Nov. 19, 1946. C. E. MILLER ET AL 2,41 1,450 MATERIAL TESTING APPARATUS Filed July 28, 1944 2828a 3|5Ia35 26 241: Fig.1. Inventors: Caries E. Miller“, Robert, J. Demar inf, b 541,47 éfxj yTheir Attorney. reamed Nov. 19, 1946 ~ 2,411,450 UNITED ‘STATES PATENT OFFICE 2,411,450 MATERIAL TESTING APPARATUS Charles E. Miller, Scotia, and Robert J. Demar~ tlni, Schenectady, N. Y.. asaiznors to General Electric Company, a corporation or New York Application July 28, 1944, Serial No. 547371 16 Claims. (Cl. "BB-F90} This invention relates to the testing of ma terials, more particularly to apparatus for test Means are provided for producing a control voltage which varies in accordance with the ing material samples, and it (has for an object difference in speeds the l retainers. This the provision of a simple, reliable, inexpensive, control voltage is utilized to control suitable and improved apparatus of this character. in the testing of many materials such as tex~ 5 electric valve apparatus to control the supply of current to the motor which drives testing tile fabrics, the apparent strength of the ma machine to e" " speeds oi’ the two 2nem= terial as determined by a testing machine varies hers. means are pro— materially with variations in the rate at vided for 3 reference volt= Which load is applied to the test sample. The ‘o 5 produces rate or" application of load to the material sample, opal the in turn, depends upon the elasticity or “stretch d the din iness” of the material. sample. Consequently, 7 has voltages the two utilised contr markedly different indications of tensile strength . voltages a-..d t are obtained from material samples having the rate. to the same actual tensile strength but having di?erent Q elasticities. Accordingly, a further object of this invention is the provision of means for con trolling a testing machine in such a manner that the rate of application of load to the test sample‘ should now he 9 had to the following spec _ and to the accompanying drawing of is independent of the elasticity of the material 20 simple, diagrammaticai sketch of Fig. 1 is a an embed-la and therefore reproducible from sample to ment of the invention and'Fig. 2 is a modi?ca sample. tion. Referring now to the drawing, a material test ing machine is illustrated as being provided with two members i and 2 for holding a sample of the material which is to he tested for tensile Another object of the invention is the pro vision of means for controlling the testing ma chine in such a manner that the application of load is substantially uniform for all materials irrespective of their elasticity. ‘ strength. _ Each of the members i and A still further object of the invention is the provision of apparatus of the character de scribed in the foregoing in which the initial rate may he a conventional pair of jaws for securely grip ping the sample. The lower mounted on a screw at which load is imposed on the same is low so - of jaws 2 i which is in threaded en gagement with a nut (not shown) within t gear box G. The nut is connected through a gear train and a'chain and sprocket drive t 35 ‘the shaft of an electric motor 6. Although theO form In thereof, carrying a, the testing invention machine into is utilizedwhich effect in. motor 53 may be of vany suitable type, it is illus has a ‘pair of members for holding the test trated as a separately excited motor. sample. One of these members is driven by an ' The upper pair of jaws is connected through electric motor in a direction to apply 'a force to a chain ‘J to a‘drum t? which is rotatably mount the sample. Means are provided for producing on the frame of the machine. ‘Secured to the a variable reference speed of which the rate of drum is a pendulum £9 comprising an arm'lla variation is substantially constant. Additional having a Weight 921 on the iree'end. . means are provided for producing a signal volt» ‘in order to cause the load to he applied to the age which is proportional to the load on the test ‘sample at a uniform rate, suitable means are material sample. The difference between the provided for. comparing the rate of application of two voltages is utilized to control the motor that substantially all possibility of shoot: is eliminated. ' . which drives the testing machine to equalize the rate at which the load is being applied to the sample with the rate of variation of the reference voltage. In one speci?c embodiment of the in vention, a movable member is driven a con“ stant speed by a synchronous motor, and an other movable member is driven at a speed hav— load to the test sample with a'constant refer ence speed, and utilizing the di?erence to con-' trol the speed of the motor so . For the purpose of providing an indication of the rate of application of load tothe test sample, the‘ slider like of a potentiometer, is mechani cally/‘connected, to the pendulum icy means of a rod 3 l, a chain it, and a sprocket 53. One end ing a predetermined relationship to the ratevat which load is being applied to the test sample. 55 of the rcd?i is provided with a pin Ha which slides in a slot in the pendulum arm.