US1841558A

US1841558A - Recording potentiometer

Info

Publication number: US1841558A
Application number: US375668A
Authority: US
Inventors: Uehling Fritz Frederick
Original assignee: Individual
Current assignee: Individual
Priority date: 1929-07-03
Filing date: 1929-07-03
Publication date: 1932-01-19
Anticipated expiration: 1949-01-19

Description

' Jan. 19, 41932. F. Fl EHLIN'G v 1,841,558

RECORDING POTENTIOMETER Filed July 5, 1929 3 Sheets-Sheet 2 Jan. 19, 1932. F. F. UELING l l 1,841,558

` RECORDING POTENTIOMETER Filed July '3,1929 3 sheets-sheet 3 mf ya 109 fb l 1d f V 52 525m: /ob 12100. 55C

D3 DL D1 g1 /ssb G INVENTOR4 the recor ing element as Patented Jan. 19, 1932 PATENT OFFICE FRITZ FREDERICK UEHLING, OF PASSAIC, NEW JERSEY RECORDING POTENTIOMETER i Application led July 3, 1929. Serial No. 375,668.

This invention relates to improved means for measuring and recording theelectromotive force of a thermo-couple, or any other electro-motive force by balancing a potentiometer against said force. The potentiometer is actuated by a motor, the operation of which is controlled by a novel form of galvanometer in combination with specially designed relays, all as hereinafter described in detail.

One of the specific objects of this invention is to provide a galvanometer which may be located at a distance from the potentiometer and which at the same time may control the operation of two or more potentiometers, each otwhich measures and records the fluctuations of independent electro-motive forces from different sources.

I attain these objects by sthe mechanism illustrated inthe accompanying drawings in which- Figure 1 illustrates all of the essential parts of the'invention for a single measurement; Figure 2 is a cross section through line 2--2 of Figure 1 to illustrate the relation between the slide wire of the potentiometer, the slide wire shoe, the recording pen, and the drum on .which the record is produced; Figure 3 is an elevation of relay R-l of Figure 2; Figure 4 is a cross section on line 4-4 of Figure 2 to illustrate on an enlarged scale, the relation between the slide wire, the slide w1re shoe and the shoe uide;.Figure 5 is an end view o illustrated in Figa commuure 1; Figure 6 is a plan view of of. similar tator and one of a Amultiplicity switches actuated thereby for closing the proper circuits to measure the electro-motive forcefrom di'erent sources; Figure 7 is an elevation of the electrically operated switches in Figure 6; Figure 8 is a cross section on the line 8-8 of Figure 6: Figure 9 is a diagram-- matic view of a multiplicity'of independently operated potentiometers for makingl 1ndependent records, and includes the vauometer with the-necessary connections for operating each of them.

Similar numerals referto similar parts throughout all offthe illustrations.

A motor 1, Figures 1 'and 5, is in geare connection with a cylinder on which the slide.

wire 5 of the potentiometer is spirally wound, as illustrated. The cylinderis mounted on a shaft 3, which is rotatably supported by a :trame 26, and is connected with the motor 1 through a reduction gearl 104,v the motor 1 56 being fastened to the frame 26 by means of .a bracket 25. The circuits which include the slide wirey 5 are connected therewith through rings 6, 7 and 112, against which rest electric contact One extreme'end of the slide wire 5 is connected with the ring 7, while the'other extreme end is connected with the ring 112. A slide wire shoe 24 may be shifted, in a manner to be'presently described, throughout the 65 entire length of the wire 5. The ring 6 iS connected with a fixed point 9 on the wire 5 by means of an imbedded wire 32. It thus follows that if a current flows through the wire 5 from ring 7 to ring 112, there will be 70 a drop in Vpotential across said wire between the point 9 and the shoe 24. It is this drop, which can be changed-by shifting the shoe 24, that I utilize to balance the electro-motive force to be measured. The curvature of the rubbing surface of the shoe 24' is concentric with the spiral form of wire 5, as illustrated in Figure 2. It is also grooved to it the wire itself, as illustrated on an enlarged scale in Figure 4. In other words, the shoe 24 has a groove which ts over the spirally wound wire and serves as a female thread, while the spirally wound wire Y serves as a male thread over which the shoe 24 fits. A iat spring 22, of the proper curva- 85 ture is fastened to the shoe 24 and rests against a guide rod 23, Figure 1, thus holding the shoe tightly against the wire. The spring 22 is cut out at each end to fit the rod 23, as illustrated in Figure 2. It thus follows that as ,the cylinder on which the wire 5 is wound, is rotated in one direction or the` other by the motor 1, the shoe 24 will shift to the left or to the right, depending upon the direction in which the motor is operi ated. The rod 23 is insulated from the -rame 26, at-30 and 31 thus permitting the measurement of the drop across Wire 5'between the point 9 and the-shoe 24 without the fear of short circuiting through the frame 26. 1c

