US2833979A

US2833979A - Precision transducer

Info

Publication number: US2833979A
Application number: US520546A
Authority: US
Inventors: Larkin B Scott
Original assignee: Perkin Elmer Corp
Current assignee: Applied Biosystems Inc
Priority date: 1955-07-07
Filing date: 1955-07-07
Publication date: 1958-05-06
Anticipated expiration: 1975-05-06
Also published as: DE1043498B; DE1043498C2; CH346608A; FR1154604A; GB820639A

Description

y 6, 1958 L. B. SCOTT 2,833,979

PRECISION TRANSDUCER Filed July 7, 1955 I 6' INVENTOR.

ZAOK/Nfi 56077 ,JTTdPp EY Unitcd States Patent 2,833,979 PRECISION TRANSDUCER Larkin B. Scott, Fort Worth, Tex., assignor to The Perkin- Elmer Corporation, Nor-walk, Conn., a corporation of New York I Application July 7, 1955, Serial No. 520,546

Claims. or. 323-435 This invention relates to precision transducers for use in electrical apparatus. The subject matter of this present invention is a continuation-impart of my copending application S. N. 380,284 and is concerned with a novel precision transducing device, by means of which a plurality of intermediate voltages may be derived from an input voltage range, and variations in such intermediate voltages may be effected smoothly and without interruption from one end of the range to the other. The new device is small and compact and it is inherently of high accuracy so that the quality of its performance does not depend upon tedious and expensive methods of manufacture. In addition, the device may be constructed to have high resolution so that it will provide a large number of increments of voltage within its range. Generally, transducers may be made in forms appropriate for alternating and direct current use, but the present invention is intended specifically for use with alternating current, and therefore a form suitable for such use will be illustrated and described in detail for purposes of explanation.

At the present time, electrical transducers in common use are, of two main types, namely, the potentiometer and the auto-transformer. The potentiometer is essentially a resistor having a plurality of taps with respective contacts or terminals and an adjustable contact arm engageable withthe terminals. A fixed reference voltage is impressed across the resistor and the voltage appearing between its lower terminal and the contact arm is then a percentage of the reference voltage equal to the ratio R /R', where R is the total resistance of the resistor and R isth'e resistance between the lower terminal and the contact arm. In the use of the device, R is frequently shunted by a low impedance, in which event the stated rclationshipbetween the voltages may not be valid, ex-

F cept when the resistance R; is small in comparison with the load imposed by the impedance. it is usually difficult, however, to make the resistance of the. potentiometer low enough to achieve the desired condition because, for example, sufiiciently low resistance would permit the flow of undesirably high currents through the device and result in a waste of power drawn from the primary voltage source. Also, the resistance Wire of the potentiometer is commonly wound in a helical coil and the contact arm slides from one convolution to the next and makes contact with each convolution at one point only. As the total resistance is lowered, it is usually necessary to reduce the total turns and this reduces the number of points, which the sliding contact may engage. As a result, the device is characterized by relatively low resolution and the steps in the output voltage may be so large as to make it impossible to adjust the device to produce a voltage acceptably close to one desired.

An auto-transformer for controlling voltage commonly takes the form of a toroidal winding of a single layer of wire upon an annular magnetic core and a moving contact or wiper, which rotates about the center of the core and contacts the turns of the Winding successively. The Wiper may be of suificient size to span two turns, in'which event the material of the wiper is usually of high resistance so that large currents are avoided when the wiper shorts two turns at the same time. This shorting of turns is advantageous in that, as the wiper is moved along the winding from one turn to the next, a somewhat more gradual change occurs in the voltage produced at the wiper with the result that variations in output voltage, which would occur if the wiper made contact with only one turn at a time, are smoothed out. While such devices are capable of being adjusted in smaller voltageincrements than would appear to be the case from the number of turns in the winding, they do not ordinarily have the smoothness or linearity desired in some applications as, for example, with analogue computing instruments. However, they are attractive in that they can be made t present a reasonably low output impedance.

The precision transducer of the invention is capable of greater resolution, smoothness, and linearity than the prior devices above-mentioned. It comprises essentially a series of terminals, one of which is a reference terminal, and means for maintaining a reference voltage on the reference terminal and voltages of predetermined values relative to the reference voltage on the respective other terminals along the series. Discrete increments of potential are tapped from along the series by electrical connection, and voltages intermediate those on the terminals are derived from inductive means positioned in magnetic flux relation to a portion of the potential developed across the series of terminals. The inductive means comprise two windings or inductive elements disposed so as to be connectible to terminals along the series. A means for rotating the windings also operates switch means which electrically connects the windings with alternate terminals along the series.

