How to change resistance resistor. Resistors. Serial compound resistors

No matter how cool, but if you do not know the designation of items in the schemes and do not know what a radiochem is, then you are not an email! But this business is fixable, do not worry ;-). I start the cycle of articles about the types and designations in the schemes of radio elements. Let's start with the most common radio element - resistor .

The RadioElement "Resistor" has an important property - electrical stream resistance. Resistors are permanent and variables. In life, constant resistors may look something like this:

On the left we see a resistor, which dissipates very greater power, so it is so big. On the right we see a small tiny SMD resistor, which dispels very small power, but at the same time perfectly performs its function. About how to determine the resistance of the resistor, you can read in the article marking of resistors. But it looks like on electrical schemes:

Our domestic image of the resistor is shown by a rectangle (left), and the overseas version (right), or as they say - Bourgeois, is used in foreign radioshem.

But this is how the labeling of power on them looks:

Variable resistors look something like this:

What is a resistor

Resistors produce mainly in the form of porcelain tubes or ceramics with metal outputs at both ends. On the surface of the tubes can be applied, for example, a layer of carbon (in carbon resistors) or even a very thin layer of precious metal (in metallic resistors).

Also, the resistor can be made of high resistivity wire (wire resistors).

The main parameter of the resistor is its constant resistance. In the region of large frequencies, the resistor, in addition to resistance, appear characteristics as the container and. These resistor parameters can be represented as the following model:

• R \u003d resistance resistive material
• CL \u003d Own capacity of the resistor,
• LR \u003d resistor inductance,
• Ls \u003d inductance of its conclusions.

Here you can see that the resistor has even components of induction and containers in addition to its own resistance. When applied in chains alternating current These features play a role reactive resistanceWhich in combination with its own resistance creates additional resistance in the scheme, which in some cases must be considered.

The main parameters of the resistors are:

• The nominal resistance is given in view of the large permissible deviations contained in the range of 0.1 ... 20%.
• Rated power - the maximum allowable dispersion power.

Rated voltage is equal to the highest voltage, which does not cause changes in the properties of the resistor, and, in particular, damage. Nominal voltage values \u200b\u200bfor most resistors ranges from several tens to several hundred volts.

Based on the size of the resistive layer or cross section of the wire, you can determine the resistance value. In electronic circuits, mostly used multilayer resistors. In the case of working with large values \u200b\u200bof current and power, a wire resistor is used.

Multilayer metallized resistors are thermally stable, they are reliable in operation and have a low noise level (important in professional electronics).

The unit of measuring the resistance is OM (symbol of omega), and mainly in the schemes is indicated by the letter - R.

From the Ohm law: resistance of the resistor in 1 ohms is such a resistance when at a voltage at its conclusions in 1 volt through it flows 1 amper.

Nominal range and color marking of resistors

Most resistors produced in the world have resistance from the so-called nominal series (E). Each of the species of the nominal row is divided into decades, and in each ten there are 6 (E6 series), 12 (E12 series), (row E24) 24 values.

These values \u200b\u200bin the decade are selected so that, taking into account the tolerance, resistance of two adjacent values \u200b\u200boverlap each other, and due to this you can pick up any intermediate resistance.

Standard resistance to resistance to resistors is 5, 10 or 20%. Neighboring values \u200b\u200bintersect in the following cases:

• for a number of E6 with a 20% admission,
• for E12 series with 10% admission,
• for a series of E24 with a 5% admission.

The magnitude of the resistance and the deviation are noted on the resistor in the form of several color rings (or points). The first colored rings (2 or 3) determine the value in Ohm, and the last ring is tolerance (deviation). A small resistors, as a rule, the amount of resistance, tolerance and temperature coefficient (TKS) is sometimes applied with 4 ... 6 color strips. For more information about the color marking of resistors, read.

In the size and power of resistors

As is known, the voltage submitted to the resistor causes the flow in it, and therefore, on such a resistor, a certain part of the power is distinguished. For good functioning, this heat resistor should dispel into the surrounding space. This ability directly depends on its size.

In electrical engineering, electronics, physics is encountered such a concept as a resistor. This is a fairly common element of electronic circuits. Those who have not come across the principles of radio engineering, to seriously understand the large number of components of any instrument. To begin, it should be understood to understand the principle of operation of such a simple and widespread element as a resistor. Without it, there is almost no electrical processing.

What is a resistor

This name originates from the English. Resist, which is translated as "resist". Therefore, the resistor is also called resistance.

Relying on such designations, as well as on the calculation of the power of the chain, select the desired equipment.

Fastening resistors

The resistor is an electrical element that most often has two exits to connect to the diagram. There are also varieties of equipment with three conclusions. They can be found among variables and trimming resistors.

Special varieties that have taps are also used. Usually there are several of them.

In modern electronics, resistors intended for surface editing are increasingly used. They look like tiny details of the rectangular shape and do not have the usual wire conclusions. Instead, two metal strips located along the edges of the resistor are designed to connect such a part.

Surface installation is made by soldering the resistance element to printed conductors located on the board.

The popularity of such parts is explained by their minimal dimensions, which meets the modern requirements of electrical equipment. Their marking has a system other than wire resistors.

The role of resistors in the scheme

The resistor is an element that can perform various functions in the electric hamme. The most common is a current-limiting, tightening and separation role.

The current-limiting resistor is a device designed to provide the required current force at which the component of the equipment will function uninterrupted.

A comprehensive (stretching) resistor is used at the input of logical components of the scheme, which is important to know only the presence or absence of voltage (logical unit or zero). The resistor in such a scheme is needed to ensure normal operation of the system so that it does not remain in suspender. An undesirable current coming from the outside to the entrance will be with the help of a tightening resistor to go into the ground. This ensures the definition of the "logical zero" position input.

Voltage divider is required to take only a certain part of the current required for proper work Electrocomponent.

Marking

There is a certain principle of allocating the basic qualities of resistors. It is widely used worldwide.

The resistor is (the photo is presented below) a small detail having a color or iconic labeling.

The main characteristic of the details of the electric hammers is its resistance, so this indicator is determined on the housing. Letter notation characterize the measurement system: R - ohms, k - kiloma, m - megaoms.

IN lately Many manufacturers go to another type of marking - color. It is easier to apply under large production volumes.

The most accurate resistors have up to 6 colors on the case. The two first stripes correspond to the voltage raid.

Having considered that it is an element of resistance in the instrument scheme of various techniques, it should be concluded that the resistor is the equipment that provides the entire system necessary for the operation of the current force.

The electrical circuit of almost any modern instrument has resistors. They can be different species. Their functions are also diverse. What is a resistor, you should know each even a novice radio amateur. As well as anyone who decided to repair any device or household appliances to repair.

From the English resistor translates as resistance. This is a passive chain element, which, due to its properties, provides the desired voltage and adjusts the current value.

To understand what a resistor is, you should have at least the most general ideas about the electrician. Resistance is measured in ohms. It is associated with the dependence with the voltage and power of the current. The conductor has a resistance of 1 ohm, if the ends of it is applied to the voltage of 1 V, and the current flows by force in 1 A. Therefore, the resistor is the control of other parameters of the electrical system.