‘ The 2,411,450 minal of the armature is connected to bus 22 opposite end of the rod is ‘connected to the chain which, as pointed out in the foregoing, is con nected to the center tap of the secondary winde l2 which engages the sprocket i3 and, at its low er end, is provided with a weight M. Thus, whenever the rod ll moves as a result of the potentiometer slider “la is rotated at a speed ing 2411. As thus connected, the thyratrons 21 and 28 rectify both half-waves of the alternating voltage and supply the recti?ed voltage to the proportional to the speed‘of the rod H. armature 6b. counterclockwise rotation of the pendulum 9, the - The speed of the motor 6 is adjusted by varying the average current conducted by the thyratrons. angular position of the pendulum. Since the weight of the pendulum remains constant, the 10 Although the thyratrons may be controlled by any suitable method, vit-is preferred to use the load on the sample varies with the length of the method of phase shift control of the grid voltage. moment arm of the weight 9b about the center of For the carrying out of this method of control, the drum 8.. Owing to theslotted connection of The load on the test sample varies with the ' a phase shifting resistance-reactance network is rod iii varies in a lengthwise direction approxi 15 provided. This network comprises a secondary .‘winding 240 of the transformer 24, resistors 30 mately in proportion to the changing length of and 3!, and capacitors 32 and 33. The resistors the moment arm of weight 9b. Thus, the posi and capacitors are connected in series relation tion of the rod H is an approximate measure of ship across the secondary winding 240. The cir the load on the sample, and the speed of the lengthwise movement of the rod is a measure of 20 cuit is traced from the left-hand terminal of the secondary winding 240 through resistor 30, ca the rate of application of load to the test sam ple. Since the speed of the potentiometer slider , pacitor 32, the common cathode connection 34, capacitor 33, and resistor 3! to the opposite ter we is proportional to the lengthwise speed of minal of the secondary winding 2430.’ the rod II, it is also proportional to the rate of The common point 360, of resistor 30 and ca 25 application of load to the test sample. pacitor 32 is connected through a resistor 35 to The reference speed with which the rate of ap the grid 210 of thyratron 21. Similarly, the com plication of load to the sample is compared, is mon point em between resistor 35 and capacitor provided by means of a synchronous motor 95 33 is connected through a resistor 36 to the grid which drives the slider 86a of a potentiometer it at constant speed. The synchronous motor as is 30 280 of thyratron 28, The capacitativereactance Xe of the capacitors 32 and 33 is chosen relatively preferably of the single-phase, self-starting type, small in comparison with the resistance R of i. e., the motor starts immediately when it is resistors 30 and 3E. vThus the alternating volt connected to a single-phase source such as rep ages across the capacitors 32 and 33 lag the volt resented by the supply line H. age of the secondary winding approximately 90 A limit switch i8 actuated by the pendulum the rod l I with the pendulum, the position of the electrical degrees. Since the voltage across the capacitors 32 and. 33 are applied to the grids 27c near the beginning of its counterclockwise ro tation serves to connect the synchronous motor it to the source it, and a limit switch as which is actuated by the synchronous motor itself serves to interrupt the connections of the synchronous and 280, the voltages of grids 2'30 and 280 lag the voltages of the anodes Z'la and 28a, respec 40 motor to the source after a predetermined amount of rotation, [thereby to prevent the slider i?a from being driven past its end position. The resistors of the potentiometers iii and it are connected in parallel with each other and inseries with the operating coil 2dr: of a line con tactor 2d across the control voltage buses 2i and 22. A. substantially constant direct voltage is supplied to the control voltage buses 2i and 22 by means of suitable rectifying means which is illustrated as a double diode electric valve 28 of which the anodes 23a. and 23b are connected to tively, approximately 90 degrees. . The effect of phase shift of the grid voltage is produced by ap-plyinga variable component of direct voltage to the grids in addition to the 90 degree lagging alternating voltage component. This is accomplished by means of a pair of elec tric‘ valves 3? and 33 connected in series rela tionship across the transformer secondary 240. The valve 3? is preferably a triode valve and the valve 38 is preferably a diode valve. The circuit is- traced from the left hand terminal of the secondary winding 25c to the anode 37a of valve 3?, cathode 37b, potentiometer 86, bus 22, arma ture 5?), through upper contacts 281) of contactor opposite terminals of the secondary winding 2% 2B in the closed position thereof to the common of the supply transformer 2d, and the cathode is connected to the bus 2i. The bus 22 is connected 65 cathode connection 3%, resistor 39, anode 38a of valve 38, cathode 38b to the opposite terminal of by means of a conductor 25 to the center tap of the secondary winding 260. Thus, the triode the secondary winding 25a of