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Nov. 6, 1945. R. K] FRAZIER 2,388,534 POTENTIOMETER Filed June 4, 1942 T0 RECEIVER ' UNDER TEST INVENTOR ' RADFORD K. FRAZ/ER ATTORNEY Patented Nov. 6, 1945 2,388,534 UNITED STATES ‘PATENT OFFICE 2,388,534 POTENTIOMETER Radford K. Frazier, Baltimore, Md., assignor to ‘f Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware ' Application June 4, 1942, Serial No; 445,742 11 Claims. (01. 178-44) This invention relates to potentiometers and plished by a potentiometer design in which the more particularly to potentiometers for use at magnetic linkage between the potentiometer im very high frequencies. pedance element and the controlled circuit is Potentiometers commercially available at this substantially zero for a predetermined position time usually comprise an arcuately shaped re of the movable potentiometer arm. sistance element over which a contacting arm is moved by the rotation of 9. centrally located shaft. Connecting terminals are attached to either end of the resistance element and a third connect ins terminal establishes contact to the rotatable arm via a ?exible brushor its equivalent. The Other objects and advantages of the invention will in part be disclosed and in part be obvious when the following speci?cation is read in con ’iunction with the drawing in which: resistance element normally occupies a circular sector of approximately 330 degrees; and the terminals making connection to the element ends are therefore approximately thirty degrees apart, the arm terminal being located centrally in this cordance with the principles of the invention. Figure 2 is a side view showing additional de tails of the potentiometer construction of Fig thirty degree sector. The circular shaped resistance element may be viewed as one turn of an inductance coil produc Figure 1 is a rear view showing the essential elements of a potentiometer constructed in ac ' ure 1. ‘ Figure 3 is a rear view of an alternative form of potentiometer also designed in accordance with the principles of the invention. Figure 4 shows a typical utilization circuit ing the type of magnetic ?eld normally asso 20 wherein the advantages of this new potentiometer ciated with such coils. This field links, not only‘ are of particular importance. with the loop formed by the resistance element . itself, but also with the loop circuit enclosed by It is to be understood that the drawing is intended to illustrate specific forms of ‘the in ' the movable contact arm and the stationary con vention, and are not to comprise a limitation on nector to the rotatable am. With direct current the content or scope of the invention. applied to the resistance element and the contact In the drawing, like parts are designated by arm rotated to one end of the element, it is like reference characters.‘ found that no potential appears between the con Referring to Figure 1, there is shown the cir tact arm terminal and the winding terminal with cular impedance element I mounted on the base which the arm is in contact. With high frequen 30 2 of insulating material by the screws 3 passing cies of the order of 100 megacycles impressed on through the mounting ears 4 which form a part the resistance element, however, considerable voltage may be measured between the contact arm terminals and the winding terminal, thus making it impossible to obtain zero voltage out put from the potentiometer. This is- particu larly detrimental in signal generator attenuators for use at the above frequencies and must be , eliminated for satisfactory operation. I have traced the source of this voltage to the magnetic coupling existing between the resistance element and the area included between the contact arm and the stationary connector establishing con nection to the contact arm. One of the principal objects of the invention is to provide an improved potentiometer for the of the impedance element I. v For frequencies greater than 80 or 90 megacycles per second a strip of copper or other highly conductive mate rial approximately one thirty-second of, an inch thick may be used for element 1 as the'reactance of the loop is su?icient to provide the desired im pedance. The arm 5 is movable over the element i upon rotation of the shaft 5, to which the arm 5 may be secured by the sweated collar ‘I. Elec trical connection to the arm 5 is established through the fixed contact arm 8- which by virtue of its form in the region of the shaft, is main tained in contact with arm 5 under spring ten 45 sion. It is to be noted that arm 5 is of somewhat unusual form for a purpose to be discussed more control of high frequency alternating currents. Another object of the invention is ‘to ‘provide fully below. Electrical connections for the ener gization of the element 1 may be made by two a new and novel potentiometer in which the out wires slipped