How a Dynamometer Works

A dynamometer is a device that can measure force or speed. Dynamometers come in several different types and are often used in automotive applications to determine how much power is available, or needed, from an engine.

Inertia

Inertia dynamometers measure the speed of objects -- large, free-spinning barrels -- that are spun by the wheels as a vehicle accelerates. They work in conjunction with a computer to precisely measure horsepower.

Hydraulic

Hydraulic dynamometers consist of one or more large drums that, in conjunction with a hydraulic braking system, apply varying levels of resistance to the driveline. A load cell, used as a brake, also measures the torque applied to the wheels, from which the horsepower of the vehicle can be calculated.

Electromagnetic

The speedometer in a motor vehicle is an example of an electromagnetic dynamometer. A metal disc connected to the wheels rotates a magnet inside a metal cup. The movement induces opposing electromagnetic currents in the cup, so it rotates and moves the speedometer needle.

References

• Explain That Stuff: Dynamometers
• Drag Source: Inertia Dynamometer
• Drag Source: Hydraulic Dynamometer