This is a rotational speed detection system in the new cone-plate viscosimeter based on photoelectric sensor.The system mostly uses the switching characteristic of photoelectric sensor.It acquires the output pulse signal from the photoelectric sensor

and tests the neighborhood signal pulse width difference to get the instantaneous attenuating angular acceleration after canceling electromagnetism actuation.With the angular acceleration

resistance moment of blood in different speed can be got

then the blood viscosity can be counted.Matlab software is used to process the acquired data

experiment results show that the system can be used to test the speed.