Optical Liquid Level Switches
Last Updated: February 12, 2025
Description
Optical liquid level switches are devices designed to detect the presence or absence of liquid at a specific level within a container. They achieve this by utilizing optical technology to monitor changes in light transmission, which indicates whether the sensor is in contact with liquid or air.
Working Principle
Optical liquid level switches operate based on the principles of light reflection and refraction. These switches typically consist of an LED and a phototransistor. The LED emits a beam of infrared light towards a prism. When the sensor is in the air, most of the light is reflected back to the phototransistor. However, when liquid contacts the sensor tip, the light's path is altered due to the similar refractive indices of the liquid and the sensor material, resulting in less light being reflected. This change in light reflection is detected by the phototransistor, allowing the sensor to determine the presence of liquid. The absence of moving parts in these sensors makes them reliable and reduces the risk of clogging or damage, offering a "fit and forget" solution .
Applications
Optical liquid level switches are used in various industries for precise liquid level monitoring. They are particularly useful in environments where it is critical to detect high or low liquid levels, such as in chemical processing plants, pharmaceutical manufacturing, and food and beverage production. These switches are also employed in marine applications for bilge water detection and in fuel management systems to prevent overfilling .
Advantages over other Liquid Level Switches
One of the primary advantages of optical liquid level switches over other types, such as float switches, is the absence of moving parts. This design reduces the likelihood of mechanical failure and maintenance requirements. Additionally, optical switches are less susceptible to issues caused by viscous or sticky liquids, which can impede the movement of float-based sensors. Their compact size and ability to provide accurate readings in challenging environments make them a preferred choice in many applications .
Limitations
Despite their advantages, optical liquid level switches have limitations. They may not be suitable for use with opaque or highly turbid liquids, as these can interfere with the light transmission and affect the sensor's accuracy. Additionally, the initial cost of optical switches can be higher compared to simpler mechanical switches, which may be a consideration for budget-conscious applications .
Considerations
When selecting optical liquid level switches, it is important to consider factors such as initial costs, operating expenses, and the specific requirements of the application. While the initial investment may be higher, the reduced maintenance and increased reliability can offset these costs over time. Durability and accuracy are key benefits, but users should also evaluate the compatibility of the sensor with the liquids being measured to ensure optimal performance. Replacement and maintenance costs are generally lower due to the lack of moving parts, which minimizes wear and tear .
from Intellisense Microelectronics Ltd.
The optical liquid level switch consists of an infrared LED and a receiver. In air, the light beam from the infrared LED is reflected back into the receiver. When rising liquid touches the tip of the sensor, the light is refracted away from the device, causing little light to return to the receiver. [See More]
- Technology: Optical
- Mounting: Side mount; Bottom mount
- Repeatability: 0.0394
- Operating Temperature: -40 to 212
from Intellisense Microelectronics Ltd.
Optical liquid level switches use the light reflection principle in the prism to detect whether there is liquid at the installation position of the sensor.These optical level sensors are compact, cost-effective and ideal for various fluids. Features: Operation indicator. NPN/PNP output. Operating... [See More]
- Technology: Optical
- Mounting: Side mount; Bottom mount
- Repeatability: 0.0394
- Operating Temperature: -40 to 212
from Intellisense Microelectronics Ltd.
The LLS.DTM12 series optical liquid level switch is a low cost single point level sensor designed for semitransparent, clear, and low viscosity liquids. The sensor is available in Trogamid or Polysulfone. The Polysulfone version with high chemical resistance is suitable for most acids and bases. The... [See More]
- Technology: Optical
- Mounting: Side mount; Bottom mount
- Repeatability: 0.0394
- Operating Temperature: -40 to 212
from Intellisense Microelectronics Ltd.
The electro-optical level sensor is used to monitor the level of liquids. The model LLS.ELS1150 is an enhanced electro-optical level switch from IMS sensors. This series utilize IMS advanced photoelectric sensor ASICs to achieve a fast, stable, cost-effective sensor with no moving parts. Equipped... [See More]
- Technology: Optical
- Mounting: Side mount; Bottom mount
- Repeatability: 0.0394
- Operating Temperature: -40 to 212
from FineTek
The SD Series optical level switch uses the principle of light reflection in a prism to sense the absence or presence of a liquid at the point where the sensor is installed in a tank, pipeline or other type of container. SDX Optical Level Switch, Lquid Level Switch. SD series is an optical level... [See More]
- Technology: Optical
- Operating Temperature: 257
from Sitron
The SOP400 Opto Eletronic Level Switches are used for level detection in liquids, independent of physical characteristics such as density, dielectric constant or the conductivity of the medium. The SOP400 provides an accurate, repeatable point level switch which can be mounted in any position,... [See More]
- Technology: Optical
- Maximum DC Voltage: 30
- Repeatability: 0.0197
- Maximum Pressure: 290
from Gems Sensors & Controls
These polysulfone level switch units are both compact and economical. They feature a variety of mountings, power requirements and electrical terminations to make it easy to find a perfect match for your application. The ELS Level Switch Series is low cost, compact, optical, level sensors with... [See More]
- Technology: Optical
- Material Temperature: 0 to 176
- Maximum Pressure: 150
- Switch Points: 1
from OPW Engineered Systems
Civacon cane probes are used to provide overfill detection where a permanent sensor cannot be properly affixed to a tank or railcar. They provide a portable, flexible solution to varying overfill requirements. Civacon cane probes utilize modern, instant-on optic principles. Temperature condition... [See More]
- Technology: Optical
- Mounting: Top mount
- Repeatability: 0.0625
- Operating Temperature: -40 to 158
from KOBOLD Instruments, Inc.
