JPS5923084B2 - variable resistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable resistor with high attenuation that causes less failure and noise even when used in high humidity or in a gas atmosphere that corrodes metals such as sulfide gas. .

Conventionally, in variable resistors, in order to lower the residual resistance and contact resistance at the terminals of the resistor, silver electrodes coated with silver-based conductive paint, etc., are provided in an exposed state, and silver electrodes are coated with conductive paint, etc., on the resistor. The slider that makes sliding contact is made of a metal with spring properties and has a low contact resistance and stable nickel plating or silver plating on the surface. The conductive part from which the central terminal is led out is made of a metal plate having spring properties that has been subjected to the same surface treatment as the slider.

There is no problem with using such a variable resistor in a normal environment, but if it is used in a corrosive gas atmosphere, especially a sulfide gas atmosphere, the surface of the metal material of the resistor contact part, including the electrode part, will be corroded and the insulating material will be damaged. This results in a high contact resistance and a large change in contact resistance at the sliding contact portion, resulting in sliding noise or poor contact when adjusting the variable resistor.

There was a particular problem with open variable resistors. In addition, short circuits, poor insulation, and
Failures due to silver microclision, including poor conductivity, were likely to occur.

As is well known, silver is a precious metal and has been widely used as a contact metal because it hardly corrodes in normal environments, has low contact resistance, and is relatively cheap for a precious metal.

In constant resistors, carbon (herein meant carbon black or graphite, each alone or a mixture of both).

) resin paint (hereinafter simply referred to as paint).

) is applied to the terminals at both ends of the resistance film, and by using a paint mainly composed of silver powder, especially on the low resistance side, the residual resistance can be lowered. By widening the adjustment range of the low resistance part, it was easily possible to achieve a residual resistance of 1Ω or less, including contact resistance.

For carbon paints that do not use silver powder, it is normally difficult to reduce the residual resistance to 10Ω or less due to the high specific resistance of carbon, and the total resistance is 1MΩ and the residual resistance is 20Ω.
The limit is a potentiometer with a maximum attenuation of about 96 DB, but if silver paint with low resistivity is used, a potentiometer with a residual resistance of 1 Ω and an attenuation of 120 DB can be easily manufactured and is now in practical use. Ta.

The slider that slides on the resistor of the variable resistor is usually made of a spring metal such as a phosphor bronze plate, and its surface is usually plated with silver to reduce contact resistance and stabilize it.

In addition, as mentioned above, the electrode parts and current collecting parts at both ends of the resistor that contact and conduct with the slider on the variable resistor board are usually made of silver plating of a copper-based metal plate, which will be explained later, or the same silver paint film. Silver-based sliding contacts made of silver, silver plating, silver paint, etc. have low contact resistance and stability under normal environmental conditions.

However, the first disadvantage of silver-based electrodes is that they easily sulfurize in harsh environmental conditions such as hot spring areas, and sulfide Ag
The surface insulating film, which is mainly made up of
There have been cases in which it has been difficult to break the slider with a contact pressure of about 100 g.

In this case, not only did the contact part become unstable due to poor contact, but when the slider was moved, the contact resistance changed significantly, causing sliding noise, etc. However, normally, the variable resistor shaft must be turned several times. As a result, it was possible to remove the sulfide insulating film.

However, in ordinary variable resistors, the thickness of the carbon paint resistance film is about 5 μm, which is relatively thin and does not have sufficient strength. Therefore, the pressure of the metal slider is increased to remove the insulating film. Although this is effective as a countermeasure against the sulfide gas, there is a contradiction in that the resistance coating is worn out and the rotational life is shortened, so there has been a demand for a countermeasure that includes this point.

As a countermeasure to this point, in variable resistors, carbon contacts are used at the contact part of the slider that slides on the resistor,
Carbon paint has sometimes been applied to the silver thread coating on the sliding electrode portion of the resistor and the contact terminal portion that makes sliding contact with the slider.