A suitable form of the new device comprises an autotransformer of toroidal form, which is made of a single wire conductor wound upon an annular core and having a plurality of terminals connected to taps at selected intervals along its coils. These taps provide the basic voltage levels in relatively large discrete increments and voltages intermediate the basic levels are derived by means of an induction potentiometer comprising a first inductive element connected across a portion of the auto-transformer and second and third inductive elements positioned in magnetic flux relation with the first inductive element and in space quadrature with each other. By varying the relative spatial disposition of the first inductive element with respect to the second and third inductive elements, the amplitude of the potentials induced in the latter two inductive elements may be varied in both phase and amplitude. Since an alternating current potential thus induced may be altered in phase so as to be out of phase with another potential of fixed amplitude and of the same frequency impressed upon the same inductive element, the variable induced potential can be made to subtract from the amplitude of the impressed potential, as well as add to it. By varying the magnetic flux linkage of such inductive element, a smoothly varying amplitude of theoretically infiite resolution can be inductively developed across the windings. This is true of both the second and third inductive elements and by appropriately arranging the second and third inductive elements in quadrature relation to each other and with adjacent terminals of the auto-transformer series of terminals electrically connected to tl e second and third in- 2 along the series of autotransformer taps.

ductive elements, the induced potential can be made to subtract from the inductive element having the highest potential impressed upon it, while the induced potential in the inductive element having the lower potential applied to it may be made to add thereto.

A switching means operatively responsive to the means for varying the disposition of the inductive elements may be made to connect the two windings of the linear synchro in hand-over-hand fashion to successive terminals When the second and third inductive elements are connected to adjacent terminals along the series, the respective potentials induced therein may be of such phase and amplitude that the algebraic sum of the induced and tapped potentials developed across each inductive element is equal to that developed across the other. Thus, by proper phasing and amplitude variation, the total output potential developed across the second and third inductive elements may he the same, at least for a portion of the operative range of the device where it is necessary to effect switching operations. This overlap is one of the advantageous features of the invention, the importance of which will appear from a more thorough understanding of the invention and its operation.

While the instrument described is a preferred construc tion for general applications, it will be understood that the physical orientation-of the autotransformer terminals and of the inductive means, together with the mechanical arrangement and coaction of the switching means, may be varied to suit the design requirements of any particular application. Such variations do not alter the desirable electrical characteristics of the device.

For a better understanding of the invention, reference may be made to the accompanying drawings, in which,

Fig. l is a schematic representation of the elements of an embodiment of the present invention,

Fig. 2 is an illustration of the output characteristics of a linear synchro,

Fig. 3 is an illustration of switching means suitable for use in the present invention,

Fig. 4 is a graphic illustration of the coarse increments of signal which are connected to the output of the device by rotation of the switching means,

Fig. 5 is a graphic illustration of the fine variation of output signal effected by rotation of the inductively coupled elements and the associated switching means, and

Fig. 6 is an illustration of the total output of the present invention showing amplitude v. rotation.

The present invention may advantageously use an internal-external gear arrangement such as that disclosed of signal change as determined by the series of terminals along an autotransformer, for instance, and also provide continuously varying induced potential in the coils of the induction potentiometer.

The theory of operation of an induction potentiometer is well known and need not be elaborated upon here, beyond mentioning the fact that such an induction potentiometer has substantially infinite resolution within the range of its operation because the variation in the potential developed by such a device is dependent upon change in magnetic flux linkage as determined by relative spatial disposition rather than a change of tapped potential determined by a physical contact such as with a Wire-wound potentiometer, for example. olution inheres in the instant invention for the same fundamental reason in that its line interpolation between the larger tapped increments of output is dependent upon a change in magnetiefiux linkage as determined by relative spatial disposition.

The feature of infinite res- The instant invention involves the use of an inductively coupled device having two elements arranged in fixed quadrature relation with each other, both being variable in spatial disposition relative to yet another inductive element. In one of its most practical forms this device takes substantially the form of a synchro. For use in the present invention, however, the synchro should preferably have linear output characteristics which may be achieved by appropriate shading of the device in a manner known and familiar to those skilled in the art.

Fig. l is a schematic representation of an embodiment of the present inventioncomprising a series of terminals, 1 through 8, spaced along an autotransformer 10, orig of which, designated by the numeral 1, is a reference terminal. A first inductive element 11 is connected across two of the

terminals

1 and 2 of the transformer 10, and second and third inductive elemepts 1 2 and 13 are disposed in quadrature spatial relation to each other and in magnetic flux linkage with the first inductive element 11. An input potential is applied to the autotransformer 10 at its extreme terminals land 8, as shown.

Fig. 2 illustrates typical output characteristics of the two quadrature windings of an induction potentiometer appropriate for use in an embodiment of the present invention. Due to the nature of the device and the fact that its output is linear over a considerable range of its operation, it may be convenient to refer to it herein as a linear synchro.