Therefore, such an element controls and limits the current. In the chain, the resistor can share the voltage. The characteristics of the resistor are the value of the nominal resistance and power, which shows how much energy it is able to dispel without overheating.

Types of resistors

All resistors are divided into three large groups. They can be variable, permanent and trimmed.

The resistance of the constant type resistor does not significantly change depending on the conditions from the outside. Small deviations from the nominal value may be caused by a change in temperature, internal noises, as well as electricity leaks.

Variable resistors can arbitrarily change resistance. To do this, the device usually has a rotating knob or slider (for example, in the radio, the sound power regulator). It allows you to smoothly change the parameters of the chain.

The trimming resistor has a screw with a slot for adjusting the current in the chain. His characteristics change quite rarely.

Semiconductor resistors

There are resistors that change their properties under the influence ambient. These include thermistors, varistors and photoresistors. The resistance of the resistor of this type is changing only under the influence of certain factors.

The thermistor reduces or increases its resistance with increasing temperature. This property is used in some types of devices, for example, in self-regulating heating cables for water pipes, pipes.

Varistors reduce their current conductivity with an increase in voltage. They are used to protect, stabilize and adjust electrical values.

Photoresistors react to sunlight or electromagnetic radiation. Most often use similar devices with a positive photo effect. If radiation gets into it, the resistor reduces its strength of resistance. Such elements are often used in sensors, relays, counters.

The chain resistor is a passive element. It does not accumulate, but absorbs the energy of such two components as the current and voltage.

The resistor does not change the parameters depending on the frequency of the current flowing through it. It works equally both in the constant and alternating current of low and high frequency. The only exception is the wire varieties that have inductance.

Resistor - linear element. Depending on the type of connection in the circuit, parallel and consistent resistors are distinguished. Their total resistance with a sequential connection is equal to their sum.

A somewhat more complex is calculated by the second type of connection. Parallel resistors are summarized from the values \u200b\u200bof inversely proportional resistance. These values \u200b\u200bare also called conductivity.

All elements of the resistance of the electrical system manufactured by GOST are combined in the series. They constitute a nominal row, which increases by multiplying the initial indicator by 1, 10, 100, 1 com, 10 com, etc. If there are values \u200b\u200bof 3, 5, then the continuation of the row is considered in dozens - 35, in hundreds - 350 .

Ratings of resistors within a number by number of serials correspond to the type of accuracy selected by the manufacturer. The most popular E24 series includes 24 basic resistance resistance indicators. Its accuracy is ± 5%.

The designation of resistor ratings in the scheme has a certain form. So, if the resistance is designed in Omah, then the number can stand the letter E or nothing at all. If the value is indicated in the kiloma, then the letter K. The number of resistance in the IOM designation has the letter M.

Marking

Small power resistors have small dimensions.

And in modern technique, it is most often used that such devices. The designation of the resistors can be applied to the housing, only read it will be extremely difficult.

In order to somehow cut the inscription, it began to apply alphabetic designations that post the number for decimal values \u200b\u200band ahead of the number for hundreds.

American resistors are labeled with three digits. The first two of them indicate the ratings of the resistors, and the third is the number of zeros of dozens added to the value.

However, in the process of production, there are cases when the labeling turns out to be applied to the side, rotated to the board. Therefore, other types of designations are used.

Color marking

For the properties inherent in the resistor, it was possible to determine from all sides, began to apply the color marking.

Resistors with a permissible change in parameters in 20% are three lines. If it is an average accuracy device (5-10% error), use only 4 markers. The most accurate copies have the designation of resistors in the form of 5-6 bands.

The first two of them correspond to the nominal details. If the bands are four, then the third of them speaks about the decimal multiplier of the first two strips. At the same time, the fourth marker talks about the accuracy of the resistor.

If the bands are only five, then the third of them is the third sign of the resistance, the fourth is the degree of indicator, and the fifth is accuracy. The sixth strip indicates the temperature coefficient of resistance (TKS).

They consider stripes from the other side where they are closer to the edge. If these are four-band varieties, the latter always go gold or silver stripes.

Varieties on manufacturing technology

In order to be deeper into the question of what a resistor is, its views should be considered by the method of production.

Wire resistors most often have a high level of inductance. They are made by winding on the wire frame.

Film metal resistors are the most common type. A thin film is applied to the plastic core. At the end of the design, the caps are put, to which wire conclusions are connected. The current in the resistor of this type is greater than the resistance in the slot in the ceramic screw groove core.

Metal organophold copies in production are performed from a thin tape. Coal resistors use graphite resistance. Integrated species are made on the basis of a scenario conductor. Such resistors may have a greater nonlinearity of volt-ampere indicators. They are used in integrated chips. In this case, the use of resistors of another species is not technological or even unreal.

Low TKS resistors and noise levels

Low TCS resistors include carbon and burgrolery varieties.

Carbon resistors operate on the basis of a pyrolytic carbon film. They have increased stability of parameters. Their small TCS is negative. Resistors resistant to impulse loads.

Borounglerous varieties have a certain amount of boron in the conductor layer. This allows you to maximize TKS.

Low noise levels have metal-plating and metal-oxygen resistors. They have good frequency characteristic and resistance to temperature fluctuations. TKS can be both positive and negative.

After reading the concept that a resistor is, you can choose correctly and apply this element of the electrical system. Being one of the most commonly used, they are found in almost all areas of human activity. Their functions are very diverse. Existing varieties provide a wide selection of similar products. At the same time, having some idea of \u200b\u200btheir design, it will be possible to repair almost any device or home appliances.

Friends, hello! In the yard of winter and the calendar tells me that weekdays flow into a pleasant holiday weekend, so it's time for a new article. For those who do not know me, I will say that my name is Vladimir Vasilyev and I lead this very radio amateur blog, so welcome!

We dealt with the concept of electric current and voltage. In it, literally on my fingers I tried to explain what is electricity. Some "plumbing analogies" applied to help.

Moreover, I was outlined for myself to write a number of training articles for completely novice radio amateurs - electronics, so it will be more - do not miss.

Today's article will be no exception, today I will try as you can highlight the topic of resistors. Resistors although they are probably the most simple radio components, but beginners can cause a lot of issues. And the lack of answers to them can lead to a complete mess in the head and lead to a lack of motivation and the desire to develop.

What is resistance?

Resistors have resistance, and what is resistance? We will try to figure it out.

To answer this question, let's go back again to our plumbing analogy. Under the influence of gravity or under the action of pump pressure, water rushes from the point of larger pressure to a point with less pressure. So the electric current under the action of voltage flows from the point of greater potential to a point with less potential.

What can prevent water movement through pipes? Water movement can prevent the condition of the pipes by which it runs. Pipes can be wide and clean, and can be ridden and generally pose a sad sight. In which case the water flow will be greater? Naturally, water will flow faster if its movement will not have any resistance.