brushes

10, 11, and 12 respectively. 60

The current which passes through the spirvally wound wire 5 starts at battery 14, asses ampere meter through wire 18 and brush 12 y to ring 112, from the ring 112 through the spirally wound wire to the ring 7, and from the attery, thus completing the circuit.

That partof the spirally wound wire 5 be.

tween the Vfixed point 9 and the shoe 24 forms part of the. circuit which includes the galvanometer andthe source of the electro-m0- tive force to .be measured. The source of electromotive"force which has been chosen to illustrate this invention is a thermo-couple 59, while the galvanometer G is of novel form, the details of which will be presently described. The circuit which .includes the couple,starts at couple 59, thence through wire 60 and brush 10 to ring 6, from the ring 6 through the imbedded wire 32 to the point 9, from the point 9 'through the spirally wound `wire 5 to the shoe 24, from the shoe 24 through a flexible wire 61 and wire 62 to the binding post 63 of the galvanometer G, from the` binding post 63 through wire 64, the pivoted coil 65 of the galvanometer, and wire 66 to the connection 33, from the connection33 through a resistance 67 tol a connection 88, from connection 88 through wire 68 A to binding post 69, and from binding post 69 through wire 70 back to the couple, thus completing the circuit. v

The galvanometer G is illustrated in more or less diagrammatic form. The coil is pivoted in the usual manner, not shown, and carries an indicating needle 72, which is electrically connected with the wire 66. The indicating needle 72 serves as one member of a contact mechanism for actuating one or the otherl ofthe relays R-1 and R- 2. The circuit which includes the relay R-l is closed when the needle makes contact with the contact screw 77, and the circuit which yoperates relay R-2 is closed when contactis made between the needle and contact screw 76. The special manner in which these relays function will be presently described. The contact screws 76 and 77 are carried by 75 and 78 respectively and are insulated from the galvanometer and from each other by insulation pieces 73 and 74. The resistance 67, al-

ready referred to, forms a very important element of this -invention and will bev described in further detail later.

Therelay R-l consists of a pair of electromagnets 42 permanently fastened'to a base plate 220 by means of bracket 43. An armature 34, Figures 1 and 3, with which the magnets react, is fastened to 'a shaft 37, which shaft is carried by bearings 38 and 39.

Twd mercury switches

40 and 41 are also fastened to this shaft. These mercury switches are of the well-known form which permits the ring)7 through brush 11 and wire 13 back to closing of a circuit when they are tilted in one direction and the opening of a circuit when they are tilted in the other direction. The armature 34 is held in its normal position against a stop 35by means of a spring 36, both the spring and stop being supported by a bracket 44. The

mercury switches

40 and 41 are so fastened to the shaft 36 that when the armature 34 is in its normal position, as illustrated, the circuit through the switch 40 will be open and the circuit through the switch 41 will be closed, and when the armature 34 is pulled out' of its normal position by reaction with the magnets 42, the circuit through the mercury switch 40 will be closedv and vthe circuit through the mercury switch 41 will be open. In other words, when the magnets 42 are energized the tilting effeet of the .armature will close the circuit through switch 140 and open the circuit through switch 41, and when the magnets 42 are de energized the spring 36 will bring the armature back to its normal position in which case the circuit through the switch 40 will be open and the circuit through the switch 41 will be closed.

Relay R-2 is of the same construction as relay R-1. The mercury switch 84 of relay R-2 corresponds with the mercury switch 41 of relay R-1, and the mercury switch 221 of'relay R-2 corresponds with the mercury switch 40 of relay R-1. The purpose of the mercury switch 221 is to close the circuit which operates the motor 1 in one direction, while the purpose of the mercury switch 40 is to close the circuit which operates the motor 1 in the opposite direction. These circuits will be referred to later.

