What are the newer types of level measurement instrumentation?
Accurate level measurement is vital in industrial processes to monitor and maintain proper media level in tanks and vessels. There are a wide variety of technologies offered for measuring level and trying to decide which technology to use is not always straightforward. The appropriate technology needs to meet your process conditions, accuracy requirements, budgetary limits, and a multitude of other factors.
Three established technologies are becoming more widely utilized due to advances in capability, decreasing costs, and an increasing level of familiarity with them in industry. These technologies are free space radar, guided wave radar (GWR), and ultrasonic level measurement.
They all operate by transmitting a wave (either electromagnetic or acoustic) and analyzing the reflected signal (generally the return time or frequency shift). Each technology offers unique advantages and is suited to specific applications, making the selection process crucial for optimal performance and cost-effectiveness.
This comprehensive article explores the fundamental principles of these three technologies, discusses their possible applications, and conducts a comparative analysis to help engineers and technicians make informed decisions for their level measurement requirements.
Technology Overview
How does Radar Level Measurement Technology Operate?
Radar level measurement, also known as free space radar or non-contact radar, operates using electromagnetic waves. These systems transmit microwaves (typically in the 6 GHz, 26 GHz, or 80 GHz frequency bands) toward the product surface and measure either the time required for the reflected signal to return, or the frequency shift of the returned signal. These two distinct operating principles are referred to as Pulsed and Frequency Modulated Continuous Wave (FMCW) systems.
Pulsed systems emit short bursts of waves and measure the time for the reflected signal to return employing the time-of-flight principle to determine the level utilizing the fundamental relationship:
FMCW employs a continuously transmitted signal and modulates frequency over time. The signal is reflected by the process media, and the echo is picked up by the device. The difference in frequency of the echo and the transmitted signal is proportional to the distance.
Relying on the frequency shift to calculate the distance offers a more robust measurement that is less susceptible to noise interference. FMCW is known for its higher measurement resolution and continuous level measurement compared to the discrete measurements of pulsed radar systems.
Kobold primarily offers 80 GHz radar sensors operating on the FMCW principle that utilize narrow beam angles for precise measurements in tanks or other closed vessels. Explore the available Kobold Radar Level Transmitters.
How Does Guided Wave Radar (GWR) Level Measurement Technology Operate
Guided Wave Radar represents an evolution in radar technology, combining the reliability of radar measurement with the precision of guided wave propagation. Instead of transmitting electromagnetic energy through free space, GWR systems guide microwave pulses along a probe (cable, rod, or coaxial) that extends into the measured medium.
This technology operates on the principle of time domain reflectometry (TDR), where electromagnetic pulses travel down the probe at the speed of light until they encounter a dielectric discontinuity at the product surface. The dielectric constant difference between air (or vapor) and the liquid creates an impedance change that reflects a portion of the signal back to the transmitter. The time for the reflected signal to return is used to calculate the distance to the media.
GWR systems can utilize various probe configurations, including single rod probes for liquids, concentric probes for low dielectric materials, and flexible cable probes for tall tanks, difficult installations, and bulk solids.
Kobold offers guided wave radar probes in a variety of configurations and custom lengths. Explore Kobold’s guided wave radar portfolio here.
How Does Ultrasonic Level Measurement Technology Operate?
Ultrasonic level measurement employs acoustic waves rather than electromagnetic to determine distance. The system generates ultrasonic pulses (typically between 20-200 kHz) and measures the time required for the acoustic echo to return from the product surface.
The fundamental principle follows the same time-of-flight calculation as radar but uses the speed of sound instead of the speed of light:
Note that the speed of sound varies significantly with changes in environmental conditions, namely temperature, and requires compensation algorithms for accurate measurement.
Kobold offers a variety of ultrasonic level transmitters to fit your application. The NUS series provides active temperature compensation and excels in both tank level and open channel flow measurements. The NEO utilizes an innovative design for reliable measurement in tanks with condensing media. Explore the full portfolio of Kobold’s ultrasonic level measurement devices.
Commonly Asked Questions
General Technology Questions
Guided Wave Radar and Free Space Radar have similar accuracies (around ±2-5mm), but guided wave is less prone to signal degradation from foam, vapor and media conditions due to its guided propagation method. Ultrasonic is generally a little less accurate than radar-based systems and the accuracy relies heavily on environmental compensation (±0.2% to 2.5% under ideal conditions).
Radar measurements, both free space and guided wave, remain virtually unaffected by temperature changes since electromagnetic wave propagation is independent of atmospheric conditions. Ultrasonic measurements require active temperature compensation as sound velocity changes with temperature.
Application-Specific Questions
GWR is best suited for in-foam applications, especially with coaxial probes designed specifically for this purpose. Lower frequency radar can penetrate light foam and vapor but may experience reduced signal strength (80GHz with its higher frequency and narrow focus is more susceptible to signal impedance from foam or vapor.) Ultrasonic systems struggle with foam and vapor as acoustic waves are absorbed or scattered by suspended particles.
GWR is the best choice for dusty conditions as guided waves are not affected by airborne particles under most conditions. Lower frequency free space radar may be able to work with some level of dust, but 80 GHz systems would likely struggle.
Ultrasonic systems are more prone to measurement errors in dusty environments due to acoustic wave absorption and scattering by dust particles and would not be recommended.
A non-contact option such as Radar or Ultrasonic is generally the best choice when dealing with corrosive chemicals. With a non-contact meter, material selection is still an important consideration as corrosive vapors could be present.
Radar antennas and housings can be manufactured from various corrosion-resistant materials, such as PP and PVDF options. Ultrasonic transducers are also offered in PP and PVDF. Certain GWR systems may be suitable for harsh conditions through the application of a coating (PTFE, PEEK) on the rod.