In the case of a pure pipeline, it will be, water will be the smallest resistance and its speed will be almost unchanged. In the ridden pipe, the resistance to the aqueous stream will be significant, and, accordingly, the speed of water will not be very.

Well, now we are transferred from our plumbing model to the real world of electricity. Now it becomes clear that the speed of water in our realities is the current strength measured in amperes. Resistance that rendered pipes into water, in the real current-carrying system there will be the resistance of the wires measured in Oma.

Like pipes, wires can resist the current. Resistance directly depends on the material from which the wires are made. Therefore, it is not at all by chance that the wires are often made of copper, as copper has a small resistance.

Other metals can have a very large electrical current resistance. So for example, the resistivity (OM * mm²) of the nichrome is 1.1. * Mm ². The amount of resistance is easy to evaluate comparing with copper in which the resistivity is 0.0175Om * mm ². Not bad yes?

When passing the current through the material with high resistance, we can make sure that the current in the chain will be less, it is enough to conduct uncomplicated measurements.

What does a resistor look like?

In nature there are absolutely different resistors. There are resistors with constant resistance, there are resistors with variable resistance. And each type of resistors finds its application. So let's stop and try to pay attention to some of them.

The name itself suggests that they have permanent fixed resistance. Each such resistor is manufactured with a certain resistance determined by the dispel power.

Dissected power - This is another characteristic of resistors, as well as resistance. The power dissipation indicates what power can disseminate the heat resistor (you probably noticed that the resistor during operation can be significantly heated).

Naturally, the factory cannot produce absolutely any resistors. Therefore, constant resistors have a certain accuracy indicated in percent. This value shows in what limits will walk the resulting resistance. And naturally, the more precisely the resistor, the more expensive it will be. So why overpay?

Also, the magnitude of the resistance can not be any. Usually the resistance of constant resistors corresponds to a specific nominal range of resistance. These resistances are usually selected from the rows of type E3, E6, E12, E24

As you can see resistors from a series of E24 have a richer set of resistance. But this is not the limit since there are nominal rows E48, E96, E192.

On electrical circuits, permanent resistors are designated by a formak rectangle with outputs. In the conditional graphic designation, the scattering power can be inscribed.

	So depicts an ordinary permanent resistor. Dispersion power may not be indicated
	Resistors with dispersible power 0.125 W
	This is an image of a resistor with a dissemination power of 0.25 W.
	Resistor with dispersible capacity of 1 W
	Resistor with a dispersible power of 2 W.

Have you ever paid attention to various "twist" in the old analog technology. For example, did you think about what you twist, adding the volume in the old one, maybe even a lamp TV?

Many regulators and various "twisters" are variable resistors. As well as permanent resistors, variables also have different scattering power. However, their resistance may vary widely.

Variable resistors serve to regulate voltage or current in the ready-made product. As I mentioned this resistor, resistance in the sound formation scheme can be adjusted. Then the sound volume will change in proportion to the angle of rotation of the resistor handle. So the housing itself is inside the device, and the same twist remains on the surface.

Moreover, there are also dual, ordered, quadruple and so on variable resistors. Usually they are used when a parallel change in resistance immediately in several sections of the circuit.

A variable resistor is very good, but what if we need a change or adjustment of resistance only at the product assembly stage?

A variable resistor is not very suitable for us. A variable resistor has a lesser accuracy than permanent. This is the possibility of adjusting, as a result of which resistance can walk in some limits.

Of course, the so-called selection of the product can be used at the product settling stage. This is an ordinary permanent resistor, only when installing it is selected from a bunch of resistors with close rates.

Selection of resistors There is a place when adjusting the product parameters is required and the high accuracy of the work is required (so that the required parameter is as smaller as possible). Thus, it is necessary that the resistor be as much as possible with 1% accuracy or even 0.5%.

So to adjust the parameters of the scheme most often apply trimming resistors. These resistors are specially invented for these purposes. The adjustment is carried out by means of a thin clock screwdriver, and after reaching the required value of the resistance, the resistor slider is often fixed with paint or glue.

Formulas and properties

When choosing a resistor, in addition to its design features, it is necessary to pay attention to its main characteristics. And its main characteristics, as I mentioned, are resistance and scattering power.

Between these two characteristics there is a relationship. What does it mean? Suppose in the scheme we have a resistor with a certain amount of resistance. But for some reason we find out that the resistance of the resistor should be significantly less than what is now.

And that's what it turns out, we put a resistor with significantly less resistance and in accordance with the Ohm's law we can get a small zap.

Since the resistance of the resistor was large, and we have a fixed voltage in the chain, then that's what happened. With a decrease in the nominal resistor, the overall resistance in the circuit fell, therefore the current in the wires increased.

But what if we put a resistor with the former power of scattering? When the current has increased, the new resistor may not withstand the load and die, his soul will fly together with a cluster of smoke from the damaged caloror

It turns out that at the value of the resistor 10 ohms, the circuit will flow a current equal to 1 A. Power that will dissipate on the resistor will be equal

See which rakes can tide on the way. Therefore, when choosing a resistor, it is necessary to watch its permissible scattering power.

Serial compound resistors

And let's now see how the properties of the chain will change with the sequential resistor location. So we have a power supply and then there are three resistors with different resistance.

Let us try to determine which current flows into the chain.

Here I want to mention, for those who are not in the subject, that electric current in the chain is only one. There is a Kirchhoff rule, which says that the sum of currents flowing into the node is equal to the sum of the currents of the flowing from the node. And since in this scheme, we have a consistent location of the resistors and no nodes and in the interrogation, it is clear that the current will be one.

To determine the current, we need to determine the chain impedance. We find the sum of all resistor s shown in the diagram.

Full resistance turned out to be 1101 ohms. Now knowing that the total voltage (power supply voltage) is 10 V, and the total resistance is 1101 ohms, then the current in the circuit is equal to i \u003d u / r \u003d 10v / 1101 Ohm \u003d 0.009 A \u003d 9 mA

Knowing the current we can determine the voltage planted on each resistor. To do this, we will also use the law of Ohm. And it turns out the voltage on the resistor R1 will be equal to U1 \u003d I * R1 \u003d 0.009A * 1000Ω \u003d 9B. Well, then for the remaining resistors U2 \u003d 0.9V, U3 \u003d 0.09B. Now you can check out all these stresses, well, as a result, the value of the power voltage as a result.

Oh, yes here you are a voltage divider. If you make a removal after each resistor, you can make sure there is still some voltage set. If at the same time use equal resistance, the effect of the voltage divider will be even more obvious.

Click to enlarge

The image shows how the voltage between different points is changing.

Since the resistors themselves are good current consumers, it is clear that when using a voltage divider, it is worth choosing resistors with minimal resistances. By the way, the power consumed on each resistor will be the same.

For the resistor R1, the power will be equal to P \u003d I * R1 \u003d 3.33A * 3.33B \u003d 11.0889W. Round and get 11W. And each resistor should naturally be calculated. The power consumption of the entire chain will be p \u003d i * u \u003d 3.33a * 10v \u003d 33.3W.