Assuming that the linear synchro or induction potentiometer comprised of windings 11, 12, and 13 will produce two

outputs

20 and 21 as shown in Fig. 2, one complete revolution of the device may be divided into twelve increments, each of which is in continuity with adjacent increments and corresponds to 30 of shaft rotation.

The induced voltage 20 appearing across terminals A and B is linear with respect to shaft rotation of the linear synchro over the first 60 of its rotation, increasing in amplitude in response to clockwise rotation. Through the next span of 60 the induced voltage 20 becomes nonlinear and then becomes linear again for a span of with respect to continuous shaft rotation, but decreasing in amplitude in response to clockwise rotation. By using two such inductive elements 12 and 13 disposed in space quadrature with respect to each other, one of the windings 12 or 13 is always operative in a region which will develop a linear potential with respect to shaft rotation, though the linear induced potential as shown at 20 and 21 may be normally decreasing in amplitude for a portion of its operative range.

A switch means rotatably mounted ofi-center with respect to the transducer housing, in a manner similar to that disclosed in my copending application S. N. 380,284, is arranged to perform a series of related switching operations by which the two output windings of the linear synchro are connected with alternateterminals 1 through 8 along the series of taps on the autotransformer 10 in accordance with the teaching of the present invention.

Fig. 3 shows such a switch arrangement. A commutator device having conducting segments disposed at five different radii is mounted in fixed relation to the housing of the transducer. Three separate switch wipers 15 rotate with the shaft 16 of the linear synchro or induction potentiometer. One of the commutator segments comprising a complete ring and labeled W is permanently connected to the output lead. Four other segments labeled A, B, C, and D are permanently connected to the four output terminals of the induction potentiometer which bear identical. designation. The four remaining commutator segments are connected to four switch wipers which are operationally comparable. to the three switch wipers disclosed in my copending application S. N. 380,284. The autotransfor-mer connections are rearranged as com.- pared with the prior disclosure, so. as to accommodate four ch p s ins a of hre en. he af .6 o he. de i e is r9ta. the

mutator segments and wipers coact in sequential switching operations to effect the connections as tabulated below:

These switching operations connect the windings of the linear synchro to successive discrete increments of potential developed across the autotransformer so that one of the windings is always electrically connected to that portion of the autotransformer output which might be considered the coarse component of the total output developed across that winding.

Fig. 4 illustrates graphically the coarse changes in output potential effected by the series of switching operations. The solid line graph 22 indicates the several amplitudes of potential impressed upon winding A-B by such electrical connections, whilethe dash line graph 23 represents the several amplitudes of potential impressed upon the winding CD by similar electrical connections. The units of measure used for. the ordinates of the graphs of Figs. 2, 4, ,5, and 6 are arbitrary units for comparison purposes and do not correspond either to actual potentials, nor does the negative designation refer to polarity but rather subtractive phase of the A. C. potentials so developed.

The same swtiching operations which effect the coarse changes in the amplitude of potential by electrical connections to the synchro windings, also determine the sense of the components of potential inductively developed across each of the synchro windings 12 and 13 by the manner in which the windings are connected to the autotransformer taps and the output is taken from the windings.

The inductively developed component of the total potential across each winding and 21 is shown in Fig. 5, the solid lines 20 again designating the amplitude of potential induced across winding A-B and the dash lines 21 designating the amplitude of potential induced across winding CD. It will be noticed that the sense of the inductively developed potential is changed by the switching operations so as to be always increasing linearly when the transducer is rotated in one direction and thereby add algebraically to the amplitude of the coarse increments. Those portions of inductively developed potential which are indicated to be negative do not, of course, have a negative polarity as such because they are A. C. in character, but such inductively developed negative portions are 180 out of phase with the coarse increment of potential impressed upon the winding by electrical connection with the autotransformer. Such out-of-phase potentials therefore may be considered to be negative in the sense that they subtract from the other component of potential impressed upon the windings.

The coaction of the switching operations is perhaps best illustrated by Fig. 6 which is a graphic representation of the total potential developed by the device throughout its total range of operation. The total linear output is seen to be the algebraic sum of a coarse component comprising discrete increments of potential and an inductively developed, linearly variable component. The switching operations are so correlated as to reverse the synchro winding input and output connections during at least a portion of that span of operation where the inductively developed potential would normally be linearly decreasing in amplitude and negative-going. By utilizing the overlap of operative function possible with the two windings, adequate time periods are afforded during which the necessary switching operations may be completed without effecting the smoothly varying continuously linear output. That is to say that though the use of each of the individual synchro windings is discontinuous in itself, there is no discontinuity or interruption of the output of the device and while the output is taken from one winding, necessary switching operations are being made with the other winding.

