Ultrasonic level transmitter measure liquid level based on the principles of ultrasonic wave propagation and reflection. They offer high accuracy and stable performance and are widely used for level measurement of various liquids, material height measurement of solids, and distance measurement. As a result, they are one of the most commonly used non-contact level measurement instruments in industrial applications.
The operating principle of an ultrasonic level transmitter is mainly based on the propagation characteristics of ultrasonic waves in a medium. Liquid level is determined by transmitting and receiving ultrasonic signals. The working principle can be summarized as follows:
An ultrasonic liquid level sensors consists of an ultrasonic transducer (probe) and a transmitter. During operation, the transducer emits ultrasonic pulses at a specific frequency. These high-frequency pulses travel at the speed of sound and are reflected when they encounter the surface of the measured medium (such as a liquid surface). The reflected echoes are received by the same transducer and converted into electrical signals.
The time required for the ultrasonic wave to travel from transmission to reception (i.e., the transit time) is directly proportional to the distance between the transducer and the surface of the measured medium. Based on the relationship between the sound velocity C and the transit time t, the distance can be calculated using the following formula:
S = C × t / 2
Where:
S is the distance from the transducer to the liquid surface
C is the propagation speed of the ultrasonic wave in the medium
t is the time from pulse transmission to echo reception
Based on their structural design, ultrasonic level transmitters can be classified into two types: integrated (compact) type and remote (split) type.
Integrated Ultrasonic Level Transmitters
Integrated ultrasonic level transmitters combine the ultrasonic probe, signal processing unit, and display into a single device. All measurement and control functions are completed within one enclosure.
Easy installation: With a compact structure, installation requires mounting only one device, eliminating complex wiring and installation procedures.
Full functionality: Suitable for harsh industrial environments, with protection ratings up to IP66/IP67. Multiple versions are available, including corrosion-resistant and explosion-proof models.
Simplified calibration: The integrated design makes calibration more straightforward and efficient, as only the complete system needs to be calibrated rather than separate components.
Integrated ultrasonic level transmitters are commonly used in storage tanks, industrial wastewater treatment systems, chemical reactors, and shallow basins.
Remote (Split) Ultrasonic Level Transmitters
Remote ultrasonic level transmitters consist of a probe and a signal processing unit installed separately. The probe is mounted at the measurement point, while the signal processing unit can be installed in a control room or another convenient location away from the measurement site. The two components are connected by a cable.
Strong immunity to interference: Separating the probe from the signal processing unit allows the electronics to be installed away from high temperature, high pressure, or strong electromagnetic interference, improving measurement accuracy and reliability.
User-friendly operation: The signal processing unit typically features a larger display and more operating interfaces, making it easier for operators to view data and make adjustments.
High adaptability: The split design is well suited for harsh measurement conditions such as high temperatures or corrosive gases and liquids. The probe can be made of special materials to withstand these environments.
Remote ultrasonic level transmitters are ideal for large storage tanks, complex process level measurement, and level monitoring in high-temperature or highly corrosive environments, especially in applications requiring remote operation or protection from on-site environmental interference.
1. Non-contact measurement
The sensor does not come into direct contact with the measured medium, so it does not contaminate the liquid. It is also not affected by corrosion or wear from the process fluid, making it suitable for corrosive and chemical environments.
2. Strong adaptability
Ultrasonic level transmitters are suitable for various types of liquids and containers, such as storage tanks, pipelines, and chemical reactors. They can operate reliably in harsh conditions including high temperature, high pressure, and corrosive environments, and are largely unaffected by medium viscosity, density, or humidity.
3. Multiple measuring ranges and material options
Ultrasonic liquid level sensor are available in different measuring ranges, such as 5 m, 10 m, and 15 m, to meet diverse industrial requirements. Probe materials such as corrosion-resistant PVDF ensure reliable measurement in aggressive liquids and environments.
4. High resistance to interference
Ultrasonic liquid level sensor offer strong immunity to interference and can operate stably in environments with strong electromagnetic fields, such as substations and transmission towers.
5. Easy installation and maintenance
With a simple structure, compact size, and light weight, ultrasonic level transmitters are easy to install and maintain. Because they do not contact the process fluid, installation does not require special consideration of corrosion or contamination.
6. Real-time monitoring and automation
Ultrasonic liquid level sensor provide real-time level measurement and can communicate with host systems or PLCs to enable remote monitoring and automated control.
Compared with other level measurement technologies, ultrasonic liquid level sensors offer the following advantages and differences:
Application range: Ultrasonic level transmitters are suitable for atmospheric-pressure vessels, while radar level transmitters have a broader application range. Ultrasonic devices are not suitable for conditions such as vacuum, very high vapor content, or heavy foam on the liquid surface.
Measurement principle: ultrasonic liquid level sensors use sound waves for measurement, whereas radar level transmitters use electromagnetic waves. This leads to different performance characteristics in practice; for example, ultrasonic waves have stronger directionality and different penetration behavior compared with electromagnetic waves.
Price and accuracy: ultrasonic liquid level sensors are generally more cost-effective, but their accuracy is moderate. In contrast, radar level transmitters are more expensive but provide higher measurement accuracy.
Non-contact measurement: Ultrasonic level transmitters perform non-contact measurement by mounting the sensor externally, enabling continuous level measurement from outside the tank and complete isolation from the measured medium.
Application scenarios: ultrasonic liquid level sensors are suitable for specific applications, such as level measurement in oil storage tanks. Radar level transmitters, however, can be used in more complex process conditions and are available in various designs, including horn, rod, and cable types.
Environmental adaptability: Ultrasonic level transmitters may not perform well in certain environments, such as those with high vapor content or heavy foam on the liquid surface. Radar level transmitters are better suited to handle these challenging conditions.
1. Consider the blind zone during installation: Ultrasonic level transmitters have a blind zone near the sensor where they cannot measure liquid levels. When determining the measurement range, leave a margin of about 50 cm. The probe should be installed approximately 50 cm above the maximum liquid level to ensure accurate level monitoring and safe operation of the transmitter.
2. Proper orientation and placement: The probe should be installed perpendicular to the surface of the measured object. Avoid measuring foamy surfaces and ensure the installation distance is greater than the blind zone (each product comes with its specified blind zone). The ultrasonic beam should avoid obstructions and should not touch the filling port or container walls. When measuring large solid objects, adjust the probe direction to minimize measurement errors.
3. Minimize electromagnetic interference: Ultrasonic liquid level sensors are sensitive to nearby electrical equipment. Signal cables should run in separate conduit away from power or lighting lines. Ensure proper shielding using conductive steel conduit, with the shield grounded at a single point to avoid potential differences that could interfere with the instrument.
4. Ensure reliable signal connections: Avoid leaving joints in the middle of signal cables, and make sure all terminal connections are tight. Loose contacts increase resistance. If a joint is necessary, it should be soldered to reduce potential issues.
5. Keep signal cables dry: Moisture, especially at connection points, can disrupt signals. When routing cables through cable trays, ensure they are properly supported and protected to remain dry.
Because ultrasonic liquid level sensors use non-contact measurement, the measured medium is almost unrestricted. They are widely used for measuring the level of liquids and solid materials and are typically applied in industries such as wastewater treatment, municipal water supply, water conservancy, food, and chemical processing.