Now I will show you what power will be for resistors having different resistance.

Click to enlarge

The power consumed by the entire chain shown in the figure will be p \u003d i * u \u003d 0.09a * 10V \u003d 0.9W.

Now we calculate the power consumed by each resistor:
For resistor R1: P \u003d I * U \u003d 0.09A * 0.9B \u003d 0.081 t;

For resistor R2: P \u003d I * U \u003d 0.09a * 0.09V \u003d 0.0081 t;

For resistor R3: P \u003d I * U \u003d 0.09A * 9B \u003d 0.81W.

Of these our calculations, it becomes a clear pattern:

• The greater the overall resistance of the chain of resistors, the less will be the current in the chain
• The greater the resistance of a particular resistor in the chain, the greater the power will be highlighted on it and the more it will warm up.

Therefore, it becomes clear the need to select the ratings of resistors in accordance with their power consumed.

Parallel compound of resistors

With a consistent layout of resistors, I think it is less understandable. So let's consider the parallel compound of resistors.

Here, in this image, the scheme shows the different location of the resistors. Although in the header, I mentioned a parallel compound, I think the presence of a sequentially connected resistor R1 will allow us to understand some subtleties.

Thus, the point is that the sequential scheme of the compound of the resistors is a voltage divider, and the parallel connection is a current divider.

Consider this in more detail.

The current flows from a point with great potential to a point with less potential. Naturally, the current from the point with the potential 10B tends to the point of zero potential - the Earth. The current route will be: Point10V - \u003e\u003e Point A - \u003e\u003e Point in - \u003e\u003e Earth.

On the site of the path point 10-lot A, the current will be maximal, well, just because the current runs in direct and is not divided into developments.

Further, according to the rule of Kirchhoff, the current will be separated. It turns out the current in the R2 and R4 resistors chains will be one and in the chain with the R3 resistor to others. The sum of the currents of these two sites will be equal to the current on the very first segment (from the power source to point A).

Let's calculate this scheme and learn the value of the current on each site.

First, learn resistance to the resistor section R2, R4

The value of the R3 resistor is known to us and is equal to 100.

Now we find the resistance of the AV site. Resistance to the chain of resistors connected in parallel will be calculated by the formula:

Yeah, substantiated in the formula. Our values \u200b\u200bfor the sum of resistors R2 and R4 (the sum is 30 ohms and is substituted instead of the formula R1) and the value of the resistor R3 is equal to 100 ohms (substituted instead of the formula R2). The calculated value of the resistance on the section AV is 23 ohms.

As you can see, fulfilling uncomplicated calculations, our scheme has simplified and curled and became more familiar to us.

Well, the complete resistance of the chain will be equal to R \u003d R1 + R2 \u003d 23Ω + 1Ω \u003d 24Ω. We found this by the formula for a serial connection. We considered it so we will not stop at this.

Now the current is on the plot to the branches (section of the point 10B - \u003e\u003e Point a) We will be able to find according to the Ohm formula.

I \u003d u / r \u003d 10V / 24Ω \u003d 0.42A. It turned out 0.42 amps. As we have already discussed this current, it will be one on the entire path from the point of maximum potential, to point A. On the section A B, the current value will be equal to the amount of currents from the sections obtained after separation.

To determine the current on each site between points A and B, we need to find the voltage between points A and V.

It is already known to be less than the supply voltage of 10V. It will be found according to the formula U \u003d I * R \u003d 0.42a * 23Ω \u003d 9.66V.

How could you notice a complete current at the exact same (equal amount of currents of parallel sections) multiplied by the resulting resistance of the first-mentioned (resistor resistor R1 we do not take into account) of the chain sections.

Now we can find the current in the chains of resistors R2, R4. For this, the voltage between points A and in the dividing the sum of these two resistors. I \u003d u / (R2 + R4) \u003d 9.66V / 30Ω \u003d 0.322A.

The current in the R3 resistor chain is also not difficult to find. I \u003d u / R3 \u003d 9.66V / 100Ω \u003d 0.097A.

As you can see with parallel, the connection of the resistors current is divided proportional to the resistance values. The greater the resistance of the resistor, the less will there be a current on this section of the chain.

At the same time, the voltage between the points A and B will relate to each of the parallel sites (the voltage U \u003d 9.66v was used for the calculations and there).

Here I want to say how voltage and current are distributed according to the scheme.

As I said the current before the branching is equal to the sum of currents after the development. However, the smart man Kirchhoff already told us.

The following is obtained: The current I on the fork will be divided into three I1, I2, I3, and then reunited in i as it was at the very beginning, we obtain i \u003d i1 + i2 + i3.

For voltage or difference in potentials, which is the same as the following. The potential difference between points A and C (hereinafter I will speak AC voltage) is not equal to the stresses BE, CF, DG. At the same time of the BE, CF, DG voltage, will be equal to each other. The voltage in the FH section is generally zero, since the voltage is simply nothing to disend (no resistors).

I think the topic of parallel connection of the resistors, I revealed, but if there are some other questions, then write in the comments than I can help

Star transformation in triangle and back

There are schemes in which resistors are connected so that it is not entirely clear where there is and where is parallel. And how to be with it?

For these situations there are ways to simplify schemes and one of them is a triangle conversion in an equivalent star or vice versa, if necessary.

To convert a triangle to the star, we will be considered according to formulas:

In order to make the reverse transformation, you need to use several other formulas:

With your permission, I will not provide specific examples, all that is required is only to substitute the specific values \u200b\u200bin the formula and get the result.

This method of equivalent transformation will serve as a good help in mutual cases, when it is not entirely clear from which side to approach the scheme. And then sometimes changing the star on the triangle, the situation clarifies and becomes more familiar.

Well dear friends That's all I wanted to tell you today. It seems to me this information will be useful for you and will bring your fruits.

I want to add more that much of the fact that I posted here very well painted in the books and, so I recommend reading review articles and download yourself these books. And it will be even better if you find them somewhere in the paper version.

P.S. I recently had one idea about how it is possible to get an interesting way to earn money on the knowledge of electronics and in general the radio amateur hobby so necessarily subscribe to updates.

In addition, a relatively recently appeared another progressive way to subscribe through the form email service Newsletons, so people subscribe and get some nice bonuses, so welcome.

And on this I really have everything, I wish you success in everything, wonderful mood to new meetings.

With N / P Vladimir Vasilyev.

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Controlled sounds of star wars, fire truck or ambulance;
Musical fan;
Electric lighting rifle;
Studying Alphabet Morse;
Polygraph;
Automatic street lamp;
Megaphone;
Radio station;
Electronic metronome;
Radio receivers, including the FM range;
A device resembling the occurrence of dark or dawn;
Alarm that baby is wet;
Protective alarm;
Music door lock;
Lamps with parallel and sequential connection;
Resistor as current limiter;
Capacitor charge and discharge;
Electric heater tester;
Reinforcement effect of the transistor;
Darlington scheme.

