittent flashing of the discharge device, the multivibrator comprising two sets of electrodes, each comprising a cathode, a controlelectrode and an anode, an input circuit connected between the cathode and the control elec trode of each set, an output circuit connected between the cathode and the anode of each set, an impedance connected in the output circuit of one of the sets of electrodes for maintaining the anode of the said one set of electrodes positive with respect to the cathode of the said one set of electrodes, an impedance connected in the output circuit of the other set of electrodes for maintaining the anode of the said other set of electrodes positive with respect to the cathode of the said other set of electrodes, two condensers connected, respectively, between the control electrode of each of the sets and the anode of the other set, means for energizing the output circuits and for applying an adjustable voltage bias on the control electrodes in order to adjust the flashing frequency, and means for adjusting the rate at which the said frequency changes in response to changes in the applied bias voltage.

patent No. 2,551,517. l

CER'I'lFl CATE 0F COR REC TI ON 35. A stroboscope having, in combination, a luminescent-discharge device, a multivibrator for causing intermittent flashing of the discharge device, the multivibrator comprising two sets of l electrodes, each comprising a cathode, a. control electrode and an anode, an input circuit connected between the cathode and the control electrode of each set, an output circuit connected between the cathode and the anode of each set, an impedance connected in the output circuit of one of the sets of electrodes, an impedance connected in the output circuit of the other set of electrodes, two condensers connected, respectively, between the control electrode of each of the sets and the anode of the other set. and means for energizing the output circuits and for applying an adjustable voltage bias on the control electrodes.

36. A stroboscope having, in combination, an oscillator for varying the flashing frequency of the stroboscope, means adjustable to vary the frequency of the oscillator to vary the flashing frequency, a plurality of scales having a common indicator adapted to occupy different positions with respect to the scales corresponding to different adjustments of the varying means, the scales and the indicator being adapted to be set relative to each other to correspond to predetermined values of the flashing frequency, means for adjusting the frequency of the oscillator to adjust the flashing frequency to the values corresponding to the relative settings of the indicator and one of the scales, whereby the flashing frequencies of the stroboscope will be caused to match with said one scale, and means whereby adjustment of the frequency-adjusting means of the oscillator may be caused to adjust the flashing frequency to the values corresponding to the relative settings of the indicator and the other scale, whereby the flashing frequencies of the stroboscope may be caused to match with said other scale.

KENNETH J. GERMESHAUSEN.

october 12, 19M.'

KENNETH JOSEPH GERHESHAUSEN.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page l, second column, line 18, for "envelope" reed --envelope l; page 2,

se cond column, line 58, for "constantcy" read-constancy; line 51.1., for "electrosert a comma;

, line T5, after potentiometer 118" inpage 5, second column, line 65, after "less" insert -than;

page li, second column, line 58, the words "It will be found" shouldbegdin a new paragraph; page 5, second column, line l2, claim 2, after Iscale" insert a comma; page 6, second column, lines 26 and 27, claim lO, strike out the words and comma "two pairs of condensers,"

comme. and before 1'means'I in line 26, same claim; and

and insert the same after the that the said Letters Patent should be read with this correction therein that the same may ccnform to the record of the case in the Patent Office.

signed and sealed this 11th day or January, A. D. 19th.

(Seal) Henry Ven Arsdele, Acting Commissionerof Patents.

CERTIEIOATE oF CORRECTION, patent No. 2,551,517. y october 12, 19145.

KENNEN JOSEPH GERMESHAUSEN.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows; Page l, second column, line 18, for "envelope'l read --envelope l; page 2, second column, line 8, for "constantcy" read constancy; line 5h., for "electrostorage read -electronstorage-; line 75, after "potentiometer 118" insert a comma; page 5, second column, line 65, after "less" insert --than; page I+, second column, line 58,the words "It will be found" should begin a v new paragraph; page 5, second column, line 12, claim 2, after "scale" insert a comma; page 6, second column, lines 26 and 27, claim lO, strike out the words and comma "two pairs of condenser-s," and insert the same after the comma and before means in line 26, same claim; and that the said Letters Patent should be read with this correction therein that the same may ccnform to the record of the case in the Patent Office.

Signed andsealed this llth day of January, A. D. 19ML.

Henry Van Arsdale, (Seal) v Actin Commissionerof Patents.

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