US3471782A - Multiple revolution type logarithmic rheostat recording and measuring device - Google Patents

Description

Oc 7. 1969 TAKAO MATSUMOTO 3 7 8 MULTIPLE REVOLUTION TYPE LOGARITHMIC RHEOSTAT RECORDING AND MEASURING DEVICE Filed Oct. 14, 1965 FIG.I

INVENTOR.

'T'H KHO NHTSILMOTO United States Patent 3,471,782 MULTIPLE REVOLUTION TYPE LOGARITHMIC RHEOSTAT RECORDING AND MEASURING DEVICE Takao Matsumoto, 60 Kuritaya, Kanagawa-ku, Kanagawa-ken, Yokohama-shi, Japan Filed Oct. 14, 1965, Ser. No. 496,042 Claims priority, application Japan, July 29, 1965, 40/ 45,595 Int. Cl. G01r 13/04 US. Cl. 324-413 2 Claims ABSTRACT OF THE DISCLOSURE A multiple revolution type multiple revolution type multiple range potential logarithmic rheostat has a wire wound in accordance with the characteristics of a logarithmic curve, a revolving contact brush, a resistor for each range, and range switching means acting to switch the respective resistors upon completion of each revolution so as to raise the minimum potential point of the reheostat to the maximum potential obtained by the immediately preceding revolution of the brush.

This invention relates to an improved multiple revolution type logarithmic rheostat.

It is often desirable to utilize a logarithmic rheostat covering a wide range or a number of digits. Usually such a logarithmic rheostat comprises an insulator plate with one longitudinal edge cut to follow a logarithmic charatceristic curve and a resistance wire wound around said insulator plate. The insulator plate is formed into an annular ring and a rotary brush is associated therewith to successively short circuit the winding turns of the resistance wire. Thus the width of the insulator plate increases exponentially from the position of minimum resistance to the position of maximum resistance so that in the rheostat covering a wide range or a number of digits the width of insulator plate at or near the maximum resistance becomes excessive thus causing winding turns at these portions to be displaced from vertical. For this reason it has been proposed to divide a predetermined logarithmic characteristic curve into a plurality of sections, each corresponding to one digit or a fraction of one range, and to use a corresponding number of logarithmic rheostats, one for each digit. By successively employing different one of logarithmic rheostats it is possible to provide a continuous characteristic curve identical to that before division. However, with the prior logarithmic rheostat it is impossible to make one complete revolution so that angle of revolution of the brush thereof was limited to about 355.

Further, since successive logarithmic rheostats for different digits or fractional ranges must be wound with resistance wires of different resistance values the yare difficult to manufacture and yet it is difiicult to provide the required accuracy. Moreover installation of many rheostats requires a large space and weight. By these reasons the prior logarithmic rheostat of the type referred to above has been limited to only 2 or 3 digits.

It is, therefore, an object of this invention to provide a novel logarithmic rheostat capable of multiple revolution.

Further object of this invention is to provide a novel logarithmic recording device which can provide a logarithmic record covering a number of digits or a wide range.

According to this invention a multiple revolution type logarithmic rheostat is provided resistors, and a range switching device is combined with the logarithmic rheostat such that when the brush is transferred from a position of minimum or maximum resistance to a position of maximum or minimum resistance, respectively, the input 3,471,782 Patented Oct. 7, 1969 to the rheostat is varied by one fractional range, thus permitting continuous rotation of the brush.

According to another aspect of this inventinon the logarithmic rheostat is utilized as one arm of a resistance bridge circuit and the difference between the outputs of the range switching device and the logarithmic rheostat is employed to acutate a servomotor which rotates the brush. With this arrangement as the input varies the brush is rotated to follow said variation to make said difference zero.

Further objects and advantages of the invention together with its organization and operation can be more fully understood from the following detailed explanation taken in conjunction with the accompanying drawings in which:

FIG. 1 shows an exploded view of the resistance winding of a single range type logarithmic rheostat;

FIG. 2 is a graph to explain the principle of this invention;

FIG. 3 is a side elevation, partly in section, of one embodiment of this invention; and

FIG. 4 is a connection diagram of a logarithmic recording device utilizing the multiple revolution type logarithmic rheostat shown in FIG. 3.