The resistor is an element of an electrical circuit that has an electric current resistance. Classify two types of resistors: constant and variables (trimmed). When modeling a electrical circuit, as well as during the repair of electronic products, it becomes necessary to use a resistor of a certain nominal value. Although there are many different denominational resistor denominations, at the moment there may not be required at hand, or there is no resistor with such a nominal. To exit such a situation, you can use both consecutive and parallel compound of resistors. How to correctly make calculation and selection of various resistance denominations, will be told in this article.

The consecutive compound of the resistors is the most elementary scheme for the assembly of radio components, it is used to increase the overall chain resistance. With a consecutive connection, the resistance of the used resistors is simply folded, but with a parallel connection it is necessary to calculate the formulas described below. A parallel compound is necessary to reduce the resulting resistance, as well as to increase power, several parallel connected resistors have a greater power than one.

In the photo you can see a parallel connection of resistors.

Below is a schematic diagram of a parallel compound of resistors.

The total nominal resistance must be calculated according to the following scheme:

R (total) \u003d 1 / (1 / R1 + 1 / R2 + 1 / R3 + 1 / R n).

R1, R2, R3 and RN - parallel to the connected resistors.

When the parallel compound of resistors consists of only two elements, in this case, the total nominal resistance can be treated according to the following formula:

R (total) \u003d R1 * R2 / R1 + R2.

R (total) - general resistance;

R1, R2 - parallel to the connected resistors.

In the radio engineering, there is the following rule: if the parallel connection of the resistors consists of elements of one nominal, then the resulting resistance can be calculated, separating the resistor's denomination to the number of connected resistors:

R (total) - general resistance;

R is the nominal parallel to the connected resistor;

N - the number of connected elements.

It is important to take into account that with a parallel connection, the resulting resistance will always be lower than the resistance of the smallest of the resistor.

Let us give a practical example: take three resistors, with the following values \u200b\u200bof the nominal resistance: 100 ohms, 150 ohms and 30 ohms. We will calculate the overall resistance, according to the first formula:

R (total) \u003d 1 / (1/100 + 1/150 + 1/30) \u003d 1 / (0.01 + 0.007 + 0.03) \u003d 1 / 0.047 \u003d 21.28.

After calculating the formula, we see that a parallel compound of resistors consisting of three elements with the smallest rates of 30 ohms, as a result, gives a general resistance in the electrical circuit of 21.28 Ohms, which is below the smallest nominal resistance in the chain by almost 30 percent.

The parallel compound of resistors is most often used in cases where it is necessary to obtain resistance with greater power. In this case, it is necessary to take resistors of the same power and with the same resistance. The resulting power is in this case calculated by multiplying the power of one resistance element for the total number of parallel connected resistors in the chain.

For example: Five resistors with a nominal value of 100 ohms and with a capacity of 1 W in each connected in parallel, have a total resistance of 20 Ohm and the power of 5 W.

With a consistent connection of the same resistors (the power also consists), we obtain the resulting power of 5 W, the overall resistance will be 500 ohms.

For any radio amateur, the resistor is the item that is needed almost every even the simplest scheme. In the trivial situation, the resistance is a coil of a wire that does not use the electric current, Konstanta is often used as a metal.

For an alternating or permanent resistor, graphite can be used in experimental purposes, the rod from which is inside the simple pencil. It has good electrical conductivity. Therefore, for a homemade resistor, its thin layer is needed, which can be applied to paper and combine the desired resistance to several hundred kiloma.

Based on graphite properties We construct a working model of a resistor on a paper carrier. At the same time, we will proceed from simple arithmetic: the longer the conductor, the greater its electrical resistance.

In the photo below, the indicator shows in megaoms.

The scoreboard shows that the graphite strip, which is 2 times longer, has, accordingly, 2 times more resistance. Please note that the width of the bands is the same.

Wide conductor has a smaller resistance.

A strip of graphite deposited on paper is easy to turn into an experimental variable resistor, or otherwise we call it - a retaint.

The idea is perfect for physics lessons. Used material from site samodelnie.ru

(permanent resistors), and in this part of the article we will talk about, or variable resistors.

Resistors of variable resistance, or variable resistors are radio components whose resistance can change from zero to nominal value. They are used as regulators of amplification, volume controls and timbre in sound reproducing radio equipment, are used to accurate and smooth up different voltages and are divided into potentiometers and strong Resistors.

Potentiometers are used as smooth regulators of amplification, volume controls and timbre, serve for smooth adjustment of different voltages, as well as used in tracking systems, in computing and measuring devices, etc.

Potentiometer Called an adjustable resistor having two permanent outputs and one movable. The constant conclusions are located along the edges of the resistor and are connected to the beginning and end of the resistive element forming the general resistance of the potentiometer. The average output is connected to a movable contact, which moves along the surface of the resistive element and allows you to change the resistance value between the average and any extreme output.

The potentiometer is a cylindrical or rectangular housing, inside of which a resistive element is located in the form of an open ring, and a protruding metal axis, which is a potentiometer handle. At the end of the axis, the plane of the current collector (contact brush) has a reliable contact with the resistive element. The reliability of the contact of the brush with the surface of the resistive layer is provided by the pressure of the slider made of spring materials, for example, bronze or steel.

When rotating the handle, the slider moves along the surface of the resistive element, as a result of which the resistance changes between the middle and extreme leads. And if there is a voltage to submit to the extreme conclusions, then the output voltage is obtained between them.

A schematic potentiometer can be represented as shown in the figure below: the extreme conclusions are indicated by numbers 1 and 3, the average is indicated by the number 2.

Depending on the resistive element, the potentiometers are divided into incomparable and wire.

1.1 Improvant.

In inspire potentiometers, the resistive element is made in the form of horseshoe or rectangular Plates of insulating material, on the surface of which a resistive layer is applied, which has a certain ohmic resistance.

Resistors S. ucho-shaped The resistive element has a round shape and rotational movement of the slider with an angle of rotation 230 - 270 °, and resistors with rectangular The resistive element has a rectangular shape and translational movement of the slider. The most popular are SP, OSP, SP3 type resistors. Figure below shows the SP3-4 type potentiometer with a horseshoe resistive element.

The domestic industry was produced by the SPO type potentiometers, in which the resistive element was pressed into the arcuate groove. The body of such a resistor is made of ceramics, and to protect against dust, moisture and mechanical damage, as well as for electrical shielding, the entire resistor is closed with a metal cap.

SPO type potentiometers have a lot of wear resistance, insensitive to overloads and are small, but they have a disadvantage - the complexity of obtaining nonlinear functional characteristics. These resistors still can still be found in the old domestic radio equipment.

1.2. Wire.

IN wire Potentiometers The resistance is created by a high-resistant wire wounded into one layer on the ring-shaped frame, which moves mobile contact for the edge. To get a reliable contact between the brush and winding contact track Cleaning, polished, or polished to a depth of 0.25d.

The device and the framework of the frame is determined on the basis of the accuracy class and the law of changing the resistance of the resistor (the law of resistance changes will be said below). Frames are made from the plate, which after winding the wires are folded into the ring, or take the finished ring for which the winding is placed.

