How to Measure the Rotation Speed of the Brushless Motor?

Different from brushed motor, brushless motor is mainly composed of rotor and stator. The stator is composed of permanent magnets and windings which control the movement of the rotor by applying alternating current. The rotor is made up of permanent magnets and magnetic materials, which can rotate under the action of the permanent magnet. Due to the simple structure and stable operation, it can effectively reduce the load and friction loss to achieve higher mechanical efficiency and better power output performance.

As for the rotational speed detection method, first of all, we need to understand the working principle. The interior is composed of stator and rotor, the motor through the electromagnetic induction principle, the electric energy into mechanical energy to achieve rotation. Its rotation speed is related to the driver output voltage (current) and load factors. During the actual measurement, the motor speed can be monitored by reading the rotor rotation angle by using a Hall sensor or a photoelectric encoder. Among them, photoelectric encoder is a widely used in measuring the position and speed of the sensor equipment, has the advantages of high resolution, high accuracy, fast response speed and so on, can accurately measure the speed. In addition, there are some professional test instruments, in the speed measurement, will be more accurate and convenient, such as multimeter, oscilloscope, frequency meter and so on.

Measuring the speed is a basic test, its principle is to use the Hall effect to sense the output signal, and then calculate the speed. The Hall effect is that when the magnetic field passes through some material, it will produce some uneven charge distribution, thus creating an electric field. When there is a flow through the material, the electric field will be perceived to generate a voltage, called the Hall voltage. Because the rotor is a permanent magnet, when the motor is running, the magnetic field of the rotor senses the Hall sensor, which generates the Hall voltage. The motor speed can be calculated by detecting the waveform of the Hall voltage. There are many methods of speed measurement, including magnetic steel pole number method, tracking pulse method and phase sequence method. Different methods are suitable for different applications, but their basic principle is to use the Hall effect to induce the motor to output the signal and calculate the rotation speed. By measuring the rotation speed, the normal operation of the motor can be ensured, and the performance and health status of the motor can be monitored. This is very important for both electronic equipment manufacturers and machinery manufacturers, because it can help them to ensure the quality and reliability of their products.

It is usually three-phase powered, so its speed is usually represented by shaft rotation per minute (RPM). The detection of rotational speed mainly includes the following three methods:

1. The Hall sensor detection

Whenever there is a charge difference between the three windings, the Hall sensor outputs a voltage pulse signal whose frequency is the actual rotation speed. Therefore, the rotational speed can be accurately determined by measuring the signal frequency of the output of the Hall sensor.

2. Inverse-EMF detection

Antielectromotive force refers to the electric potential generated by the load through the electromagnetic induction effect in the direction of the motor to the load, which is proportional to the motor speed. The principle of inF detection is to use this to calculate the speed of the motor. The specific implementation method is to add a measuring resistance between the two windings of the motor, and then detect the inF voltage in each rotation cycle, and use any measuring device to calculate the speed.

3. Photoelectric detection

Photoelectric detection method can be used to measure parameters such as the position, velocity and acceleration of a rotating object. The specific implementation method is to build a photoelectric detection device with LED and photosensitive battery, and put it around the rotating object and make it close to the rotating surface. When the rotating object passes through the photoelectric detection device, the LED will emit light on the photosensitive cell, generating a current and output a voltage signal. By measure the frequency and the amplitude of the output voltage signal.

The position of the detection device is very important. No matter what method is used, the detection device needs to be placed at the rotating shaft to accurately measure the rotation speed. The appropriate detection accuracy must be selected. Different measurement methods have different accuracy, so it is necessary to choose suitable measurement methods to ensure the measurement accuracy. The stability of the test results is also important. Considering the influence of various factors on rotational speed, it is recommended to take multiple tests and average to obtain accurate results. According to different motor types and application scenarios, you need to choose different rotational speed detection methods and detection instruments. Pay attention to safety issues. During the speed measurement, attention should be paid to avoid the risk of electric shock. If you need to touch the rotating shaft, please wear insulating gloves to avoid human accidents.

The above is our VSD motor to share with you about brushless motor speed measurement expertise. For more information, please contact our professional customer service personnel to answer. Thank you for clicking and watching.