In a previous article the resistors basic principles have been described and their classification, according to the use and structure, has been shown. Here following we will discuss about their classification according to the configuration, application and colours code.

Classification according to the configuration

Resistors can be classified, according to the used configuration, in the following categories:

Chip resistors: They are generally standard, passive components that are helpful for derating voltage and current controlling and they are used in integrated circuits (IC) to allow an high integration. A thin film technology is used for their manufacturing and their composition can be made from different materials: a powdered carbon and a resin binder is used for the carbon composition ones, ceramic and metallic materials for the cermet ones. Chip resistors like metal alloy, metal foil, metal film, tantalum and wirewound can be also found in the market. Lately the demand for high precision chip resistors has increased, especially for the ones with low resistance and small temperature coefficient of resistance. Another configuration is the array one: a resistor chip array includes many resistors in a single package.

Pictures courtesy of Vishay Electronic Company

Resistor - Capacitor (RC) networks: They are integrated circuits that include, in a single chip, resistor - capacitor arrays. Four basic technologies are used for their manufacturing : wirewound, thin film, metal film and thick film. While the wirewound RC networks are simple, in fact they are often wound by hand, the other ones are more complex. In the thin film technology, for example, a thin layer of semiconductor or magnetic material is deposited over a ceramic, metal or semiconductor base. This technology is preferred in the applications that require low noise levels, good stability and high class performances at very high frequencies. The metal film technology is used in simple circuit, the thick film one is used for its good reliability, low cost, low weight and circuits miniaturization. The RC networks specification parameters include the power rating, the capacitance, the temperature coefficient, the resistance and the resistance tolerance that is the percentage deviation from a nominal resistance value. The RC networks are generally used to eliminate the electromagnetic interference and radio frequency interference at the I/O ports of a PC and its peripherals, workstations etc.

RC network - Picture courtesy of RCD

Resistor-Capacitor- Diode (RCD) networks: They are built on silicon substrates using the thin film technology that allows a very good performances at high frequencies. They are excellent for high speed- frequency data and communication applications, supplying very good performances, reducing significantly cost and space. The integrated RC networks, at higher frequencies, are better than standard RC networks for reliability, for mechanical and electrical performances and stability.

Current Sensing Resistors (CSR): They transform the current flowing through them in a voltage fall. Measuring this voltage fall allows the current through the resistor to be measured. The construction materials and the configuration styles are parameters that must be considered for their realization. Materials comprise carbon film, carbon composition, metal film, metal alloy, ceramic composition, thin film, thick film and wirewound. About the configuration styles we must consider the single resistor, the resistors network and the resistor chip array. The CSR specification parameters include : the resistance range measured in Ohm, the power rating that is the maximum power level that a CSR supports, the tolerance specified as percentage, the continuous operating voltage measured in volts, the operating temperature, the temperature coefficient parameter that measures the rate at which the nominal resistance value changes as a temperature function, the terminal numbers.

Current sensing resistors - Courtesy of CTS

Classification according to the application

Resistors can be classified, according to the used application, in many categories. Here following we will describe briefly some of them.

Automotive: Resistors are largely used in the automotive area. They are used in the: Body Control Systems; Drive Train & Starter/Alternators; DC/DC Converters; Lighting Supplies; Engine Management & Ignition/Injection Systems; Electrical Replacement of Mechanical Functions; Hybrid/Electric Vehicles. Metal film series, by Welwyn Components for example, are suitable to all the above mentioned automotive areas. They have a power rating, at 70°C, from 0.4 to 0.75 Watt, a limiting element voltage from 200 to 350 Volts, tolerances down to 0.5% , a temperature coefficient down to 50 ppm/°C. To learn more @: http://www.welwyn-tt.com/pdf/datasheet/MFR.PDF

MFR series - Courtesy of Welwyn Components

Aerospace: Last September Vishay Intertechnology has launched in the market the new VPR221Z ultra-high-precision Z-Foil resistor. This resistor, in TO-220 configuration, has a TCR (Temperature Coefficient of Resistance) of ± 0.05 ppm/°C, a PCR (Power Coefficient of Resistance) of 4 ppm/W and Load Life Stability of ± 0.005 % (50 ppm). To learn more @: http://www.vishay.com/docs/63116/vpr221z.pdf

VPR221Z - Courtesy of Vishay Int.