Both Ultrasonic and Free Space Radars can be used to measure the flow rate of water in open channels. These devices’ electronics come with pre-programmed algorithms for a variety of common weir and flume layouts that allow the level sensor to output a flow rate based on the level reading.
Generally, ultrasonic sensors are more common for open channel measurements as an industry standard because of their cost effectiveness and historical uses, however free space radar is another option that offers a more accurate and robust solution at a slightly higher initial investment.
Radar systems require minimal maintenance, primarily antenna cleaning and periodic calibration verification. GWR systems need occasional probe cleaning and inspection for mechanical damage. Ultrasonic systems require infrequent transducer cleaning, temperature sensor calibration, and atmospheric compensation verification.
When to Use Each Technology
The technology is ideal for measuring most liquids and some bulk solids as long as the material has a high enough dielectric constant to provide sufficient reflection. High-frequency radar systems (80 GHz) are particularly effective for small tanks and narrow nozzles. Some other niche applications are measuring through plastic roofs and gas blanketed tanks.
Consider radar for applications involving extreme temperatures, high pressures, vacuum, or corrosive environments where non-contact measurement provides operational advantages. The technology performs exceptionally well in clean liquid applications.
GWR is the preferred choice for applications requiring the highest accuracy and reliability. This technology works better in foam-prone applications and challenging dielectric conditions where free space radar may struggle.
Select GWR for narrow tanks, stilling wells, or applications with significant obstructions where beam spreading could cause measurement errors.
Ultrasonic technology is used for general liquid level measurement where cost-effectiveness is paramount. It is also well-suited for open-channel flow measurement for water and wastewater applications. The technology performs excellently in clean water applications and can be effective for corrosive liquids when proper materials are selected.
Choose ultrasonic for applications requiring simple installation, where electromagnetic interference is a concern, or media with low dielectric constants. The technology is particularly effective for level measurement in rectangular tanks and applications where multiple measurement points are required.
Advantages and Disadvantages Comparison
Radar
- Non-contact measurement eliminates contamination risks and mechanical wear
- Unaffected by temperature, pressure, humidity, or gas composition variations
- Excellent accuracy (±2-5mm) and resolution (0.1mm) for high-frequency systems
- Wide measurement range capabilities (up to 66 feet)
- Possible to measure through light dust and vapor
- Suitable for elevated temperature and pressure conditions
- Can be programmed to filter out certain obstructions
- Higher initial cost compared to ultrasonic systems
- Requires sufficient dielectric constant for reliable measurement (>1.8 εr)
- Beam spreading can cause false echoes from tank walls or internal structures
- Performance will be degraded by heavy foam or vapor
Guided Wave Radar
- Excellent accuracy (±2-5mm) and repeatability (<2mm)
- Outstanding performance in foamy applications (with appropriate probe selection)
- Unaffected by atmospheric conditions, temperature, or pressure variations
- Can work effectively with lower dielectric materials (>1.4 εr)
- Minimal beam spreading eliminates false echo problems
- Probe materials for corrosive applications
- Suitable for narrow tanks and confined spaces
- Requires immersion into the media (not a non-contact option)
- Probe can be subject to mechanical damage or coating buildup
- Higher initial cost
- More complex installation, especially for long probe lengths
- May require periodic cleaning in fouling applications
- Cable or rod length limitations in very tall tanks
Ultrasonic Level Measurement
- Lower initial cost compared to radar technologies
- Good accuracy in clean liquid applications
- Effective for open channel flow measurements
- Multiple sensors can be used for multiple measurement points economically
- Well-established technology with extensive application history
- Works with low dielectric constant media (<1.5 εr)
- Requires temperature compensation for accurate measurement
- Performance affected by humidity, vapor, and atmospheric conditions
- Cannot penetrate most foams
- Limited range compared to radar systems
- Acoustic absorption by dust or suspended particles impedes reading
- May experience interference from acoustic noise sources
- Temperature sensor failure can significantly impact accuracy
How do I choose a level measurement technology?
The selection of the appropriate level measurement technology depends on multiple factors including application requirements, environmental conditions, accuracy needs, and budget constraints.
Radar technology offers the best balance of performance and versatility for general industrial applications, particularly in harsh environmental conditions and where the need for a non-contact measurement is a factor. Radar would not be recommended in environments with heavy vapor or dust, applications with substantial foam, or where interface levels need to be measured.
Guided Wave Radar provides outstanding accuracy and reliability for critical applications, especially where foam or low dielectric media requirements exist. The technology's higher cost is often justified by superior performance.
The few cases where GWR would not be recommended are very tall tanks, as the installation requirements become unwieldly or tanks with agitators that could damage the probe.
Ultrasonic technology remains an excellent choice for cost-sensitive applications, particularly in water and wastewater treatment, where environmental conditions are relatively stable, and high accuracy is not critical. Ultrasonic should be avoided when foam is present, in vaporous or dusty conditions, around extensive acoustic noise, or in high wind environments.
What are the future trends and considerations for level measurement technologies?
The evolution of level measurement technologies continues with advances in signal processing, antenna design, and digital communication protocols. Higher frequency radar systems are becoming more common, offering improved performance in challenging applications.
Smart sensor technologies incorporating advanced diagnostics, predictive maintenance capabilities, and enhanced signal processing algorithms are becoming standard features across all three technologies. These developments deliver improved reliability, reduced maintenance costs, and better integration with modern digital control systems.
Next Steps
If you want to learn more about Radar and Ultrasonic measurement technologies and how they can be used to monitor and control your specific processes, schedule a free engineering consultation with one of Kobold’s application engineers today.