What Materials Are Suitable for Ultrasonic Level Sensors? Industrial Application and Selection Pitfall Avoidance Guide

Índice espetáculo

Introduction

In the field of industrial automation, silos, storage tanks, conveyor lines, packaging equipment, and water treatment systems all require precise control of one core piece of information: where is the material right now?

Traditional liquid level meters or material level meters usually come with display headers, menu settings, and local reading functions; however, the focus of this article is on the lower-level ultrasonic material level/ranging sensors that are easier to integrate into automation. These sensors typically do not emphasize on-site display but instead output core signals directly to PLCs, DCSs, IO-Link gateways, or controllers, such as:

  • Switching output: PNP / NPN, used for high-level, low-level, in-position detection, and anti-overflow alarms;
  • Analog output: 4–20mA / 0–10V, used for continuous liquid or material level height monitoring;
  • Digital communication output: RS485, Modbus, etc., used for multi-point networking, remote data acquisition, and smart device integration.

From an engineering application perspective, ultrasonic sensors are by no means products that “can only measure water.” They are widely applicable to liquids, solids, granules, powders, and some complex surface targets. Currently, major manufacturers in the industrial sensor and instrumentation industry clearly apply ultrasonic technology to liquid level, solid level, granule, powder, and complex target detection scenarios.

However, they are not omnipotent. The core of the stability of ultrasonic measurement does not depend on the color, transparency, or luminescence of the material, but rather on a more fundamental factor: the acoustic reflection capability of the material surface and the stability of the on-site air medium.

Core Ranging Principle: Why Does the “Acoustic Characteristic” of the Material Determine Applicability?

The basic principle of the ultrasonic level sensor is TOF (Time of Flight).

The sensor probe emits a beam of high-frequency sound waves. The sound waves propagate through the air, reflect upon encountering the material surface, and the echoes are received by the probe. The control circuit calculates the distance based on the time difference between the emission and reception of the sound waves:

Distância=Speed of Sound×Round-trip Time2\text{Distance} = \frac{\text{Speed of Sound} \times \text{Round-trip Time}}{2}
Tempo de voo

If the overall installation height of the silo or storage tank is known, the system can further calculate the height of the liquid level, material level, or remaining space.

Ultrasonic Measurement Focuses on “Acoustic Reflection,” Not Color

Unlike photoelectric sensors, sensores ultra-sónicos mainly rely on the propagation of sound waves and echo reception. Therefore, they are typically not directly affected by the following visual or optical factors:

  • The shade of the material’s color;
  • Whether the surface is transparent;
  • Whether the surface is glossy;
  • The intensity of ambient light;
  • Whether the target is reflective.
Aplicações de monitorização ambiental para salpicos de poeiras líquidas de várias cores

Because of this, ultrasonic sensors can be widely used for measuring solids, liquids, granules, and powders, and are completely free from the limitations of target color, glossiness, and transparency. Ultrasonic level sensors can accurately identify transparent, dark, high-brightness, or structurally complex objects, and to a certain extent, can penetrate the interference of dust and fog.

Key Factors Affecting Measurement Stability

The core factors that truly determine whether an sensor de nível ultrassónico is suitable include:

  • Whether the surface can form effective echoes: Flat, hard, and dense surfaces are more prone to reflect sound waves;
  • Whether the material absorbs sound: Soft materials like sponge, foam, and fibers easily absorb acoustic energy;
  • Whether the surface fluctuates violently: Liquid tumbling, stirring, and material impact will cause the echo signal to jump;
  • Whether there is an excessive amount of foam, dust, or steam: These factors will absorb and scatter sound waves or change the speed of sound;
  • Whether the installation angle is correct: The probe should be as perpendicular to the average surface of the target as possible;
  • Whether the range, blind zone, and beam angle match: The selection logic for short distances in small tanks and narrow spaces in large silos is completely different.

In short, the ultrasonic level sensor measures “echoes.” As long as the material can feedback stable and sufficiently strong echoes, it can usually provide highly reliable measurement results.

