speed measurement
Speed measurement is used to determine the frequency of rotation of rotating bodies. Mechanical, magnetic, photoelectric and inductive encoders are used for measurement. The rotational speed "n" corresponds to the number of revolutions, e.g. of a shaft, per time unit. Speed specifications are made in Hertz( Hz), revolutions per minute (rpm) or in the angular velocity Klein- Omega in 1/s.
Tachogenerators are used to record rotational speeds. They are generators which are driven by the rotating part via shafts. The generated generator voltage is proportional to the speed. Tachogenerators are used to detect speeds up to 3000 rpm. The speed-dependent AC voltage can also be converted into a pulsating DC voltage. Either the amplitude or the frequency is used to evaluate the generator voltage. Tachogenerators provide output voltages from 20 V to 60 V. The advantage is that they can be connected directly without an amplifier. Disadvantages are that they cannot be connected everywhere, they are not contactless, they are subject to wear and tear, and they absorb torque.
Digital speed sensors: to measure the speed, one or more markings can be placed on the circumference of the rotating part, which are scanned inductively, optically or magnetically. The speed is determined by counting the sampled pulses during a constant time interval.
Inductive speed sensors are used for very high and also very low speeds. They have no feedback effect on the measured object. In active inductive speed sensors, the shaft, which is provided with a groove or elevation, rotates in the field of a permanent magnet. This causes the magnetic flux in the coil to change so that a voltage pulse is induced. The speed is determined by counting the voltage pulses in a fixed unit of time.