The NSD series optical level switch is a low cost solid-state level sensor suited for clear, translucent, and non-coating low viscosity liquids. The NSD functions by detecting the difference in refraction between the liquid and air. An infrared LED inside the lens transmits a beam of invisible... [See More]
- Technology: Optical
- Configuration: Normally Closed (NC)
- Construction: Solid-state switch
- Maximum Pressure: 150
from Baumer Ltd.
Most ultrasonic sensors are based on the principle of measuring the propagation time of sound in the air. Ultrasonic frequencies outside the range of human hearing are emitted by the sensor. Sonic energy reflected by an object or target is picked up by the sensor ’s receiver. The highly... [See More]
- Technology: Optical
- Maximum Current: 0.2000
- Construction: Solid-state switch
- Maximum DC Voltage: 30
from Gems Sensors & Controls
Flange Mounting. No Threads Needed. Ideal for Thin Wall Tanks. The easy solution for thin wall tanks 1/4" thick (6 mm): ELS-1100FLG Series Level Switch. No threads needed with these flanged units. Slip through a .75" (19 mm) hole and tighten the jam nut; a Viton ® gasket forms a tight seal. [See More]
- Technology: Optical
- Maximum Pressure: 150
- Maximum DC Voltage: 30
- Material Temperature: 0 to 176
from Baumer Ltd.
Most ultrasonic sensors are based on the principle of measuring the propagation time of sound in the air. Ultrasonic frequencies outside the range of human hearing are emitted by the sensor. Sonic energy reflected by an object or target is picked up by the sensor ’s receiver. The highly... [See More]
- Technology: Optical
- Maximum Current: 0.0150
- Construction: Solid-state switch
- Maximum DC Voltage: 30
from Gems Sensors & Controls
Temperatures to 212 °F. HTS Version - 1/2" Long. UL Approved. Slightly larger than the ELS-1100, the "HT" or High Temperature version is made from high performance Isoplast plastic. While maintaining broad chemical compatibility, these units also handle fluid temperature to 212 °F (100... [See More]
- Technology: Optical
- TTL: TTL Compatible
- Maximum DC Voltage: 12
- Maximum Pressure: 150
from Gems Sensors & Controls
Teflon ® Body and Prism. Ideal for Ultra-High Purity Applications. Chemically Resistant. When high purity or resistance to chemical attack is vital, ELS-1100TFE sensors are the ultimate solution. They feature a pure Teflon ® body and prism construction. Even the Hypalon ® vapor barrier... [See More]
- Technology: Optical
- Maximum Pressure: 150
- Maximum DC Voltage: 30
- Material Temperature: 0 to 176
from Gems Sensors & Controls
Fused Glass Prism for High Pressures. Excellent Price-to-Performance Ratio. Ideal for Corrosive Environments. The enhanced ELS-1150 series is the highest performing electro-optic level switch from Gems ™ Sensors. At just 1.38" (35 mm) long, the ELS-1150 has been upgraded with a micro-processor... [See More]
- Technology: Optical
- Maximum Pressure: 2500
- Construction: Electro-mechanical switch
- Material Temperature: -40 to 212
from Gems Sensors & Controls
Smallest Size. TPE Over-Molded Electronics. Durable Enough to Handle Harsh Environments. Not only is the ELS-950 the smallest electro-optic liquid level sensor in our arsenal, but it also carries the highest operating temperature capability at 230 °F (110 °C). The Polysulfone housing ensures... [See More]
- Technology: Optical
- Material Temperature: -40 to 230
- Maximum Pressure: 250
- Switch Points: 1
from Gems Sensors & Controls
Rugged brass housing. Smallest Size. TPE Over-Molded Electronics. Durable Enough to Handle Harsh Environments. The ELS-950M Series represents Gems ™ smallest electro-optic level sensor developed to monitor a broad range of media including OHV type fluids. Our UL approved design features a... [See More]
- Technology: Optical
- Switch Points: 1