All types of resistors have their own resistor symbols which are used when a circuit diagram is drawn. This page will explain the different standards which are used for resistor symbols and display the most common symbols. Standards for resistor symbols Several standards exist, which describe how the different components should be displayed. In the past a lot of countries or even industries used their own standards, which can be confusing. Nowadays the IEC 60617 standard is international standard for these electronic symbols. However the local standards are still used from time to time. In general, the ANSI standard is still common in the United States. Some examples of standards which describe resistor symbols: IEC 60617 (International) ANSI Y32 / IEEE 315 (US) – old DIN 40900 (Germany) – old AS 1102 (Australia) – old Sometimes the symbol for a particular device is different when it is used in another field of application. Other symbols are used in electronics then for example in architecture and buildings. On top of this, many local deviations from the international standards exist. The following table shows the most common resistor symbols for electronics design. Schematic symbols Type Abbreviation IEC (International) ANSI (US) Fixed resistor R Heating resistor Variable resistors VR Potentiometer Trimming potentiometer Rheostat Preset resistor Dependent resistors Photo resistor orLight dependent resistor LDR Varistor or Voltage dependent resistor VDRRVMOV NTC thermistor NTCRT PTC thermistor PTCRT Magneto resistor orMagnetic dependent resistor MDR Read more in the Resistor Guide E-Book.
Standard resistor values In 1952 the IEC (International Electrotechnical Commission) decided to define the resistance and tolerance values into a norm, to ease the mass manufacturing of resistors. These are referred to as preferred values or E-series, and they are published in standard IEC 60063:1963. These standard values are also valid for other components like capacitors, inductors and Zener diodes. The preferred values for resistors were established in 1952, but the concept of the geometric series was already introduced by army engineer Renard in the 1870s. The standardization of resistor values serves several important purposes. When manufacturers produce resistors with different resistance values, these end up approximately equally spaced on a logarithmic scale. This helps the supplier to limit the number of different values that have to be produced or kept in stock. By using standard values, resistors of different manufacturers are compatible for the same design, which is favorable for the electrical engineer. Aside from the preferred values, many other standards related to resistors exist. An example is standard sizes for resistors, or the marking of resistors with color codes or numerical codes. Power ratings of resistors are not defined in a norm, therefore often is deviated from the above described series. Preferred values or E-series As basis the E12 has been developed. E12 means that every decade (0.1-1, 1-10, 10-100 etc) is divided in 12 steps. The size of every step is equal to: One could also say every value is 21% or 1.21 times higher than the last, rounded to whole numbers. Because of this, all resistors with a tolerance of 10% overlap. The series looks as follows: 1– 1.2 – 1.5 – 1.8 – 2.2 – 2.7 – 3.3 – 3.9 – 4.7 – 5.6 – 6.8 – 8.2 – 10 etc. All these values [… read more]
Standardization is a key element in the design of electronic components. A huge amount of effort and money is saved by having standards for resistor sizes, values, markings, symbols and measurement methods. Although international standards like the IEC (International Electrical Commission) and national standards such as ANSI (American National Standards Institute) are widely accepted, resistor manufacturers often use their own definitions. Therefore it is always important to carefully check the manufacturers’ documentation. Resistor color code Practically all leaded axial resistors up to one watt are marked with the electronic color code (international standard IEC 60062). The resistor color code is a marking system with colored bands that are painted on the resistor body. Together they indicate the resistor value and tolerance. Resistors can have 3, 4, 5 and 6 bands. The resistor color code chart is a handy table to decipher the coding system. Resistor color code calculator This interactive tool let’s you adjust a resistor within seconds and returns the resistance value, tolerance and temperature coefficient. It even indicates if the resistor belongs to an E-series (preferred values). Resistor SMD code SMD (Surface Mount Device) resistors are marked with a (alpha)-numerical code to indicate the resistor value and tolerance. Often these resistors are too small for the resistor color code. Two popular marking systems exist: the 3 and 4 digit code and the EIA-96 code. Resistor values Soon after resistors became mass produced, a system with preferred values was developed to minimize the number of different sizes that had to be produced. Now preferred values for resistors and other electronic components are defined in the international standard IEC 60063. The preferred values for electronics are defined in E-series. Resistors are manufactured with a certain tolerance. The preferred value system is set up that each the tolerance of each resistor [… read more]