# Information About Ohmmeters

An ohmmeter is an electrical instrument that measures electrical resistance, the opposition to an electric current. Micro-ohmmeters (microhmmeter or microohmmeter) make low resistance measurements. Megohmmeters (aka megaohmmeter or in the case of a trademarked device Megger) measure large values of resistance. The unit of measurement for resistance is ohms (Ω). The original design of an ohmmeter provided a small battery to apply a voltage to a resistance. It uses a galvanometer to measure the electric current through the resistance. The scale of the galvanometer was marked in ohms, because the fixed voltage from the battery assured that as resistance is decreased, the current through the meter would increase. Ohmmeters form circuits by themselves, therefore they cannot be used within an assembled circuit.

# How Does an Ohmmeter Work?

• An ohmmeter is an electronic device that measures electrical resistance, such as that of a circuit component. Electrical resistance is a measure of how much an object resists allowing an electrical current to pass through it. Determining electrical resistance can be useful in engineering, to determine how much energy must be supplied to a circuit in order to get it to work as desired. Ohmmeters come with different levels of sensitivity--some are designed to measure low-resistance materials, while others measure higher resistance.

## Ohmmeter Function

• An ohmmeter functions by passing a constant current or voltage though an object, such as voltage from a battery, and then measuring the resulting voltage with an ammeter after it passes through the resistance. The higher resistance the material has, the less current will pass through it. An ohmmeter is typically not used to measure resistance across an entire circuit, but rather through different parts of the circuit, although it can be used to test that a circuit is not broken. Components of a circuit can be removed and tested individually for resistance.

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## Calculating Electrical Resistance

• Ohmmeters work based on the Ohms law, which states that electrical resistance equals the voltage that passes through a resistance divided by the constant current through the resistance. An ohmmeter supplies the constant current and measures the resulting voltage, and then displays the resulting resistance calculation on a gauge based on this principle. Electrical resistance is given in terms of Ohms, a unit which is indicated with the Greek letter Omega. (It looks like a horseshoe with the opening at the bottom.)

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20th Jan 2015

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