US2321659A - Variable frequency stimulator - Google Patents

Description

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VARIABLE FREQUENCY STIMULATOR Filed Feb. 5. 141

A I Ir f@ Patented June 15, 1943 VARIABLE FREQUENCY STIMULATOR Harold V. Connerty and Walter'Henry Johnson,

Washington, D. C

Application February 3, 1941, serial No. 377,272

claims. (C1. 12s- 422) This invention relates to a variable frequency stimulator.

The principal object of the invention is to provide a device for automatically and rhythmically stimulating biological nerve, muscle or nervemuscle preparations. It may also `be used to stimulate the nerves and muscles of humans; for example, in the treatment of diseases or disorders. It is particularly well adapted for use as a stimulator both for research and for routine student use in physiological and pharmacological laboratories and in other branches of biological activity and study.

A further object of the invention is to provide a device which automatically supplies'variable frequencies of stimulation ranging from approximately 1 stimulus every 6 seconds to an upper limit of about 10,000 stimuli per second. A corollary of this feature is the fact that the time interval between any two successive stimuli at a given frequency Within the operating range is absolutely constant.

A still further object is to provide not only variable frequencies of stimulation, but also to provide independent and variable control of the intensity of the stimuli through all values between the limits of zero and maximum.

Another important object of the invention is the provision of means connected in the circuit for operating a synchronous recording device which may be made to indicate both visibly and audibly, as well as to record, the exact moment of application of and the exact frequency of the stimuli.

A further object of the invention is the provision of means for interrupting the stimulating electrode and recording circuits while maintaining operation of the visual indicating device in order that adjustments of frequency and intensity Of the stimuli may be made prior to their application, if desired.

A still further feature is the fact that the intensity of the stimulating current does not vary with change of frequency of the stimulus but, when desired, can be varied, as mentioned above, by adjusting the intensity control.

Another feature of the invention resides in the production of an ideal type of stimulation which consists 0f a succession of pure unidirectional and instantaneous currents, there being no current flow in the intervals.

Still other objects and advantages of the device Will become apparent in considering the fol lowing specification and drawing, in which the single figure is a schematic circuit diagram of one, and the preferred, embodiment of the invention.

Current lis, supplied to the circuit either directly from a direct current source or, if an alternating current source such as at I0 is used, the same is converted, through a conventional rectifier filter system I5, to direct current.

The rectied andiiltered current is fed to a 20,200 ohm voltage divider 20 which is connected across the output of the rectifier-filter system and the desired voltages are tapped off. 'Ihe voltage divider is grounded 200 ohms from the negative end to provide a C bias 25 for the beam tetrode hereinafter explained.

Shunted across approximately a 50 and a 100 volttap on the voltage divider is a 10,000 ohm potentiometer 26, the purpose` of which is to control the screen potential of a variable mu current limiting pentode tube 21, a function of which is to act as a constant current resistor connected in the plate circuit of a hot cathode grid glow tube 28. The resistance of this current limiting tube 21 in conjunction with one of two xed condensers 29 having respective capacities of 0l5 and 0.01 microfarad, either one of which can be selected by a switch 30, is shunted across the grid glow tube 28 in series with a 500 ohm resistor 3U from the anode to the cathode to cause this tube to function as a relaxation oscillator, the frequency of which is controlled within the limits of the selected condenser by varying either the screen potential or the control grid bias of the current limiting pentode 21 by potentiometer 26 or variable resistor 3|, or both.

The control grid bias of the current limiting pentode 21 is controlled by a 3 megohm variable resistor 3l connected in series with the cathode of the current limiting tube 21, the movable contact arm of which connects on the one hand to the control grid of the current limiting pentode 21 and on the other hand through a 50,000 ohm xed resistor 32 to the anode of the hot cathode grid glow tube 28.

The grid of the grid glow tube is maintained at a constant negative potential of 6 volts by a C battery 33 acting through a 75,000 ohm resistor 34. By this means thus far described, complete and uniform variation of frequency is obtainable, ranging from one impulse every six seconds to in the vicinity of 5,000 impulses per second.

The source of voltage is applied to the anode or plate of the grid glow tube through the current limiting pentode 21 which acts as a constant current resistor to charge the selected con- -denser 29 which is connected between the cathode and anode of the grid glow tube. When the potential applied to the anode reaches the striking or ionization potential, the tube conducts and the condenser is discharged. At all voltages below the striking potential the tube fails to conduct and this allows the potential to build up in the condenser until the striking voltage is reached, the value of which is determined by the negative potential applied to the grid. The diS- charge of the condenser lowers the anode DOtential of the grid glow tube below the `extinction voltage. This allows the gridI to regain control and stops the conduction through the tube. A new charge must be built up in the condenser before another discharge can occur. Therate at which the charge in the condenser is vbuiltuplis determined by the capacity of the condenser and by the resistance of the current limitingpentode, which is controlled by the positive potentialof the screen grid and the negative potential ofthe control grid. The 'function of the 500` ohm lresistor 30 is to prevent excessive peak current .from owing through the gridglow tube.