For resistors with accuracy not exceeding 10 - 15%, the frames are made from the plate, which, after winding the wires, turn into a ring. Material for the frame is insulating materials, such as Ghetinax, textolite, fiberglass, or metal - aluminum, brass, and the like. Such frames are easy to manufacture, but do not provide accurate geometric sizes.

Frames made of finished rings are made with high accuracy and used mainly for the manufacture of potentiometers. The material for them is plastic, ceramics or metal, but the disadvantage of such frames is the complexity of the winding, as special equipment is required for its winding.

The winding is performed by wires from high-tech alloys electrical resistance, for example, Konstanta, Nichrome or Manganin in enamel isolation. For potentiometers, wires from special alloys based on noble metals, which have reduced oxidation and high wear resistance. The diameter of the wire is determined on the basis of the valid current density.

2. The main parameters of variable resistors.

The main parameters of the resistors are: full (nominal) resistance, form functional characteristic, minimum resistance, rated power, level of rotation noise, wear resistance, parameters characterizing the behavior of the resistor during climatic influences, as well as dimensions, cost, etc. However, when selecting resistors, it most often pay attention to the nominal resistance and less often on the functional characteristic.

2.1. Nominal resistance.

Nominal resistance The resistor is indicated on its housing. According to GOST 10318-74, preferred numbers are 1,0 ; 2,2 ; 3,3 ; 4,7 Om, kiloma or mega.

In foreign resistors, preferred numbers are 1,0 ; 2,0 ; 3,0 ; 5.0 Om, kiloma and mega.

Allowable resistance deviations from the nominal value are mounted within ± 30%.

Full resistance of the resistor is the resistance between the extreme leads 1 and 3.

2.2. Form functional characteristic.

The potentiometers of the same type may differ in functional characteristic that determines the resistance of the resistor between the extreme and middle output when the resistor handle changes. In the form of the functional characteristic, potentiometers are divided into linear and nonlinear: The linear resistance value changes in proportion to the movement of the current collector, the nonlinear it changes according to a certain law.

There are three basic laws: BUT - linear, B. - logarithmic, IN - back logarithmic (indicative). For example, to adjust the volume in the sound-reproducing equipment, it is necessary that the resistance between the average and extreme output of the resistive element changed return logarithmic law (B). Only in this case, our ear can perceive a uniform increase or decrease in volume.

Or in measuring instruments, such as sound frequency generators, where variable resistors are used as frequency elements, also requires their resistance to change logarithmic (B) or return logarithmic law. And if this condition is not executed, the generator scale will be uneven, which makes it difficult to accurately install the frequency.

Resistors S. linear The characteristic (a) is used mainly in voltage divisors as adjusting or trimming.

The dependence of resistance from the angle of rotation of the resistor handle for each law is shown on the chart below.

To obtain the desired functional characteristic, large changes in the potentiometer design are not made. For example, in wire resistors, the winding of the wires lead with a changing step or the frame itself makes a changing width. In inspire potentiometers, change the thickness or composition of the resistive layer.

Unfortunately, adjustable resistors have relatively low reliability and limited service life. Often owners of audio equipment, operated for a long time, have to hear the rustles and cracks from the loudspeaker when the volume control is rotated. The reason for this unpleasant moment is to disrupt the contact of the brush with the conductive layer of the resistive element or the depreciation of the latter. Sliding contact is the most unreliable and vulnerable place of the variable resistor and is one of the main cause of the output of the part.

3. Designation of variable resistors in the schemes.

On the concept schemes Variable resistors are indicated as well as permanent, only an arrow is added to the main symbol pointing in the middle of the case. The arrow indicates the regulation and simultaneously indicates that this is the average output.

Sometimes there are situations where the requirements of the reliability and duration of operation are presented to the variable resistor. In this case, smooth regulation is replaced with a stepped, and the variable resistor is built on the database with several positions. Connect resistors of constant resistance are connected to the switch contacts, which will be turned on in the circuit when turning the switch knob. And in order not to clutter the diagram with a switch with a set of resistors, only a symbol of a variable resistor with a sign indicate step regulation. And if necessary, the number of steps additionally indicate.

To control the volume and timbre, the level of recording in the audio reproducing stereo equipment, to control the frequency in signal generators, etc. Applied dual potentiometerswhose resistance changes simultaneously when turning general axis (engine). In the schemes, the symbols of the resistors included in them are located as close as possible to each other, and the mechanical communication, which ensures the simultaneous movement of the engines, is shown either two solid lines or a single dotted line.

The belonging of the resistors to one dual unit is indicated according to their positional designation in the electrical circuit, where R1.1 is the first diagram of a resistor of a dual variable resistor R1, and R1.2 - Second. If the symbols of the resistors are at a great distance from each other, then the mechanical communication is denoted by segments of the dotted line.

Industry produced dual variables of resistors, in which each resistor can be controlled separately because the axis of one passes inside the tubular axis of the other. In such resistors, there is no mechanical connection that provides simultaneous movement, therefore, it is not shown in the diagrams, and belonging to the dual resistor indicate according to the positional designation in the electrical circuit.

In portable household audio equipment, for example, in receivers, players, etc., often use variable resistors with a built-in switch, which is connected to power to power into the device circuit. In such resistors, the switching mechanism is combined with the axis (handle) of the variable resistor and when the knob is reached, the extreme position affects the contacts.

As a rule, in the circuits of the switch contacts are located near the power supply in the power supply of the feed wire, and the switching of the switch with the resistor is denoted by a dotted line and a point that one of the sides of the rectangle is placed. It is understood that the contacts are closed when driving from a point, and open when moving to it.

4. Strip resistors.

Strong resistors They are a type of variables and serve for a single and accurate setting of radio-electronic equipment during its installation, adjustment or repair. As trimmed, both variable resistors of the usual type with a linear functional characteristic, the axis of which is performed "under the slot" and is equipped with a locking device and resistors of a special design with the increased accuracy of the resistance value setting.

In the bulk of its mass, the rapid resistors of the special design make a rectangular shape with flat or ring resistive element. Resistors with flat resistive element ( but) Have a translational movement of the contact brush carried out by a micrometric screw. In resistors with a ring resistive element ( b.) Move the contact brush is carried out by worm transmission.

At large loads, open cylindrical resistor designs are used, for example, PEVR.

On the schematic diagrams, trimming resistors are indicated as well as variables, only instead of the regulatory sign uses a sign of trimmed regulation.

5. Turn on the variables of resistors to the electrical circuit.

In electrical circuits, variable resistors can be used as reostat (adjustable resistor) or as potentiometer (voltage divider). If the current must be adjusted in the electrical circuit, the resistor includes a retake, if the voltage, then include the potentiometer.

When the resistor is turned on reostat Middle and one extreme conclusion. However, such an inclusion is not always preferable, since a random loss of the average contact with a resistive element is possible in the regulatory process, which will entail an unwanted electric circuit breaking and, as a result, a possible way out of the order or electronic device as a whole.

To exclude a random chain rupture The free output of the resistive element is connected to the movable contact so that when disrupting the contact electrical circuit Always remained closed.