When a carbon paint film is coated on the silver thread electrode, the contact resistance and resistance value will be lower than when the surface is a silver paint electrode because carbon has a much higher specific resistance than silver. Although the contact resistance was about 10Ω for the carbon type, compared to 1Ω or less for the silver thread, contact failure due to sulfurization was considerably improved.

That is, when the contact surface is made of carbon paint, the oxide film on the surface is extremely thin and does not grow to a thickness of about 20λ or more, and the sulfide oxide is often gasified, so the normal contact resistance is However, it has the characteristic that large contact resistance defects are unlikely to occur.

In this way, the anti-sulfurization method of coating the silver electrode of a variable resistor with carbon paint was effective in improving the defects of the silver electrode, but on the other hand, it was accompanied by a deterioration in the performance of the variable resistor due to an increase in contact resistance. In many cases, further improvements including this point have been requested.

Carbon paint is coated on the resistor of the variable resistor and the silver electrode of the current collector to reduce malfunctions and noise even when used in high humidity or gas atmospheres that corrode metals such as sulfide gas. The improvements also serve as countermeasures against failures such as insulation defects and short circuits caused by silver migration.

Regarding this matter, the present applicant's U.S. Publication No. 57-5424
The invention is described in detail in the specification of the invention described in No. 4 (Utility Model Application No. 52-62134).

Related to the silver paint electrode configuration of a variable resistor and measures against sulfurization and silver migration, the following conventional techniques are known: (1) U.S. Pat. 3)% 1987-76550 (4) Utility Model Application No. 48-39441 (5) Utility Model Application No. 50-22137 (6) Utility Model Application No. 52-43040 (7) Bel l Te1ephon Labor
aiory 1955 Report The Be1l
System Technical Journal V
ol, 34. P 1115-1145 novem-
ber 1955A6,5ilver Migrato
n 1nElectrical In5ulatoin
There is a conventional technique described in et al.

Here, (7) details the migration of silver.

In addition, (1) shows the general structure and manufacturing method of the resistor of a variable resistor, (3), (4), and (6) show measures against sulfurization of silver electrodes, and (2) and (5) show how to prepare silver electrodes. shows migration countermeasures.

As shown in the above-mentioned prior art, a configuration in which a carbon paint resistance film is applied on top of the silver paint film on both end electrode portions of the resistor of a variable resistor is generally known.

The present invention aims to further improve conventional measures against harmful gases such as sulfide gas and against migration of silver electrodes.

In addition, the present invention reduces contact resistance in implementing the above-mentioned measures against harmful gases and silver migration to enable high attenuation (by making the resistance curve of low resistance low and smooth), thereby reducing the deterioration of variable resistor performance. The purpose of this invention is to improve the reliability of variable resistors using silver electrodes by eliminating failures due to sulfurization and silver migration of the resistor and sliding parts of the variable resistor.

The main features of the present invention are as follows.

That is, (1) a plurality of resistor sliding contacts 5i1, 5i,... A narrow silver exposed window A is left in contact with at least one of them, and the other silver film parts are covered with the resistor sliding contact 5-1. , 5, 2, etc. (in this specification, carbon blank or graphite alone or a mixture of both) is in contact with at least one of the following: Refers to a conductive film made by applying resin paint as the main material.

(2) When the resistor slider piece 5a comes into sliding contact with the conductive electrode portion at the end of the resistor 6, a current collector that comes into sliding contact with the silver film of the current collector section 7 is formed. A plurality of current collector sliding contacts 5 of the slider piece 50.
5 Leaving a narrow silver exposure window A in contact with at least one of the openings 1 and 2,
The other silver film portion is placed on the current collector sliding contact 51□.
, 5Il:12.......cover the contacting carbon layer.

Therefore, in (1) and (2) above, in areas where there is little damage from sulfur-based gas, etc., the slider has multiple sliding contacts, and some of the sliding contacts are not always present. The contact resistance and residual resistance of the variable resistor is approximately 2Ω because it is in direct sliding contact with the silver film part.
Since it is as small as below, there is no decrease in the attenuation of the variable resistor.