the supply trans valve 27 is in parallel circuit relationship with former. The primary winding 2% of supply capacitor 32 and the diode valve 38 is in parallel transformer 25 is connected to a suitable source ‘ of alternating voltage such as represented by the 50 circuit relationship with capacitor 33.1 When the valves 3? and 38 are conducting, two supply lines 26. As thus connected, the charges are placed on the capacitors 32 and 33, valve 23 operates as a full wave recti?er to sup and as a result, a component of direct voltage ply a recti?ed voltage to the buses 2i and 22, is applied to the grids 2'80 and 280. The com As shown, the separately excited ?eld winding 5d bination of this direct voltage component with of the motor 6 is connected across the'buses' 2i the lagging alternating component produces the and 22. , _ The armature 6b of the motor 5 is supplied from suitable electric valve means illustrated as a pair of thyratrons 21 and 28. The anodes 211a . effect of phase shift of the grid voltage and cor responding variation of the average current transmitted by the thyratrons. and 28a of these thyratrons are connected to op-v 70 The amount of phase shift of the grid voltage of the thyratrons, and consequently the amount posite terminals of the. supply transformer sec of current transmitted by the thyratrons, can be ondary winding 24a, and the cathodes 21b and varied by varying the relative conductivities of 28b are connected through conductor 29 and the the triode valve 31 and the diode valve 38. This main contacts 20b of contactorZil to one ter minal of the motor armature 6b. The other ter 75 is ‘accomplished simply by varying the conduc 5 2,411,450 tivity of the triode valve. For this purpose, the cathode 31b of the triode valve is connected to the slider 16a of'potentiometer l6, and the control grid 31c is connected to the slider Illa of poten tiometer ID. If the voltage of the grid 31c becomes less neg ative or increasingly positive with respect to the voltage of the cathode 31b, the conductivity of As a result, the grid voltages of the thyratrons 27 and 28 are retarded to such an extent - that’ the thyratrons supply a minimum current to the armature of the motor 8 which therefore rotates at a low creeping speed. I ‘ The direction of rotation is such as to drive the lower pair oi’ Jaws 2 in an upward direction. However, as pointed out, the lower pair of jaws valve 31 is increased. This has the effect of ‘re tarding the phase of the grid voltage of the 10 2 are in their uppermost position with the clutch between the motor and the screw 3 disengaged thyratrons 27 and 28 thereby to decrease the our so that there is no movement of the jaws at this rent supplied to thearmature 6b of the motor 6. ‘ point in the operation. Conversely, if the grid voltage becomes increas-' The test sample is now ?rmly secured in the ingly negative with respect to the cathode volt The test run is age, the phase of the thyratron grid voltage is 15 upper and lower jaws i and initiated by shifting the lever 55 to engage the advanced and the current supplied to the arma clutch to complete the driving connections be ture is correspondingly increased, tween the motor '8 and the screw 3. The shift With the foregoing understanding of the ele ing of the clutch lever 45 opens contacts 48 to ments and their organization in the completed lnterupt the holding circuit for the operating system, the operation of the system itself will 20 coil of the field contactor 4i. In response to readily be understood from the following detailed deenergization, the field contactor drops out to description. It is assumed that the apparatus is open its normally open contacts 4lb, 4E0, and Md in the position in which it is° illustrated in the and to close its normally closed contacts die and drawing with the lower jaws 2 in their upper 4i)‘. Contacts 4m in opening interrupt the hold most position. At the lowermost position of the lower jaws 2 during the previous test run, the 25 ing circuit for the coil 4la so that the contactor 4! cannot be picked up by a subsequent movement limit switch 40 which is ‘actuated by the screw of the lever 435. i I 3, closed its contacts to complete an energizing The lower jaws 2 start downwardly at a very circuit for the operating coil 41a of the ?eld con low speed to remove the stretch from the sample. tactor 41. In response to energization, contactor 4| closed its normallyb‘pen contacts 4lb, Me, and 30 When the stretch is completely removed, the pendulum 9 begins to rotate in a counterclockwise 41d andopened its normally closed contacts Me direction thereby to apply load to the test sam and 4|)‘. The opening of contacts Me and 4| f ple. After a very small amount of rotation oi.’ and the closing of contacts Mia and 4| 0 reversed the connections of the ?eld winding 6a to pro 35 the pendulum 9, the contacts of a limit switch l8 actuated by the ‘pendulum 9 are closed to com vide for rotation of the motor 6 in a direction to plete an energizing circuit for the operating coil drive the lower jaws 2 toward their uppermost 47a of a relay 41. In response to energization, the position. The closing of contacts 41d completed relay 41 opens its normally closed contacts 4'"; a sealing-in