optical The Quadbeam^TM Altenating Light Principle design is to improve the measurement reliability of the optical suspended solid and turbidity instrument. Sensor that use  Quadbeam^TM  technology compensate for most sources of measurement erroe, providing unrivalled accuracy and reliability when compared with competative System.
The most basic method of suspended solid measurement is obtain by shining a light of know intensity a fixed distance through a medium to a photocell detector .