In addition, in areas where damage from sulfur-based gases is severe, some sliding contacts of the slider always make sliding contact with the silver film coated with a carbon layer, so the contact resistance and residual resistance of the variable resistor are approximately 2
It is safe at around 0Ω, and there is no failure where the resistance value of the exposed silver film increases significantly.

In addition, since the invention has a structure in which a narrow silver exposure window sufficiently bordered by a carbon layer is provided on the silver film, failures due to sulfide gas, etc. are reduced, insulation failure due to migration of external silver, short circuits, etc. There are almost no breakdowns.

Thus, the present invention prevents the performance of the variable resistor from deteriorating as a whole and improves its reliability.

Next, an embodiment of the present invention will be explained in comparison with a conventional example with reference to the drawings.

Fig. 1 is a sectional view of a conventional variable resistor example, Figs. 2 to 5 show a variable resistor implementing a part of the present invention, Fig. 2 is a sectional view thereof, and Fig. 3 is the same variable resistor. Fig. 4 is an enlarged sectional view of the central terminal portion of the resistor, Fig. 4 is an enlarged sectional view of the contact state of the slider, Fig. 5 is a plan view of the insulating substrate, and Fig. 6 is shown in Figs. 2 to 5. FIG. 3 is an electrical equivalent circuit diagram of a variable resistor.

FIG. 7 and FIG. 8 are diagrams showing an embodiment of a current collecting section in the present invention, and FIG. 9 is a diagram showing an embodiment of a terminal portion at both ends of a resistor.

FIG. 10 shows the current collector shown in FIG. 7 and the resistor shown in FIG. 9 of the present invention.
FIG. 3 is an enlarged cross-sectional explanatory diagram of a combination of low-resistance terminal portions.

Here, FIG. 1 is a sectional view of the most common conventional variable resistor, and 13 is an insulating substrate with a horseshoe-shaped resistor 1 on it.
6, and external terminals 14 are provided at both ends of the resistor 16, respectively.
．． 14 is fixed.

Reference numeral 11 denotes a rotating shaft, and a spring slider 15 that slides on a resistor 16 is fixed to the lower surface of the shaft's large diameter.

17 is a sliding body made of spring metal, the tip of which is the slider 1.
5, and the left side base is fixed to the substrate 13 together with another external terminal 14.

FIGS. 2 to 5 show examples of variable resistors implementing a part of the present invention.

In the figure, 3 is an insulating substrate made of a phenolic laminate or ceramic, 6 is a horseshoe-shaped variable resistor resistor formed on this substrate and coated with carbon paint, 6B
are the terminals formed at both ends of each resistor, and are usually coated with silver paint and baked to reduce residual resistance.

7 is a current collector surrounded by the resistor 6 at the center of the insulating substrate, and the ring-shaped central electrode IC is the terminal portion 7.
B through a conductive path 7A.

Also, like the resistor terminal parts 6B and 6B, the current collecting part 7 is made of silver pane or the like in order to reduce residual resistance and equivalent contact resistance.

The external terminals 4 connected to the terminal portions 6B, 6B, and 7B are made of a metal plate according to conventional technology, and are fixed to the insulating substrate 3 through retaining holes using eyelets integrated with the terminals 4 or separate studs. has been done.

Note that the resistor 6, the current collector 7, etc. may be formed separately and attached to the insulating substrate 3 in an overlapping manner.

Reference numeral 2 denotes a protective cover fixedly installed to cover an insulating substrate 3 to which a resistor 6 etc. are fixed, and a rotary shaft 1 rotatably pivoted through a central hole on the upper surface of the protective cover 2 is connected to the substrate 3 on the lower surface of its large diameter. A slider 5 having slider pieces 5A and 50 that come into sliding contact with the upper resistor 6 and the center electrode 7C of the current collector 7 is fixed.

