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In the field of industrial liquid level measurement, radar technology has reached a high level of maturity. Whether in petrochemicals, chemical processing, energy, or water treatment industries, radar level transmitters have become the de facto standard. Yet a persistent challenge remains in practical engineering projects: Why do some applications strongly favor guided wave radar while others insist on conventional radar level transmitters? Simply citing “contact/non-contact” as the reason often fails to justify the actual engineering decisions.In fact, guided wave radar and radar level gauges are not simply interchangeable. They address two distinct types of uncertainty issues, based on different measurement assumptions, and thus each has its own validity and limitations.The essence of liquid level measurement is not “measurement.”In industrial settings, liquid levels are not ideal, stable, or clearly defined geometric interfaces.Any liquid level measurement inherently involves navigating uncertainty, primarily manifested in three aspects:1. Interface UncertaintyFoam, emulsification, turbulence, and blurred stratification render the “liquid surface” itself indistinct.2. Uncertainty in transmission pathwaysSteam, dust, pressure fluctuations, and internal tank structures render signal propagation unpredictable.3. Sensor Status UncertaintyCondensation, material buildup, crystallization, aging—altering the sensor's own “operating boundary conditions”The fundamental difference between guided wave radar and radar level gauges lies not in which is more advanced, but in how they position uncertainty in entirely different ways.Radar Level TransmitterThe radar level gauge transmits microwave signals downward via its antenna. Electromagnetic waves propagate through the vapor space inside the tank, reflect off the liquid surface, and return to calculate the liquid level.Its technical advantages are clear:• Fully non-contact, avoiding medium corrosion, adhesion, and contamination• Suitable for high-temperature, high-pressure, highly corrosive, and sanitary conditions• Capable of ultra-wide measurement ranges, ideal for large storage tanks and spherical tanks• Eliminates mechanical risks like probe scaling or deformation during long-term operationFor these reasons, radar level gauges are virtually irreplaceable in applications such as crude oil storage tanks, refined oil tanks, and large vertical chemical tanks.However, it is important to note that all these advantages are built upon an implicit premise:The liquid level must be a “clearly identifiable target in space” in electromagnetic terms.When this premise is compromised, the challenges faced by radar level gauges become immediately apparent:• Steam density variations cause propagation attenuation and refraction• Foam and dust introduce scattering and false echoes• Internal components like agitators and coils create strong reflectionsViolent liquid surface fluctuations causing unstable echoesIn such scenarios, radar level transmitters are not “unusable,” but their performance becomes highly dependent on algorithms, echo recognition strategies, and engineering expertise to accurately pinpoint the true liquid level amidst complex echoes.Guided Wave RadarGuided wave radar employs a different measurement logic.Instead of allowing electromagnetic waves to propagate freely within the tank, it confines the signal to travel near the guide wave body via a probe rod or steel cable. This design fundamentally alters the distribution of measurement uncertainty:• Fixed signal path significantly reduces spatial environmental impact• Insensitive to vapor, foam, dust, and other gas-phase interferences• Easier acquisition of identifiable echoes from low-dielectric-constant media• Stable echo structure enhances repeatability and trend controlConsequently, guided wave radar often achieves more stable signal acquisition in challenging conditions characterized by complex spatial constraints, strong vapor interference, and weakly reflective media.However, this stability comes at a cost. The advantages of guided wave radar are achieved through direct contact with the medium, which also defines its clear limitations:• The probe may experience material buildup, crystallization, or polymerization•High-viscosity media may coat the guided wave body, causing echo attenuation•Strong mechanical vibrations or liquid level impacts can affect cable stability•In ultra-long-range, large-diameter tanks, structural and installation constraints are significantIn other words, guided wave radar reduces “spatial uncertainty” but significantly increases the influence of sensor surface conditions on measurement results.The dielectric constant is not a matter of “whether it can be measured.”In engineering discussions, dielectric constant is often simplified to “whether it can be measured,” but in practical applications, it primarily affects measurement margin and stability.• For radar level gauges, a low dielectric constant means weak reflections. When combined with spatial interferences like steam or foam, echoes are easily drowned out.