through the apertures 9 and I0 and put vs. rotation characteristic in the low output 60 soldered in place. Apertures H in the base 2 are position is independent or the applied frequency. provided for convenience in mounting the Yet another object of the invention is to pro vide an improved potentiometer for use with high assembly. Turning to Figure 2, the side view of the po frequency alternating currents in which the out tentiometer of Figure» 1 shows the bushing l5 put voltage measured between the connector to 55 mounted in the base 2 and secured by the nut 16. the movable arm and one end of the impedance The shaft 6 passes through the'bushing' l5 and element is substantially zero when the movable is kept in place by the O-shaped washer II which arm is in contact with said end of said imped is snapped into the groove l3. The collar 1 is ance ' sweated on the shaft 6 and secures the arm 5 The above objects and advantages are accom 60 thereto, contact between the arm 5 and the fixed element. _ ' ' > . v2 arm a being maintained by the tension exerted A typical signal generator attenuator circuit ' as a result of the deformation of the shaft end is shown in Figure 4, with the radio frequency of the arm 8 shown in the drawing. ' In the potentiometers ?nding wide present ap source I9 connected to the potentiometer 28 through the resistor 2|. The ladder attenuator plication, the rotatable arm'is generally straight network and selector switch are connected to the in form or, if not straight, is symmetrical so that terminals 22 and 23 of the potentiometer. With the net e?ect from the standpoint of magnetic the potentiometer arm rotated to the maximum clockwise position along the impedance element of the potentiometer, viewing the potentiometer linkage is the same as if a straight arm were employed. Considering the potentiometer of Fig ure 1 and visualizing a straight contact arm in 10 from the rear as shown in this ?gure, no input use, it is seen that the circuit including the ?xed . voltage is delivered to the input of the attenuator arm 8 and the contact arm 5 would be electrically network when using‘ a potentiometer of my de- ‘ linked to the impedance element by the magnetic ' sign, whereas there has always existed a residual ?eld linkage, and even with the arm in contact voltage where attenuators of the previous design ' with the impedance element aperture 9, there will 15 were employed. ‘In the event that coupling exists still be an output voltage developed between ?xed arm 8 and the connection to the aperture 8, between the power circuit and the controlled cir cuit external to the potentiometer, as indicated the magnitude of this voltage being controlled by by the arrow 25, the potentiometer may be de the intensity of the current in element i, the fre signed along the line which I have previously quency of that current, and the area included 20 enumerated and this undesired‘voltage cancelled between the ?xed arm 8 and the movable arm 5. out when the potentiometer arm is in contact By using an arm 5 having a bend of approxi with one of the end ‘points of the impedance mately the shape shown, the voltage appearing element. This potentiometer is of great value in between the ?xed arm 8 and the aperture 8 when any application where it is desired tocontrol the the arm 5 is in the position shown as a result of 25 intensity of a high frequency alternating current the ?ux linking with the area I! is made to op by the varying of the position of a contact, espe pose and cancel the residual voltage introduced cially where very small or zero output potential by all other undesired coupling in the potentiom is desired at a limiting position of the potenti eter structure. That zero output is thus attained‘ ometer contact movement. The‘ circuit just de is due to the fact that the net ?ux linkage be 80 scribed, however, has been included merely as a tween the potentiometer element loop and the out speci?c illustration of the application ofv this po put loop is reduced to zero. To the ?ux linkages tentiometer and it is not intended to limit the ap normally existing, there are added, when the arm plication of the invention to this particular class 5 is in engagement with one end of the element i, of service. ' > the ?ux linkages of reverse sense‘ occurring 85 It will be obvious that many changes and mod through the area l2 enclosed by arm I and the i?cations may be made in the invention without ?xed arm 8. The net ?ux from the current ?ow departing from the spirit thereof as expressed in ing in element A linking the controlled output the foregoing description and in the appended terminal circuit (arm 8 and terminal aperture 9) claims. is thus brought to zero. A bend in the contact 40 What I claim is: arm 5 or ?xed arm 8 so reversely linking the ?ux 1. In a potentiometer, an impedance element, from element I may therefore be conveniently _a movable contact member engaging said element, and accurately referred to as a de-gaussing bend, and a current take-off member electrically con and the relative con?guration of these two mem nected with said contact member, said members bers be referred to as a de-gaussing con?guration. 