Here, in the present invention, the slider 5 slidingly contacts the resistor 6.
The contact point with the resistor 6 of the plurality of sliding contacts 5i1, 5i2, etc. of the resistor slider piece 5a is centered around the center of the rotating shaft 1. It is placed on the radiation that passes through it.

In addition, the plurality of sliding contacts 5゜1j502 of the current collecting part sliding piece 50 that is in sliding contact with the center electrode of the ring-shaped current collecting part 7 are connected to the rotating shaft 1.
The variable resistor is provided on the same circumference as the center of the variable resistor in order to make it more compact.

Here, as shown in FIG. 2, for convenience of explanation, it is assumed that one of the sliding contacts 51 is located in the same direction as the resistor slider piece 5a with respect to the center of the rotating shaft, and the other The sliding contact 5°2 is assumed to be diagonal to this.

The variable resistors shown in FIGS. 2 to 5 above are more advantageous than most of the conventional variable resistors shown in FIG. The sliding body 17 made of spring metal shown in the figure is also unnecessary.

FIG. 6 shows an electrical equivalent circuit of the variable resistor.

The contact resistance between the slider piece 5a of the slider 5 that slides on the resistor 6 and the resistor 6 is Rcr, and the slider piece of the slider 5 that slides on the center electrode IC of the current collector T. 50 and the current collector electrode 70 is Rcc, the contact resistance Rc is the sum of the above and is expressed as Rc + Rcr + Rcc, which is connected in series between the resistor 6 of the variable resistor and the intermediate terminal 7B. It turns out.

Here, it is convenient for measurement and analysis to include the resistance R7 of the current collecting section including the conductive path 7A of the current collecting section 7 in series with the contact resistance Rc as the total equivalent contact resistance Rct.

In order to widen the attenuation and adjustment range of the variable resistor, low contact loss LCR is required between the slider and the resistor, and between the slider and the current collector.

It is desirable to lower Rco.

If a low-resistance carbon paint is coated 77 on the silver conductor fins of the resistor's terminals and current collectors, the silver surface exhibits a liquid contact resistance of about 0.5 to 2 Ω or less. , the contact resistance increases about 10 times, and the minimum of Rcr and Rcc is about 3 to 10 Ω each, and the total contact resistance R
c is at least about 5 to 20Ω, and the contact resistance Rc must be 2
It is very difficult in manufacturing to bring the resistance within 0Ω, and there were many products that failed to meet this specification.

In addition, in order to smoothly adjust the variable resistor and prevent a decrease in attenuation, R12 and R23 shown in FIG. 6 are connected to the slider 5, the first terminal 6A on the low resistance side, and the third terminal on the high resistance side, respectively. 6X and each as an adjustment resistance.

In the standard circuit used, where the input voltage is applied to the third terminal 6A' of the variable resistor, the first terminal 6A is grounded, and the attenuated output is obtained from the intermediate terminal 7B (second terminal), the input impedance on the output side is low. In this case, it is especially desirable to lower the contact resistance Rc, and generally the ratio of the contact resistance Rc to R12, which is the input impedance of the variable resistor, is Rc/R12.
It is desirable to keep the ratio of R
It is necessary to lower c.

On the other hand, even if the resistance on the high resistance side is somewhat high, there is no practical problem.

Here, as the silver paint for forming the conductive film of the terminal electrode part 6B of the resistor 6 and the current collecting part 7, a phenolic resin liquid or the like is used at a ratio of 20 to 60% per 100% weight of flaky silver powder with an average particle size of 5 μm or less. % and solvent etc. are added and mixed before use.

As a result, the contact resistance becomes approximately 0.5 to 3 Ω or less.

In addition, for the carbon layer, a phenolic resin liquid tube of 25 to 70 parts and a solvent, etc. are added and mixed to the total weight of about 40 parts of low-resistance carbon black such as acetylene black and about 60 parts of graphite powder with a particle size of 15 μ or less. and use it.

