The dynamometer is a machine used to determine the torque of any machine with rotating wheels. Torque is any force which tends to cause rotation around an axis and is measured in revolutions per minute, otherwise known as RPM. During testing, a dynamometer is coupled to a machine while the meter exerts a breaking force in order to calculate the RPM. Two basic types of dynamometers are the absorption or passive dynamometer and the universal or motoring dynamometer. The absorption dynamometer is used for driving purposes while the universal dynamometer is used for both driving and absorption purposes. Within these two categories various types of dynamometers exist for a myriad of applications.
One of the most important types of dynamometers is the engine dynamometer. An engine dynamometer is hooked up directly to the engine of a car in order to measure torque. While there are a variety of engine dynamometer types, the two most popular are the hydraulic and electric configurations. The water break dynamometer is variety of the hydraulic type. A water break is an absorption dynamometer as it can only absorb power and cannot power an engine. This particular dynamometer is connected to the crankshaft of an engine and water is fed into the meter. A rotating blade inside the machine churns the water and creates the needed breaking force against the crankshaft. The power of the engine is determined by the resulting heat of the reaction. The more water injected into the dynamometer, the greater the breaking force.
An AC and a DC are both examples of electric engine dynamometers. A DC dynamometer is simply a direct current motor or generator that converts the energy created by the crankshaft of an engine into electricity. An AC dynamometer is simply an alternating current motor or generator. Both are universal dynamometers as they can both absorb power and power the engine. AC meters are state of the art and more frequently used on racing engines. The DC meter is not adept at measuring and powering a racing engine as it is designed for engines running at lower speeds. Because of this, AC dynamometers are extremely expensive and only a few AC testing facilities exist in the United States.
The eddy current dynamometer is a type of Chassis dynamometer. That is, the instrument measures the twisting motion---and the subsequent power---generated by the wheels of an automobile. This type of dynamometer consists of an iron core or disc which rotates inside a magnetic field. The eddy currents that are subsequently generated act as the breaking force. This type of dynamometer requires an external cooling system to dissipate the heat generated by the breaking force against the apparatus being tested. An eddy current dynamometer is a type of absorption dynamometer as it can only absorb power and not power a machine.
