DC Tachogenerator is a micro special motor whose output electromotive force is proportional to the speed. The polarity of the output electromotive force changes when the direction of rotation is changed. When the tested mechanism is coaxially connected with the speed measuring generator, as long as the output electromotive force is detected, the speed of the measured mechanism can be obtained, so it is also called a speed sensor.
1. The main advantages of DC tachometer are: when the output is zero, there is no residual voltage; the output slope is large, the load resistance is small; and the temperature compensation is easy.
2. The main disadvantages are: due to the existence of brushes and commutators, the construction and maintenance are relatively complicated, and the friction torque is large; the output voltage has ripple; the forward and reverse output voltage is asymmetric; and it interferes with the radio.
DC speed-measuring generator A speed-measuring generator adopting a DC motor structure. The output DC voltage is proportional to the speed and the polarity is related to the steering.
DC speed generator can be divided into electromagnetic type and permanent magnet type according to the excitation method.
According to the armature structure, it can be divided into slotted armature, slotless armature, hollow armature, and disc printed winding armature.
The electromagnetic type uses a separate excitation type, which is not only complicated but also has a large output voltage variation, which is not used much.
The permanent magnet type stator is made of high-performance permanent magnetic steel, which has a small output voltage change, is little affected by temperature changes, has a small linear error, and has a high output slope.
There are many applications of DC speed generators with permanent magnet slotted armature.
The working speed of the permanent magnet low-speed DC tacho generator can be as low as ten or hundreds of revolutions per minute or have a higher output slope.
The brushless DC speed measuring generator is a speed measuring generator without a brush and a commutator structure, which is a combination of a motor and an electronic circuit.
There are two types of DC speed generators: permanent magnet type and electromagnetic type. Its structure is similar to that of a DC generator.
The permanent magnet type uses high-performance permanent magnetic steel excitation, which is less affected by temperature changes, small output changes, high slopes, and small linear errors.
The electromagnetic type uses a separate excitation type, which is not only complicated but also affected by factors such as power supply and the environment, and the output voltage changes greatly, so it is not used much.
DC speed generators made of permanent magnet materials are also divided into limited angle speed generators and linear speed generators. They are used to measure the speed of rotation or linear motion, respectively, and their performance requirements are similar to DC speed generators, but their structures are somewhat different.
The working principle of a DC speed generator is the same as that of a DC generator. In a constant magnetic field, the rotating armature conductor cuts the magnetic flux, and an induced electromotive force is generated between the brushes. At no load, the output voltage of the motor is directly proportional to the speed. At the time of load, the voltage drop caused by the load resistance, armature resistance and brush contact resistance, the effects of temperature changes, magnetic pole and armature hysteresis and eddy current, armature response, cogging effect, and commutation process on the induced electromotive force The influence of the value makes the linearity of the output characteristics of the motor [the relationship between the output voltage U and the speed n, that is, U = f (n)] worse; the contact voltage drop between the brush and the commutator causes an insensitive area.