The circuit which includes the switch 41 of relay R--l starts at battery 93, thence through wire 94 to binding post 47, from binding post 47 through flexible connection 95, mercury switch 41 and lexible connection 96 to magnets 42, from magnets 42 through

wires

97 and 90 to binding post 46, from binding post 46 through wire 98 to binding post 69, from binding post 69 through wire 68, resistance 67 and wire 66 to the indicating needle 72 and, when the indicating needle touches contact screw 77 back to the battery n Words, aslong as the needle 72 touches the contact screw 77` so long will the armature fiexible connection 83, mercury switch 84 and flexible connection 85 to magnets 86, from magnets 86 through wirel 87 to binding post 57, from binding post 57 through

wires

89 and 90, to binding -post 46, from binding post 46 through wire 98 to binding post 69, from binding post 69 through wire 68, resistance 67 and wire 66 to the indicating needle 72, and when the needle 7'2 touches the contact screw 76, back to the battery 8l through wire 79-and binding post 80, thus completing the circuit. It thus follows that when the needle 72 touches the contact screw f 7 6, magnet 86 will be energized thus tilting the switch 84 which immediately breaks the circuit. As soon as the circuit through the mercury switch 84 has been broken, the armature and the mercury switches will be brought back to their,` normal position, as illustrated, in which case the circuit through switch 84 will again be closed and the cycle will repeat itself. In other words, as long as the needle 72 touches the contact screw 76, so long will the ,armature and mercury switches of relay R-2 continue to oscillate.

In further reference to the galvanometer G, it is obvious that the force of the delicate needle of a galvanometer is not suflicient to make reliable contact without the use of some external force. In the ordinary recording galvanometer the indicating needle is utilized to close electrical circuits by the assistance of some outside force, as for example., a depressor bar which is brought into place at regular intervals. It is through the use ot the resistance 67 that I eliminate the use of similar mechanical m'eans. lustrate the function of the resistance 67` let us assume that the needle 72 has been deflected, just suliicientlyf to touch the contact screw .77. In such a case the contact resistance between the needle 72 and the contact screw 77 would be'too high to allow suf- `tcient flow to actuate the relay R--l in the manner already described. It is obvious, however, that some current of very low magnitude will flow, even though it be not suicient to actuate the relay. This flow throughl this circuit which includes the'resstance 67, regardless of its low magnitude, will cause a drop in potential across the resistance 67, which drop will cause a flow through the circuit which includes pivote'd coil 65,

wires

64, 62 and 61, shoe 24, 'the spiral wire of the potentiometer between 24 and the point 9,-w-

ires

32, 60. the thermo-couple, and wire 70. The battery 93 is of such a polarity that this additional iow through the pivoted coil 65, as caused by the drop across the resistance 67,

To ilwill increase the tension of the needle 72 against the contact screw 77. As soon as this tension has been increased, the flow through the needle 72 and the resistance 67 will also increase, and as this ilow increases, the increased drop in potential across the resistance 67 will still further increase the flow through the pivoted coil 65, thereby still further increasing the tension of the needle 72 against the contact screw 77. In other words as soon as the slightest contact has been made between the needle 72 and the contact screw 77, the mechanical force between the needle 72 and the contact screw 77 will be built up almost immediately to a point where sufficient current willflow through the needle to actuate the relay REI.

Similarly let us assume that the needle 72 has been deflected just sufficiently to touch the contact screw 76. In such a case the contact resistance between the needle 72 and the contact screw 76 will again be two high to allow sutlieient flow to actuate the relay R-2 in the manner already described. It is again obvious, however, Athat some current of very low magnitude will flow, even though it be not sufficient to actuate the relay. This flow,

through the circuit-which includes the resistance 67, regardless of its low magnitude, will cause adrop in potential across the resistance 67, which drop will cause a flow through the circuit which includes pivoted coil 65,

wires

64, 62 and'61, shoe 24. the spiral wire of the potentiometer between 24 and the point 9, wires 32. 60, the thermo-couple. and the wire 70. The battery 8l is of opposite polarity7 to that of battery 93 and such that the additional flow throughthe pivoted coil 65, as caused bythe drop across-the resistance 67 will increase the tension of the needle 72 against the contact screw 76. 1 As soon as this tension has been increased. the flow through the needle 72 and the resistance 67 will also increase, and as this iiow increases` the increased drop in potential across the resistance 67 will still further increaselthe fiow through the pivotefl coil 65, thereby still further increasing the tension of the needle 72 against the contact screwr76. In other words. as soon as the slightest contact has been made between the needle 72 and contact screw 76, the mechanical torce between the needle 72 and the contact screw 76 will be'built up'almost immediatelyy to a point where s'uicient current will flow through t-he needle to actuate the relay R-2.

