Liquid Level Sensors Advantages in Level Measurement and Differences to Liquid Level Switches

As science and technology rapidly develop, various methods to measure liquid level have been invented, from rulers used in ancient time, to photoelectric, ultrasonic and radar gauges used by now. Liquid level sensor is a kind of pressure sensor measuring liquid level, which is suitable for level measurement in industries like petrochemical engineering, metallurgy, electricity, pharmacy, water supply and sewage, environmental protection and so on. For that the domestic market of magnetic flap level sensors developing continuously, the level sensor industry enjoys a bright future.
The reason for the wide application of level sensors attributes to the principle and features of the sensor.
Level sensors (static pressure liquid gauge / level transmitter / liquid level sensor / water level sensor) is a kind of pressure sensor that measures liquid level. Inputting type of static pressure level transmitter (liquid level gauge) adopts advanced isolated diffused-silicon sensitive elements or ceramic capacitor pressure-sensitive sensors from abroad. Based on the principle that the static pressure of tested liquid is in proportion to liquid level, the sensor transfers static pressure into electric signal, and convert it to standard electric signal (commonly 4~20mA/1~5VDC) by temperature compensation and linear modification.
Level sensors can transfer the variations of material level parameters into standard current signal, and remotely transmit to operation controlling room for centralized display, alarming or automatic control of secondary meters or computers. With its favorable structure and installation methods, the sensor is ideal for continuous measurement of liquid and material level  in special conditions like high temperature, high pressure, strong erosion, easy crystallization, blockage-proof, non-condensation and powdery or granular materials. Therefore this sensor can be applied for measurement and control in many industrial processes.
Level sensors and level switches are two kinds of most frequently used liquid or material level measurement devices, but few people understand the relation and difference between them, which is important for device selection. Now please allow we ISWeek to demonstrate the relationship between level sensors and level switches.
Difference between level sensors and level switches
Level switch is a kind of controller which opens inlet or outlet water valve according to signal output by level sensors to keep a constant water level. In other words, a level switch outputs a switch signal after confirming level height, and then level sensor transfers this signal into electric signal and output.
The electrical signal can be processed, such as connect to PLC data collector or professional display device to output liquid level. Although sharing the same working principle, a level switch is a switch controlling circuit, while a level sensor is a circuit component for voltage and current transformation.
For liquid level measurement, we ISWeek would like to recommend two kinds of products: photoelectric level sensor and level switch sensor.
What is a photoelectric level sensor?
Photoelectric level sensors is a new contact-type of level measurement and control device. It works with the principle of light reflection and refraction when going through an interface between two different mediums. For that it is featured with simple structure, high positional accuracy, no mechanical components, high sensitivity, corrosion resistance, and compact size, the sensor is gradually accepted by the market.

  1. despite of other parameters like temperature, pressure, density and electricity, level output is only related to whether the probe touches the liquid level.  Thus this sensor is featured with high detection accuracy, high repeatability, fast response and precise level control. This sensor needs no calibration and can be installed and use directly.
  2. with a relatively compact size, the photoelectric level sensing probe can be divided an installed in limited space, which means that it is suitable for use in spacial tanks. Also, several photoelectric sensors can be installed in a single object to form a multipoint level sensor or transforming controller.
  3. Since that inside the sensor,all elements are encapsulated with resin, and that there are no movable parts, this photoelectric liquid level sensor can be highly reliable, long-lasting without maintenance.

British SST low-cost Liquid Level SensorsLLC200A3SH

Optomax Basic Series Liquid Level Sensors

LLC low-cost series liquid level sensors are used for single point. For mass OEM client, there is a special design containing an infrared emitter and a detector which are precisely located and installed to ensure that they can achieve perfect optical coupling in the air. When the conical end touches the liquid, IR light will transmit out of the conical surface, so that strength of the light reaches the detector will be weakened.
Features of low-cost photoelectric level sensor LLC200A3SH
(1)fast response,
(2)10mA driving current, photoelectric transistor switch output.
(3)working temperature:-20~85℃,M12 thread.
(4)lead: 250mm 24AWG,8mm, tin-plating.
Typical applications of low-cost photoelectric level sensor LLC200A3SH:
spring pool, leakage detection, automatic beverage dispenser, medical treatment, compressor, printer, water pump, household appliances, oil level monitor, HVAC, machine tool, high=low level switch, water level control, automotive electronics.
Electrical parameters of low-cost photoelectric level sensor LLC200A3SH

Supply voltage (Vs) At will
Supply current Nominal 10mA
Type of output Photoelectric tube (digital)
Output signal
Operating temperature 25 ~ 80°C
Storage temperature -30 °C ~ 85 °C


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