In this way, if the base is the above-mentioned silver paint film and a low-resistance carbon paint is coated on top of it, the contact resistance will be approximately 5.
~20Ω.

When the surface is a silver paint film, in addition to the increase in contact resistance due to the sulfide gas mentioned above, there is a problem of lower insulation between electrodes due to silver migration, and this is particularly noticeable when the silver film is in a positive electric field.

On the other hand, by forming a carbon layer on the surface, the lifespan due to sulfide gas increases by about 3 degrees.

Here, in addition to the above, if a carbon paint with a medium or high resistance of several Ω or more is pre-coated on the lower surface of the silver film in a wider area than the periphery of the silver film, the anti-migration effect will be increased several times in terms of its life.

Here, the effect of forming a carbon layer on the silver film as described above is usually not so great, but especially under high humidity, the effect of preventing failures due to silver migration in exposed silver parts is extremely large, and as a result, the above Migration is significantly improved by forming carbon layers above and below the silver film.

Therefore, in the present invention, as shown in FIGS. 4 and 5, the current collector 7, which is the conductor of the variable resistor, is coated with a carbon paint resistance film 70, which has a relatively high resistance value and strong adhesiveness, as the lowermost layer on the substrate 3. is formed in advance wider than the periphery of the middle layer, a silver paint film with excellent conductivity, and on top of the silver paint film 1a, a low-resistance carbon layer 7 is also provided, which is also wider than the periphery. be.

Furthermore, the terminal portion 6B, which is a conductor at the end of the resistor 6, has the same configuration, and has a variable resistor configuration that does not cause failures due to sulfide gas or silver migration. .

Here, the resistor slider piece 5a and the current collector slider piece 50 of the slider 5 of the variable resistor shown in FIGS. 2 to 4 are movable contacts whose surface films are constantly rubbed by sliding. Therefore, there are fewer electrical contact and noise problems at this contact surface.
Furthermore, when the object to be contacted is a carbon paint film on a resin substrate, the contact area is wide because the rigidity is low, and the airtightness of the contact surface is improved to some extent.

Therefore, as mentioned above, it is possible to use a spring metal plate made of phosphor bronze or the like with nickel or silver plating.
In areas with a semi-fixed variable resistor, such as hot springs, where sulfide gas is severe, sulfidation resistance can be improved by coating the above-mentioned electrical contact portions with the carbon layer.

Of course, even better results are obtained when plated with gold, rosemium, etc.

Generally, there are only a few areas where silver thread contacts cause damage to variable resistors due to sulfur-based gas, and in areas where the resistance is 95 or higher, this is often not a problem.

The use of levered contacts with silver thread on the exposed surface to reduce residual resistance and contact resistance, and to provide a low and smooth low resistance curve, is desirable and necessary for high attenuation as a high performance standard variable resistor. It is a condition.

Therefore, as will be described later, a silver layer is formed only on the low-resistance terminal side of the resistance section 6 of the variable resistor and a part of the intermediate layer and surface layer of the multi-electrode layer of the corresponding current collecting section 7 in order to lower the resistance and contact resistance. When adjusting the slider 5 and moving it to the medium-high resistance terminal side, the current collecting part that comes into contact with the slider is directly connected to the carbon because it is not a big problem to reduce the resistance and contact resistance. A layer may be formed.

When the variable resistor is adjusted in this way, the contact resistance Rc becomes the 6th
As shown in the figure, when the resistance value of the adjustment resistor R12 between the ground terminal 6A and the slider 5 is low, the contact resistance value Rc is also lowered to keep the contact resistance Rc below a certain proportion proportional to the adjustment resistance value R12. By doing so, it becomes possible to obtain a variable resistor with a wide variable attenuation range and substantially low noise.

Furthermore, the carbon paint coating and heat treatment on the lower and upper surfaces of the silver film are performed at the same time as the manufacturing method of the resistor, and by common use of its medium-high resistance and low resistance, excellent sulfurization and migration characteristics can be achieved without increasing the overall process. A variable resistor can be obtained.