It will be notedthat the batteries 8l and 93 are of diii'erent polarity. 'lhis is an important feature of the invention since the drop in potential across the resistance 67. it 1 ,221, and wire 108 the needle and the screw has been made. Likewise the drop in potential across the resistance 67, if caused by battery 8l, must be of the opposite polarity to cause Va flow through ,the pivoted coil 65, in the manner already stated, to force the 4needle 72 tighter against the contact screw 76 after the initial contact between the needle 72 andthe contact' screw 76 has been' made.

To further illustrate the operation of the apparatus, let us assumethat the dro in potential between the shoe 24 and the point 9, as caused by the How from battery 14, exactly balances the electro-motive force from the thermo-couple 59.. In such a case the flow through the pivoted coil ofthe galvanometer will be zero, the'needle 72 will be in zero position, as illustrated, in which case it touches neither of the contact screws 76 or 77. However, if the ,electro-motive force of the thermo-couple increases, the needle 72 of the galvanometer will be deilected in a clockwise direction against the contact screw 76. As soon as this occurs, a delicate electric flow will be permitted through the needle 72, wire 66, the resistance 67

wires

68, 98, 90, 89, 87, magnets 86, mercury switch 84, wire 82 and battery 81. Although this delicate flow may not be sufficient to actuate the relay, it will never theless cause a drop across the resistance 67, which drop, in the4 manner already stated, will build up a pressure between the needle 72 and the contact screw 76 until there is suficient ow'to tilt the armature and mercury switches of relay R-2. As soon as the mercury switch 221 has been tilted by the magnet, the circuit through the motor 1 to operate it 1n a given direction will be closed. This circuit starts at A,battery 52 and continues through wire 51, wire 105, mercury switch to motor 1 and lfrom motor l back to the battery through wire 53. The motor 1 is so wound that when the circuit through the mercury switch 221 is closed it will rotate the cylinder on which the wire 5 1s splrally wound, in the proper direction to move the shoe 24 toward the right in the manner described. As previously stated, as soon as the mercury switches have been tilted by the magnet 86, the circuit through the switch 84 will be broken thereby permitting the mercury switches to come back to their normal position, as illustrated'. This cycle w1ll repeat itself as long as the indicating needle 2 touches the contact screw 76. By virtue of the consecutive closing and` opening of the mercury switch 221 it is obvious that the motor 1 will cause the contact shoe 24 to move to the right as long as the relay R 2 continues to oscillate. As the shoe 24-moves `toward the right, the drop across the spiral wire 5 between the point 9 and the shoe 24 will increase until the point has been reached where this drop a in balances the electromotive force of tg; couple, in which case needle 72 of the galvanometer will again assume its zero position, as illustrated, the oscillation of relay R2 will cease and the motor will stop.

Likewise if the electro-motive force of the thermo-couple decreases, the needle 72 of the galvanometer will be deflected in a counterclockwise direction against the contactscrew 77. As soon as this occurs, a delicate electric Iflow will be permitted through the needle 72,

wire 66, the resistance 67,

wires

68, 98, 90, f

97, magnet 42, mercury switch 41, wire 94 and battery 93. Although this delicate flow may vnot be sufficient to actuate the relay, it will Vmotor 1 back to the battery through wire 53. .The motor l is so wound that when the circuit through thel mercury switch 40 is closed it will rotate the cylinder on which the wire 5 is spirally wound, in the proper direction to move the shoe 24 toward the left in the manner described. As previously stated, as soon as the mercury switches have been tilted by the magnet 42, the circuit through the switch 41 will be broken, thereby permitting the mercury switches tocome back to their normal position, as illustrated. This cycle will repeat itself as long as the indicating needle 72 touches thecotact screw 77. By virtue of the consecutive closing and opening of the mercury switch 40 it 1s obvious that the motor 1 will cause the contact shoe 24 to move to the left so long as the relay R-l continues to oscillate.l As the shoe 24 moves toward the left, the drop in potential across the spiral wire 5 between the point 9 and the shoe 24 will decrease until the point has been reachedwhere this drop again balances the electro-motive vforce of the couple, in which case the needle 72 of the galvanometer will again assume its zero position, as illustrated the oscillation of relay R-1 will cease and the motor will stop.