• For guided wave radar, low dielectric constants similarly weaken reflections. However, due to concentrated energy and high coupling efficiency, identifiable echoes are often maintained.This does not imply guided wave radar is “immune to dielectric constant effects,” but rather that it transforms the challenge into: Can a stable impedance transition be formed along the guided path?Interface MeasurementIn processes such as oil-water separation, extraction, and sedimentation, interface measurement serves as a critical control parameter. Guided wave radar can generate multiple reflection points at both gas-liquid and liquid-liquid interfaces when the dielectric constant difference between the two phases is sufficiently large, enabling simultaneous measurement of liquid level and interface. This capability is fundamental to guided wave radar but is not inherently guaranteed; it depends on:• Whether the dielectric constant difference between the two phases is sufficiently pronounced• Whether the interface is clear and stable• Whether the probe consistently remains within the interface transition zoneIn cases of unstable interfaces, severe emulsification, or blurred stratification, radar or other measurement methods may prove more suitable.Emphasis on anti-interference capabilityA frequently overlooked yet critically important fact is that:• Radar level gauges are primarily influenced by spatial conditions• Guided wave radar is primarily affected by the surface condition of the sensorThis means the “interference resistance” of the two technologies cannot be simply compared.In steam-filled reactors with complex internal structures and bubbling foam, radar level gauges face significantly increased difficulty in echo recognition;Meanwhile, guided wave radar may become a long-term maintenance burden in media prone to crystallization, adhesion, or polymerization.ConclusionFrom an operational cycle perspective, each technology excels at addressing distinct challenges:• In clean, large-scale, non-contact-intensive applications, radar level gauges demonstrate superior long-term reliability• In complex spaces where signals are prone to interference and measurement stability is paramount, guided wave radar maintains controllability more effectivelyThe core of engineering selection has never been about “short-term measurability,” but whether long-term failure modes are acceptable.When operating conditions meet assumptions, technological advantages become evident; when assumptions are disrupted, even the most “advanced” instruments face significant challenges.Understanding this is more important than memorizing whether to choose guided waves or radar.

Guangdong Kaidi Energy Technology Co., Ltd. Christmas GiftIlluminating warmth with technology, safeguarding every reunion with craftsmanship.As Christmas starlight adorns the night sky and the warmth of reunion fills our hearts, we understand that behind every sparkle lies the quiet pulse of energy; behind every act of warmth, the silent guardianship of technological craftsmanship.Guangdong Kaidi Energy Technology Co., Ltd. aspires to be the most reliable light among the festive illuminations—empowering the future of energy with innovation, making reunions brighter and winters more consistently warm.Like our level gauges, precise, dependable, and always online, safeguarding the security of every industrial process.This holiday season, Kaidi wishes to be your most steadfast “guardian”—measuring with pinpoint accuracy, ensuring blessings return in abundance.Wishing you and your team a Merry Christmas and a prosperous New Year. May your endeavors rise steadily like liquid levels, reaching new heights!Thank you for your trust and choice this past year. Our “cooperative liquid level” remains consistently stable and abundant. We look forward to continuing ourjourney together in the new year. Merry Christmas and prosperous business!

In industrial control, security surveillance, and smart device applications, RS-485 communication is widely adopted in various instrumentation systems due to its high interference immunity, long transmission distances, and support for multipoint communication. However, when debugging RS-485 communication, many engineers frequently encounter a question: Why must a 120-ohm terminating resistor be added at both ends of the bus? This article will thoroughly analyze the function and principles of terminating resistors by integrating instrumentation applications with real-world operating conditions.I. Introduction to RS-485 CommunicationRS-485 communication is a differential transmission method, whose main characteristics include:Strong anti-interference capability: Differential signals effectively suppress electromagnetic interference (EMI).Long transmission distance: RS-485 supports a maximum transmission distance of up to 1200 meters.Multi-point communication: RS-485 supports communication among up to 32 devices (nodes) on a single bus.In practical applications, the RS-485 communication bus typically adopts a bus-type structure. Impedance matching at both ends of the communication line requires special attention, which is the key consideration in terminal resistor design.II. The Necessity of Termination ResistorsIn RS-485 communication, termination resistors are not optional but an essential component for ensuring communication quality. Specifically, the role of termination resistors is reflected in the following aspects:Preventing Signal Reflection: During data transmission, signals encountering impedance mismatch at the end of the transmission line may reflect back onto the bus. This reflection introduces interference on the bus, compromising data integrity and causing communication instability.Achieving Impedance Matching: The characteristic impedance of RS-485 communication cables is typically around 120 ohms. To ensure effective signal transmission and prevent reflections, a 120-ohm terminating resistor must be used to absorb excess signal energy, thereby matching the cable's characteristic impedance.Ensuring Data Integrity: Without a terminating resistor, reflected signals superimpose onto the original signal, causing waveform distortion that leads to data errors or communication interruptions. This issue becomes particularly pronounced during long-distance or high-speed transmission.III. Why