The angular velocity of rotating cone in shear-pool is the main information source of a cone-plate blood viscometer

and its precision depends on the photoelectric sensor and fluted disc.The error sources of angular velocity device are analyzed

that is

the pointolite characteristic of photoelectric sensor

and the angular error due to the cyclical swing and the machining inaccuracy of fluted disc.Since the cone angular velocity is monotone decreasing and the angular error is random in one cycle but is cyclical variation during the whole detecting process

a rational cubic spline interpolation algorithm is adopted to decrease the angular error.Experimental results show that this method can improve the precision of angular velocity and reduce the production cost of sensor.