circuit for the operating coil No of the ?eld contactor 4! in parallel with the con 40 and closes its normally open contacts 4'10. In closing, the contacts 410 connect the synchronous tacts of the limit switch 40 so that the contactor remained picked up after the contacts of the limit switch 40 opened in response to the upward movement of the jaws 2. motor l5 to the source H for rotation in a direc tion to rotate the slider l6a of potentiometer IS in a counterclockwise direction. - As the slider iGa moves in a counterclockwise In the uppermost position of the lower jaws 2, 45 direction along the potentiometer 16, it taps off ' a clutch (not shown) in the testing machine is and applies increasingly positive voltages to the disengaged to interrupt the driving connection cathode 31b of the valve 31. As _a result, the, ’ between the motor 6 and the screw 3. Assuming conductivity of the valve 37 is decreased and that the motor 6 was stopped with the machine in this position by pressing the stop pushbutton 50' the phase of the grid voltages of the thyratrons 21 and 28 is advanced. The advance in phase of switch 42, it is now necessary to restart the motor the grid voltages of the thyratrons increases the 6. This is done by momentarily depressing the current supplied to the armature of the motor start pushbutton switch 43 to close its contacts 6 thereby increasing the speed of the motor 6 and thereby complete an energizing circuit for also the downward speed of the jaws 2 driven the operating coil 20a of the line contactor 20. 55 and thereby. The increasing downward speed of In response to energization, the line contactor the jaws 2 increases the speed of the counter closes its main contacts 20b and interlock con tacts 20c and opens its normally closed dynamic _ clockwise rotation of the pendulum 9 so that the slider Illa of the potentiometer H! which is driven braking contacts 20d. The contacts 20:1 in open by the pendulum begins, to overtake the slider ing interrupt the dynamic braking circuit l6a of the potentiometer l6 which is driven by through the dynamic braking resistor 44 in par 60 the synchronous motor. allel with the armature, and the main contacts \ When the speeds of the two sliders become 2% in closing complete the connections ‘of the equal, there will be'no further increase in the armature to the cathodes 21b and 28b of the thyratrons 21 and 28. The closing of contacts 65 speed of the motor 6. This is an indication that the rate 'of application of load to the test sample, 200 in parallel with the contacts of the start push button switch 43 completes a holding circuit for - i. e., the rate of increase of load on the test sample, is proportionate to the constant speed‘ the operating coil of the line contactor so that of the slider lSa and is therefore uniform. the start pushbutton switch 43 may now be re ‘If, owing to some nonuniformity of the sample leased. V . 70 or other cause, the rate of application of load to With the sliders Illa and lGa of the potentiom the test sample should tend to decrease, the slider eters J0 and IS in the positions in which they Illa will begin to lag the slider Ilia. The result are illustrated, the voltage of the grid 310 of the is that the voltage applied to the grid 310 does valve 31 is so positive with respect to the voltage of its’ cathodethat the valveis fully conducting. 75 ‘not increase in a positive direction as rapidly as the voltage applied to the cathode 31b. Conse ' acnneo quently. the conductivity of the valve 31 decreases thereby to advance the phase of the grid voltage of the thyratrons 21 and 28 and to increase the speed of the motor 6. On the other hand, if, owing to some nonuniiormity in the sample or other cause, the load on the sample increases at a rate faster than that determined by the con stant speed 0! the synchronous motor iii, the slider Illa will lead the slider lea. with the result carries a pendulum 53 which corresponds to the . pendulum 9 of the Fig. 1 modi?cation. When the axis of the rotor coil 49b is at right angles to the axis of the stator coil 49a, the volt age induced in the rotor coil is ‘zero. For all other positions of the rotor coil, the induced voltage is proportional to the sine of the angle between the-axis of the rotor coil and the zerov position. The moment arm of the pendulum 53 about the that the voltage of the, grid 31c becomes in 10 rotational axis of the drum 52 is proportional creasingly positive with respect to the voltage a or the cathode 3112. This increases the conduc to the sine of the angle between the axis of the pendulum and the zero or vertical position there tivity of the valve 31 and retards the phase of As pointed out in connection with the modi the grid voltages of the thyratrons-Z'i' and 3:8 ' ‘of. ?cation of Fig. l, the load on the material sample “thereby to decrease‘the speed of the motor 6. ‘in the testing machine is proportional to the Thus, the rate oi application of load to the‘test moment arm of the mn'dulum about its center . ‘of rotation. Owing to the mechanical connec test. tion between the rotor coil 4% and the drum At some point in the downward travel 01 the 52, the rotor coil is rotated through they same 20 lower jaws 2, the test ‘sample is