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A fixed resistor reduces electricity flow and is measured in Ohms. Resistor size ranges from pin to book size. There are two types of fixed resistors: carbon and metal film. When selecting a resistor, consider its value, tolerance, and wattage. Metal film resistors have higher accuracy but cost more. Consider the intended use of the circuit and test before installation.
A fixed resistor is part of an electrical circuit and is used to reduce the flow of electricity. Resistance is measured in Ohms and is typically shown as a number and then as a unit; for example, a 750 ohm resistor would be written as 750 ohms. Resistor size is based on the number of Ohms and can range from pin size to book size.
Resistors are of two classes: fixed and variable. A fixed resistor is set to a specific value and cannot be changed. A variable resistor is capable of handling fluxes at a specific level and lower. This is an important distinction and determines when and where to use a resistor.
When selecting a resistor, it is important for a person to consider three things: the value of the resistor, its tolerance, and its wattage. The value is measured in Ohms. Tolerance indicates the upper and lower limits of actual performance, measured as a plus and minus percentage. For example, a tolerance of 10% means that the resistor operates within a range of 10% of the resistance value listed in the specification.
The power rating shows the upper limit of the power that the resistor can handle and is measured in watts. To calculate power, a person can multiply the resistor’s resistance value by the square root of the current. If the rated power is exceeded, the resistor will fail. A rule of thumb is to use a resistor with a power rating of twice the actual power needed.
There are two types of fixed resistors: carbon and metal film. Carbon film resistors are designed for general use and are fairly cheap to manufacture and purchase. These units have a tolerance of 5%, with power ratings of 1/8 Watt (W), 1/4 W and 1/2 W. The main problem with this type of resistor is the fact that they generate electrical noise.
A metal film resistor is best used when a higher tolerance is required. These units have a higher level of accuracy than carbon film resistors due to the nature of the materials used. There is a corresponding price increase, but it may be worth increasing the cost to protect the other components in the circuit.
When looking at the different types of resistors, people should think about the intended use of the circuit. They should select a manufacturer with a good reputation for quality and consistency, and take the time to test the resistor and circuit before installation to ensure all specifications are correct.
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