What Is a Tachogenerator?
A tachogenerator is a sensor that is attached to a rotating shaft and outputs a DC voltage signal in response to the rotation speed.
It is used to detect the rotational speed of a shaft and is abbreviated as TG. The “tacho” in tachogenerator is derived from the Greek word takhos, which means speed, and a device used to measure the rotational speed of an engine is called a tachometer.
A generator is a device that generates electricity. The name “tachogenerator” is derived from the fact that a tachogenerator is a device that both measures RPM and generates electricity. Tachogenerators are used in a wide range of fields because of their compact size, high reliability, and ability to measure rotation speed with high accuracy.
Uses of Tachogenerators
Tachogenerators are mainly used to detect the rotation of moving equipment.
They have long been used in tachometers and speedometers for automobiles and ships. By attaching a tachogenerator to the rotating shaft of an engine or other equipment, it is possible to calculate the speed from the rotation speed. In recent years, inexpensive and highly accurate pulse generators are often used as an alternative.
It is also used to control rotation speed in machine tools. It is also used for positioning of robot arms, etc. In general, they are used for equipment that requires high-precision rotational speed control and position control.
In addition, it may be used for general-purpose rotational speed measurement applications. It may be used to detect the moving speed of a crane or the speed of an arm drive.
Principle of Tachogenerators
A tachogenerator consists of a rotor, brushes, and stator/casing.
1. Rotor
The rotor is a component that rotates with the rotating shaft. A coil is wound inside.
The coil is a wire wound around the core of the rotor and is used to generate a DC voltage through changes in the magnetic field. As the rotor rotates, the magnetic flux passes through the coil, inducing an induced electromotive force in the coil.
Since the positive/negative direction of the induced electromotive force is reversed depending on the direction of rotation of the shaft, the direction of rotation can be determined in addition to the rotation speed.
2. Brush (Commutator)
The commutator is a component that comes into contact with the rotor of the tachogenerator. It is used to switch the polarity of the voltage applied to the coil. It is mainly composed of carbon and other materials.
Wear may increase with prolonged use, and periodic maintenance or replacement may be required. In addition, if the brushes contact the wrong position or if the contact is deteriorated by dirt or rust, accurate rotation speed detection may not be possible.
3. Stator and Casing
The stator is the component that provides the magnetic field to the rotor. Permanent magnets are mainly used.
The casing protects the rotor and permanent magnet inside, and serves to protect them from external environmental influences. It is generally housed in a metal casing and supported by bearings.
The casing is made of durable, heat- and corrosion-resistant materials. Steel and stainless steel are examples. In some cases, high-precision machining techniques are required.
Connectors for input and output are often installed in the casing. This allows signals output from the tachogenerator to be taken out and supplied externally. The casing also has holes or slits for mounting, which are used for mechanical fastening or as wiring passages.
How to Select a Tachogenerator
When selecting a tachogenerator, the rotational speed range and output voltage should be taken into consideration.
Tachogenerators output a signal of rotational speed within a certain range. Therefore, it is important to check the rotational speed range of the target equipment. It is necessary to select a tachogenerator to be used within that range.
The output voltage and other factors must also be selected to match the requirements of the system to be used. Generally, the output of a tachogenerator is a DC voltage, but it is possible to incorporate a circuit to convert it to AC if necessary.