ruptured. At angle as that through which the pendulum is the‘ lower end of the downward travel of the . sample is maintained uniform throughout the rotated. ‘ Since the'load on the material sample. jaws 2. the limit switch at closes its contacts to and the voltage induced in the rotor coil are complete an energizing circuit for the operating both proportional to the sine of this angle, the coil Ma of the ?eld contactor M‘ which. respon sively to energization reverses the ?eld connec 25 induced voltage is thus a measure of the load on the material sample. _ tions of the ?eld_,winding do to the source. This This voltage is stepped up by means of a trans reverses thedirection of rotationof the motor ii ;former 5d and recti?ed by suitable means which and'ca'uses it to drive the screw- t and the pair is illustrated as a bi-phase half wave recti?er of jaws 2 in an upward direction. This con valve 55 of which the anodes 55a and 5512 are 30 tinues until the jaws ‘2 reach their uppermost connected to opposite terminals of the secondary position and the clutch in the machine is disen winding of the transformer and the twin cathodes gaged to interrupt the driving connections be 55c and 55d are connected through a potentiome tween the motor 6 and the screw 3. ter 56 and a ?xed resistor 5'! to the center tap The vsynchronous motor to continues driving the secondary winding. The potentiometer 56 the slider iGa until it reaches its limiting posi 35 of serves for initially adjusting the rectified volt tion in which the limit switch it opens its con age across the conductors 5B and 58. tacts to disconnect the synchronous motor from The re mainder of the modification of Fig. 2 is identi cal with corresponding parts of the modi?cation itsupper position by means oi.’v a pawl and ratchet of Fig. 1 and consequently it is omitted from the 40 mechanism (not shown) is manually returned by the source H’. The pendulum, which is held in the operator to its initial position. drawing. In return- - limit switch i8_ are opened to deenergize the operating coil d'la of the contactor 4'5. In re 7 , - In connecting the induction voltage regulator 69 in place of the potentiometer iii of Fig. l, ing to its initial position, the contacts of the ‘ the conductor 58 of Fig. 2 is connected to the sponse to deenergization, the contactor 8'! drops 45 conductor 60 of Fig. 1 which is connected to the grid’ 31a of the triode valve 31; and the‘ con out to open its normally open contacts die and ductor 59 of Fig. 2 is connected to the conductor close its normally‘ closed contacts 4%. In clos iii of Fig. l. . ing, the contacts Alb complete the connections ‘The operation of the system of Fig. 2 is iden-m of the synchronous motor its to the source i‘i with the operation ofthe system of Fig. 1 through the contacts of a limit switch to and 50 tical except that the signal voltage proportional to the reverse ?eld winding/ I50; of the synchronous load on the material sample is supplied by the motor i5. In response to this reverse energiza induction voltage regulator Ml instead of being tion,‘ the motor it rotates in~the reverse direc‘» supplied by the potentiometer In of Fig. 1. tion to return the slider i?a to its initial posi tion in which the contacts of the limitswitch W 55 Although in accordance with the provisions of the patent statutes this invention is described are opened to disconnect the synchronous motor from the source it. At the beginning of the reverse rotation, the contacts of the limit switch i9 are reclosed thereby leaving the system in 60 a reset conditionior a subsequenttest. as embodied in concrete form and the principle thereofhas been explained, together with the best mode in which it is now contemplated applying that principle, it will be understood that the apparatus shown and described is merely illustrative and that the invention is not lim ited thereto, since alterations and modi?cations will readily suggest themselves to persons skilled coiiéi?b. The stator coil is ‘supplied from a suit 65 in the art without departing from the true spirit of this invention or from the scope of the annexed able source of alternating voltage which ‘is repclaims. ' resented in Fig. 2 by the two supply lines 58. In the modi?cation illustrated in Fig. 2, the potentiometer it of Fig. 1 is replaced by an induc tion voltage regulator dB. This regulator has a stator coil 639a and an inductively related rotor What we claim as new and desire to secure by This source may be and preferably is the same Letters Patent of the United States is: _ as the single phase alternating voltage source i. In combination, a material testing machine, 2% of Fig. 1. The rotor member upon which 70 an electric motor for driving said machine to the rotor coil 6% is mounted is mechanically apply a load to a material specimen, a reference connected by means of a shaft 5!], or other suit able coupling means, to the shaft of the testing machine drum '52. The drum. 52 corresponds to the drum 8 of the modi?cation of Fig. 1 and 75 speed device and means responsive to the dif ference between the speed of said reference speed device and the rate of application of load to 2,411,450 said material'specimen for controlling said motor to ‘equalize said rate and said speed. 