What is a Dynamometer?
A dynamometer is a device used for measuring force, moment of force (torque), or power. For example, the power produced by an engine, motor or other rotating prime mover can be calculated by simultaneously measuring torque and rotational speed (rpm).
A dynamometer is also used to determine the torque and power required to 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 or passive dynamometer. A dynamometer that can either drive or absorb is called a universal or active dynamometer.
In addition to being used to measure the torque or power characteristics of a machine under test (MUT), dynamometers are employed in a number of other roles. In standard emissions testing cycles, dynamometers are used to offer simulated road loading of either the engine (using an engine dynamometer) or full powertrain (using a chassis dynamometer). Actually, beyond simple power and torque measurements, dynamometers can be used as part of a testbed for a variety of engine development activities such as the calibration of engine management controllers and detailed investigations into combustion behaviour.
In an engine dynamometer, water flow, proportional to the preferred applied load, creates resistance to the engine. A controlled water flow through the inlet manifold is directed at the centre of the rotor in each absorption section. This water is then expelled to the outer dynamometer body by centrifugal force. As it is directed outward, the water is accelerated into pockets on the stationary stator plates where it is decelerated. The continual acceleration and deceleration causes the dynamometer to absorb the power produced by the engine. Through this transfer of energy the water is heated and discharged.
An important component of a dynamometer is its data acquisition system. The system is typically comprised of two units (a Commander and Workstation), connected by an Ethernet cable. The Commander, a desktop computer operated by Windows-based software, allocates commands to the Workstation, a touch-screen operated unit in a rugged industrial enclosure. The Workstation operates the precision load and throttle control systems, collects the data, and sends it to the Commander to be processed, stored and analysed.
The Workstation’s success, and therefore the data acquisition system’s accuracy, depends on its ability to correctly measure data in the dynamometer tests. Central to these measurements is the precision of its pressure transducers, which measure airflow in the intake manifold, oil pressure and other fluid pressures. The operator is interested in different pressures of fluids so having the capability of bringing in different pressures while running the engine is very important.
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