From an understanding of the present invention, it may be. appreciated that the principle of operation by which the major divisions of potential are interpolated is based upon the magnetic flux relation of movable inductive elements. This is a most important feature of the present invention which in ideal operation affords the possibility of infinite resolution of such interpolation by the rotational displacement of one inductive element with respect to another. The present invention is therefore not inherently limited as to resolution as were many prior art devices, because the fine degree of change of the transfer of energy from one such element to another is primarily achieved by relative spatial disposition, rather than physical electrical contact such as is found in a wire-wound potentiometer, for instance.

Another most important feature of the present invention is that it is a transformer type of device, offering a relatively very high input impedance as compared to its output impedance. A transducer constructed in accord ance with the teaching of the present invention therefore offers very desirable impedance characteristics.

Since many changes could be made in the specific combinations of apparatus disclosed herein and many apparently. different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as being illustrative and not in a limiting sense.

I claim:

1. An electrical apparatus, which comprises a series of terminals, one of which is a reference terminal, means for maintaining a reference voltage on the reference terminal and voltages of predetermined values relative to the reference voltage on the respective other terminals along the series, and means for deriving voltages intermediate those on the terminals, said means including a first inductive element connected across two of said terminals along said series, second and third inductive elements positioned in magnetic flux relation with said first inductive element and in quadrature relation with each other, means for continuously varying the magnetic flux relation of said second and third inductive elements with respect to said first inductive element, at least one of said second and third elements producing a linear potential at all times, and means for alternately connecting said second and third inductive elements to successive terminals along the series.

2. An electrical apparatus, which comprises a series of terminals, one of which is a reference terminal, means for maintaining a reference voltage on the reference terminal and voltages of predetermined values relative to the reference voltage on the respective other terminals along the series, and means for deriving voltages intermediate those on the terminals, said means including a first inductive element connected across two of said terminals, second and third inductive elements positioned in magnetic flux relation with said first inductive element and in quadrature relation with each other, means for rotatably varying the magnetic flux relation of said second and third inductive elements with respect to said first inductive element, and means operably connected with said last-named means for connecting said second and third inductive elements to alternate terminals along said series, said means being syncl'ircnizcd to effect said connections dur- 0 7 ing the respective li near ranges of the potentials induced in said second and third inductive elements.

I 3.. An electrical apparatus, which comprises a series of terminals, one of which is a reference terminal, means for maintaining a reference voltage on the reference terand voltages of predetermined values relative to the reference voltage on the respective other terminals along the series, and means for deriving voltages intermediate those on the terminals, said means including a first inductive element connected across two. of said ter minals, second and third inductive elements positioned in magnetic flux relation with said first inductive element and in quadrature relation with each other, means for rotating said second and third inductive elements whereby to vary their magnetic flux linkage with said first inductive element, and switch means responsive to said rotation for alternately connecting said second and third inductive elements to sequential terminals along said series, said switch means being synchronized to effect said connections during the respective linear ranges of the potentials induced in said second and third inductive elements.

4. An electrical apparatus, which comprises a series of terminals, one of which is a reference terminal, means for maintaining a reference voltage on the reference terminal and voltages of predetermined values relative to the reference voltage on the respective other terminals along the series, and means for deriving voltages intermediate those on the terminals, said means including a first inductive element connected across two of said terminals, second and third inductive elements positioned in magnetic flux relation with said first inductive element and in quadrature relation with each other for inducing overlapping linear potentials in said second and third inductive elements, means for connecting said second and third inductive elements hand-over-handto successive terminals along said series, and means operably connected with said last-named means for varying the magnitude and phase of 8 the potentials induced in said second and third inductive elements so thatthe algebraic sum of the linear portion of the induced voltage and the tapped voltage in said second element is always equal to the algebraic suni'o'f the linear portion of the induced voltage and the tapped voltage'in'said third'element. f

5. 'An-electrieal apparatus which comprises a series'of terminals, one of. which is areiereiice, termina'hfrneans for maintaining a'reference voltage on the reference terminal and voltages of predetermined. values 'relativeftollthereference voltage on the respective other terminals along the series, and means forderiving voltages intermediate those on the terminals, said means including a first inductive ele ment connected across two of said terminals, second and third inductive elements serially connected and positioned in magnetic flux relation with said first inductive element and in quadrature relation with each other, means for connecting said second and third inductive elements handover-hand to successive terminals along said series, and means operably connected with said last-named means for varying the magnitude and phase of the potentials induced in said second and third inductive elements so that same total potential is developed across each said element from its common serial connection to a reference point throughout the common linear range of the induced potentials.

References Cited in the file of this patent UNITEDSTATES PATENTS 7 620,365 Rowe Feb. 28, 1899 1,066,747 Muller Jul-y 8, 1913 2,324,822 Champlin July 20-, 1 943 2,366,679 1 St. Palley Ian. 2, 1945 FOREIGN PATENTS 233,180 Germany Apr; 1, 191.1