2. In combination, a material testing machine, an electric motor for driving said machine to apply a load to a material specimen, a reference speed device, means for producing a control volt ?rst mentioned motor to equalize. the speeds of said sliders thereby to e?ect the application of load to said specimen at a constant rate. , 7. In_ combination, a material testing machine having a pair or members for holding a material age having a predetermined relationship to the specimen,’ an electric motor connected to drive di?erence between the speed of said reference one of said members, a pivotally mounted pen speed device and rate of application of load to dulum connected to the other of said members to said material specimen, and electric valve means 10 provide for increasing the load on said specimen responsive to said voltage for controlling said in response to movement of said motor driven motor to equalize said rate and said speed. ' member, means for producing a control voltage having a predetermined relationship to the dif-v 3. In combination, a material testing machine, an electric motor for driving said machine ‘to ierence between the rate or increasing the load on apply a load to a‘ material specimen, a syn 15 said specimenv at a constant rate comprising a chronous motor, means responsive to the dife synchronous motor,,a source of substantially con ference, between the speed of said synchronous stant control voltage, a potentiometer having its ' motor and the rate of applicationof load to said slider connected to be driven by said synchronous material specimen for producing a control volt motor and a second potentiometer having its age, and electric valve means responsive tov said 20 slider connected to be driven in response to move voltage for controllingsaid motor to equalize said rate and said ‘speed. 4. In combination, a material testing machine, ment of said pendulum, and an electric valve pro vided with an anode,‘a cathode connected to one ' of said sliders and a grid connected- to the other an electric motor for driving said machine-to ap of said sliders for controlling the supply of cur ply a load to a material specimen, a synchronous 25 rent to said ?rst motor to equalize the speeds ' motor, means for producing a control voltage _ of said sliders thereby to eifect application of having a predetermined relationship to the dif load to said specimen at a constant rate. ference between the speed of said synchronous 8. In combination, ‘a material testing machine, _ motor and the rate of application of load to said an electric motor for driving said machine to material specimen comprising a potentiometer 30' apply agload to a material specimen, electrical having its slider connected to be driven by said means vfor producing a reference voltage varying synchronous motor and a second potentiometer , substantially linearly with time, means respon having its slider connected to be driven by said sive to application of load to said material speci machine at a speed proportional to the rate of men for producing a signal control voltage sub application of load to said specimen, and electric 35 stantially proportional to the load on said ma valve apparatus responsive to said voltage for terial specimen, and electric valve means respon controlling said motor to equalize the speeds of sive to the di?’erence of said voltages for control said sliders. > , ling said motor to equalize the rates of variation 5. In combination, a material testing machine of said voltages thereby to effect application of having a pair of members for holding a material 40 load to said specimen at a constant rate. specimen, an electric motor connected to drive one 9. In combination, a material testing machine, of said members, a pivotally mounted pendulum an electric motor for driving said machine to connected to the other of said members to provide apply a load to a material specimen, means for for increasingly loading said specimen in response producing a reference voltage having a substan to movement of said motor driven member, a syn 45 tially constant rate of variation, an induction volt chronous motor, a ?rst member driven by said age regulator responsive to application of load synchronous motor at a constant speed, a second producing a signal control member driven in response to movement of said voltage proportional to said lead, and means re pendulum at a speed proportional to the speed of sponsive to the difference of said voltages for con said pendulum, means for producing a control 50 trolling said motor to equalize the rates 01' varia voltage having a predetermined relationship to tion of said voltages thereby to e?'ect application the di?erence between the speed 01' said ?rst of load to said specimen at, a constant rate; member and the speed of said second member, and 10. In combination, a material testing machine, electric valve apparatus responsive to said control voltage for controlling said motor to equalize the 55 an electric motor for driving said machine to apply a load to a material specimen, means for pro speeds of said ?rst and second members thereby ducing a reference voltage having a substantially to cause load to be applied to said specimen