Abstract: A handheld tachometer includes a body that controls light output, and calculates a rotational velocity of an object based on incident light reflected from the object, and a reflector that is positioned at a light output terminal of the body, to adjust an angle of output light or incident light. The reflector can be adjusted by driving a step motor. The body may also have a motor control interface for a user to adjust the driving direction and degree of the step motor.

Abstract: A method for measuring an ultrasonic viscosity includes applying a driving voltage to a plurality of first piezoelectric transducers provided along an outer wall circumference of a pipe at constant intervals to generate a torsional wave on a surface of the pipe, receiving the torsional wave propagated along the surface of the pipe through a plurality of second piezoelectric transducers provided along the outer wall circumference of the pipe at constant intervals while being spaced from the first piezoelectric transducers at a certain distance in a longitudinal direction of the pipe to convert the torsional wave into a voltage signal, calculating an attenuation and a propagation velocity of the torsional wave based on the time for the propagation of the torsional wave and the converted voltage signal, and measuring viscosity of the fluid in the pipe based on the calculated attenuation and propagation velocity of the torsional wave.