45 having a cooperating con?guration enclosing a In cases where the potentiometer isto be em de-gaussing area when said contact member is in ployed in conjunction with a known circuit con engagement with a predetermined end of said ?guration, the reverse couplingmaytbe adjusted element. ‘ in the design to also balance out other undesired 2. In a potentiometer, an impedance element, potentials induced in portions of the controlled 50 a movable contact member engaging said ele circuit external to the structure of the potenti ment, and a current take-oil’ member electrically ‘ connected with said contact member, one of said As an alternative design, the arrangement of members having a lateral bend intermediate its Figure 3 shows a potentiometer securing the free length de?ning with said other member a' de dom from magnetic coupling between the imped 55 gaussing area when said movable contact mem ance element and the controlledcircuit in a some ber is in engagement with a predetermined end what different manner. As before, an arm I1 is of said impedance element. secured to the rotatable shaft 8 by the collar 3. In a potentiometer, an impedance element, a 1, and the outer end of the arm ll moves over movable contact member engaging said element, the impedance element i which is secured to the 60 and a current take-oil member electrically‘ con _ base 2 by the screws 3 passing through the mount nected with and underlying said contact member, ing ears 4. Connection to the impedance ele said current take-off member having a bend in ment is established by soldering wires in the aper termediate its length de?ning with said movable tures 9 and it. Contact to the movable arm is contact member a de-gaussing area when said afforded by the ?xed arm i 8, which is roughly 8 65 movable contact member is in engagement with shaped in form. Arm i8 is dished in form of a a predetermined end of said impedance element. spring washer in the region of the shaft v8 ‘to pro 4. In a potentiometer, an impedance element vide a contact in tension with arm i‘i. By virtue occupying an arcuate sector of less than 360°, of the form of the ?xed arm it, which has'also means for making electrical connection to said the shape of a de-gaussing bend an area i2 is 70 impedance element at a plurality of points, a included between the movable and ?xed arms in movable contact arm engaging said impedance the minimum output position of the movable arm, ‘ element, and stationary current take-oi? means whose sign of coupling is such as to oppose the electrically connected with said contact arm and residual coupling existing between'the impedance having a terminal intermediate the extremitiesv ometer proper. element and the controlled circuit. _ 75 or said impedance element, said contact arm and " 2,388,534 said current take-off means having a cooperat ing con?guration enclosing a de-gaussing area when said contact arm is in engagement with a predetermined end of 'said element. 5. In a potentiometer, an impedance element of arcuate form occupying less than 360° of arc, means for making electrical connection to said impedance element at a plurality of points, a 3 i therewith, a load impedance, means for connect ing one terminal of said load impedance to one of said end terminals of said impedance element, a stationary current carrying member connected to the other terminal of said load impedance, a movable contact member displaceable over the length of said impedance element connected to said stationary current carrying member, the contact arm rotatable in engagement with said connections to said load impedance forming a sec impedance element about an axis of rotation 10 ond loop circuit receiving energy from said ?rst passing substantially through the center of our vature of said arcuately formed impedance ele ment, current take~oif member extending sub loop circuit via space coupling addition to the energy transferred through said contact member, said stationary current carrying member and said ‘ stantially radially from said axis of rotation, said movable current carrying member having a coop contact arm being'provided with a bend in the 15 erating con?guration when said contact member plane of rotation de?ning with said current take is in engagement with one of said end terminals ’ o?‘ member a de-gaussing area when said moi? forming a third loop circuit magnetically coupled able. contact arm is inengagement with a pre to said ?rst loop circuit with a sense opposing the determined connection point to said impedance coupling between said ?rst loop circuit and said 20 second loop circuit. 