Dynamometer, or “dyno” for short, is a device for measuring force, moment of force or power. For example, the power produced by an engine, motor or other rotating prime mover can be calculated by simultaneously measuring torque rotational speed (rpm).

A Dynamometer consists of an absorption (or absorber/driver) unit, means for measuring torque and rotational speed. An absorption unit consists of some type of rotor in a housing. This rotor is coupled to engine or other equipment under test, free to rotate at whatever speed is required for test. Some means is provided between this rotor and housing of dynamometer. This means for dynamometer developing can be frictional, hydraulic, electromagnetic, or otherwise, according to type of absorption/driver unit.

One means measuring is to mount Dynamometer housing so that its free for turn except as restrained by torque arm. The housing can be made free to rotate by using trunnions connected each end of the housing to support it in pedestal-mounted trunnion bearings.

The torque arm is connected to dynamometer housing and weighing scale is positioned so that it measures the force exerted by dynamometer housing in attempting to rotate. The torque is force indicated by scales multiplied by the length of the torque arm measured from center of the dynamometer. A load cell transducer can be substituted for the scales in order to provide an electrical signal that is proportional to torque.

Another means to measure torque is connect engine to dynamometer through a torque sensing coupling or torque transducer. A torque transducer provides an electrical signal that is proportional to the torque.With electrical absorption units, its possible determine torque by measuring the current drawn (or generated) by absorber/driver. This is generally less accurate method and not much practiced in modern times, but it may be adequate for some purposes. When torque and speed signals are available, test data can be transmitted a data acquisition system rather than being recorded manually. Speed and torque signals can also be recorded by a chart recorder orplotter.

Dynamometer can also be used to determine the torque and power required operate a driven machine such as a pump. In that case, a motoring or driving dynamometer is used. A dynamometer that is designed to be driven is called an absorption passive dynamometer. A dynamometer that can either drive or absorb is called a universal or active dynamometer.

In addition to being used to determine the torque or power characteristics of a machine under test (MUT), dynamometers are employed in number of other roles. In standard emissions testing cycles such as those defined by US Environmental Protection Agency (US EPA), dynamometer are used to provide simulated road loading of either engine (using an engine dynamometer) or full powertrain (using a chassis dynamometer).

In fact, beyond simple power and torque measurements, dynamometers can be used as part of a testbed for variety of engine development activities such as calibration of engine management controllers, detailed investigations into combustion behavior.

Common applications for dynamometers include general purpose, automotive, aircraft or aerospace, chain or belt drives, gearboxes, fluid power systems gas or diesel engines, industrial, marine, transmissions, and turbines. All dynamometer will typically have speed and power feedback for performance testing and monitoring. Typical features include encoders other speed / position sensors, torque arms, reaction sensors. Common dynamometer interfaces include integral control console, separate console, computer, modem or remote control. Features common to dynamometers include PID control, flow control or throttling, data acquisition, logging, alarms, motor power analysis, and engine exhaust analysis

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