Understanding Dynamometers and Power Measurement

A dynamometer is a device used to measure torque and rotational speed simultaneously, which allows for the calculation of power. Dynamometers are widely used in testing engines, motors, and other rotating machinery.

There are generally two main types of dynamometers based on how they interact with the power source:

• Absorption Dynamometers: These types absorb the power produced by the engine or motor and convert it into heat, which is then dissipated. Examples include Eddy current dynamometers, hydraulic dynamometers, and prony brakes. They measure the power output at the shaft.
• Transmission Dynamometers: Also known as torque meters, these dynamometers measure the torque transmitted through a shaft without absorbing the power. They are placed inline with the drivetrain. By measuring torque and speed, they can calculate the power being transmitted.

Transmission Dynamometers Measure Brake Power

The power measured by a dynamometer at the output shaft of an engine or motor is called brake power. It represents the actual usable power delivered by the engine or motor after accounting for frictional losses within the engine itself. Transmission dynamometers are designed to measure this transmitted torque and speed, thus measuring the brake power.

Let's look at why other options are generally not measured directly by a transmission dynamometer:

• Alternate power: This is not a standard term in power measurement for engines.
• Indicated power: This refers to the theoretical power developed inside the engine cylinders before accounting for internal friction losses. It is typically calculated from cylinder pressure diagrams (using indicators) and engine speed, not measured directly by a dynamometer on the output shaft.
• Specific power: This term usually refers to power per unit of mass, volume, or area (e.g., power-to-weight ratio). While brake power can be used to calculate specific power, the dynamometer itself measures the absolute brake power.

Therefore, a transmission dynamometer directly measures the torque and speed of the rotating shaft, and from these values, the brake power is calculated.