In electrical circuits, resistors are used to regulate current. A huge number of different types are produced. To determine in all the variety of details, for each, the symbol of the resistor is introduced. They are marked in different ways, depending on the modification.
Types of resistors
A resistor is a device that has electrical resistance, its main purpose is to limit the current in an electrical circuit. The industry produces various types of resistors for a wide variety of technical devices. Their classification is carried out in different ways, one of them is the nature of the change in resistance. According to this classification, 3 types of resistors are distinguished:
- Fixed resistors. They do not have the ability to arbitrarily change the resistance value. According to their purpose, they are divided into two types: general and special applications. The latter are divided according to their purpose into precision, high-resistance, high-voltage and high-frequency.
- Variable resistors (they are also called adjusting). Possess the abilitychange the resistance with the control knob. In terms of design, they are very different. There are combined with a switch, dual, triple (that is, two or three resistors are installed on one axis) and many other varieties.
- Trimming resistors. They are used only when setting up a technical device. Their adjustment bodies are accessible only with a screwdriver. A large number of different modifications of these resistors are produced. They are used in all kinds of electrical and electronic devices, from tablets to large industrial installations.
Some types of resistors discussed are shown in the photo below.
Classification of components by mounting method
There are 3 main types of mounting of electronic components: hinged, printed and for micromodules. Each type of installation has its own elements, they vary greatly in size and design. Resistors, capacitors and semiconductor devices are used for surface mounting. They come with wire leads so that they can be soldered into the circuit. Due to the miniaturization of electronic devices, this method is gradually losing its relevance.
Smaller parts are used for printed circuit wiring, with or without leads for soldering into the printed circuit board. To connect with the circuit, these parts have contact pads. Printed wiring has significantly contributed to the reduction in the size of electronicproducts.
Smd resistors are often used for PCB and micromodule mounting. They are very small in size and can be easily integrated into printed circuit boards and micromodules automatically. They are available in various nominal resistance, power and sizes. The latest electronic devices predominantly use smd resistors.
Rated resistance and power dissipation of resistors
Nominal resistance, expressed in ohms, kiloohms or megaohms, is the main characteristic of the resistor. This value is given on the circuit diagrams, applied directly to the resistor in an alphanumeric code. Recently, the color designation of resistors has often become used.
The second most important characteristic of a resistor is its power dissipation, which is expressed in watts. Any resistor when current passes through it heats up, that is, it dissipates power. If this power exceeds the allowable value, the destruction of the resistor occurs. According to the standard, the designation of the power of resistors on the circuit is almost always present, this value is often applied to its case.
Tolerance of nominal resistance and its dependence on temperature
The error, or deviation from the nominal value, measured as a percentage, is of great importance. It is impossible to absolutely accurately manufacture a resistor with the declared resistance value, there will definitely be a deviation from the specified value. The error is indicated directly on the body, often in the form of a code of colored stripes. She is rated atpercentage of nominal resistance value.
Where there are large fluctuations in temperature, the dependence of resistance on temperature, or the temperature coefficient of resistance, abbreviated as TCR, measured in relative units ppm / ° C, is of considerable importance. TKS shows by what part of the nominal value the resistance of the resistor changes if the temperature of the medium increases (decreases) by 1°C.
Conditional graphic designation of the resistor in the diagram
When drawing schemes, compliance with the state standard GOST 2.728-74 for conventional graphic symbols (UGO) is required. The designation of a resistor of any type is a 10x4 mm rectangle. Based on it, graphic images are created for other types of resistors. In addition to the UGO, the designation of the power of the resistors on the circuit is required, this facilitates its analysis when troubleshooting. The table below shows the constant resistance UGOs with an indication of the power dissipation.
The photo below shows fixed resistors of different capacities.
Conventional graphic designation of variable resistors
UGO variable resistors are applied to the circuit diagram in the same way as fixed resistors, according to the state standard GOST 2.728-74. The table shows an image of these resistors.
The photo below shows variable and trimmer resistors.