In practice, the inclusion of the rheostat is used when the variable resistor wants to be used as an additional or current-limiting resistance.

When the resistor is turned on potentiometer All three conclusions are activated, which allows it to use the voltage divider. Take, for example, a variable resistor R1 with such a nominal resistance that will extinguish almost all power supply voltage coming on the HL1 lamp. When the resistor knob is unscrewed to the extremely top according to the position, the resistance of the resistor between the upper and middle conclusions is minimally and all the power supply voltage enters the lamp, and it glows with complete potassium.

As the resistor handle moves down the resistance between the upper and middle output will increase, and the stress on the lamp will gradually decrease, which will not shine not full of heat. And when the resistance of the resistor reaches the maximum value, the voltage on the lamp will fall almost to zero, and it will go out. It is according to this principle that the volume is controlled in the sound-reproducing equipment.

The same stress divider schema can be depicted slightly differently, where the variable resistor is replaced with two permanent R1 and R2.

Well, in principle, and everything I wanted to say about resistors of variable resistance. In the final part, we consider a special type of resistors, the resistance of which is changed under the influence of external electrical and non-electrical factors.
Good luck!

Literature:
V. A. Volga - "Details and nodes of radio-electronic equipment", 1977
V. V. Frolov - "Radiosham's Language", 1988
M. A. ZGUT - "Legend and Radioshem", 1964

According to GOST, resistors whose resistance cannot be changed during operation, is called permanent resistors. Resistors with the help of which various adjustments are carried out in the equipment by changing their resistance, are called variable resistors (among radio amateurs often used by their old, incorrect, name - potentiometers). Resistors whose resistance changes only in the process of establishing (settings) of instruments using a tool, such as a screwdriver, are called trimmed.

In addition, a variety of incomplete nonlinear resistors are used in the radio electronic apparatus:

varistors whose resistance is much changed depending on the voltage applied;

thermistors, or thermistors, the resistance of which varies in significant limits when the temperature and voltage change;

photoresistors (photoelements with an internal photoelectric effect) - devices, the resistance of which decreases under the influence of light or other radiation (this resistance also depends on the applied voltage).

Permanent resistors of widespread use are made with a deviation from the nominal (admission) of ± 5, ± 10, ± 20%. Deviations ± 5 and ± 10% are included in MAP-

ring resistor and designated near the face value. On small-sized resistors, instead of designation ± 5%, the figure I is indicated (which denotes the first accuracy class), and instead of ± 10% - digit II (second accuracy class). Resistors who do not have such designations deviation from. The nominal may be up to ± 20%.

The accuracy class characterizes only a certain properties of the resistor. But it should not conclude that the device in which the resistors only use the first accuracy class will work better than the device in which this principle do not adhere to. This should not even strive. The accuracy class indicates only the ability to use a resistor in certain circuits or devices.

Thus, the permanent resistors used in the measuring equipment must have a small deviation of the resistance from the nominal value. Hydraulic resistors of ultrasound types, BPL, IHP used in such equipment are made with a deviation from a nominal value of ± 0.1; ± 0.2; ± 0.5; ± 1 and ± 2%. These tolerances are usually indicated in the labeling of the resistor.

Allowable deviation from the nominal value of resistance, that is, the suitability of this resistor for use in any particular case is determined by which the chain will stand a resistor. For example, in the transistor collector circuit, in the control grid circuits of the lamps (in high frequency amplification cascades, in a low frequency amplifier, in a triode or pentode detector, or an electronic radiation setting indicator), as well as in the signal mesh chain of the frequency converter, in The AGU chains, in the diode detector AM signals, in the unleashing filter circuit of the control grid of the electronic lamp, can practically be used inspire resistors with any deviation from the nominal value.

The resistor used in the circuit shielding grid lamps of the UHF, UPF, UPC, the frequency converter and the heteroodine, to be selected with the permissible deviation from the nominal value of ± 20%, although, when adjusting the machine, to fit the normal cascade mode, you may have to select a resistor experienced way.

Resistors with permissible deviation from a nominal value of ± 10% can be used - in the emitter circuit of the transistor, , discriminator), in the smoothing filter of the rectifier, in the unleashing chains, in the frequency correction chains, negative feedback LF amplifiers, tone controller, automatic displacement to the control grid of the heated lamp (cathode part of the lamp). To establish a normal mode when adjusting and adjusting the equipment, resistors in the correction chains, feedback and in divisors often have to be selected by experimentally.

As additional resistances for voltmeters (millivolithomethmeters), the resistors of the types of types, BLP, MGN, having the smallest deviation of the resistance from the nominal value (± 0.5-2%), are best applied.

Resistors used in high-frequency circuits (in vibrational circuits, chains of control grids and anodes of lamps), should only be hopeless. In such chains, inspire resistors are used, the inductance of which is completely insignificant. Strong the power dissipated in those chains where these transistors are used, very small, it makes it possible at the expense of small size of the resistors (with low scattering capacity, the size of the resistors can be very small) reduce simultaneously to a possible minimum and added resistors to these chains Capacity.

It should be noted, however, that miniature incomplete resistors with resistance over 1 Mom are unreliable in work. It is explained by the fact that the conductive path in such resistors to increase resistance is performed as a spiral on the surface of the ceramic cylindrical body. Therefore, with a relatively large number of turns, the conductive path has a very thin carbon layer, which is easily destroyed, especially in conditions of high humidity and with overheating. If there is still a need to use resistors with such nominal resistance values, then from resistors of the aircraft with nominal resistances above 1 Mom, resistors should be used SU-0.5 resistors or resistors having even greater rated power of scattering, and therefore large dimensions. Such resistors work more stable.

Limit voltage, i.e., the largest voltage that does not cause violations of the normal operation of the resistor with the resistance R nom (OM) is the value of the DC voltage or the active voltage of the alternating current U. (B), which is permissible to apply to the resistor (voltage drop on the resistor) so that thermal losses on it do not exceed the scattering power R (W) resistor. This voltage can be calculated by the formula:

U \u003d \\ / p r nom

If the heating temperature of the resistor does not exceed the rated temperature (t nom), then the power of the scattering in this calculation is taken equal to the nominal P \u003d rnn; at higher heating temperatures (up to the maximum allowable T maximum value) R must be reduced accordingly.

The main damage to the resistors is a break and change of resistance. In case of damage, incomplete permanent resistors are usually not repaired, but replaced with new ones. In amateur equipment, if there is a need for this, self-made wire resistors can be used. With careful manufacture, such homemade parts are not inferior to the manufacturing industry.

Variables and wire resistors in some cases can be repaired. A malfunction in variable resistors usually occurs during their long-term operation. Signs of malfunctions are, for example, rustling and cod in the speaker's loudspeaker, breaking the smooth adjustment and the appearance of the bands on the TV screen, etc. One of the reasons for this may be drying the lubrication of the rubbing parts of the resistor or their oxidation and contamination.