Material Types Most Suitable for Ultrasonic Level Sensors

1. Various Liquids: From Clean Water and Wastewater to Certain Chemical Liquids

Liquids are one of the most common and technologically mature application targets for ultrasonic level sensors. Suitable liquids for measurement include:

  • Clean water, pure water, circulating water;
  • Sewage, wastewater, rainwater;
  • Coolant, cleaning fluid;
  • Mud, turbid liquid, settling tank liquid level;
  • Certain chemical liquids;
  • Oils, waste oil, lubricating fluid;
  • Liquid levels in storage tanks, vats, and water tanks.

Ultrasonic liquid level/material level sensors can not only be used for liquid and solid level detection but are also suitable for open channel flow monitoring, and can adapt well to transparent or turbid liquids, relatively dirty surfaces, and other complex targets. Their typical application scenarios cover industrial liquid level monitoring, water treatment, chemicals, and oil tanks.

Sensor ultrassónico para deteção de nível de líquido em recipientes químicos

Why are liquids generally more suitable? The surfaces of most liquids are relatively flat and continuous, which can form a very clear sound wave reflection interface. As long as the liquid surface is not violently tumbling and the foam is not thick, ultrasonic sensors can usually achieve highly stable distance measurement or liquid level monitoring.

Typical applications include:

  • Water treatment pool liquid level monitoring;
  • Sewage well and collection well liquid level alarms;
  • Chemical storage tank continuous liquid level acquisition;
  • Equipment water tank high and low-level control;
  • Oil tank and coolant tank allowance detection;
  • Open channel or open flume height measurement.

Liquid Conditions to Watch Out For: Although liquids are extremely suitable for ultrasonic measurement, the following potential risks still need to be evaluated in actual applications:

  • Whether there is excessively thick foam on the surface;
  • Whether there is intense mechanical stirring in the tank;
  • Whether the environment is filled with large amounts of high-temperature steam;
  • Whether the probe surface is prone to condensation and material buildup;
  • Whether the liquid surface has obvious tilting or vortices;
  • Whether there are structural interferences such as stirring paddles, ladders, or pipes inside the container.

Overall, if it is just non-contact measurement of ordinary clean water, sewage, oil, or chemical liquids, an ultrasonic level sensor is usually a very economical and easy-to-integrate preferred solution.

2. Regular Hard Solid Materials: Metal, Glass, Plastic Sheets, etc.

In addition to liquids, ultrasonic sensors are also very suitable for detecting hard, regular, and relatively flat solid targets. Typical materials include:

  • Metal plates;
  • Glass plates;
  • Hard plastic sheets;
  • Wooden boards;
  • Cardboard stacks;
  • Pallets, boxes, workpieces;
  • Large-sized flat objects;
  • Block materials with flat surfaces.

It must be emphasized that ultrasound is better suited for detecting “large and flat” solid surfaces, whereas its detection performance on soft or irregular targets is not ideal. This characteristic is crucial in industrial selection.

Why do hard flat surfaces work well? Hard flat surfaces generally possess two major acoustic advantages:

  1. Strong sound reflection: The surface material is dense and not prone to absorbing acoustic energy;
  2. Stable reflection direction: If the sensor is installed vertically, the echo can return to the probe along the original path to the greatest extent.

Therefore, in distance detection, in-position detection, object height detection, and stacking height detection, ultrasonic sensors perform extremely stably.

Altura de empilhamento da carga

Typical applications include:

  • Board stacking height detection;
  • Box in-position detection;
  • Pallet distance detection;
  • Robot obstacle avoidance;
  • Internal workpiece position monitoring in equipment;
  • Carton height or presence detection on packaging lines.

Installation Suggestions: When measuring hard solids, ensure as much as possible that:

  • The sensor squarely faces the target surface;
  • The target area is larger than the beam coverage area;
  • The surface is not overly tilted;
  • Avoid having edges, holes, or strongly irregular structures squarely face the probe;
  • For smooth metal or glass surfaces, even a slight angular deviation can cause the echo to deflect, resulting in a loss of signal.

