Optical Level Switch Principle

Optical level switches are specialty devices which are employed for measurement of level in some special areas. Their operation basically depends upon the light transmission, reflection or refraction characteristics of the substance whose level is to be measured. They employ visible, infrared or laser light for level measurement. Their working is based upon the principle of total internal reflection.

A typical optical level sensor consists of

  1. Light emitting diodes i.e. LEDs,
  2. prisms and
  3. phototransistors.

LEDs emit infrared radiations whereas phototransistors act as a trigger by generating a digital output depending upon the existence or absence of fluid. “When a translucent liquid meets the point where the light contacts the prism, the light is reflected into the water and does not allow the photo transistor to energize.”

Both the LED and phototransistor are housed enclosed inside a plastic dome at the top of the device. In case of absence of liquid, infrared light from the LED gets internally reflected from the dome to the photocell.

These switches can detect levels of all types of liquids such as clear, translucent, reflective, and opaque. Sometimes, they can measure levels in case of solids too. With the help of manifold photocells, a sensor becomes competent enough to measure numerous levels.

They are available in following two major designs:

  • Contacting Type
  • Non-contacting Type