Abstract—Fast speed measurement and control signals are
required for feedback control applications. In the proposed
technique, a rotating magnetic field (RMF) is used to measure
the speed and the variation in speed with high accuracy. In
addition to a 400 Hz, three-phase input voltage circuit and an
output zero-crossing detector circuit, a contact-type synchro is
used as a primary transducer. A balanced three-phase ac voltage
is applied to the stator windings of synchro, which produces an
RMF. The frequency of electromotive force induced in the rotor
circuit of synchro depends upon the speed of rotor or rotating
member. The RMF revolves at a speed of 24 000 r/min, which
is purposely kept very high in comparison with the speed of the
rotor or rotating member. Thus, the measurement becomes very
fast and the change in speed is sensed within 2.5 ms. The time
response of the proposed scheme is also compared with the time
response of a dc tachogenerator. A digital storage oscilloscope
and a microcontroller are used for measurement of the output.
The 16-b digital output of the microcontroller is made available
as a feedback signal for control applications. The high accuracy
of measurement of the proposed technique is also successfully
used for calibration of different contact- and noncontact-type
tachometers.
Index Terms—Calibration of tachometer, rotating magnetic
field, speed measurement, speed transducer, tachometer