3. Granular Materials and Powders

Granules and powders are the type of materials that most test engineering experience in ultrasonic level applications.

Os sensores ultra-sónicos são utilizados para a deteção do nível de material em armazéns

Common materials include:

  • Plastic granules;
  • Grains, corn, wheat, soybeans;
  • Feed pellets;
  • Sand, stone, ore particles;
  • Cement, lime powder, mineral powder;
  • Chemical powders;
  • Wood chips, pellet fuel;
  • Food powders, starch, flour.

In scenarios such as storage tanks, silos, and tanker trucks, ultrasonic level sensors are often used for level measurement of liquids, slurries, liquefied gases, as well as solid powders and granules.

Why are granules and powders “measurable but complex”? The difficulty lies not in the inability of ultrasound to reflect, but in the fact that the surface morphology of such materials is usually irregular. In a silo, powder and granular materials typically form a conical pile after dropping, and the angle of its slope is known in engineering as the Angle of Repose. When sound waves hit an inclined material surface, the echoes easily diffuse reflect, resulting in the sensor not receiving a sufficiently strong signal.

Furthermore, powder materials can also cause the following problems:

  • Generating massive dust during dropping;
  • Loose material surfaces causing sound waves to be absorbed or scattered;
  • Uneven surfaces leading to unstable echoes;
  • Material buildup on the silo walls easily generating false echoes;
  • Complex silo structures, internal crossbeams, or pipes causing acoustic interference;
  • Dust adhering to the sensor probe surface, reducing emission and reception efficiency.

Under what conditions are granules/powders more suitable for ultrasound? The success rate of ultrasonic measurement is higher when the following conditions are met:

  • The silo is not particularly deep;
  • The dust is not in a continuously high-concentration diffuse state;
  • The material particles are relatively large and the surface is quite dense;
  • The level height changes slowly;
  • The installation position can effectively avoid the feed inlet;
  • The sensor can aim at the average material surface as much as possible;
  • The selected sensor has a small beam angle to reduce wall reflection interference;
  • The site allows for echo debugging or filtering processing.

When should you be cautious? The following scenarios require extreme caution during selection, and sample testing should be conducted first if necessary:

  • Ultrafine powders or extremely light, highly fluffy powders;
  • Continuous dropping environments accompanied by high dust;
  • Extremely high and highly narrow silos;
  • The angle of repose of the material surface is too large;
  • Complex structural components exist within the silo;
  • Environments with strong vibration or strong airflow;
  • Accompanied by noticeable high-temperature steam or corrosive gases.

For the measurement of granules and powders, it is recommended not to only look at the “upper limit of the range,” but to comprehensively consider the beam angle, blind zone, echo processing algorithms, enclosure protection rating, dustproof structure, and reasonable installation position.

Which Materials Are Unsuitable or Prone to False Alarms?

Truly professional selection advice must not only state “what can be measured” but also clearly specify “when it is not recommended to use.” This is an important standard for judging whether a supplier has profound engineering experience.

1. Sound-Absorbing Materials and Soft Irregular Surfaces

Schematic diagram of ultrasonic sensor sound waves being absorbed by sponge

The following materials are generally not suitable for stable measurement using ordinary ultrasonic sensors:

  • Sponge, foam cotton, thick styrofoam;
  • Felt, cotton, textile fibers;
  • Extremely fluffy powders or lightweight materials with very loose surfaces;
  • Irregular soft packaging bag surfaces.

Core Reason: These materials absorb or scatter large amounts of acoustic energy. After the sound wave is emitted, a sufficiently strong and concentrated echo cannot be formed, and the sensor is extremely prone to having no signal, jumping values, or false alarms. In short, soft or extremely irregular-surfaced targets are not ideal objects for acoustic measurement.

