Fundamentals of water level sensors
By: Temitayo Oketola | Originally published on 5/28/2024
As the world has become increasingly concerned with environmental conservation, efficient industrial processes and effective management of water resources, the importance of water level measurement cannot be overstated. For instance, the prediction of flood events, the operation of wastewater treatment facilities and the monitoring of reservoirs to meet agricultural needs all require the accurate measurement of water level.
Water level sensors play a crucial role in many industries today, offering precise measurements of water levels across various settings, such as open lakes and confined spaces of industrial tanks. However, water level sensors come in different types, ranging from mechanical floats to sophisticated radar and ultrasonic sensors, to cater to diverse needs with precision and accuracy.
Understanding the water level sensors entails a deep dive into the different types available, the principles that govern their operation and their different applications. Understanding the basics of these sensors equips engineers to select the right sensor for a specific need.
Common types of water level indicators
Pressure transducers
Pressure transducers are among the most used water level sensors due to their accuracy, reliability and simple mode of operation. These sensors are typically submerged in water and operate by measuring and converting the pressure exerted on them by the water into an electrical signal.
At the heart of a pressure transducer is a pressure-sensitive element (such as a piezoelectric sensor, strain gauge or a capacitive cell). When submerged in water, this pressure-sensitive element experiences hydrostatic pressure proportional to the depth of the water above it. As a result of the hydrostatic pressure, the pressure-sensitive element experiences a deformation, which is then converted to an electrical signal that is measured and interpreted as water level. The relationship between the hydrostatic pressure and the height of water above the pressure-sensitive element is shown below.
Ultrasonic level sensors
The ultrasonic water level sensor operates on the principle of sound wave reflection to measure the distance of the surface of the water. This sensor is typically mounted at the top of a tank so that its position is fixed and its height relative to a reference point (such as the bottom of the tank) is known. In order to measure the water level, ultrasonic sensors transmit ultrasonic waves through air until the waves encounter the water surface. The water surface reflects the waves to the ultrasonic sensor. By calculating the time it takes for the waves to travel to the water surface and back, the sensor can determine the height between itself and the water surface. The water level is then determined by subtracting this measured distance from the known height of the sensor above the reference point.
Engineers find the ultrasonic water level sensors very useful in applications such as flood management, reservoir monitoring and controlling water treatment processes.
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Float level sensors
The float level sensors operate by using the principle of buoyancy to monitor and measure liquid levels. This level sensor features a float that is less dense than the liquid it is in. As a result, it moves up and down with the change in liquid level. This movement is converted into a readable level indication or transmitted as an electrical signal to a control system.
Float level sensors’ simplicity, reliability and accuracy make them commonly used in water tanks, sump pump systems for flood percentage, and in the food industry to ensure the accurate filling and processing of liquids.
Optical water level sensors
The optical water level sensors operate based on the principle of light reflection and refraction. These sensors typically feature an LED and phototransistor that detect the presence or absence of liquid at a specific level. Their operation involves emitting a beam of light from an LED toward a prism.
If the sensor is in the air, most of the infrared light is reflected and detected by the phototransistor. However, when liquid makes contact with the sensor tip, it alters the light’s path due to the similar refractive indices between the liquid and the sensor material. This causes less light to be reflected to the phototransistor, allowing the sensor to detect liquid at that specific level.
Conclusion
Water level sensors are important devices helping engineers detect and measure water levels for various processes across a broad range of industries. While this article presents the basic working principles of some these sensors, several considerations must be made before choosing one for a specific application. Therefore, it is recommended to reach out to liquid level sensor suppliers to discuss application requirements.
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