A dynamometer that is made to be driven is called an absorption or passive dynamometer. A dynamometer that can drive and/or absorb is called a universal or active dynamometer, and one that is required to measure how much force would be needed for a machine to operate is called a motoring or driving dynamometer.
Different Kinds of dynamometers include Dry Friction, Hydraulic, Eddy Current. All these dynamometers fall under two main categories: Engine and Chassis Dynamometers.
The engine dynamometers measure power and torque directly from the engine’s crankshaft when the engine is taken out of the vehicle. These do not account for power losses in the drive train. When the dynamometer is connected to the vehicle’s drive wheels, it is called a chassis dynamometer.
The chassis dynamometers on the other hand measure the power delivered to the surface of the drive roller by the drive wheels. This is measured when the vehicle is parked on the rollers, turned on and the output is measured. Chassis Dynamometers are either fixed or portable.
Portable Dynamometers are traditional inertia style dynos and are designed to reliably measure horsepower and torque. This allows the turner to try different modifications on engines and different systems to produce direct results with various accuracies.
Portable dynamometers have different advantages. They are easily mounted in a short period of time, they can be used indoors or outdoors, they have fast torque control, and they are easy to use. Depending on the application, some of the standard equipment used with portable dynamometers are absorber module, trunnion module, housing adapter plate, torque calibration arm, optional equipment, adapter plates for flywheels, engine cooling tower, trunnion module and control and instrumentation systems.