If the on-site process mandates detecting such materials, consider:

  • Increasing the target reflection surface or changing the installation angle;
  • Shortening the actual detection distance;
  • Using sensors with larger acoustic power or specific operating frequencies;
  • Must be verified through actual on-site testing;
  • If necessary, decisively switch to weighing methods, radar, mechanical limit switches, or other detection principles.

2. Liquids with Extremely Thick Foam or Violent Fluctuations on the Surface

Foam is a very typical and tricky interference factor in ultrasonic liquid level measurement. Slight, thin foam can sometimes be improved through algorithmic filtering and installation optimization, but if the liquid surface is covered with a thick layer of foam, the ultrasound is highly likely to be completely absorbed and scattered by the foam layer, leading to violent fluctuations in measured values, and the sensor may even only measure the “foam surface” instead of the true liquid level height.

Scenarios prone to problems include:

  • Fermentation tanks, aeration tanks;
  • Strongly stirred reaction kettles;
  • Foam cleaning tanks;
  • Liquids containing large amounts of surfactants;
  • Containers in high-speed filling or draining operations;
  • Violently tumbling liquid surfaces in vats.

Response Suggestions: For foam, violently fluctuating liquid surfaces, and dust environments, the following measures are recommended:

  • Install the sensor in a relatively calm area of the liquid surface, making sure to avoid feed inlets and the stirring center;
  • Use a waveguide tube or stilling well to physically isolate the foam and improve the stability of the liquid surface;
  • Set reasonable filtering times in the control system;
  • Confirm the actual thickness of the foam on-site; if the foam is consistently extremely thick, decisively evaluate alternative solutions such as radar or hydrostatic transmitters.

3. Vacuum Environments and Extreme Steam/Condensation Environments

The physical characteristics of ultrasound dictate that it must rely on air or other gaseous media for propagation. Without a propagation medium, sound waves absolutely cannot reach the target. Therefore, ordinary air ultrasonic level sensors absolutely cannot be used inside a vacuum tank. This is a limitation determined by fundamental physical principles, not a technical difference between sensor brands.

Furthermore, extreme high-temperature steam and condensation environments also pose severe challenges:

  • Excess steam alters the density of the air medium, thereby changing the speed of sound and causing inaccurate distance measurement;
  • A large amount of condensed water adhering to the probe surface will severely attenuate the acoustic signal;
  • Temperature gradients inside the container will cause sound wave propagation errors (Note: Our products are standardly equipped with a temperature compensation function to address this issue);
  • Long-term high-humidity and high-temperature environments may affect the lifespan of internal electronic components (Note: Our products undergo rigorous aging tests before leaving the factory to ensure long-term stability);
  • Corrosive gases may damage ordinary enclosures or transducer materials (in this case, our anti-corrosion probe and sensor series should be selected).

Just as the applicable temperature and pressure ranges are emphasized in much liquid level meter documentation, ultrasonic sensors also have their distinct physical boundaries. Cautious selection is particularly recommended in the following scenarios:

  • Vacuum tanks or high-pressure sealed containers;
  • High-temperature steam tanks, strong condensation environments;
  • Strongly corrosive gas environments;
  • Equipment with violently changing internal temperatures;
  • Conditions where steam continuously scours the probe installation position.

Industrial Integration Guide: How to Select ISSRSensor Ultrasonic Sensor Parameters Based on Material?

As an underlying sensor manufacturing factory, when assisting customers with selection, we never just stop at “can it be measured,” but are dedicated to translating complex material characteristics into specific sensor parameters. For PLCs, DCSs, or lower-level equipment control systems, the core demand is always to obtain an electrical signal that is stable, repeatable, and easy to integrate.

The ISSRSensor industrial ultrasonic sensor series is widely used in scenarios such as ranging, liquid level, material level, transparent material detection, double-sheet detection, and deviation correction detection. When selecting, it is recommended to focus on evaluating the following parameters:

1. Range and Blind Zone: Avoid Being “Greedy for Large Range”

Ultrasonic sensors usually have a close-range unmeasurable area, known as the “Blind Zone.” Within the blind zone, after the sensor has just emitted a sound wave, the transducer is still in the ringing recovery stage and cannot reliably receive echoes at extremely close distances.