To eliminate the cod, the variable resistor must be disassembled, rinse with solvent (gasoline, alcohol, etc.), wipe with a clean cloth and slightly lubricate the oil (wipe and lubricate it is not only the axis, but also the surface of the attachment itself).

But if you cannot disassemble the variable resistor for some reason, it is impossible or undesirable, then in the lid you can drill a hole and using a syringe to enter the resistor to its axis and the mobile contact sleeve several drops of pure gasoline, and then the same amount of machine oil. The axis of the variable resistor at the same time turns all the time to turn into one and the other side. After lubrication, the hole in the lid should be sealed with a piece of paper or pour the resin.

Sometimes, with a deterioration in contact between the conductive path and the current-piece drive, the cod and the rustles can be eliminated in the radio equipment by covering the resistor to the resistor with a thin layer of graphite lubricant used for some vendors of the car. But at the same time it is necessary to remember that the resistance of the high-level resistor can slightly decrease, since the graphite lubricant has a conduit.

In the case of an internal cliff of a variable resistor with linear addiction The resistance used as a row (engine is connected to one of the extreme conclusions), it is possible to restore its performance very simply, especially if the openness occurred directly from the output. To do this, it is enough to change the conductors, connected to the extreme conclusions of the resistor. Such switching leads to the fact that the damaged place wire resistor It turns out on the non-working plot. The maximum and minimum adjustment values \u200b\u200bare obviously changed in places.

With parallel connection of two resistors, the total chain resistance can be calculated by the formula:

R total \u003d R 1 R 2 / (R L + R 2),

where R 1 and R 2. - Accordingly, the resistance of each of the resistors.

In the case of a sequential connection of resistors, the total chain resistance is equal to the sum of the resistance of the resistors included in the chain.

How to increase or decrease resistance to the resistor. Resistors with a constant resistance of a large value (3 ... 20 MΩ), if necessary, can be made from the resistors of the type of aircraft with a denomination of 0.5 - 2 mΩ. For this, a cloth moistened in alcohol or acetone, you need to gently wash off the paint from the surface, and then after drying, connect the resistor to the me-gas memeter and, washing the conductive layer with a soft rubber band for ink, adjust the resistance value to the required value. This operation should be done very carefully, washing the conductive layer evenly from the entire surface.

The resistor treated in this way is then covered with insulating varnish. If you use alcohol varnishes for this purpose, then after the coating, the amount of resistance will slightly decrease, but. As the lacquer drying, the value will restore it again. For the manufacture of a resistor, the source resistor in order to increase reliability it is necessary to take a large rated power (1 - 2 W).

A simple way can be increased in two to four times and resistance of an alternating resistor. To do this, a thin skin, and then a sharp knife, or a razor scrape along the edges of the attachment, a part of a graphite conductive layer (along its entire length). The greater the resistance of the hilt must be, this layer is already left.

If required, on the contrary, reduce the resistance of an alternating resistor, then the conductive layer along the edges of the pensions can be smoked by a soft pencil. After this, it is necessary to wasteively wipe the blade moistened in alcohol to remove the crumbs of graphite, otherwise the cods in the loudspeaker occur in the loudspeaker.

Method of picking resistor with low tolerance. If you need to install a resistor with a small tolerance in any particularly important chain of the device (for example, ± 1%), A s. The disposal is only resistors with a large tolerance (for example, ± 5%), then adjust the resistance value, using instead of one two separate resistors with a large tolerance (for example, ± 5%).

One of these two resistors should have the amount of resistance close to the nominal, but not exceeding the nominal value (for example, 95.5 com instead of 100 com): The second resistor, included in series with it, must have a resistance value less than the gap between the resistance value of the first Resistor and its real value (for example, 3.9 com instead of 4 com). This resistor included consistently with the first allows us to obtain the overall resistance of the value close to the nominal value (95.5 kΩ + 3.9 kΩ \u003d 99.4 kΩ; the deviation from the nominal 100 com is only 0.6%).

Fig. 6. Some ways to include variable resistors:

a - to obtain dependences close to the indicative; b. - to obtain dependences close to the logarithmic; in - Schedule change graphs

How to make a variable resistor with non-linear resistance dependence. When designing various devices, it is often necessary to use variable resistors with a nonlinear (logarithmic or indicative) dependence of resistance from the angle of the axis of the rolling contact.

The nonlinear dependence of the resistance close to the logarithmic and indicative can be obtained in a resistor of type A, which has a linear dependence, if you turn it on accordingly according to the figure. b, but or b. On the same figure (Fig. 6, in) The type of resistance change curves is shown. However, it should be borne in mind that the input resistance of such a regulator changes (four times at extreme positions of the engine), however, the use of such regulators in many cases is quite possible.

How to make a dual variable resistor. A simple method of manufacturing a dual variable resistor is shown in Fig. 7, but. You can make it from two conventional variables of the same type (A, B or B) resistors, with at least one of the pair resistors should be with the switch (TC - D). After removing the cover from the resistor having a switch, the switch of the switch is bended as shown in the figure. The second resistor at the end of the axis cut the slot, follow the way that the curved leash is free, but without a noticeable backlash included in the slot. Dual resistors are then strengthened on the P-shaped metal bracket. To protect the resistors from dust entering, they are closed with covers: in the lid (without switch), the hole for the axis is done and this cover is put on the first resistor. The lid, removed from the first resistor, if there is no other, put on the second resistor.

A compact dual resistor with a linear resistance dependence can be made of two standard variables of SP-1 resistors. The most difficult operation is an assay of the axis, the dimensions of which are shown in Fig. 7, b. Engines that need to be pre-removed from disassembled resistors, spoofed with a file splipped parts of the axes, sit on a new total axis diametrically opposite to each other (Fig. 7, in). Between the engines should be laid washer. The end of the axis after installing the engines are spawned. The assembled dual resistor is tightly closed with a metal ribbon with petals (Fig. 7, d), which, after the assembly, is froze along the forming cylinder.

The quality of the collected pair of resistors can be checked on the installation, the diagram of which is shown in Fig. 7, d. It is a DC bridge, which includes checked resistors in the shoulders. If the characteristics of both resistors of the pair are completely the same, then the arrow indicator (a milliammeter with a current of deviations in each direction from the middle of the scale of 1 mA) will be when the pair axis is rotated in the middle of the scale. In practice, however, some discrepancy of the characteristics of the resistor pair can be observed, so there will be the best of several pairs of the ladder of the indicator arrows at full turn of the axis of the paired resistor will be the smallest.

Fig. 7. Methods for getting variable resistors

How to lengthen the axis. In order to lengthen the axis of the variable resistor, you need to choose a brass or steel rod of the same diameter as the axis, as well as a metal tube, the inner diameter of which should be equal to the axis diameter.

At the end of the axis of the variable resistor, it is usually lying - a flat section for fixing the handles. The additional rod must also be lying so that the rod and axis applied to each other lying (sawed surfaces) formed as if continuing each other. If after that, between the cut surfaces, lay a thin elastic gasket (for example, from rubber) and closer the muffle from a piece of metal tube, the axis and the rod will turn out to be firmly connected to each other.

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