Rotational Speed (Rev) is the number of turns (which are different from the frequency) that are rotated around the center of the circle in a unit of time. Common speeds include rated speed and maximum speed.
The speed is expressed in revolutions per minute. The unit is expressed as RPM. RPM is the abbreviation of Revolutions Per minute, which is transfer/minute.
It is represented by the symbol "n"; its international standard unit is rps (rev / sec) or rpm (rev / min).
Motor tachogenerators are widely used in a variety of speed or position control systems. In the automatic control system, it is used as a component for detecting the speed of the motor to adjust the motor speed or feedback to improve the stability and accuracy of the system. It can be used as a differential or integral component in the solving device, or as an acceleration or delay signal. To measure the speed of various moving machinery in swinging or rotating and linear motion. Motor speed measuring generators are divided into DC and AC.
DC motor tachogenerators are available in both permanent magnet and electromagnetic versions. Its structure is similar to that of a DC generator. The permanent magnet type is excited by high-performance permanent magnet, which is less affected by temperature change, small output change, high slope and small linear error.
The electromagnetic type adopts the other excitation type, which is not only complicated but also affected by factors such as power supply and environment, and the output voltage changes greatly and is not used much. The DC motor tachogenerator made of permanent magnet material is also divided into a limited angle motor tachogenerator and a linear motor tachogenerator. They are used to measure the speed of rotation or linear motion, respectively, and their performance requirements are similar to those of DC motor tachogenerators, but the structure is somewhat different.
The AC motor speed measuring generator has three types: hollow cup rotor asynchronous motor speed measuring generator, cage rotor asynchronous motor speed measuring generator and synchronous motor speed measuring generator.
1 Hollow cup rotor asynchronous motor tachogenerator: mainly composed of inner stator, outer stator and cup rotor rotating in the air gap between them. The field winding and the output winding are embedded on the stator and are 90 degrees apart from each other in space. The cup rotor is made of a non-magnetic material. When the rotor does not rotate, the magnetic field generated by the cup rotor current after excitation is perpendicular to the output winding axis, and the output winding does not induce the electromotive force; when the rotor rotates, the magnetic field generated by the cup rotor coincides with the output winding axis, in the output winding. The magnitude of the induced electromotive force is proportional to the rotational speed of the cup rotor, and the frequency and the excitation voltage frequency are the same regardless of the rotational speed. The output voltage phase is reversed when inverted. The cup rotor is the key to transmitting signals, and its quality plays a big role in performance. Because its technical performance is superior to other types of AC motor tachogenerators, its structure is not very complicated, and its noise is low, no interference and small volume. It is the most widely used AC motor tachogenerator.
2 Cage rotor asynchronous motor tachogenerator: similar to the AC servo motor, because the linearity of the output is poor, it is only used in occasions where the requirements are not high.
3 synchronous motor tachogenerator: an alternator with a permanent magnet as the rotor. Since the output voltage and frequency change simultaneously with the rotational speed, the direction of rotation cannot be discriminated, and it is inconvenient to use, and is rarely used in the automatic control system, and is mainly used for direct measurement of the rotational speed.