Choose 120 Euros?The RS-485 communication standard specifies that the characteristic impedance of the communication cable is approximately 120 ohms. Therefore, adding 120-ohm terminating resistors at both ends of the bus effectively achieves impedance matching, thereby ensuring stable communication.What happens if there is an impedance mismatch?Excessively high resistance: Signal reflections remain unabsorbed and continue to interfere with communication.Excessively low resistance: Signal energy loss becomes excessive, adversely affecting transmission distance.Therefore, the 120-ohm terminating resistor has been proven through extensive practical testing to be the optimal choice. It delivers the best matching effect—simple and effective.IV. Correct Procedures in PracticeTerminating resistor placement: Terminating resistors should only be added at both ends of the bus, not at intermediate nodes. Each node does not require additional resistors, as this may affect impedance matching and cause unnecessary signal loss.Common resistor selection: For most applications, 120-ohm, 1/4-watt metal-film resistors suffice. While termination may not be mandatory for short-range communication (e.g., within a few meters), it remains critical for long-distance transmission or high-speed communication.V. Practical Case Study: The Importance of Termination ResistorsA chemical plant initially failed to install termination resistors when using an RS-485 bus for long-distance sensor data transmission. This resulted in data packet loss and frequent alarm issues, with communication stability significantly deteriorating as the number of nodes increased. After adding termination resistors, signal reflection phenomena disappeared, and data transmission became more stable and reliable. This case vividly demonstrates the critical role termination resistors play in ensuring the stability of 485 communication.VI. Common MisconceptionsEach node requires a terminating resistor: Incorrect! Terminating resistors should only be placed at both ends of the bus. Resistors should not be added between nodes, as this would compromise overall impedance matching.Short-distance communication does not require terminating resistors: While communication may sometimes function normally over short distances, terminating resistors still enhance reliability when signals face interference or operate at higher transmission rates.Terminating resistors can have arbitrary values: Incorrect! The resistor value must match the bus's characteristic impedance; selecting 120 ohms is best practice.VII. Summary and RecommendationsAlthough seemingly insignificant, the terminating resistor is a critical component in RS-485 communication, ensuring stable and reliable data transmission. When designing and debugging RS-485 communication systems, it is imperative to connect 120-ohm terminating resistors at both ends of the bus in accordance with standards. Particular attention should be paid to this design detail during long-distance transmission or multi-node communication to prevent potential communication instability. Properly configuring the terminating resistor significantly enhances the overall communication quality of the system, ensuring the stable operation of instruments and control equipment.

In recent years, radar level gauges have been progressively replacing ultrasonic level gauges as the more prevalent non-contact level measurement technology in field measurement applications across industries such as chemical, petrochemical, power generation, food and beverage, wastewater treatment, and powder storage and transportation. This trend is driven not by a single factor but by a combination of factors, including: differences in physical principles, environmental adaptability, measurement accuracy and stability, process compatibility, digitalization and intelligent diagnostic capabilities, and improvements in total cost of ownership.While ultrasonic level transmitters retain competitiveness in low-cost and simple operating conditions, radar level transmitters are poised to become the mainstream technology in future developments. This study reviews the differences and application boundaries between the two technologies, synthesizing key considerations for selecting appropriate measurement techniques based on academic research and engineering practice.                                                                                                                                      Radar Level Transmitters and Ultrasonic Level TransmittersI. Physical Characteristics Differences Between Electromagnetic Waves and Sound WavesUltrasonic level transmitters measure distance by timing the propagation of sound waves, making them highly susceptible to temperature, humidity, gas composition, and turbulence. For instance, in high-temperature steam environments, fluctuations in the speed of sound through air can cause measurement errors. Simultaneously, foam and mist can absorb or scatter ultrasonic signals, generating false echoes.In contrast, radar level transmitters emit microwave or millimeter-wave electromagnetic signals. Electromagnetic waves are virtually unaffected by temperature and humidity in gaseous phases, enabling effective penetration through steam, mist, and dust. Both manufacturer reports and academic studies indicate that radar echo stability significantly outperforms ultrasonic performance in steam clouds, dust-filled enclosed compartments, and agitated vessels.                                                                                                                  