Standard designation for resistor resistance
It is customary for international standards to designate the nominal resistance of a resistor on the circuit and on the resistor itself a little differently. The rules for this notation, along with sample examples, are given in the table.
| Full designation | Abbreviated designation | ||||||
| Unit of measurement | Design. units rev. | Nominal limit resistance | on the diagram | on the body | Nominal limit resistance | ||
| Ohm | Ohm | 999, 9 | 0, 51 | E51 or R51 | 99, 9 | ||
| 5, 1 | 5E1; 5R1 | ||||||
| 51 | 51E | ||||||
| 510 | 510E; K51 | ||||||
| Kilohm | kOhm | 999, 9 | 5, 1k | 5K1 | 99, 9 | ||
| 51k | 51K | ||||||
| 510k | 510K; M51 | ||||||
| Megaohm | MOhm | 999, 9 | 5, 1M | 5M1 | 99, 9 | ||
| 51M | 51M | ||||||
| 510M | 510M | ||||||
The table shows that the designation on the diagrams of resistors of constant resistance is made by an alphanumeric code, first comes the numerical value of the resistance, then the unit of measurement is indicated. On the body of the resistor, it is customary to use a letter instead of a comma in the digital designation, if it is ohms, then E or R is put, if kiloohms, then the letter K. When designating megaohms, the letter M is used instead of a comma.
Colour-coded resistors
The color designation of the resistors was adopted to make it easier to put information about the technical characteristics on their case. For this, several color strips of different colors are applied. In total, 12 different colors are accepted in the designation of the strips. Each of them has its own specific meaning. The color code of the resistor is applied from the edge, with low accuracy (20%) 3 strips are applied. If the accuracy is higher, you can already see 4 bars on the resistance.
When the resistor is highly accurate, 5-6 strips are applied. For a marking containing 3-4 strips, the first two indicate the resistance value, the third strip is a multiplier, this value is multiplied by it. The next bar determines the accuracy of the resistor. When the marking contains 5-6 strips, the first 3 correspond to the resistance. The next bar is the multiplier, the 5th bar is the accuracy, and the 6th bar is the temperature coefficient.
There are reference tables for deciphering the color codes of resistors.
Surface Mount Resistors
Surface mount is when all the parts are located on the board from the side of the printed tracks. In this case, holes for mounting elements are not drilled, they are soldered to the tracks. For this installation, the industry produces a wide range of smd components: resistors, diodes, capacitors, semiconductor devices. These elements are much smaller in size and technologically adapted for automated installation. The use of smd components can significantly reduce the size of electronic products. Surface mounting in electronics has almost supplanted all other types.
With all the advantages of the installation in question, it has a number of disadvantages.
- Printed circuit boards made using this technology are afraid of shocks and other mechanical loads, as smd components are damaged.
- These components are afraid of overheating when soldering, because they can crack from strong temperature drops. This defect is difficult to detect, it usually appears during operation.
Standard designation of smd resistors
First of all, smd resistors differ in size. The smallest size is 0402, a little more is 0603. The most common size of a smd resistor is 0805, and a larger one is 1008, the next size is 1206 and the largest is 1812. Resistors of the smallest size have the lowest power.
The designation of smd resistors is carried out by a special digital code. If the resistor has a size of 0402, that is, the smallest, then it is not marked in any way. Resistors of other sizes additionally differ in the tolerance of the nominal resistance: 2, 5, 10%. All these resistors are labeled with 3 digits. The first and second of them show the mantissa, the third - the multiplier. For example, code 473 reads like this R=47∙103 Ohm=47 kOhm.
All resistors that have a 1% tolerance and a size greater than 0805 have a four-digit marking. As in the previous case, the firstthe numbers show the mantissa of the denomination, and the last digit indicates the multiplier. For example, code 1501 is decoded as follows: R=150∙101=1500 Ohm=1.5 kOhm. Other codes are read similarly.
The simplest circuit diagram
The correct designation of resistors and other elements on the diagrams is the main requirement of state standards in the design of electronic and electrical products. The standard establishes rules for the conventions of resistors, capacitors, inductors and other circuit components. The diagram indicates not only the designation of a resistor or other circuit element, but also its nominal resistance and power, and for capacitors, the operating voltage. Below is an example of the simplest circuit diagram with elements designated according to the standard.
Knowing all the conventional graphic symbols and reading alphanumeric codes for circuit elements will make it easy to understand the principle of the circuit. In this article, only resistors are considered, and there are quite a few circuit elements.
