PPT on Dynamometers

DynamometersAnand Kumar

ME/13/710Tuesday, May 2, 2023

Dynamometers

Types of Dynamometers

Absorption Dynamometers

Transmission Dynamometers

Conten

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Tuesday, May 2, 2023 2

Dynamometer

Dynamometer is a device to measure the output (brake power) of a prime mover. The power is measured by applying the frictional torque by means of a brake. By knowing the frictional torque, the power of the engine can be calculated.


Types of Dynamometers

Absorption DynamometersI. Prony Brake DynamometersII. Rope Brake Dynamometers Transmission DynamometersI. Belt Transmission DynamometerII. Torsion Dynamometer

Absorption Dynamometers

In these types of dynamometers, the entire power produced by the prime mover is absorbed by the frictional resistance of the brake and is transformed into heat, during the process of measurement

Examples of such dynamometers are • Prony brake dynamometer.• Rope brake dynamometer.

Prony Brake Dynamometer

It works on the principle of converting power into heat by dry friction.

In this method of measuring horsepower is to attempt to stop the engine by means of a brake on the flywheel and measure the weight which an arm attached to the brake will support, as it tries to rotate with the flywheel.




It consists of two wooden blocks placed around a pulley fixed to the shaft of the prime mover, whose power is to be measured. The blocks are clamped by means of two bolts and nuts. A helical spring is provided between the nut and the upper block to adjust the pressure on the pulley to control its speed.


The upper block has a long lever attached to it and carries a weight W at its other end. A counter weight is placed at the other end of the lever that balances the brake when unloaded. Two stops are provided to limit the motion of the lever.



When the brake is to be input in operation, the long end of the lever is loaded with suitable weight W and the nuts are tightened until the prime mover shaft runs at a constant speed and the lever is horizontal position. Under these conditions, the moment due to weight W must balance the moment of the frictional resistance between blocks and pulley.


Rope Brake Dynamometer

It consists of a number of turns of rope wound around the rotating drum attached to the output shaft. One side of rope is connected to a spring balance and the other to a loading device.

The power is absorbed in friction between the rope and the drum. The drum therefore require cooling.

Rope brake is cheap and easily constructed. It is not very accurate because of changes in the friction

coefficient of the rope with temperature.


Rope Brake Dynamometer

The upper end of the ropes is attached to a spring balance while the lower end is kept in position by applying a dead weight. In order to prevent the slipping of the ropes over the flywheel, wooden blocks are placed at intervals around the circumference of the flywheel. . During operation of the brake, the prime mover is made to run at constant speed.


Transmission Dynamometers

In these dynamometers, the energy is used for doing work. The power developed by the prime mover is transmitted through the dynamometers to some other machine where the power is suitably measured.

This type of dynamometer can be classified as follows: • Belt Transmission Dynamometer• Torsion Dynamometer


Belt Transmission Dynamometer

A belt transmission dynamometer consists of driving pulley, rigidly fixed to the shaft of the prime mover. There is another driven pulley mounted on another shaft, to which the power from pulley is transmitted.


Belt Transmission Dynamometer

The pulleys are connected by means of a continuous belt passing round the two loose pulleys, which are mounted on the lever. The lever carries a dead weight at the one end, and a balancing weight is attached at the other end.


Torsion Dynamometer

A torsion dynamometer is used to measure large power developed by a turbine or marine engines. A large number of torsion dynamometers are used to measure the angle of twist.


Engineering

PPT on Dynamometers