Mechanical or electrical device for measuring the thrust or torque machines, machine or engine. Depending on the operating principle of dynamometers are divided into two types, brake and transmission; measurements absorb first power unit of the subject, and the second pass it without interfering with the duty cycle. Brake dynamometers are a wide variety of designs; These include, for example, brake Prony, hydraulic and electromagnetic brake. Usually, the engine or mechanism which capacity is determined to some influences shaft, wherein the rotational force to the torque or load cell is measured directly. Thus, as a rule, tachometer measured shaft speed. Comparing the results of these measurements are input or output power of the machine. Shown in Fig. Prony brake 1 has the following elements: drum mounted on the shaft, which is transmitted to be measured power, friction brake, brake lever, and scales.
When you rotate the drum brake friction and the associated brake lever also tend to turn, but it prevents goods whose value is measured by a weight scale, and determines the rotational force on the shaft. According to the results of this measurement and tachometer readings are desired power. Prony brake is used when measuring the characteristics of low-speed engines constant power.
Hydraulic brake can measure the power of high-speed units, for example, large turbines. A special kind of dynamometer is a so-called roller for determining traction or braking forces trucks and cars. Often circuit brake dynamometer includes an electric generator.
It works from the test engine, and its output signal is fed to a set of resistors, which absorb the measured power in electrical form. Measured value of the absorption necessary for resistive loads and determined the required capacity. In the electromagnetic dynamometer brake on the drive shaft associated with the test unit, attached metal disk located between the poles of a magnet with rotary yoke. When the disk rotates between the magnetic poles therein inductive eddy currents resulting from the interaction with the magnetic field which tends to pivot bracket; the force required to hold the bracket from rotating, and determined the unknown quantity.
Electromagnetic dynamometer may be provided in a miniature device suitable for measuring the characteristics of small engines.
Transmission dynamometers. In torsional dynamometer using a strain gauge associated with the elastic drive shaft are measured torsional deformation of the shaft. Deformation alter the electrical resistance strain gauge, and previously calibrated display can obtain readings in the desired units of power. These dynamometers are used in the characterization of marine engines.
Most electric dynamometers is a motor generator DC rotating support. In measurements of the power consumed by the test unit, a dynamometer acts as a motor; base its stator is mounted on bearings and can be rotated, and the rotor is rigidly connected to the rotor mechanism checked. When exposed to a dynamometer to test the stator unit tends to turn after his cage, but hold the lever associated with weights; rotational speed is determined tachometer. If the measured power output of any engine, the electric dynamometer operates as an electric generator. Electric dynamometer is used to measure the characteristics of low-power machines; they are easily rearranged, just changing the speed of rotation or the value of the output of the DUT load.
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