Common Non-Contact Liquid Level Measurement Methods and Their Characteristics

Liquid level measurement is widely used in petroleum, biochemistry, pharmaceuticals, and food and beverage industries. With many measurement methods on the market, selecting a suitable and cost-effective liquid level measurement method is often challenging. To choose the right liquid level sensor, you need to understand the properties of the measured liquid as well as the advantages and limitations of different sensors. Below is a brief introduction to common non-contact liquid level measurement methods and their characteristics.

Non-contact measurement is the mainstream approach today because the sensing element does not contact the measured liquid, making it suitable for viscous, corrosive, or contaminating media. Common non-contact methods include radioactive level gauges, ultrasonic level meters, laser distance sensors, and radar level gauges.

Radioactive level gauge

Nuclear radiation emitted by sources (such as gamma rays) has strong penetrating ability and attenuates differently through media of varying thickness. Radioactive level gauges use this principle to measure level. The radioactive source is mounted outside the tank in a point or narrow configuration, with the detector installed opposite it. Radioactive level gauges offer high precision and are suitable for applications where no part contacts the measured medium. Neutron sources can also be used. Installation is convenient and measurement accuracy is high.

Ultrasonic level meter

Ultrasonic waves travel at a relatively constant speed in a medium and reflect from the liquid surface. Ultrasonic level meters calculate level by measuring the time between emission and echo. Their performance can be affected by energy loss during propagation. Ultrasonic meters are easy to install and flexible, but performance degrades in steam, dust, or foam environments. Typical range is limited compared with radar in high-explosion-risk applications, and for high-temperature tanks there may be issues.

Laser distance sensor level meter

Laser level meters operate like ultrasonic meters but use light instead of sound. A laser beam reflects from the liquid surface and the time or phase difference is converted to level. Laser beams are narrow and focused, making them suitable for narrow openings and high-temperature, high-viscosity media. Laser sensors are easy to install and calibrate and are cost effective for continuous level or limit detection. They are not suitable for transparent liquids and oils without reflective markers, nor for foamy or vaporous environments that interfere with the beam.

Radar level meter

Radar level meters commonly use frequency-modulated continuous wave technology. A microwave emitter and receiver are mounted at the tank top and emit frequency-modulated waves toward the liquid surface. The returned echo experiences a delay proportional to the distance. Radar meters offer long range, high accuracy, and minimal maintenance and are suitable for harsh conditions and high-contamination media such as asphalt. However, installation is more complex and cost is higher.