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An electric torque wrench is a planetary torque multiplier or a "Gearbox" mated to an electric motor. At the end of the "gearbox" is a reaction device that is used to absorb the torque. This allows the operator of the tool to use the electric torque wrench with very little effort.
These tools are primarily used anywhere accurate torque is required on a nut and bolt, or where a stubborn nut needs to be removed.
These planetary torque multiplier gearboxes have multiplication ratios up to 4000:1. The correct torque output is adjusted by controlling the voltage.
The tool has an internal computer that shuts off the voltage at a certain level that is adjusted by the operator of the tool. Because of the internal electronics, the electric torque wrench can operate from 110 or 220 volts. It can adjust in an instant up to 253 volts. Since the tool is operated by electricity, there is a waterproof version of the electric torque wrench available.
One benefit of the electric torque wrench is that it plugs into any wall outlet. Also, it runs virtually silently.
The electric torque wrench is sometimes confused with a standard impact wrench, because it looks similar, but it actually a totally different tool. An electric torque wrench is driven by continuous gearing, and not by the hammers of an impacting wrench. This is why an electric torque wrench has very little vibration, and an extreme amount of repeatability and accuracy. The electric torque wrench was first patented in Germany in 1984 by Alkitronic.
Electric torque wrenches have different models capable of 65Nm up to a max of 42,160Nm.