Comparative Selection of Water Level Sensors

　　Currently, the most commonly used water-level sensors can be broadly classified, according to their measurement principles, into mechanical float-type, photoelectric float-type, ultrasonic, capacitive, pressure-based, bubble‑type, radar, and other types, each with its own advantages and disadvantages.

　 　Mechanical float type and photoelectric float type All of these devices rely on mechanical gear reduction to generate carry and borrow signals for encoding. To ensure reliable coding, they typically output Gray code. With a wide measurement range—up to 80 meters—they offer significant advantages: simple operating principles, fewer sources of error, and relatively low cost. However, they also have drawbacks: complex machining, substantial operational resistance, short service life, and comparatively high civil‑engineering costs. Consequently, this type of sensor is clearly unsuitable for urban road‑flood monitoring systems.

　　 Ultrasonic level meter It determines the position of the liquid or solid surface by analyzing the echo signal generated when ultrasonic waves emitted by the sensor are reflected off the surface. As a non-contact sensor, it is particularly well suited for applications involving small temperature variations, relatively calm water surfaces, and minimal wave action. However, ultrasonic sensing has specific requirements for reflective targets, is highly sensitive to environmental factors, and tends to exhibit significant measurement errors. Advantages: no direct contact with the measured medium, excellent corrosion resistance, simple installation, and easy maintenance. Disadvantages: relatively high cost; ultrasonic performance is strongly influenced by the gas composition of the transmission medium and the geometric characteristics of the container, making it unsuitable for media containing bubbles or suspended particles; susceptible to electromagnetic interference, with generally moderate accuracy, and prone to abrupt data fluctuations when deployed in outdoor settings. Consequently, this type of sensor remains ill‑suited for environments such as urban road‑flood monitoring.

　　 Capacitive level sensor It measures the liquid level by detecting changes in capacitance between the capacitor’s two plates. Advantages: compact size, easy implementation of remote transmission and adjustment; suitable for corrosive and high-pressure media. Disadvantages: accurate measurement requires constant dielectric constants of both the medium and the liquid surface; the measurement range is limited by the length of the metal probe; it places stringent demands on the container material; and the measured medium must be conductive. Consequently, this sensor remains unsuitable for applications such as urban road‑flood monitoring.

　　 Pressure-type water level gauge Installation is straightforward, and the measured medium is generally required to be relatively clean. In road‑flood monitoring, however, the permeable sump inevitably becomes clogged with sediment, leading to failure. The bubble‑type water level sensor is, in essence, a pressure‑based device: it injects air from the bottom of the container into the liquid via an air supply line. Gas will only enter the container through the tube and form bubbles when the air pressure in the supply system equals the hydrostatic pressure at the container’s base. At that point, measuring the air pressure in the supply system allows conversion to the static pressure at the measurement location, from which the liquid level can be determined. Advantages: excellent corrosion resistance; capable of measuring high‑temperature media. Disadvantages: relatively low accuracy and higher maintenance costs. This sensor is likewise unsuitable for environments such as urban road‑flood monitoring.

　　 Radar water level gauge It is also a non-contact sensor that determines the position of the liquid or solid surface by analyzing the microwave signals (short-wavelength electromagnetic waves) it emits and their reflections from the liquid surface. Advantages: It is relatively insensitive to external environmental factors such as temperature, humidity, and fog, offers high measurement accuracy, and is easy to install; it can measure liquid levels inside pressure vessels while largely ignoring the effects of high temperature, high pressure, scaling, and condensates; it maintains no direct contact with the measured medium; exhibits strong corrosion resistance; and can operate in vacuum environments. Disadvantages: It is expensive; its performance is influenced by the vessel’s geometry and material properties; and it is susceptible to electromagnetic interference. Consequently, this type of sensor remains unsuitable for use in urban road‑flood monitoring systems.