Radar level gauges demonstrate significant advantages in anti-interference performance.II. High-frequency and FMCW technologies enhance measurement resolution.Traditional pulse radar has limited resolution, but with the development of 24 GHz and 80 GHz high-frequency bands and FMCW (Frequency Modulated Continuous Wave) technology, the resolution and interference resistance of radar level gauges have significantly improved.High-frequency radar features a narrower beam angle, reducing wall echo interference;80 GHz technology enables smaller antenna sizes, making it more suitable for compact vessels;FMCW delivers higher signal-to-noise ratio and dynamic range, enabling detection of weak echoes—particularly advantageous for liquids with low dielectric constants.These advancements enable radar to perform exceptionally well in containers with complex geometries, narrow tanks, and agitated conditions.                                                                                                                                    Level measurement in mixing tanks is more stable and reliable.III. Reduced Blind Spots and Installation FlexibilityUltrasonic probes typically have a ±10mm “blind zone,” making accurate measurement difficult when liquid levels are too close to the container top. In contrast, high-frequency radar can often reduce the blind zone to just a few centimeters, significantly enhancing feasibility for small tanks or shallow tanks.This eliminates the need for engineers to install bypass pipes or extension tubes to reduce the blind zone, simplifying installation complexity and reducing maintenance points. For industries requiring frequent cleaning, such as food and pharmaceuticals, this simplified installation is particularly crucial.IV. Measurement Reliability Under Foam and TurbulenceIn fermentation, dairy, papermaking, and chemical reaction processes, liquid surfaces are often covered by foam or bubbles. Ultrasonic waves scatter energy within foam, frequently causing signals to be completely attenuated and interrupting measurements.Radar, however, relies on dielectric constant differences. Even when a foam layer exists on the liquid surface, it can identify the true liquid surface echo in most cases. Through signal processing algorithms, radar distinguishes between foam reflections and liquid surface reflections, enhancing data reliability.                                                                                                                           Easily identify foam levels, with measurements as reliable as ever.V. Long-Range and High-Precision PerformanceFor large tanks or silos exceeding 20 meters in height, ultrasonic signal attenuation and sound velocity fluctuations significantly reduce measurement accuracy. Radar, with its superior signal penetration and interference resistance, maintains stable measurements across ranges of 30–120 meters or even longer.Additionally, radar typically achieves accuracy within ±1–2 mm, whereas ultrasonic systems generally maintain only ±5–10 mm precision. In chemical reactors, batching processes, or industries requiring strict inventory management, this accuracy gap can directly impact production quality and economic efficiency.VI. Intelligent Systems and Remote DiagnosticsModern radar level transmitters widely support industrial protocols such as HART, Modbus, and Profibus, while progressively integrating Bluetooth and wireless communication. This enables engineers to perform parameter configuration, waveform diagnostics, and firmware upgrades from safe zones or remote workstations.In contrast, while ultrasonic level transmitters also offer digital versions, they lag behind in waveform processing, diagnostic algorithms, and remote upgrade capabilities. Academic research indicates radar level transmitters hold greater advantages in intelligent diagnostics and Industry 4.0 integration.VII. Cost and Lifecycle ConsiderationsHistorically, radar level transmitters were limited by their higher cost. However, with the mass production of integrated 80 GHz chips and antennas, prices have significantly decreased. Many plants conducting lifecycle cost assessments have found that while radar level gauges have a higher unit price than ultrasonic gauges, they offer superior overall economics by reducing false alarms, downtime, and maintenance costs.Consequently, in applications demanding high safety and reliability (such as petrochemical tank farms and hazardous chemical storage tanks), an increasing number of enterprises are opting for radar level gauges.VIII. Application Boundaries and Selection RecommendationsNot all scenarios require radar. In budget-sensitive, open-environment applications where measurement accuracy is not critical—such as open channels in water treatment plants or small reservoirs—ultrasonic technology remains a cost-effective solution.Scenarios where radar is preferred: High-temperature environments, condensing steam, foaming conditions, dusty atmospheres; large tanks, deep silos, remote operations; process control points requiring high precision and continuous monitoring.Scenarios where ultrasonic is preferred: Low-cost water tanks/channels, simple operating conditions, low-risk storage tanks.Hybrid strategy: Deploy radar at critical points and ultrasonic at secondary points to optimize overall investment and operational efficiency.ConclusionRadar level gauges are gradually replacing ultrasonic level gauges, driven by the convergence of mature technology, enhanced adaptability to operating conditions, and the trend toward industrial intelligence. With the widespread adoption and decreasing cost of 80 GHz high-frequency FMCW technology, this replacement trend will accelerate. Ultrasonic technology will retain its market share in certain low-cost, low-risk applications, but radar level gauges are undoubtedly the future mainstream.