It is obvious from the above that the shoe 24 will move from left to right or vice versa in exact proportion to any change in the electro-motive force of the couple. I therefore provide a pen arm 19 which is fastened to the shoe 24,' as illustrated in Figures 1, 2, and 5. At the end of the pen arm is fastened a pen or marker 20 which rests against a paper chart wound on a cylinder 21. The cylinder is mounted on a shaft which is supported by

bearings

28 and 29 and is rotated atl a constant velocity by a clock movement 27. It thus follows that a curve will be automatical- `ly drawn showing all variations in the eleca given electro-motive force may thus be changed by adjusting the variable rheostat 15.

Figure 9 illustrates an arrangement for actuating a multiplicity of recording units, each measuring independent electrical variables and all controlled by a single galvanom'eter G. The four recording units V, lV,

X, and Y, as illustrated, are operated respectively by motors 1a, 1b, lc'and 1d. Each recordmg unit consists of a spirally wound potentiometer, the same as already described and illustrated in Figure 1. The first recording unit V has its wire. 5a spirally wound s on a cylinder which isrotated by the motor 1a with which it is in gear connection through a chain drive 184. Similarly the rotatable cylinders of the recording units W, X, and Y are' operated respectively by motors 1b, 1c, and 1d through the chain drives 19T, 198 and 199. In order to eliminate a redescription of each recording unit, I have utilized the same numbers for similar parts as used in Figure 1, except for the fact that the numerals of recorders V, lV, X, and Y have the suflixes a, b, c and d respectively. The only difference in these recording units and the recording unit illustrated in Figure 1 Vis the chain drive already mentioned and a novel method of supplying electric current to each of the potentiometers from a single source 14. The manner in which this is accomplished will be presently described. The numerals referring the galvanometer G and relays R-l and R-2, Figure 9, and such other parts as are used in connection with each of the recording units, are the same as in Figure 1 soas to further simplify this description.

D1, D2, D3, and D4 are each three-pole switches to be referred to later which, one at a. time, connect the galvanometer G and relay R-l and relay .l-2, Figure 9, with the recording units V, W, X, and Y respectively, already above referred to. The three-pole switches, D1, D2, D3 and D4 are electrically actuated by a commutator in such a way that the actuating circuits are consecutively closed so that only one of the switches is closed at a time. The three-pole electrically o perated switches D1, D2, D3 and D4 may be of any form, but as a matter of convenience I have illustrated a form which consists of a pair of magnets143, Figures 6 and 7, fastened to a base plate 223. The magnet is provided with an armature 180, Figure 7, which is fastened to two

arms

171 and 172. These arms are carried by

bearings

124 and 125 and the armature is normally held in a fixed upright position by means of a spring 176, Figure 7. The fixed upright position of the armature is determined by the stop 173 against which the arm 172 rest-s due to the tension of the spring.

Extensions

150, 158 and 166 are fastened to the armature, as illustrated, and are insulated from it and from each other by means of the insulation piece 170. Contact

pieces

149, 157 and 165 are provided with which the

extensions

150, 158 and 166V respectively make electrical contact when they are depressed by the action of the magnet 143. The

contact pieces

149, 157 and 165 are respectively supported by

insulation uprights

148, 156 and 164. It

'thus followsthat three independent electrical connections, one betweenthe binding posts 14.7 and 152, one between the binding posts 155 and 160, and the other between the

binding posts

163 and 168 will be made when the magnets 143 are energized, and broken when the magnet is deenergized.

