Analysis of the working principle of the speed sensor

- Oct 10, 2019-

With the advancement of science and technology and the development of industry, rotational speed sensors are widely used in rotating machinery, rail transit, automobile transportation and other fields. Long-life, high-reliability, accurate measurement of rotational speed sensors are increasingly valued and favored by the industry.

The speed sensor is roughly classified into four types: eddy current type, magnetoelectric type, Hall type and magneto resistance type. Among them, the magnetoelectric speed sensor is a passive speed sensor, also known as a passive speed sensor; correspondingly, the eddy current, Hall and magnetoresistive speed sensors are active speed sensors, also known as active speed sensors, A power circuit provides external voltage supply to the sensor. When external power is not available, the active speed sensor generates a no speed signal.

The process of collecting the speed signal can actually be regarded as the speed measurement process of the rotating part. The eddy current and magnetoelectric types commonly used for rotational speed measurement have also been applied to the measurement of automobile wheel speed signals. In comparison, the eddy current type rotational speed sensor works reliably, the signal is strong, and the speed measurement is easy to realize. The price is moderate, and it is less affected by environmental factors (such as temperature, water, oil, various dusts, etc.). Based on the above advantages, electricity The eddy current speed sensor is widely used in the collection of speed signals.

Speed sensor works

When the drive shaft rotates, the drive shaft drives the belt for material transport. During the conveying process, the belt will slip, and the driving shaft will rotate, but the belt will not follow the rotation, eventually causing the belt to break and causing damage to the equipment.

In view of this situation, we propose to install two transmission devices on a belt filter. One transmission device is mounted on the driving wheel, and the driving device is driven by the driving wheel. The transmission device is connected to the gear, and the speed of the gear is measured. The speed of the driving wheel is output; the other transmission is driven by the belt, and the transmission drives the gear through the bearing, and the rotation speed of the belt is measured by measuring the rotation speed of the gear. Finally, according to the measured speed of the driving wheel and the belt, when the belt speed is lower than a certain value, an alarm is issued and the switching quantity is output.

The schematic diagram of the transmission is as follows:


 Schematic diagram of belt speed measurement


Active wheel speed measurement

Most of them output pulse signals (approx. sine waves or rectangular waves). Methods for measuring the rotational speed of a pulse signal include a frequency integration method (that is, an F/V conversion method whose direct result is voltage or current), and a frequency operation method (the direct result is a number). In the automation technology, the rotational motion speed is measured more, and the linear motion speed is often measured indirectly by the rotational speed. The DC tachogenerator converts the rotational speed into an electrical signal. The tachometer requires a linear relationship between the output voltage and the speed, and requires a steep output voltage and good time and temperature stability. The speed measuring machine can be generally divided into two types: direct current and alternating current. The rotary speed sensor is in direct contact with moving objects. When the moving object is in contact with the rotary speed sensor, the friction causes the roller of the sensor to rotate. A rotating pulse sensor mounted on the roller sends out a series of pulses. Each pulse represents a certain distance value so that the line speed can be measured. In the electromagnetic induction type, the gear is mounted on the rotating shaft, and the outer side is the electromagnetic coil. The rotation is due to the passage of the tooth gap, and the voltage of the square wave is changed, and the rotation speed is calculated. The rotary speed sensor has no direct contact with the moving object, and the edge of the blade of the impeller is coated with a reflective film. When the fluid flows, the impeller rotates. When the impeller rotates, the optical fiber transmits and reflects once, generating an electric pulse signal. The speed can be calculated from the number of pulses detected.