Medical: In the medical area the resistors are used in the : Defibrillator Charge Control; Defibrillator Pulse Protection; ECG High Gain Amplification; X-Ray Supply; Ultrasound & MRI (Magnetic Resonance Imaging) Scanners. Precision Measurement VSMP series, by Vishay Int., is based on Bulk Metal Foil Technology. These resistors are excellent for applications that require high precision and stability. They have TCR: ± 0.2 ppm/°C typical, PCR: 5 ppm at rated power, Load Life Stability (70°C for 2000 hours): ± 0.005%. To learn more @: http://www.farnell.com/datasheets/71876.pdf

VSMP series top view

High Voltage resistors: Nicrom Electronic, by its thick film technology, can reach tolerances until 0.05 %, temperature coefficients better than 10 ppm/°C, voltage coefficients lower than 0.003 ppm/V and stability less than 0.1-0.2% after 1000 hours at rated power. Its resistors, in the new serie 1000, can arrive up to 400 kV in air. To learn more @: http://www.nicrom-electronic.com/Serie_1000.pdf

Precision resistors: HR/ HVA/HVS ultra precision resistors, made by PRC, have values from 0.1Ω to 10 MΩ , tolerances from ± 0.01 % to 0.005 %, stability until ± 0.001 % year at 25°C, temperature from -65°C to 125°C. To learn more @:
http://pdf.directindustry.com/pdf/precision-resistor/prc-2008-product-ca...

Precision resistors - Courtesy of PRC

Surge Resistors: STEC-028 surge resistor, Supertech Electronic manufacturer, can suffer until a 10kV discharge current. To learn more @ : http://supertech.manufacturer.globalsources.com/si/6008800039268/pdtl/Me...

STEC - 028 / Courtesy of Supertech Elect.

Telecom resistors: RK73 is a series of resistors that targets high performance telecommunication applications. RK73-RT (flat chip resistors ) is the last update release. These resistors have an optimum anti-sulfuration characteristic, very good heat and weather resistance, high stability and reliability due to the triple-layer structure of electrode. To learn more @: http://www.koaspeer.com/pdfs/res68.pdf

RK73-RT Series / Courtesy of KOA

Avionics: The electronics equipments installed in the planes and dedicated to their driving are indicated by the "avionics" term. The TMC series thick film chip resistors meets both avionics and military high reliability requirements, including aerospace systems, weapon systems, aircraft and communication equipment. This series has a failure rate of 0.01% or even less. To learn more @: http://news.thomasnet.com/companystory/516311

TMC thick film chip resistor - Courtesy of IRC

Classification according to the colours code

Resistors can be classified, according to their resistive value, by a sequence of coloured rings that can be 4 for the standard ones, 5 ÷ 6 for the precision ones.

Standard resistors: In these resistors the first and second ring are the resistive value, the third is the multiplier, the fourth is the tolerance.

Precision resistors: In these resistors the first, second and third ring are the resistive value, the fourth is the multiplier, the fifth is the tolerance and the sixth is the temperature coefficient.

SMD resistors: They have printed a number with three digits: the first and second digit indicate the resistive value, the third indicates the numbers of zero to be added. For example: 211 = 2-1-0 = 210 Ω .

At every colour is associated a number, as you can see in the below table :

To read the resistive value correctly it is better to put the tolerance values (generally gold) on the right. Let's finish this subject reading the resistive value of the below resistor:

the first ring (starting on the left) is brown =1; the second ring is black = 0; the third ring is black = 0; the fourth ring (the multiplier) is brown = 10; the fifth ring (the tolerance) is brown = ± 1%. So the resistive value is 1-0-0 x 10 = 1000 = 1k Ω with tolerance of ± 1 %.

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Read the Italian version: Elettronica di base: Resistori parte II

Read also: Base Electronics: Resistors Configuration