In electrical circuits, resistors are used to adjust the current. A huge number of different types are produced. To determine the whole variety of details, a symbol for the resistor is introduced for each. They are marked in various ways, depending on version.
Resistor Types
A resistor is a device that has electrical resistance, its main purpose is to limit the current in the 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. By appointment, they are divided into two types: general and special use. The latter are divided according to purpose into precision, high-resistance, high-voltage and high-frequency.
- Variable resistors (also called adjusting resistors). They have the ability to change the resistance using the control knob. In terms of design, they are very different. There are combined, with the switch, dual, built (that is, two or three resistors are installed on the same axis) and many other varieties.
- Trimmer Resistors. They are used only during the configuration of a technical device. The tuning bodies are available only for screwdrivers. A large number of different modifications of these resistors are produced. They are used in all kinds of electrical and electronic devices, ranging from tablets to large industrial plants.
Some types of resistors considered are shown in the photograph below.
Classification of components by installation method
There are 3 main types of installation of electronic components: mounted, printed, and for micromodules. Each element is designed for its own elements, they vary greatly in size and design. For surface mounting, resistors, capacitors and semiconductor devices are used. They are available with wire leads so that they can be soldered into the circuit. In connection with the miniaturization of electronic devices, this method is gradually losing its relevance.
For printed wiring, more small-sized parts are used, with conclusions for soldering into the
printed circuit board or without them. To connect to the circuit, these parts have pads. Printed installation significantly contributed to the reduction of the size of electronic products.
For printed and micromodular wiring, smd resistors are often used. They are very small in size, easy to integrate automatically in the circuit board and micromodules. They are available in various nominal resistance, power and size. The latest electronic devices mainly use smd resistors.
Nominal resistance and power dissipation of resistors
The nominal resistance, expressed in ohms, kilo-ohms or megaohms, is the main characteristic of a resistor. This value is given on the circuit diagrams, applied directly to the resistor in the alphanumeric code. Recently, the color designation of resistors has often been used.
The second most important characteristic of a resistor is power dissipation, it is expressed in watts. When a current passes through it, any resistor heats up, that is, it dissipates power. If this power exceeds the permissible value, the destruction of the resistor occurs. According to the standard, the designation of the power of resistors in the circuit is almost always present, this value is often applied to its body.
Nominal resistance tolerance and temperature dependence
Of great importance is the error, or deviation from the nominal value, measured in percent. It is impossible to exactly manufacture a resistor with the declared resistance value, there will certainly be a deviation from the given value. The error is indicated directly on the case, often in the form of a code of colored stripes. It is estimated as a percentage of the nominal resistance value.
Where there are large temperature fluctuations, the dependence of the resistance on temperature, or the temperature coefficient of resistance, is abbreviated , the abbreviation is TKS, measured in relative units ppm / ° C. TKS shows how much of the nominal resistance of the resistor changes if the temperature of the medium increases (decreases) by 1 ° C.
Conventional graphic designation of the resistor in the circuit
When drawing schemes, compliance with the state standard GOST 2.728-74 for conventional graphic symbols (UGO) is required. The designation of any type of resistor is a 10x4 mm rectangle. Based on it, graphic images are created for other types of resistors. In addition to UGO, the designation of the power of resistors in the circuit is required, this facilitates its analysis when troubleshooting. The table below shows the UGO of constant resistance with indication of power dissipation.
Below the photo shows the constant resistors of different capacities.
Conditional graphic designation of variable resistors
UGO of variable resistors are applied to the circuit diagram in the same way as constant resistors, according to the state standard GOST 2.728-74. The table shows an image of these resistors.
The photo below shows the variable and tuning resistors.
Standard designation of resistor resistance
By international standards, it is customary to denote the nominal resistance of a resistor on the circuit and on the resistor itself in slightly different ways. The rules of this designation along with sample examples are given in the table.
| Full designation | Abbreviation |
| unit of measurement | Identification units rev. | Nominal limit. resistance | on the diagram | on the case | Nominal limit. resistance |
| Ohm | Ohm | 999.9 | 0.51 | E51 or R51 | 99.9 |
| 5.1 | 5E1; 5R1 |
| 51 | 51E |
| 510 | 510E; K51 |
| Kilohom | kohm | 999.9 | 5,1k | 5K1 | 99.9 |
| 51k | 51K |
| 510k | 510K; M51 |
| Megaom | Megohms | 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 resistor case, it is customary to use the letter instead of a comma in the digital designation, if it is ohms, then E or R is put, if it is kilo, then the letter K. When designating megaohms, the letter M is used instead of the comma
Resistor color coding
The color designation of the resistors was adopted to make it easier to put information about the technical specifications 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 stripes. Each of them has its own specific meaning. The color code of the resistor is applied from the edge, with a low accuracy (20%) 3 strips are applied. If the accuracy is higher, 4 strips can already be seen on the resistance.
With high accuracy, 5-6 strips are applied. For markings containing 3-4 strips, the first two indicate the value of resistance, the third strip is the 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 resistance. The next bar is the multiplier, the 5th bar corresponds to accuracy, and the 6th bar corresponds to the temperature coefficient.
For decoding color codes of resistors, reference tables exist.
Surface Mount Resistors
Surface mounting is when all the parts are located on the circuit board from the side of the printed tracks. In this case, the holes for mounting the 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 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 superseded all other types.
With all the advantages of this installation, it has several disadvantages.
- Printed circuit boards made using this technology are afraid of shock and other mechanical stresses, as this will damage the smd components.
- These components are afraid of overheating during soldering, because they can crack from strong temperature changes. This defect is difficult to detect, it usually manifests itself during operation.
Standard Designation for 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 the smd resistor is 0805, and larger is 1008, the next size is 1206 and the largest is 1812. The smallest size resistors also 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 of these resistors are 3-digit marked. The first and second of them show the mantissa, the third - the multiplying factor. For example, code 473 reads as follows: R = 47 ∙ 10 3 Ω = 47 kΩ.
All resistors that have a 1% tolerance and a frame size greater than 0805 are marked with four numbers. As in the previous case, the first digits indicate the nominal mantissa, and the last digit indicates the multiplier. For example, the code 1501 is decoded as follows: R = 150 ∙ 10 1 = 1500 Ohms = 1.5 kOhm. The rest of the codes are read in the same way.
The simplest circuit diagram
The correct designation on the diagrams of resistors and other elements is the main requirement of state standards in the design of electronic and electrical products. The standard establishes rules for the designation of resistors, capacitors, inductances and other circuit components. The diagram shows not only the designation of the resistor or other circuit element, but also its nominal resistance and power, and for capacitors - the operating voltage. The following is an example of a simple circuit diagram with elements designated by standard.
Knowing all the conventional graphic symbols and reading alphanumeric codes to circuit elements will make it easy to understand the principle of operation of the circuit. In this article, only resistors are considered, and there are a lot of circuit elements.