A commutator C, Figure 6, is provided, which automatically closes consecutively four such switches D1, D2, D3, and D4, Figure 9,

already referred to. The commutator C, Figure 6, consists of a shaft 125 properly supported by bearings, on which four rings 113, 114, 115 and 116 are respectively connected with the

segments

129, 130, 131 and 132 of a commutator, a cross section of which is illustrated in Figure 8. The rings 113, 114, 115 and 116 are respectively provided with electric contact brushes 120, 119, 118, and 117. The brushes are respectively supported by insulation posts 121,` 122, 123, and 124. Another electric contact brush 128 is provided for the segments of the commutator and is supported by an insulation piece 127. It will be noted that the segments of the commutator are not concentricy with the axis about which they revolve. This condition is purposely provided so that `at no time will the brush touch more than one of the segments. The shaft 125 which supports the commutator, is driven by a clock 126 or by any ,other motive means in a counter-clockwise direction. The brush 128 is in the form of a spring which rests on one segment at all galvanometer G and relays R--l and R-2 in Cil CII

`D3 and D4 are closed 'the same way as illustrated in Figure 1 and will automatically record the electro-motive force of the couple 59a. If the electro-motive force of the couple 59a is balanced by the drop across the potentiometer between the point 9a and the shoe 24a there will be no change in the position of the pen arm 19a. On the other hand, lif there is a change in tne electro-motive force of the couple 59a since the switch D1 was last closed, the penvarm 19a will adjust itself accordingly and in the manner already described. Similarly if the three-pole switches D2, D3, and D4 are consecutively closed by commutator C not shown in Figure 9, the

pen arms

196, 190 and 19d will adjust themselves as required to balance .any change in the electro-motive forces from the couples 596, 59e and 59d respectively. Only one of the three-pole switches D1,-` D2, at a time. By means of the commutator, already referred to, these three-pole switches will close consecutively for a period of about one quarter of a minute, thus making it possible for the

pens

19a, 196, 190 and 19d to adjust themselves Vto the electro-motive force of their respective couples at regular intervals.

In the position illustrated, Figure 6, the brush 128 is in contactwith the segment 131. In this position the circuit through the magnet 143 is closed. The action of this magnet closes switch D thus connecting the post 147 with post 152, the post 155 with post 160, and the post 163 with the post 168, all as previously described. This circuit 'which close-s the three-pole switch D starts at battery 138 thence through

wires

139 and 140, to binding post 141, :trom binding post 141 through magnet 143 to binding post 144,l from binding post 144 through wire 145 to brush 117, from brush 117 through ring 116 to segment 135, and thence through the brush 128, and wire 137 back to the battery. As the commutator rotates, the brush 128 will consecutively come in contact with the

segments

131, 132, 133 and 134, thus respectively closing the circuit through the electrically operated switches D1, D2, D3, and D4 of Figure 9. The circuit which closes the switch D1 includes the brush 117 and

wires

145 and 140, Figure 6, as described, while the circuits which similarly close the switches D2, D3 and D4 respectively include the brush 118 and

wires

145 and 181, the brush 119 and

wires

145 and 182, and the brush 120 and

wires

145 and 183.

The electric current through the potentiometers of the recording vunits V, W, X and Y, Figure9 come from a single source already mentioned. The source of current is la battery 14, from which the current Hows through the wire 13, Figure 9, to ring 7a1of recording unit V, from ring 7a through the spirally wound wire 5a to ring 112e, from ring 112e through wire 210 to ring 76 of recording unit Leagues A W, from ring 76 through the spirally wound wire 56 to ring 1126, from ring 1126 throu h wire 209 to ring of the recording unit from `ring 7c through the spirally wound wire 5c to the ring 1120, from the ring 1120 through wire 208 to ring 7 al of the recording unit Y, from the ring 7d through the spirally wound wire 5d to ring 112d, from 112Z through wire 18 -to the milliampere meter 17, and from the milliampere meter 17 through wire 16 and the adjustable resistance 15 back to the battery. In order to establish different calibrations for the recording units V, W, X and Y, I cause a diierent rate of electric flow through the

wires

5a, 56, 5c and 5d respectively. This is accomplished by shunting

variable resistances

187, 188, 189 and 190 across the 'respective pote'ntiometers, as illustrated. The variable resistance 187 is connected with the rings 7a and 112a through the wires 200 and 201 respectively. 4Likewise the

variable resistances

188, 189 and 190 are respectively connected with rings 76 and 1126, rings 7c and 1120, and rings 7d and 1120 through

wires

202 and 203, wires 204 and 205, and wires 206 and 207. It thusfollows that fthe ratios between the calibration of units V, W, X, and. Ycan be definitely established by adjusting the respective resistances 187 188, 189 and 190 an'd the constant electric flow to establish the desired calibration can be maintained by adjusting the variable resistance 15` as required to keep the needle of the amperefmeter 17 at a fixed point.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. In a device of the class described, the combination with a potentiometer, of a galvanometer, a resistance, a circuit which includes the potentiometer, the galvanometer .and the resistance, and a circuit controlled by thegalvanometer which includes the resistance.

