Adjustment of tachogenerators
Tacho generators are usually referred to as low-power direct (less often alternating) current generators, mechanically connected to the drive and used to control the speed of rotation. Adjusting the tachogenerator in addition to tests of a general nature, it has some specific characteristics.
The characteristics of the tachogenerator must be removed before it is connected to the mechanisms. For the device, use small permanent engine with a wide range of speed regulation.
First of all, it is recommended to determine the magnetization characteristic E = f (Авв) with a constant speed n... In this case, it is necessary that the speed n was close to the operating speed of the drive. According to the magnetization characteristic, the magnitude of the excitation current of the tachogenerator, taken as nominal, is specified. Because of the action residual magnetism at the same speed and excitation current, the tachometer voltage values may differ by 1 — 3%.
Next, determine the speed characteristics of the tachogenerator E = e(n) at constant nominal field current. It is initially increased to a value equal to 120% of nominal, then decreased to nominal, then the speed is increased in steps and the characteristic E = e(n). Then the speed and excitation current are reduced to zero. In addition, the excitation current is again increased to the nominal value and again the characteristic E = e(n). The speed characteristic by which the tachogenerators are calibrated is taken as the average value between the two characteristics taken.
If in normal operation the load on the armature of the tachogenerator does not change, then the speed characteristic U = e(n) at a constant load resistance.
Finally, in variable load drives of the tachogenerator, the external characteristics U = e(n) at constant speed and excitation current. The armature current is varied by a rheostat connected to the tachogenerator which simulates the load.
After the tachogenerator is connected to the drive, its alignment must be checked, the accuracy of which allows to minimize the ripple of the rotating voltage.
