Level Measurement

What is an optical level sensor and how does it work?

The optical level sensors can be used for high temperature and high-pressure applications it is used for point level sensing. So these sensors can be used for point level detection and also for the continuous monitoring of solids and liquids. These sensors would measure the level of liquids that have suspended solids, optical level sensors can be used for measurement of corrosive, organic, and aqueous liquids in industry. The optical level sensor is composed of an infrared LED and a light receiver. These sensors are capable to sense the decrease or change in level by the transmission of infrared light emitted from an infrared diode.

The optical level sensor requires infrared, visible, or laser light for its operation, the level measuring is depended upon the light-transmitting, and reflecting properties of the process material. The optical level switches have both contacting and non-contacting type.

How is an optical level sensor constructed?

The optical level sensor has an infrared LED, receiver, and a prism, The light is transmitted from the LED to the prism. These sensors can provide point level measurement, the light source and detector are shielded from each other and they are mounted in an enclosed housing as shown in the above image.

How does an optical level sensor work?

The operation of the optical level sensor is very simple and these sensors work with infrared or visible radiation. The optical sensor has a light source and mostly it would be an LED and it has a photoelectric detector which could be a photodiode, phototransistor, and photo-resistor. The light will be transmitted or directed towards the cone-shaped prism. If the cone is above the liquid then the light will be reflected back from the cone to the detector, if the cone is below or submerged in the liquid, then the light will be reflected into the liquid and it won’t reach the detector. So if the detector doesn’t receive any light then the light detector circuit would activate a control relay contact for alarms or control. The optical level sensors are solid-state devices so that it can be used for a wide range of applications and they are reliable too. We must properly select the construction material and mounting location for our sensor to work efficiently and we can use these sensors in aqueous, organic, or corrosive liquids. We can adjust the photocell or the detection electronics so that these sensors can detect levels according to the need. These level sensors can measure the level of clear as well as reflective or opaque liquids, by using multiple photocell certain solids can be detected too.

We can use laser light insted of infrared and the advantage of the laser light is that it is more concentrated so it could penetrate dust or steam and the laser light will be reflected from most solids and liquid surfaces.

What are the advantages of optical level sensor?

  • It is compact
  • There are no moving parts
  • It can be used for high temperature and pressure applications
  • It can detect less amount of liquid
  • They are immune to electromagnetic interference
  • It can be used in an explosive environment
  • It can be used for high and low intermediate level detection in large and small tanks

What are the disadvantages of optical level sensor?

  • The probe could erode during time
  • They are invasive and it is because the sensor is in contact with the process liquid
  • Reading could take time due to bubbles, coating, or tanks that are mirrored

What are the applications of optical level sensor?

  • Tank level measurement
  • It can be used for leak detection
  • It can be used to detect the level of liquids with suspended solids


post-graduate in Electronics & communication.

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