2. In a device of the class described, the combination with a potentiometer, of a galvanometer, a resistance, means for actuating the potentiometer in one direction, means for actuating the potentiometer in the opposite direction, a circuit which includes the potentiometer, the galvanometer and the resistance, a circuit controlled by the galvanometer which includes the first actuating means and the resistance, and a second circuit controlled by the galvanometer which includes the second actuating means and the resistance.

3. In a device vof the class described, the combination-with a galvanometer having an indicating needle, of a contact piece with which the needle makes electrical contact when deflected in one direction, a second contact piece with which the needle makes elecpotentiometer, the galvanometer and the resistance.

4. In a device of the class described, the combination with a galvanoineter having a pivoted coil and an indicating needle, of a re-v sistance, a source of electro-motive force, a potentiometer, an electric circuit which includes the potentiometer, the pivoted coil, the resistance, and the source of electro-motive force, a contact piece with which the needle makes electrical contact when defiected in one direction, a second contact piece with which the needle makes electrical contact when deflected iii the opposite direction, a circuit for actuating the potentiometer in one direction vwhich includes the first contact piece, the needle and the resistance, and a circuit for actuating the potentiometer in the opposite direction which includes the second contact piece, the needle and the resistance.

5. In a device of the class described, the combination with a potentiometer, of electrical means for actuating the potentiometer in one direction, electrical meansfor actuating the potentiometer in the opposite direction, a galvanometci having a pivoted coiland an indicating needle, a resistance, a circuit which includes the potentiometer, the resistance and the pivoted coil, a contact piece with which the needle make-s electrical contact when deflected in one direction, a battery of a given polarity, a circuit which includes the first electrical means, the battery, the contact piece, the needle and the resistance, a second contact piece with which the needle makes electrical contact when defiected in the opposite direction, a battery of opposite polarity, anda circuit which includes the second `electrical means, the second battery, the second contact piece, the indicating needle and the resistance.

6. In. a device of the class described, the combination with an electric switch, of a sec ond electric switch, electro-magnetic. means Lfor simultaneously' closing the first switch and opening the second switch, a spring for simultaneously opening the first switch and closing the second switch when the electromagneticmeans is deenergized, a third electrical switch, a fourth electrical switch, electromagnetic means for simultaneously closing the third switch and opening the secondv switch, a spring for simultaneously opening the third and closing the fourth switch whenu the second electromagnetic means is deenergized, a galvanometer having a pivoted coil and an indicating needle, a resistance, a cir.- cuit which includes the resistance, and the A,pivoted coil, a contact piece'with which the needle makes contact when defiected in one direction, a battery of given polarity, a circuit which includes the battery, the contact piece, the needle, the resistance, the second switch and the first electromagnetic means, a second contact piece with which the needlemakes contact when deflected in the opposite direction, a second battery of opposite olarity, a circuit which includes the secon battery, the second contact piece, the needle, the

resistance, the fourth switch and the second electromagnetic. means, a potentiometer, electrical means for actuating the potentiometer in one direction, a second electrical means for actuating the potentiometer in the opposite direction, a circuit which includes the first electrical means and the first electric switch, and a circuit which includes the second electrical means and a third electric switch.

7 In a device of the class described, the combination with an electric switch, of a second electric switch, electromagnetic means for simultaneously closing the first switch and opening the second switch, a spring for simul taneously opening the first switch and closing the second switch when the electromagnetic means is deenergized, a third electrical switch, a fourth electrical switch, electromagnetic means for simultaneously closing the third switch and opening the fourth switch, a spring for simultaneously opening the third and closing the fourth switch when `the second electromagnetic means is deenergized, a galvanometer having a pivoted coil and an indicatingv needle, a resistance, a potentiometer, a circuit which includes the resistance, the potentiometer and the pivoted ond contact piece with which the needle makes contact when deflected in the opposite direction, asecond battery of opposite polarity, a circuit'which includes the second battery, the second contact piece, the needle, the resistance, the fourth switch and the second electromagnetic means, electrical means for actuating the potentiometer in one direction, a second electrical means for actuating the potentiometer inthe opposite direction, a circuit which includes the first electrical means and the'first electric switch, and a circuit which includes the second electrical means .and a third electric switch.