As schematically shown in FIG. 1, the conventional logarithmic rheostat of one range or digit comprises a number of winding turns of fine resistance wire 10 wound around a thin annular insulator plate 11 with said turns normal to the direction of adjustment for the substantial portion of the insulator plate but slightly inclined at the end of maximum width, and a brush (not shown) rotated around the rheostat to vary the resistance value thereof. The one longitudinal edge of the insulator plate 11 corresponds to logarmithmic inclination, so that if the width of the insulator plate 11 at 0 is equal to 1, then the width at 3601f would be 10 which means that the ratio between the minimum width and the maximum width is very large. As the width of the insulator plate is limited by its maximum width, the minimum width should be very narrow which is undesirable from the standpoint of accuracy as well as assembly. Moreover, as the wider portion has a tendency of large flexure, winding turns become deformed or oblique to the vertical as viewed in FIG. 1 which also affects the accuracy of the rheostat.

When, as shown in FIG. 2, the logarithmic characteristic of one range is divided into four equal sections, a-b, b-c, cd and d-e then the minimum and maximum widths of each section would be 1 and 1.778, respectively. Also the potential value of each section would increase from 1 unit at the minimum width to 1.778 units at the maximum width. According to the instant invention only one section, for example, the section a-b is adapted to form a rotary logarithmic rheostat. In the section a-b, if it is designed such that the rotational angle at a is 0 degree and that at b is 360 degrees then points a and b coincide or are positioned very closely.

FIG. 3 shows a side view of the rheostat corresponding to the above mentioned section a-b. The rheostat comprises a number of turns of a resistance wire 10 wound upon a ring formed insulator plate 11 which is suitably supported in a casing 13. A brush 15 carried by a shaft journalled in ball bearings 14 cooperates with the resistance wire 10. The brush and the opposite ends of the resistance wire are connected to three terminals 16. As pointed above since the points a and b are closely positioned the brush 15 functions to engage simultaneously both points a and b, thus short circuiting these points and hence providing the function of continuous multiple revolution. According to this invention, the above-mentioned rheostat is combined with a range switching device for switching several resistors consisting of a resistor designed to raise the minimum potential point of said rheostat to the maximum potential of said rheostat obtained at the termination of the first complete revolution of said brush, a resistor designed to raise the minimum potential point of said rheostat to the maximum potential of said rheostat obtained at the termination of the second complete revoluction of said brush, and successive resistors corresponding to the sections and designed similiarly. According to the combination of the above-mentioned rheostat with several resistors and range switching device, a multiple revolution type rheostat having a logarithmic characteristic of a relatively wide range can be obtained.

FIG. 4 illustrates an application of the novel logarithmic rheostat to a potentiometer type balancing circuit in a recording apparatus wherein the logarithmic rheostat LR and an auxiliary resistor R connected in series therewith comprise one arm of a resistance bridge circuit, the remaining arms thereof being comprised by resistor R R and R The bridge circuit is energized by a source of constant direct current via serially connected fixed resistor R and a variable resistor R The ratio of resistances of resisotrs R and LR is selected to be 1 to 0.778, where the logarithmic curve is divided into four equal sections, and the relative values of resistances of LR, R R R and R are selected to satisfy an equation As a result the potential of the brush 15 of the logarithmic rheostat varies from the minimum one unit to the maximum 1.778 units. When the brush transfers to the point b of the maximum resistance value the output from the range switching device is increased by 1.778 times by an external range switching device 20, whereby transfer from the maximum to minimum or vice versa is effected very smoothly. As can be noted from FIG. 4 even when the logarithmic rheostat LR is short circuited by its brush 15 excessive current and the damage caused thereby are positively prevented by the presence of resistors R R R and R The range switching devices 20 comprises a plurality of resistors having values of l kiloohm and 1.778 kiloohms or their multiples where the logarithmic characteristic is divided into two sections for example, and the selector switch 21 associated therewith is operated manually or automatically in response to the magnitude of an input signal applied to an input terminal 22. The output of the bridge circuit derived out through the brush is differentially combined with the input signal and the difference between them is applied to AC amplifier 24 via a chopper 23. The output of the amplifier is supplied to a servomotor 25 which drives the brush 15 of the potentiometer LR as well as a recording pen 26 which is carried by a cord 27 passing around a pulley 28 connected to the servomotor. Although not shown in the drawing suitable reduction gearing may be provided between the servomotor and the brush and pulley.