The provisionv of'twofrequencycontrols-2S and 3 l, rather thanone, affords greaterzlatitudeiin the `range of the ,frequencies zdevelopeid, due to .the

fact that the currentciiowing*throughapentode `tube is a function bothof thefscreen .voltage and of the .control-grid voltage. In .effect `.the screen voltage control :26;serves as a verniera'djustment for the resistance of the '.variablemu pentode tube'2'i.

The impulses originating Nin the oscillator .circuit just described are applied to the control -grid of a beam power tetrode 35' throughaone 0 mcrofarad coupling vcondenser 35, the .grid `of l'which tetrode-tube receives a negative `bias of approximately minus Jto 'minus v20l Yvolts through a one megohm grid A'leak resistor 31 -which is connected to the negative tap of the lvoltage divider 20.

The screen of the beam'tube is maintained atta ipositive voltage of approximately200 volts vby conductor connected to `-a-`suitable Ltap'on'the voltage divider. A one microfarad'by-pass condenser 38 is connected "betweenthe scre'cnrand the cathode *whichv is grounded.

`Connected in seriesjbetween' the`anodeof the beam tube and thehigh'potential' end of the Vvoltage divider isithe primary 'coil .3950i a.2700 i ohm output .transformer '40.

Between the anode of the beam'tetrode 35 and the anode of the grid glow tube'23 is connected a one megohm resistor 4| in series with a'0.015

'fixed condenser 42, Vwhich `furnishes `inverse or negative feed back and stabilizes the circuit.

.Every timethe grid glow `tube-'28 conducts, the grid of ythe 4grid glow .amplifier tube is excited through theorie microfarady coupling .condenser 36. .This causes .the rplate -current .to .vary lac- -cordingly andA results in. an induced current inthe secondary coil 43 of the transformer,..which-in .turn furnishes the stimulatingcurrent.and.the

rcurrent which operates aA recording device..and .an

'indicator tube,'to be subsequentlyldescribed, all

v of which operations .are synchronous.

scope, is a series ofalmost perfectly straight-par- `allel fvertical :lines .of --ecmal4 lfamplitude and of .ode ray tuning indicator tube 50.

perfectly regular and even spacing. Of course, the usual reference line connects the vertical lines at the bottom.

The peak voltage is constant and substantially independent of frequency.

Connected across the 500 ohm terminal and the negative terminal of the secondary coil of the transformer is a 5,000 ohm potentiometer 46 having a movable arm 4l, which arm is connected through one pole5 l of a double pole single throw switch 52 to one end of a 1000 ohm resistor 48. The other end of the resistor 48 is connected Ato a binding post 49 which furnishes current for Va stimulating electrode 50. The two ohm tap 44 of the secondary coil 43 of the output transformer isadapted-to be connected through the second pole 53 of switch 52 to binding post 54, which in conjunction with a second binding post 55 connected to the common negative 45 of the secondary of the output transformer, supplies the -operating current for the recording device 56, one form of which may be what is knownas a signal magnet. However, .any recording device ,having ra two ohm impedance, suchas a loud speaker, is .within the purview of this invention. The common negative in conjunction withanother bindingy post51 is .connected to thesecond electrode 58 which, in `conjunction with elecv trode 50, forms a pair of stimulating electrodes.

Connected to the highpotential end of the secondary coil43 is one-plate of a condenser 59 of `approximately .000001.microfarad, the other plate of which is connected to the grid-of a cath- VThe target 6| of the tuning indicatorisconnected to a 200 volt source, .preferably on the voltage 4divider 2U. `A

-one megohm resistor 52 is connected between The `quencyfis being selected in the oscillating circuit throughy the -several vadjustments provided. After the electrodes have beenapplied to the object be- `ing stimulated, the switch `52 may be closed and Ithe-impulses will `forthwith be directly imparted Atothe object throughvthe-electrodes, and a syn- `chronouscurrent willxsimultaneously operate the recording device 56.

A,pulses may be Ireadily adjusted by the variable The intensity of the irnresistance 46 shunted across the high potential .winding of the. secondary coil of the transformer Aand-thenegative lead 45.

'Particularly -in instances where the'device is being used for laboratory experiment or class- ,room demonstration, -the stimulating electrodes Vare suitably connectedto the tissue or object being investigated, such as a muscle, Aand the signal magnet oftthe recording device 'isf-connected to a conventional stylus whichinturn is set-up to mark on any suitabledevice 'suchasa smoked cylinder,I whereby, when the ysingle throw double pole switch 52 is closed, VVVstimuli will .be applied to the tissue or object andthe -signalmagnet of Vthe recording device will fbe caused to function and will impart markings to the smoked rcylinder, thereby'indicating the exact instantof vapplication of each stimulus Van'dthe intervalbetween successive stimuli. In Ithis connection .ther-ewillalso lbe .a -stylus v connected to the mov -ing ,endzof the'rmuscle being stimulated, vwhereby a. wave .denoting both .the 'frequency and amplitude of the contractions developed in the muscle as a result of receiving the impulses from the stimulating electrodes are also recorded on the smoked cylinder and may be referred to the marks on the cylinder made by the signal magnet.