Therefore, when selecting, one must simultaneously confirm: the minimum detection distance, maximum detection distance, installation height, highest/lowest level points, internal structure of the tank, and the target surface’s reflection capability. Range, blind zone, and the actual measurement scope are core parameters that constrain each other.

Selection Logic:

  • Short distance/small containers/small workpieces: Prefer high-frequency, small-range, small-blind-zone sensors;
  • Medium storage tanks or water tanks: Choose medium range, equipped with models that have stable analog outputs;
  • Large silos/large spaces: Choose low-frequency, large-range models with narrower beam angles;
  • Dust or granular materials: Prioritize signal strength, beam angle, and correct installation angle;
  • Narrow containers: A narrow beam angle must be selected to prevent the sound beam from hitting the silo walls and generating false echoes.

Never blindly pursue an extra-large range just “to be on the safe side.” An oversized range not only brings a larger blind zone but also leads to a wider beam, lowered resolution, and introduces more on-site interferences that are hard to handle. The correct approach is: a range that just covers the actual detection distance and leaves a reasonable engineering margin is sufficient.

2. Frequency and Beam Angle: Balancing Penetration, Resolution, and Anti-Interference

The operating frequencies of ultrasonic sensors typically range from tens of kHz to hundreds of kHz, with different frequencies corresponding to distinct acoustic characteristics:

  • Low-frequency ultrasound: Propagates further and is extremely insensitive to air attenuation, making it more suitable for large silos and rough surfaces; but its beam is usually wider, and its resolution is relatively lower.
  • High-frequency ultrasound: Highly concentrated beam, extremely high resolution, and smaller blind zone, making it very suitable for short-distance precision detection; the disadvantage is noticeable signal attenuation over long distances.

For powder and granular materials, choosing a narrower beam angle can effectively circumvent wall reflections and internal structural component interference. For large flat liquid surfaces, the requirements for the beam angle are relatively loose, but attention must still be paid to avoiding feed inlets, stirring paddles, or drop pipes.

3. Output Signal: Closely Matching PLC/DCS Control Needs

The output format of the ultrasonic level sensor directly dictates how it will integrate into your automation architecture.

  • Switching Output (PNP / NPN)
    • Applicable scenarios: High/low-level alarms, overflow protection, empty silo detection, workpiece in-position and presence detection.
    • Lógica: When the material reaches the set threshold, it directly outputs an ON/OFF signal to the PLC. Very suitable for simple in-position detection on packaging equipment or full water tank alarms.
  • Analog Output (4–20mA / 0–10V)
    • Applicable scenarios: Continuous liquid/material level monitoring, storage tank allowance estimation, DCS trend recording.
    • Lógica: 4–20mA industrial standard has exceptionally strong anti-interference capabilities and is suitable for long-distance transmission; 0–10V has simple wiring and is suitable for shorter distances or internal integration inside equipment electrical control boxes.
  • Digital Communication Output (RS485 / Modbus, etc.)
    • Applicable scenarios: Centralized monitoring of multiple tanks, remote networking communication, docking with smart gateways, and IoT platform integration.
    • Advantage: It can not only read distances but also acquire the running status and diagnostic information of the sensor.

The key to selection is not the more functions the better, but that the output format must perfectly match the customer’s existing control system.

4. Enclosure Material, Protection Rating, and On-Site Environment

That a material is theoretically suitable for ultrasonic measurement does not mean that a sensor of any exterior form can withstand the rigors of the on-site environment. When selecting, it must be confirmed whether the site has the following challenges:

  • Is an IP67 or even higher protection rating required?
  • Will it be exposed to water vapor, high concentrations of dust, or oil stains for a long time?
  • Are corrosive chemical gases present on-site, and are anti-corrosion probes (such as PTFE material) needed?
  • Are there extreme high and low-temperature environments or mechanical impacts?
  • Is the equipment installation space limited, requiring a compact structure?
  • What are the specific installation standards for on-site flanges, threads, or brackets?

