All over the real world, the RPM sensor is a very essential instrument. For example, rotating machinery needs speed sensing for functional systems, including control, monitoring, and safety. Turbine engine rotor speeds must be monitored closely to maintain safe operation. A motor driver needs to monitor the car speed for safe driving; this car speed is taken from the RPM sensor.
What is an RPM sensor?
The device that is used to measure the rotational speed of any rotating shaft, disk, or object is called an RPM sensor. RPM stands for Revolution Per Minute.
The rotation speed of a shaft or disk, such as that of a motor or other machinery, is measured and indicated by an RPM meter, and it is shown as RPM on any HMI screen.
The instrument known as the rpm sensor measures the speed of the machine while it is in operation. It is also commonly referred to by other names, such as an RPM gauge and a rev counter.
It may operate on an optical, electrical, or electromagnetic basis.
RPM Sensor Working Principle.
The RPM sensor working principle can be electromagnetic, electronic, or optical-based. That means the basic working principle depends on types of RPM sensors. Different types of RPM sensors operate using various methods.
Inductive sensor for RMP measurement: Inductive speed sensors utilize electromagnetic induction to determine the speed of a spinning object. They are typically made up of a coil and a magnetic core that produce voltage when a metallic target on a rotating object passes near the sensor.
An inductive sensor is a device whose operation depends on a changing magnetic field in an inductive coil. When a metal object enters into the field of action, it is captured and recognized. It uses a unique generator that creates a certain amplitude of oscillation. When an object made of metallic or ferromagnetic material reaches the unit's field of action, its oscillations change, indicating its existence.
Hall effect sensor for RPM measurement: Hall effect RPM sensors work on the Hall effect principle, which states that the presence of a magnetic field causes a voltage to be developed in a conductor. These sensors usually use a magnet placed on the rotating object and a Hall-effect sensor to measure the speed. Unlike inductive sensors, a Hall Effect sensor's output signal does not vary by the rate of change of the magnetic field. The outcome voltage is typically in the mV range and is amplified by an integrated electronics circuit located inside the sensor enclosure. The final output voltage signal is typically in digital waveform pulses (square form). Each tooth that comes into contact with the sensor surface causes one waveform pulse. The amplitude of the output signal waveform remains constant, but the frequency changes correspondingly with rpm. Therefore, by counting the wave pulse, it is easily possible to calculate the rpm.
Advantages of Hall Effect Sensor
- The non-contact sensing feature provides greater durability.
- Durable and dependable in adverse circumstances, resistant to dust, moisture, and vibration.
- It is engineered to operate across a wide range of speeds, even at near-zero velocity.
- Variations in the magnetic field may have an impact on accuracy.
- Sensing distance is limited in comparison to other sensor types.
- Additional components may be required for signal conditioning.
Optical sensor for RPM measurement: Optical RPM sensors use light to measure the speed of a spinning object. They usually have an infrared LED and a photodiode to measure the amount of light reflected or interrupted by the revolving object. This device can be classified into two types based on how it senses speed: transmissive type and reflective type.
Reflective type: The photosensor detects whether the light transmitted by the LED is reflected by the revolving wheel or not.
Advantages of Optical Speed Sensor
- Non-contact sensing minimizes wear and tear, hence increasing longevity.
- Excellent precision and accuracy, especially in clean environments.
- Dust, wetness, and vibration have a minimal impact.
- Sensitivity to variations in ambient light can affect the sensor's performance.
- In general, the cost is higher than for other types of sensors.
- It requires more complicated circuitry, which can lead to increased design complexity.
Study more: Vibration Sensor Working Principle and Applications.
RPM Sensor Types.
Digital- These rpm meters contain electrical circuitry, a processor, a sensor, and an LCD or LED display. Such instruments can carry out statistical calculations. Digital tachometers are becoming more popular, and instead of dials and needles, they provide numerical readings on a display.
Analog—These RPM meters furnish a needle-and-dial interface. These devices do not have the ability to save measurements or calculate information such as average deviation. The speed turns into voltage using an external frequency-to-voltage converter. As a result, this voltage is displayed on an analog voltmeter marked with the RMP scale.
Contact and Non-Contact RPM Meters—The contact type requires physical contact with the rotating shaft. On the other hand, non-contact rpm meters, which are highly efficient, convenient, and accurate, make no touch with the rotating shaft.
Time and Frequency Measuring Tachometers— The time-based digital tachometer determines the equipment's rotational speed by measuring the time interval between incoming pulses. The frequency measurement instrument calculates speed by measuring the frequency of incoming pulses. It is more accurate for high-speed measurements, and the rotation of this tachometer is determined by the revolving shaft.
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