Experiment 5(b): Measurement of Rotational Speed using Opto-Coupler

Setup:

• The setup is almost similar to electromagnetic pick-up. The only difference exist in sensor module is, here a slotted optocoupler is used as sensor instead of electromagnetic pick-up.
•  A slotted optocoupler consists of an IR transmitting (Source) and receiving (Detector) LED pair.
• They are confined inside a plastic package separated from each other by a small air gap (slot).
•  There is a small hole in the package on both side in a line so that the transmitted IR ray from source can directly fall on the receiving LED.
• The optocoupler has been placed in such a way that the slotted disc connected with the motor shaft will pass through the air gap between the source and detector. 

Fig.1 Signal Conditioning and Processing Unit

Working Principle:

• When the teeth of the disc comes exactly in between the source and detector of the sensor, the IR ray is obstructed so we get a logic low signal (0V) at the output.
•  And we get a logic high (5V) signal at the output when the IR ray is not obstructed by the disc.
• Hence we get 15 pulses at the output per one rotation of the motor.

Fig.2 Sensor Module

The signal conditioning and processing unit does the same thing what it does in electromagnetic pick-up. Procedure is also same as that of electromagnetic pick-up.

Observation:

Sl no	Supply voltage	Frequency at Wave shaper Output	Frequency at Multiplier output