Scenario Examples: The water treatment industry values waterproofing and anti-corrosion more; powder silos heavily value dustproofing and anti-adhesion; packaging equipment demands fast response speed, small blind zones, and ease of compact installation.

5. Specific Process Extended Detection: Transparent Materials, Double Sheets, and Deviation Correction

The technical boundary of ultrasonic sensors goes far beyond material level measurement. Because they physically do not rely on optical characteristics at all, in highly challenging scenarios where photoelectric sensors tend to fail, ultrasound is often the only reliable solution.

The ISSR industrial ultrasonic sensor series not only excels at completing distance measurement and level monitoring but is also widely used in:

  • Precise detection of transparent films/fully transparent labels;
  • Double-sheet or overlap detection of paper, metal foil, and plastic film;
  • High-precision deviation correction of packaging material edges;
  • Real-time distance feedback on automated production lines.

In the papermaking, lithium battery, highly reflective film, and high-end printing industries, ultrasound has utilized acoustic transmission, reflection, and attenuation differences to achieve a stability far exceeding that of photoelectric principles. Therefore, in modern industrial automation, ultrasonic sensors should not merely be viewed as “liquid level meters”; they are, in fact, core non-contact acoustic detection components capable of outputting diverse control signals.

Quick Judgment Table: Which Materials Are Suitable for Ultrasonic Level Sensors?

Material Type Applicability Main Reason Selection and Installation Suggestions
Clean water, sewage, coolant High The liquid surface is continuous and flat, and the echo is clear and stable Take care to avoid violently fluctuating and foamy areas, and confirm the installation height
Oils, waste oil High The surface can usually form a stable mirror-like reflection Evaluate on-site oil mist, steam concentration, and ambient temperature
Chemical liquids Medium-High The vast majority of liquids can form effective reflections Must confirm corrosiveness, select anti-corrosion probes as appropriate
Mud, turbid liquids Medium-High Sound wave propagation is completely unaffected by liquid color and turbidity Pay attention to preventing excessive bottom deposition, liquid surface fluctuation, and surface foam
Metal plates, glass plates, hard plastic High Hard flat materials are dense, and the acoustic echo is extremely strong Must ensure the sensor is installed vertically squaring the target surface
Boxes, pallets, cardboard stacks High Large target reflection area, stable and reliable signal Avoid having workpiece edge features or inclined surfaces face the probe
Grains, plastic granules Medium-High The particle size is large enough to form an effective acoustic reflection surface Focus on evaluating the material’s angle of repose, and avoid the dust area of the feed inlet
Cement, mineral powder, chemical powder Medium Irregular surfaces easily lead to scattering, and dust absorbs acoustic energy On-site testing is strongly recommended; narrow beam, high power models are preferred
Sponge, foam, cotton, and other soft materials Low Soft materials severely absorb sound waves, and echoes are extremely weak It is highly unadvised to use normal ultrasound directly; alternative solutions should be considered
Liquid surfaces covered with thick foam Low The foam layer will completely absorb and scatter sound waves Consider installing a waveguide tube, or switch to radar/hydrostatic principle equipment
Inside vacuum tanks Not Applicable Lacking an air medium, sound absolutely cannot propagate in a vacuum Belongs to a physical limitation; liquid level meters based on other principles must be chosen
High-temperature steam environments Low-Medium Steam alters the speed of sound in the medium, and condensation adhesion affects the probe Must be equipped with temperature compensation function, confirm the risk of condensation buildup

Conclusion: To Judge Whether It Can Be Measured, the Core Lies in “Acoustic Reflectivity” and “Environmental Medium”

In summary, the ultrasonic level sensor is a non-contact measurement solution with an extremely wide application range, exceptionally high cost-effectiveness, and great ease of integration into PLC/DCS systems. It performs exceptionally well in the following scenarios:

  • Liquid levels in various containers (water treatment, sewage, oil tanks, chemical storage tanks);
  • Hard flat solid detection (distance control of boxes, plates, pallets, workpieces);
  • Allowance monitoring of granular materials and certain powder silos;
  • Non-contact precise recognition of transparent, dark, and highly reflective targets.