As is well known in the art the potentiometer type balancing circuit or bridge operates to make the output of the amplifier 24 zero. Assuming now that the input signal is gradually decreasing from its maximum value. In this case the resistor having the maximum value is selected by the selector switch 21, and the servomotor 25 continuously rotate the brush 15 to maintain the difference between the input signal and output from the bridge circuit zero. When the brush is brought to the point a of minimum resistance value the logarithmic rheostat will be short circuited but at this time while the potential of the brush becomes larger than the minimum value but smaller than the maximum value and is still lagging than the instantaneous value of the input signal so that there is 'no fear of rapid reversal of the servomotor. When the short circuit is removed and the brush is transferred to the point of maximum resistance the selector switch 21 is transferred to the resistor of lower range and the servomotor continuous to rotate to drive the brush from the point b of the maximum resistance towards the point a of the minimum resistance.

In this way, as the input voltage gradually decreases the selector switch 21 is operated several times to switch ranges whereby the brush 15 is rotated several revolutions and a record corresponding to the dotted exponential curve of FIG. 2 will be drawn by the recording pen 26. Conversely, when the input signal varies from minimum to maximum, similar but reverse operation is effected.

While there is no theoretical limit in the number of division of the logarithmic characteristic curve, actually 2 to 10 are desirable and 2 to 4 are most suitable.

An example of numerical data is illustrated hereunder. In this example the logarithmic characteristic curve was divided into four equal sections and for the sake of convenience the width of the insulator plate at the angle of rotation of zero degree was taken as the reference unit and the resistance values were expressed by taking the resistance value of the auxiliary resistor as the reference unit.

Angles 0t Width of the The logarithmic rheostat of this invention capable of multiple revolution is especially useful for logarithmic recording device covering a wide range or involving many digits. Such a recording device can provide a continuous record of multiple ranges or digits and the record obtained has the same accuracy and value for all ranges or digits and is more easy to observe than linear record.

What I claim is:

1. A multira-nge logarithmic balancing bridge type signal recording device, comprising, in combination, an annular insulating plate the width of which corresponds to a logarithmic curve; a resistance wire wound for less than 360 degrees upon said plate along its whole width, said resistance wire having input and output terminals at the same radii and closely adjacent each other, said resistance wire constituting a logarithmic rheostat the resistance characteristics curve of which corresponds to one section obtained by dividing a predetermined logarithmic characteristics curve into a plurality of equal sections; a brush supported by a rotary shaft to be rotated along said resistance wire in contact with said wire and having a width capable of short-circulating both said terminals when it is brought to the minimum or maximum resistance position of said resistance wire; a plurality of resistors provided between said rheostat and an input signal terminal and comprising a first resistor designed to raise the minimum potential point of said rheostat to the maximum potential of said rheostat obtained at the termination of the first complete revolution of said brush, a second resistor designed to raise the minimum potential point of said rheostat to the maximum potential of said rheostat obtained at the termination of the second complete revolution of said brush, and further resistors corresponding to said sections and designed similarly; a range switching device for switching said resistors per revolution of said brush so as to raise the minimum potential point of said rheostat to the maximum potential obtained by the immediately preceding revolution of the brush, thereby to cause during continuous revolutions of the rheostat continuous resistance variations in correspondence to a logarithmic characteristics curve.

2. A recording device according to claim 1, in which said resistance wire is provided with an auxiliary resistor and the resultant resistance of said resistance wire and auxiliary resistor is made to correspond to a predetermined logarithmic characteristics curve.

References Cited UNITED STATES PATENTS 2,870,408 1/1959 Draganjac 324115 3,405,359 10/196-8 Gilrnan et a]. 324115 XR 2,941,147 6/1960 McKinlay 324-132 XR 6 3,029,336 4/1962 Ferra'r 324100 XR 3,281,685 10/1966 Talbot 324-100 XR 3,317,877 5/1967 Matsumoto 338-89 RUDOLPH V. ROLINEC, Primary Examiner ERNEST F. KARLSEN, Assistant Examiner US. Cl. X.R. 32379; 324-115

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