Measurement of resistance is an important aspect of electrical and electronic engineering. Resistance is a fundamental property of a material or component that opposes the flow of electric current. It is measured in ohms (Ī©) and is denoted by the symbol "R."
There are various methods and instruments used to measure resistance accurately. Some of the common methods include:
Ohm's Law Method: This is a basic method where Ohm's law (V = IR) is used to measure resistance. A known voltage (V) is applied across the resistor, and the current (I) passing through it is measured using an ammeter. The resistance can then be calculated using Ohm's law (R = V/I).
Wheatstone Bridge: The Wheatstone bridge is a widely used method for precise measurement of resistance. It consists of four resistors arranged in a diamond shape with a voltage source connected across two opposite corners and a galvanometer connected across the other two corners. By adjusting the ratio of the resistors, the bridge can be balanced, and the unknown resistance can be calculated.
Potentiometer Method: A potentiometer is a device that measures an unknown voltage by comparing it with a known voltage. It can also be used to measure resistance by using a known resistance and adjusting the potentiometer until the voltage across the unknown resistance matches a reference voltage.
Digital Multimeter (DMM): A digital multimeter is a versatile instrument that can measure various electrical quantities, including resistance. It works by passing a known current through the resistor and measuring the resulting voltage drop. The resistance is then calculated using Ohm's law.
Four-Wire (Kelvin) Method: This method is used to accurately measure low resistances, typically below 1 ohm. It eliminates the effects of lead resistance by using separate current and voltage sensing wires. The current is passed through the resistor using one pair of wires, while another pair of wires measures the voltage across the resistor.
Megohmmeter (Insulation Resistance Tester): Megohmmeters are used to measure high resistances, particularly for insulation testing. They apply a high voltage to the component and measure the resulting current to determine the resistance.
When performing resistance measurements, it's essential to consider factors such as temperature, contact resistance, and lead resistance, which can affect the accuracy of the measurement. Calibration and compensation techniques are often employed to mitigate these effects.
Keep in mind that advancements in technology may have introduced new methods or improvements to existing techniques beyond my last knowledge update in September 2021.