a in a device of the dass described, the

combination with a cylinder, of a wire wound on the cylinder and electrically insulated from it, a ring on the cylinder with which one end of the wire is electrically connected, a second ring on the cylinder with which the other end of the'wire is electrically connected, a third ring on the cylinder with which a point on the wire between its two ends is electrically connected, a battery, an adjustable resistance, an ammeter, a circuit which includes the first ring, the wire, the second ring, the batt-ery, the adjustable resistance and the ammeter, an electric contact shoe which rests against the wire, means for shit-' ing the shoe in either direction. along the length of the wire, a galvanometer, and a circuit which includes the galvanometer, the third ring and the shoe.

9. In a device of the class described, the

combination with a cylinder, of a wire wound on the cylinder and electrically insulated from it, a ring on the cylinder with which one end of the wire is electrically connected,

` a second ring on the cylinder with which the (ill other end of the wire is electrically connected, a third ring on the cylinder with which a point on the wire between its two ends is electrically connected, a battery, an adjust able resistance, an ammeter, a circuit which includesthe first ring, the wire, the second ring; thel battery, the adjustable resistance and the ammeter, a shoe with a groove that fits over the wire substantially as described, a spring for pressing the shoeagainst the wire, a guide for limiting the motion of the shoe to a ,single direction parallel to the axis of the cylinder, means for rotating the cylin-4 der in either direction, a galvanometer for controlling the rotating means substantially as described, and a circuit which includes the galvanometer, the shoe, and the third ring.

10. In a device of the class described. the combination with a cylinder, of a-thread on the cylinder consisting of a spirally wound wire, a shoe with a groove to fit the thread, means for moving the shoe along the thread in either direction, a ring on the cylinder electrically connected with one end of the thread, a second ring on the cylinder electrically connected with the other end of the thread, a third ring on the cylinder electrically connected with the thread at a point between its two ends, an electric circuit which includes the thread, the first ring and the second ring, and an electric circuit which includes the shoe, the third ring and the thread between 'the third ring and the shoe.

ll. In a. device of the class described, 'the combination with a cylinder, of means for rotating the cylinder on its axis, a thread on the cylinder. consisting of a wire spirally wound on and insulated from the cylinder, a shoe with a groove to fit the thread, a guide for preventing the revolving of the shoe about the axis of the cylinder, a ring on the cylinder electrically connected with one end of the thread,` a second ring on the cylinder electrically connected with the other end of the thread, a third ring on the cylinder electrically connected with the thread at a point between its two ends, a brush for making electrical contact with the first ring, a second brush for making electrical contact with the second ring, a third brush for making electrical contact with the third ring, a variable resistance, a battery, an ammeter, acircuit which includes the variable resistance, the battery, the ammeter, the first brush, the first ring, the thread, the second ring andthe second brush, a galvanometer for controlling the rotating means, and a circuit which includes the galvanometer, the shoe, the third ring, the third brush and the thread between the third ring and the shoe.

12. In a device of the class described, the combination with a cylinder, of electrical means for rotating the cylinder in one direction, electrical means forv rotating the cylinder in the opposite direction, a thread on the cylinder consisting of a wire spirally Wound on and insulated from the cylinder, a shoe with a groove to fit the thread, means for pressing the shoe against the thread, a guide for limiting the motion of the shoe to a fixed l path parallel to the axis of the cylinder, a

ring on' the cylinder electrically connected with one end of the thread, a second ring on the cylinder' electrically Aconnected with the other end of the thread, a, third ring on the cylinder electrically connected with the thread at a fixed point between its two ends, a brush for making electrical contact with the first ring, a second similar brush for the second ring, a third similar brush for the third ring, an electric circuit which includes the iirst brush, the first ring, the thread, the second .ring and the second brush, a galvanometer, an electrical resistance, an electric circuit which includes the galvanometer,the

resistance, the third brush, the third ring, the

shoe and the thread between the third ring and the shoe, an electric circuit which includes the resista-nce and the first rotating means, and an electric circuit which includes the resistance and the second rotatino' means.

rarrz FREDERICK UEHING.