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Micah Fomichev
Micah Fomichev

Tachogenerator _TOP_

A tachogenerator, or tachometer generator, is an electromechanical device used to accurately measure the speed of engines and motors. In fact, a tachogenerator can measure the speed and direction of all manner of rotational devices once connected and will output a voltage proportional to the rotation around its own shaft. In other words, a tachogenerator can convert mechanical energy into electrical energy. A tachogenerator is commonly used to handle voltages between 0 and 10 volts and is classed as a precision instrument. We supply solid shaft, blind shaft and hollow shaft types of tachogenerator.


A tachogenerator can be found in various kinds of machine tool and other equipment where the measurement of speed and direction is essential. These include electric motors, conveyor belts, engines, fans and mixers. Consumer products where you would expect to find a tachogenerator would be in a washing machine or a food processor. A tachogenerator is also used in voltage control and current limiting circuits to protect equipment from overheating or to protect other components within an electromechanical device.

Solid shaft tachogenerators are connected to a shaft which, in turn, is connected to an external rotational device. It is the rotation of the external device which turns the tachogenerator shaft and thus generating a very specific range of voltages in accordance with the speed and direction of the shaft. Tachogenerators can indicate rotational direction due to the fact that if a tachogenerator shaft is reversed, the output voltage polarity will change. The solid-shaft tachogenerator is best suited to high load applications.

A Hollow-shaft tachogenerator differs internally from solid shaft tachogenerators in that they are designed with four magnetic poles rather than two. This design allows for the tachogenerator to work with lower voltage loads. An example of the use of a DC hollow shaft tachogenerator is to sense the speed of an elevator. The DC tachogenerator is installed in the hoisting equipment on the traction sheave that drives the cables. It enables the accurate control of cable speed to make sure that the lift stops at the right floor and does so smoothly.

The REO 444 R2 B0.06EG Radio Energie tachogenerator is most often used when mounted on to the back of a DC Motor. It supplies the connected DC drive with a voltage that is linear to speed typically expressed as a voltage against speed e.g. 60V/1000RPM.

A variable reluctance tachogenerator consists of a ferromagnetic gear wheel with 15 teeth rotating close to a magnet and coil assembly. The total flux N linked by the coil is given byN(θ)=10+4cos150 milliweberswhere θ is the angular position of the wheel relative to the axis of the magnet. If the angular velocity of the wheel is 6000 r.p.m, then the frequency of the output signal is _________ kHz.

A tachogenerator gauges the speed of rotation of a shaft or disk (from Greek: tachos = speed, metron = measure) as in a motor or other machine. The device usually displays the rate of revolutions per minute (rpm) on a calibrated analogue dial.

Over recent years, the control process of electric rotating machines has undergone a number of changes linked to the development of new technologies and new material. In the majority of cases, these machines need a speed measuring device a tachogenerator or encoder which gives an accurate measurement of the speed (RPM) in the closed loop process.

The use of digital drives or PLC's in automated systems suggests the use a digital speed sensor (encoder) to control the speed of the motor. However, the electronics usually permits the drives with inputs of 0-10V to use an analog speed sensor (tachogenerator). Therefore, the use of tachogenerators is possible for a lot of applications. The advantages are in excellent performances and a low time constant.

A tachogenerator is an electric generator that provides a voltage proportional to the speed. As tachogenerators are key components in automated systems. They must be strong, reliable, accurate, sensitive and stable. These analogical sensors (DC tachogenerators, AC tachogenerators, brushless DC tachogenerators) are adapted to every industry like machine tools, proportioning systems, handling and lifting systems, lifts, paper manufacturing machinery, textile machines, glass production lines, rolling mills, railway industry, etc.

These sensors are manufactured in different mechanical variations and frame sizes, and also in various electrical characteristics i.e. voltages between 2 volts and 6000 volts at 1000 rpm, rotating speed up to 12000 rpm, machines with shaft and bearings, machines with hollow shaft. Tachogenerators are available from different manufactures but in 1949 Radio-Energie started to make tachogenerators and the REO444 type followed shortly and established itself as the industry standard and has been copied many times.

This study presents a precise speed control method for Brushless Direct Current (BLDC) Motors using an electronic tachogenerator (ETg) instead of an electro-mechanical tachogenerator. Most commonly used three-phase BLDC motors have three position sensors for rotor position data to provide commutation among stator windings. Aforementioned position sensors are usually Hall-effect sensors delivering binary-high and binary-low data as long as the motor rotates. These binary sets from three Hall-effect sensors can be used as an analogue rotor speed signal for closed loop applications. Each position sensor signal is apart from 120 electrical degrees. By using an electronic circuitry, a combination of position sensor signals is converted to the analogue signal providing an input to a PI speed controller. To implement this, a frequency to voltage converter has been used in this study. Then, the analogue speed signal has been evaluated as rotor speed data in comparison with the reference speed. So, an ETg system has been successfully achieved in place of an electro-mechanical tachogenerator for BLDC motor speed control. The proposed ETg has been tested under various speed conditions on an experimental setup. Employed tests and obtained results show that the proposed low-cost speed feedback sub-system can be effectively used in BLDC motor drive systems. Through the proved method and designed sub-system, a new motor controller chip with a speed feedback capability has been aimed.

The voltage V.sub.N of the mains or line 32 supplies the electric motor 31 via a rectifier 33. The motor speed is measured by a tachogenerator 22, which is linked mechanically to a non-illustrated motor shaft of the electric motor 31. The tachogenerator 22 generates the actual rotational speed value and makes this value available to a speed controller unit 23, which makes a comparison between the set point 21 and this actual speed value and supplies to a current controller unit 26 an output signal corresponding to the desired control behavior. The current controller unit 26 uses this and the information relating to current level, which is recorded by a current converter 25, to form a control signal for the rectifier 33. 041b061a72


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