Prony Brake Dynamometer
The simplest form of absorption type dynamometer is a pony brake dynamometer, as shown in fig. It consists of two wooden locks placed around a pulley fixed to the shaft of an engine whose power is required to be measured.
Prony Brake Dynamometer Diagram
A counterweight is placed at the other end of the lever which balances the brake ' when unloaded. Two stops S, S are provided to limit the motion of the lever. When the brake is to be put in operation, the long end of the lever is loaded with suitable weight W and the nuts are tightened until the engine shaft runs at a constant speed and the lever is in a horizontal position. Under these conditions, the moment due to the weight W must balance the moment of the frictional resistance between the blocks and the pulley.
From the above expression, we see that while determining the brake power of the engine with the help of a pony brake dynamometer, it is not necessary to know the radius of the pulley, the coefficient of friction between the wooden blocks, and the pressure exerted by tightening of the nuts.