We are manufacturer, supplier of D. C Tachogenerators which is known as an electrical version of tachogenerators, used for the measurement of speed. It has an armature that is placed in the permanent magnetic field. Then it is coupled to the machine, whose speed needs to be measured. When the machine's shaft revolves, the armature also revolves in the magnetic field. This results in the production of e.m.f. which is proportional to the product of the flux and speed, that are needed to be measured. In these D. C Tachogenerators, direction of rotation is directly proportional to the polarity of output voltage.