How does the photoelectric encoder disk measure the speed of the motor? What are the characteristics?
 
The methods of speed measurement are divided into two categories: direct method and indirect method. The direct method is to directly observe the mechanical motion of the machine or motor, and measure the mechanical operation law within a specific time to measure the speed of the mechanical motion. The indirect method is to indirectly determine the rotational speed due to the relationship between other physical quantities that change due to the mechanical movement of the machine or motor and the rotational speed. There are many physical quantities related to the rotational speed that change due to the mechanical motion of the machine or the motor, so there are also many ways to indirectly measure the rotational speed.
1. Measurement method of speed of photoelectric encoder disc
The photoelectric code disc speed measurement method is to fix a photoelectric code disks on the end shaft of the motor rotor. One or more light-transmitting gratings are set on the photoelectric reflect photomask, and each grating has a corresponding photosensitive element behind it. As the motor rotates, the photoelectric encoder disk also rotates. When the fixed light source illuminates the photoelectric encoder discs, the light passing through the grating is received by the photosensitive element and generates a pulsed electrical signal. If the code number of the photoelectric encoder is 1 and the number of pulses measured in time t is N, then the rotational speed n=60N/(t*1). The greater the number of codes on the coded disk, the higher the measurement accuracy.

Second, the Hall element speed measurement method
As the name suggests, this method uses Hall switch elements to measure the rotational speed. Like the photoelectric encoding disk speed measurement, the Hall element speed measurement method also installs a disc on the motor shaft. There are several pairs of small magnets on the disc. The more small magnets, the higher the resolution, and the Hall switch is fixed on the small magnet. Near the steel, when the motor rotates, the small magnetic steel on the disc will pass through the Hall switch once, each time the small magnetic steel passes, the Hall switch will output a pulse, and the number of pulses per unit can be calculated to determine the rotational speed of the rotating body .

3. Centrifugal speed measurement method
Centrifugal tachometers use the centrifugal force generated when an object rotates to measure the rotational speed.
We all know the conversion formula of centrifugal force and rotational speed: g=r×11.18×10-6×n2
Where g is the centrifugal force, r is the radius of curvature of the trajectory, and n is the rotational speed (r/min).
When the rotating shaft of the centrifugal tachometer rotates with the measured object, the weight on the centrifuge leaves the shaft center under the action of inertial centrifugal force, and drives the pointer to rotate through the transmission system. When the spring reaction torque on the pointer and the inertial centrifugal torque are balanced, the pointer stops at the scale value indicated after the deflection, which is the measured speed value. This is the principle of a centrifugal tachometer. When measuring the speed, the end of the tachometer should be inserted into the center hole of the motor shaft, and the shaft of the tachometer should be concentric with the shaft of the motor, otherwise it will be easy to sound and read accurately.

Four, tachometer generator speed measurement method
A tachogenerator is a micro-motor whose output electromotive force is proportional to the rotational speed. The rotational speed is measured using the relationship that the armature electromotive force E of the DC generator is proportional to the rotational speed of the generator. When measuring the speed, the tachogenerator is connected to the shaft end of the motor under test, and converts the mechanical speed of the motor under test into a voltage signal output.

Optrytech Technology Co., Ltd. specializes in the development and production of photoelectric code discs for more than 15 years. It can produce glass code discs, metal code discs, film code discs, photoetching high-precision encoder discs, and reflective code discs according to the requirements of drawings. Code discs, incremental code discs, transmissive code discs, and etched code discs can be customized according to drawings.
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