6. In an alternating current system, a source 10, In an alternating current system, a source element. , ‘ of periodic electrical energy, an impedance ele- _ ment connected across said source and forming a _ of periodic electrical energy, an impedance ele ment provided with two end terminals connected loop circuit therewith, a load impedance, means across said source and forming a loop circuit adjustably and galvanically connecting said load ‘therewith, a load impedance, means for connect impedance to said ?rst impedance element, ing one terminal of said load impedance to one whereby a second loop circuit is formed by said of said end terminals of said impedance element, load impedance and the connecting means as a stationary current carrying member connected sociated therewith, said second loop circuit in to the other terminal of said load impedance, a herently being magnetically coupled to said ?rst 30 movable contact member displaceable over the ‘loop circuit, and means for introducing magnetic length of said impedance element connected to coupling opposing said inherent coupling between said stationary current carrying member, the said ?rst 100p circuit and said second loop cir- ' ‘connections to said load impedance forming a second loop circuit receiving energy ‘from said 7. In an alternating current. system, a source 35 ?rst loop circuit via space coupling in addition of periodic electrical energy, an impedance ele to_the energy transferred through said contact ment connected across said source and forming a member, said stationary ‘current carrying mem loop circuit therewith, a load impedance, means ber and said movable current carrying member adjustably and galvanically connecting said load having a cooperating con?guration when said impedance to said ?rst impedance element, 40 contact member is in engagement with that end whereby a second loop circuit is formed by said terminal of said impedance element connected load impedance and the connecting means as- to said load impedance forming a third loop cir cuit magnetically coupled to said ?rst loop circuit 7 sociated therewith, said second loop circuit in , herently being coupled to said ?rst loop circuit, I with a sense opposing the coupling between said , and means for introducing magnetic coupling op 45 ?rst loop circuit and said second loop circuit. T posing said inherent coupling between said ?rst 11. In an alternating current system, a source 7 loop circuit and said'second loop circuit with a of periodic electrical energy, an impedance ele magnitude developing a voltage equal to said in ment provided with two end terminals connected herent coupling when said adjustable means is across said source and forming a loop circuit in engagement with a predetermined point on’ 50 therewith, a load impedance, means for connect said ?rst mentioned'impedance.. , . ing one terminal of said load impedance to one 8. In an alternating current system, a source of said end- terminals of said impedance element, of periodic electrical energy, an impedance ele a stationary current carrying member connected ment provided with two and terminals connected to the other ‘terminal of said load impedance, a across said source and forming a loop circuit 55 movable contact member displaceable over the cuit. . therewith, a load impedance, means adJustably and galvanically connecting said load impedance to said ?rst impedance element, whereby a sec ond loop circuit is formed by said load impedance and the connecting means associated therewith, said second loop circuit inherently being coupled to said ?rst loop circuit, and means for introduc length of said impedance element connected to said stationary current carrying member, the connections to said load impedance forming a second'loop circuit receiving venergy-from said ?rst loop circuit via space coupling in addition. to the energy transferred through said contact member, said stationary current carrying mem ing magnetic coupling opposing said inherent ber and said movable current carrying member coupling between said ?rst loop circuit and said having a cooperating con?guration'when said second loop circuit, with a magnitude developing 66 contact member is in engagement with that end a voltage equal to said inherent coupling when terminal of said impedance element connected to said adjustable means is in engagement with a , said load impedance forming a third loop circuit predetermined one of said end terminals. magnetically coupled to said ?rst loop circuit with 9. In an alternating current system, a source a sense opposing and equal to the coupling be of periodic electrical energy, an impedance ele .70 tween said ?rst loop circuit and said second loop ment provided with two end terminals connected circuit. . across said source andiorming a loop circuit RADFORD K. FRAZER.