Here, as described above, the plurality of sliding contacts of the slider piece 50 of the slider 5 that is welded to the current collecting part 7 are on the same circumference, and here, two sliding contacts located diagonally sliding contact 5゜11
5Il:12, one of which is in the same direction as the antibody sliding contact piece 5I.

Next, the center electrode γC of the ring-shaped current collector, which is one of the requirements of the present invention (for simplicity, it may be referred to as the ring-shaped current collector 7C or simply the current collector 7C).

) is shown in FIGS. 7 and 8.

Here, the right terminal is defined as the low resistance side, that is, the ground terminal side.

Here, part A shown by multiple points is the exposed part of the silver film fin, the shaded part AC is the part where the low resistance carbon layer 77 is provided on the silver film fin, and C is the part where only the carbon layer is provided. Part.

In the ring-shaped current collector IC shown in Fig. 7, the part corresponding to the low resistance start terminal at the bottom right exposes the silver film fin shown by many points A.
However, in other parts, a low-resistance carbon layer is coated on top of the silver film to prevent contact resistance from increasing due to sulfurization (A
(indicated by C).

Here, the low resistance side of the resistor 6 of the variable resistor is the terminal electrode part 6
A silver film containing B is advantageous because it has low residual resistance and contact resistance, but depending on the location, there is a risk of an increase in contact resistance due to sulfide gas or the like.

Therefore, when the resistor slider piece 5a of the slider 5 comes into sliding contact with the conductive electrode portion at the end of the resistor 6, it comes into sliding contact with the silver film of the ring-shaped current collector IC. The plurality of current collector sliding contacts 5I:l □ 5U...
A narrow silver exposure window A in which at least one of the...
, and the rest of the silver film is covered with a carbon layer.

The ring-shaped current collector IC shown in Fig. 8 is a high resistance part of a variable resistor.The left side is a carbon layer C1 The upper right middle resistance part is a silver film coated with a carbon layer AC1 The lower right low resistance part is exposed silver It is part A.

FIG. 9 and FIG. 10 show the resistor section 6 of the variable resistor of the present invention.
An example of the embodiment of the terminal portions at both ends is shown.

Here, in accordance with the current collecting part 7, for example, only the terminal part of the lowest resistance film layer is coated with silver as an intermediate layer, and then a plurality of resistor slider pieces 5 of the slider 5 are coated on top of the terminal part. Resistor sliding contact 5a,,5(,.

5. Leaving a narrow silver exposure window A in contact with only a part of... It's straining.

Here, when the slider 5 is adjusted to the terminal electrode part of the resistor 6 near the lower right terminal part 6B, a plurality of sliding contacts 5I, .
5. Sliding contact on the silver film AC coated with the carbon layer,
5-2 slides directly onto the exposed silver film A.

Here, since the silver exposed window A is sufficiently surrounded by a carbon layer, there is almost no failure due to silver migration.

Note that the resistor slider piece 5a of the slider 5, the resistor 6, and the current collector slider piece 5a. The relationship between the current collector 7 and the current collector 7 can be arbitrarily determined, and the principles of the present invention can be applied not only to rotary type variable resistors but also to sliding type variable resistors.

As described above, the present invention has a slider having a plurality of sliding contacts, and is suitable for use in areas where there is little damage from sulfur-based gas, etc.
Since the sliding contacts of the parts are necessarily in direct sliding contact with the silver film part, the contact resistance and residual resistance of the variable resistor are small, about 2Ω or less, and there is no reduction in the attenuation of the variable resistor.

In addition, in areas where damage from sulfur-based gas, etc. is severe, some sliding contacts of the slider always make sliding contact with the silver film coated with a carbon layer, so the contact resistance and residual resistance of the variable resistor are It is stable at about 20Ω, and the resistance value of the exposed silver film does not increase significantly.

