dynamometer(redirected from dynamometric)
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a device for measuring force or moment; it consists of a force component (elastic element) and a reading device. In the force component, the force to be measured is converted to a deformation, which is transmitted to the reading device directly or through a gear mechanism. Dynamometers can measure forces ranging from several newtons (fractions of a kilogram-force) to 1 meganewton (100 tons-force). According to their principle of operation, a distinction is made among mechanical (spring or lever), hydraulic, or electrical dynamometers. Two principles of operation are sometimes used in the same dynamometer. Dynamometers are distinguished according to purpose as reference and operational (general-purpose and special) types.
Reference dynamometers are intended for testing and calibrating operational dynamometers and for monitoring the stresses of machines during the testing of the mechanical properties of various materials and products. Reference dynamometers are categorized as first-class, second-class, or third-class according to their degree of accuracy. First-class dynamometers are designed for checking second-class reference dynamometers, which in turn are used for testing and calibrating third-class dynamometers and for checking general-purpose dynamometers. Third-class dynamometers are used for checking and calibrating testing machines and devices; they are built with elastic elements in the form of locking clamps of the bending-strain type and locking clamps or bars that undergo compressive or tensile strain.
General-purpose operational dynamometers are used for measuring the tractive force of farm and truck tractors, locomotives, and oceangoing and river tugboats (drawbar dynamometers), as well as for determining the forces that develop in structures and machinery during the application of external forces. Special-purpose operational dynamometers are used for determining torque moments, the pull force of aircraft and hydraulic propellers, braking forces, and cutting and feed forces. In metal-cutting lathes and similar machines they are often not separate devices but are incorporated into a complex of testing devices (dynamometric insert, dynamometric wheel, and so on). Operational dynamometers are divided into two classes according to their accuracy: the first class has an error of ±1 percent, and the second class has an error of ±2 percent (of the limiting value of the load). Dynamometers with recording devices are called dynamographs, and dynamometers with reading or indicating devices are called gauges.
Electrical dynamometers, which consist of a transducer to convert the deformation to an electric signal and a secondary device to amplify and record the signal, are the most promising types. Resistance (tensoresistance), inductance, piezoelectric, and vibration-frequency transducers are used. The most widely used type is the resistance transducer, with an elastic element and tensoresistance grids. When a load is applied, the elastic element and the tensoresistance grids are deformed, causing an imbalance in the currents of the resistance bridge to which the grids are connected. The signal is amplified and recorded by the secondary device, which has a scale graduated in units of force.
Medical dynamometers are designed for measuring the force of various muscle groups in the human body. In some medical dynamometers the measurement of the force is based on the compression of a metal spring connected to a dial indicator. Mercury, hydraulic, electrical, and pendulum medical dynamometers are also used. The multidynamometer machine developed by A. V. Korobkov and G. I. Cherniaev, which makes it possible to isolate the action of various muscle groups and to measure their force under equal conditions, is widely used.
REFERENCESMalikov, G. F., A. L. Shneiderman, and A. M. Shulemovich. Raschety uprugikh tenzometricheskikh elementov. Moscow, 1964.
Osokina, A. P. Tipizatsiia ispytatel’nykh mashin i vesoizmeritel’nykh priborov. Moscow, 1965.
S. I. GAUZNER