The foregoing is a description of our invention and the manner in which it functions. This description, however, is only to be considered as illustrative and not restrictive in any sense, since it is recognized that the invention has Wider applications than those referred to in the foregoing and it is intended that this invention shall encompass all equivalent elements and circuits which will perform similar results coming within the spirit of this invention.

Having thus described our invention, what we claim is:

l. A variable frequency stimulator comprising a source of direct current, a variable oscillator circuit comprising a current limiting tube connected between said current source and a relaxation oscillator tube, an electron amplifying tube, an output transformer, said amplifying tube being coupled to the output of said oscillator tube, the primary coil of said transformer being connected in series between the anode of said amplier tube and said voltage source, a resistor and condenser connected in series with each other and in series between the anodes of the amplifier and oscillator tubes to act as a negative feed back in the circuit to stabilize the same, and a pair of applicator electrodes connected to the secondary coil of said transformer.

2. A variable frequency'stimulator comprising a source of direct current voltage, a Variable oscillator circuit comprising a current limiting tube connected between said current source and a relaxation oscillator tube, an electron amplifying tube having a grid, an output transformer, said amplifying tube grid being coupled to the output of said oscillator tube, the primary coil of said transformer being connected in series between the anode of said amplifier tube and said voltage source, a resistor and condenser connected in series with each other and in series between the anodes of the amplifier and oscillator tubes to act as a negative feed back in the circuit to stabilize the same, and a pair of applicator electrodes connected to the secondary coil of said transformer, and a cathode ray indicator connected to the high potential end of said secondary coil to indicate the frequency of the current discharge through the applicator electrodes.

. 3. A variable frequency stimulator comprising a source of direct circuit voltage, a variable oscillator circuit comprising a current limiting tube connected between said current source and a relaxation oscillator tube, an electron amplifying tube having a grid, an output transformer, said amplifying tube grid being coupled to the output of said oscillator tube, the primary coil of said transformer being connected in series between the anode of said amplifier tube and said voltage source, a resistor and condenser connected in series with each other and in series between the anodes of the amplifier and oscillator tubes to act as a negative feed back in the circuit to stabilize the same, and a pair of ap- ,plicator electrodes connected to the secondary coil of said transformer, a cathode ray indicator connected to the high potential end of said secondary coil to indicate the frequency of the current discharge through the applicator electrodes and a switch connected in the circuit of the positive electrode whereby the switch may be opened to permit adjustment of the frequency of the impulses, as indicated by said cathode ray indicator following which the switch may be closed, and impulses are then discharged from said electrode.

4. A variable frequency stimulator comprising a voltage source, a variable oscillator circuit connected thereto, an amplifier tube having a grid, which is coupled to the output end of said oscillator circuit, an output transformer having its primary coil connected in series with the anode of said amplifier tube and said voltage source, a pair of applicator electrodes connected to the secondary coil of said transformer, a cathode ray indicator tube connected to the high potential end of said secondary coil to indicate the frequency of the current discharge through the applicator electrode, a lead tapped off said secondary of the transformer near the negative end, said lead being operatively connected to a magnet of an indicating device, said applicator electrodes being respectively positive and negative, the lead to said negative electrode also being connected to said magnet and a single lpole double throw switch connected in the circuit of the leads to the positive applicator electrode and the magnet whereby the switch may be opened to permit the adjustment of the frequency of the impulses as indicated by said cathode ray indicator following which the switch may be closed to permit the impulses to be discharged through the applicator electrodes and also actuate said magnet of the indicating device. f

5. A variable frequency stimulator comprising a voltage source, a variable oscillator circuit connected thereto, an amplifier tube having a grid, which is coupled to the output end of said oscillator circuit, an output transformer having its primary coil connected in series with the anode of said amplifier tube and said voltage source, a pair of applicator electrodes connected to the secondary coil of said transformer, a cathode ray indicator tube connected to the high potential end of said secondary coil to indicate the frequency of the current discharge through the applicator electrodes, a lead tapped off said secondary of the transformer near the low potential end to provide an impedance match with that of an indicating device, said lead being operatively connected to a magnet operating said indicating device, said applicator electrodes being respectively positive and negative, the lead to said negative electrode also being connected to said magnet, a single pole double throw switch connected in the circuit of the leads to the positive applicator electrode and the magnet whereby the switch may be opened to permit the adjustment of the frequency of the impulses following which the switch may be closed to permit the impulses to be discharged through the applicator electrodes and also actuate said magnet of the indicating device and a variable potentiometer having a movable arm connected across the ends of the secondary winding of the transformer, said movablearm being connected to one stimulating electrode, the other electrode being connected to the low potential tap of said secondary coil, whereby the intensity of the stimulating impulses may be readily varied.

HAROLD v. CONNERTY. WALTER HENRY JOHNSON.

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