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Optomax Basic Range of Liquid Level Switches

The Optomax Basic range of liquid level switches are an analogue optics only solution designed to meet the demand of price sensitive, high volume OEM applications.

The miniature sensor is solid state, containing only an infra-red LED and phototransistor which are optically coupled by the tip when the sensor is in air. When the sensing tip is immersed in liquid, the infra-red light escapes making the phototransistor output change state. The sensor can detect the presence or absence of almost any liquid type, oil or water based.

Because the Optomax Basic range of liquid level switches only contains Optoelectronic components the customer is responsible for interfacing the sensor to their application with technical support from SST. OEM applications can be very price sensitive so by removing the circuit protection, voltage regulation, processing electronics and output stage, the sensor cost is significantly reduced. Available in 3 wire (common cathode/emitter) and 4 wire (galvanically isolated) configurations.

With housing options for internal or external sensor mounting and available in two chemically resistant housing materials, Polysulfone, the standard choice for most applications or Trogamid, which is typically used in food and beverage applications.

The Optomax Basic Range of liquid level switches are only sold in high volumes and have an minimum order quantity of 500 units.


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Part Numbering Guide


Supply Voltage (Vs) Any with suitable LED current limiting resistor
LED Forward Current (If) 10mA recommended
Output Signal Phototransistor open collector. Refer to circuit diagrams on datasheet
Operating Temperature -25 to +80ºC
Storage Temperatures -30 to +85ºC
Housing Materials Polysulfone (Standard)
or Trogamid
Sensor Termination 24AWG, 250mm PTFE wires, 8mm tinned
Operating Pressures 0 to 20bar (M10x1 thread)
or 0 to 7bar (All other threads)


Sensor mounted from inside the vessel (M10x1 thread)


Sensor mounted from outside the vessel (M12x1, 1/2″ SAE, 1/4″ NPT threads)



3-wire version

Basic 3 wire

4-wire version*

Basic 4 wire

*The 4-wire version provides galvanic isolation between the input (IR-LED) and the output (Phototransistor)


3-wire version

Wire Designation
Red LED Anode
Green Output
Blue 0V

4-wire version

Wire Designation
Red LED Anode
Green Output
Blue 0V LED
Black 0V Phototransistor


  • Optics only solution
  • Customer is responsible for interfacing the sensor to their application
  • 3-wire (common cathode/emitter) and 4-wire (galvanically isolated) versions available
  • MOQ of 500 units
  • Polysulfone or Trogamid housing material options
  • Internal or external mounting options
  • High pressure option available


  • Solid state so no moving parts to cause unreliability
  • Small in size so they can be installed in applications where space is limited
  • Can detect tiny amounts of liquid when positioned correctly, ideal for leak detection
  • Fast response time
  • Repeatable switching point
  • LED current limiting resistor and phototransistor pull-up resistor can be built in to the sensor on request
  • Very robust permitting use in a wide range of fluids and chemicals
  • Low in cost for price sensitive applications


Liquid sensing 001_450

When in air the infrared light is reflected back to the detector


Liquid sensing 002_450

When in liquid the infrared light is refracted and the output switches

  • This field is for validation purposes and should be left unchanged.