at a constant rate of variation, means for producing constant rate. a signal voltage proportional to the load on said 6. In combination, a material testing machine ‘having a pair of members for holding a material 60 material specimen, and means responsive to the di?erence of said voltages for controlling the motor specimen, an electric motor connected to drive one to equalize the rates of variation of said voltages of said members, a pivotally mounted pendulum thereby to effect application of load to said mate connected to the other of said members to pro rial specimen at a constant rate. vide for increasing the load on said specimen in 11. In combination, a material testing machine, response to movement of said motor driven mem 65 an electric. motor for driving said machine to ber, means for producing a control voltage having apply a load to a material specimen, an electrical a predetermined relationship to the diil'erence device for producing a reference voltage having a between the rate of increasing the load on said substantially constant rate of variation, means specimen and a constant rate comprising a syn-1' responsive to the application of load to said mate chronous motor, a potentiometer having its slider 70 rial specimen for producing a signal control volt connected to be driven by said synchronous motor age having a rate of variation proportional to- the and a second potentiometer having its slider con rate of application of load to said material speci nccted to be driven in response to movement of I said pendulum, and electric valve means respon men and means responsive to the difference of sive to said control voltage for controlling said 75 such voltages for controlling said motor to equalize the rates of variation of said voltage thereby to QAZEAEQ e?ect application 0! load to said specimen at a of said reference‘ voltage and said signal voltage thereby to effect application of load to said speci constant rate. men at a substantially constant rate. having a pair of members for holding a material specimen, an electric motor connected ‘to drive one of said members, a pivotally mounted pen chine comprising an electric motor for applying a load to a material specimen, a source of reference 12. In combination, a material testing machine ‘ 1%. Control apparatus for a material testing ma- , predetermined rate of application of load to said material specimen, to provide for increasingly loading said specimen means for producing a signal voltage correspond in response to movement of said motor driven ing to the rate of application of load to said speci m member, means for producing a reference voltage men by said motor, and means responsive to the having a substantially constant rate of variation, di?erence of said voltages for controlling said an induction voltage regulator driven by said motor to equalize said rates. pendulum for producing a signal control voltage 15. Control apparatus for a material.testing proportional to the load on said‘ material speci machine comprising an electric motor for applying 15 ' dulum connected to the other of said members ‘ voltage corresponding to a men, and electric valve means responsive to the diiference of said voltages for controlling said motor to equalize the rates of variation of said voltages thereby to effect application of load to said specimen at a constant rate. 13. In combination, a material testing machine having a pair of members for holding a material specimen, an electric motor connected to drive one of said members, a pivotally mounted pendulum connected to the other of said members to provide for increasingly loading said specimen in response to movement of said motor driven member, elec a load to a material specimen, a source of refer ence voltage, means for producing a signal volt age corresponding to the rate of application of load to said specimen, and electric valve means responsive to the di?erence of said voltages for controlling said motor to maintain the rate of application of load to said specimen constant. 16. Control apparatus for a material testing a , machine‘ comprising an electric motor for apply ing a load to a material specimen, a source of as reference voltage corresponding to a predeter mined rate of application of load to said specimen, means comprising an induction voltage regulator trical means for producing a direct reference volt age having a substantially‘ constant rate of varia responsive to the load appliedto said specimen for producing a signal voltage corresponding to the rate of application of load to said specimen tion, an induction voltage regulator I driven by said pendulum for producing an alternating volt age having an e?ective value proportional to the load on said specimen, means for rectifying said alternating voltage to produce a direct signal con trol voltage proportional to said load, and electric and electric valve means responsive to the diifer - ence of said voltages for controlling said motor to valve means responsive to the dl?erence of said 35 reference voltage and signal voltage for control ling said motor to equalize the rates of variation 'e?ect application of load to said specimen at said predetermined rate. CHARLES E. MILLER. RQBERT J. DEMARTINI.