In addition, since the silver exposed window A in the present invention has a narrow structure sufficiently bordered by a carbon layer, there is almost no failure such as poor insulation or short circuit due to migration of outer silver, which reduces failure due to sulfide gas etc.G) .

Thus, the present invention can provide a variable resistor that has excellent damping and adjustment characteristics as described above, and has excellent performance and high reliability over a long life against migration and pollutant gases such as sulfide gas. .

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a conventional variable resistor example, Figs. 2 to 5 show a variable resistor implementing a part of the present invention, Fig. 2 is a sectional view thereof, and Fig. 3 is the same variable resistor. FIG. 4 is an enlarged sectional view of the center terminal portion of the resistor, FIG. 4 is an enlarged sectional view of the contact state of the slider, FIG. 5 is a plan view of the insulating substrate, and FIG. 6 is the same as that of FIGS.
6 is an electrical equivalent circuit of the variable resistor shown in FIG. 5. FIG. 7 and FIG. 8 are diagrams showing an embodiment of a current collecting section in the present invention, and FIG. 9 is a diagram showing an embodiment of a terminal portion at both ends of a resistor. FIG. 10 shows the current collector shown in FIG. 7 and the resistor shown in FIG. 9 of the present invention.
FIG. 3 is an enlarged cross-sectional explanatory diagram of a combination of low-resistance terminal portions. 1.11: Rotating shaft, 2,12: Protective cover, 3゜13:
Insulating substrate, 4, 14: terminal, 5, 15: slider, 6, 1
6: Resistor, 7: Current collector, 17: Sliding body, A: Exposed silver film, C: Carbon layer, 〇2 Silver film coated with a carbon layer on the surface.

Claims (1)

[Scope of Claims] 1. A slider 5 that is fixed to a rotating shaft and that slides on a horseshoe-shaped resistor 6 and a current collector 7 provided concentrically on the surface of an insulating base 3 comes into sliding contact with the resistor 6. A plurality of sliding contacts 5i1, 5i2 of the resistor slider piece 5i...
...The contact point with each resistor 6 is provided on a radial line passing through the center of the rotation axis, and the plurality of resistor slides are in sliding contact with the silver film of the conductive electrode portion at the end of the resistor 6. Moving contact 5i 1.5i. A narrow silver exposed window A is left in contact with at least one of the parts, and the other silver film parts are placed in contact with the resistor by sliding contact. Child 5i,, 5i,...
A variable resistor characterized in that at least one of the resistors is coated with a contacting carbon layer. 2. A base coating is applied in advance with a resistive film mainly made of carbon to a wider area than the periphery of the silver film of the conductive electrode portion at the end of the resistor 6, and a conductive film mainly made of silver is formed thereon,
2. The variable resistor according to claim 1, further comprising a carbon layer covering a wider area than the periphery of the silver film. 3. Sliding of the current collector part 7 of the slider 5, which is fixed to the rotating shaft and is in sliding contact with the current collector part 7 and the horseshoe-shaped resistor 6 provided concentrically on the surface of the insulating base 3. A plurality of sliding contacts 5゜1y502 of the child piece 50...
...The contact points with each current collector 7 are provided at a distance on a concentric circle passing through the center of the rotating shaft, and the resistor slider piece 5
When A comes into sliding contact with the conductive electrode part at the end of the resistor 6, the plurality of current collecting part sliding contacts 5°1°502... which come into sliding contact with the silver film of the current collecting part 7・・・・・・・・・・・・
・Silver exposure window A with a narrow width that at least one of them contacts
, and the other silver film part has a carbon layer on which at least one of the sliding contacts of the current collecting part 5°11502 is in contact. A variable resistor characterized by being coated. 4. A resistive film mainly made of carbon is pre-coated with a base coating wider than the peripheral area of the silver film of the current collecting part 7, and a conductive film mainly made of silver is formed on top of the base coating. 4. The variable resistor according to claim 3, wherein the carbon layer covers a wider area than the outside.