De Prony brake

A Prony brake (named after the French engineer Gaspard de Prony 1755-1839 ) is a dynamometer to measure torque. Other designations are wood or brake shoe brake.

It essentially consists of two adjustable brake shoes, which are connected to a rotatable lever ( bars) and usually consist of a dynamometer ( Dynamometer ) or from a load weight. To measure the torque of a drive to said axis, varies the pressure to the brake shoes of the Prony brake or moves and / or increase the weight on the lever arm to the motor is decelerated to the appropriate speed. From the product of the distance between the brake shoe and the mid- point of the weight or dynamometer, the torque at the set speed can be determined:

The mechanical power is calculated from the ratio of work done and the time needed for it. If the duration of a whole revolution, so is the speed and the work done is the product of the force and the length of the path, ie the circumference, and therefore

Since the lever is hard to keep up with balancing weight in balance, you usually determined by the Prony bridle only the starting torque of an electric motor. Here, the rotor of the electric motor is decelerated to a near standstill.