However, engineering rigor and caution must be maintained when facing the following extreme conditions:

  • Strongly sound-absorbing soft materials and extremely fluffy lightweight powders;
  • Liquids with surfaces covered in thick foam or tumbling violently;
  • Vacuum environments, high-temperature steam, or strong condensation environments;
  • Dust silos with abnormally complex internal structures.

For the engineering selection of automation engineers, the most reliable method is never to merely read product promotional headlines, but to make a comprehensive judgment combining the material’s own acoustic characteristics, the on-site installation space, the matching degree of range and blind zone, the size of the beam angle, the required output signal, and the actual environmental medium conditions.

If you are looking for stable and reliable ultrasonic level/ranging sensors for silos, storage tanks, water tanks, packaging equipment, or automated production lines, you are welcome to visit the ISSRSensor industrial ultrasonic sensor series page, or contact ISSRSensor to obtain professional sample testing support and selection parameter suggestions.

FAQ

Q1: Do the color or transparency of the target material affect the measurement results of an ultrasonic level sensor?

A1: No, they do not. Ultrasonic sensors rely on the principle of sound wave reflection (i.e., the propagation and rebound of sound waves), rather than optical properties. Therefore, they can reliably and accurately detect transparent, dark, or highly reflective materials, making them a highly dependable alternative in scenarios where photoelectric sensors might fail.

Q2: Can ultrasonic level sensors be used to measure granular and powdered materials?

A2: Yes, but caution is required when selecting a model. While they are capable of measuring grains, plastic pellets, and dense powders, extremely irregular surface morphologies (such as steep angles of repose) and heavy airborne dust can scatter or absorb sound wave energy. For such applications, it is strongly recommended to select a sensor with a narrow beam angle and sufficient transmission power, and to install it away from the material inlet.

Q3: Are ultrasonic level sensors suitable for liquids with a thick layer of foam covering the surface?

A3: Generally, no. A thick, continuous layer of foam acts as a soft, sound-absorbing material that completely absorbs and scatters ultrasonic waves. This results in weak signals, erratic readings, or even the sensor measuring only the “top of the foam” rather than the actual liquid level. For liquids with significant foaming, it is recommended to use a waveguide-assisted measurement system or to switch to radar or hydrostatic sensors instead.

Q4: Why cannot ultrasonic sensors be used in a vacuum environment?

A4: This is due to a fundamental physical limitation. Ultrasonic sensors operate based on measuring the “Time of Flight” (TOF) of sound waves. The propagation of sound requires a physical medium (such as air or other gases). In a vacuum, the absence of a medium to carry sound waves back and forth between the sensor and the target object makes measurement entirely impossible.

Q5: What is the “blind zone” of an ultrasonic sensor? Why shouldn’t I simply choose a sensor with the largest possible measurement range?

A5: The blind zone refers to the immediate area directly in front of the sensor; within this zone, the sensor cannot reliably receive echo signals because the transducer is still in its “recovery phase” immediately after transmitting a sound pulse. Sensors with a larger maximum measurement range typically feature a larger blind zone, a wider beam angle, and relatively lower resolution. Therefore, you should select a sensor whose measurement range precisely covers your actual detection distance (while allowing for a reasonable engineering margin) to avoid unnecessary interference.

Q6: Can ultrasonic sensors measure soft materials such as sponges, cotton, or felt?

A6: This is strongly discouraged. Soft, porous, or fluffy materials tend to absorb significant amounts of acoustic energy. When sound waves strike these surfaces, they fail to generate a sufficiently strong and focused echo to reflect back to the sensor probe; this often results in signal loss or false readings.

Q7: How do high-temperature steam and condensation affect ultrasonic measurements?

A7: Extreme steam environments alter the density of the air medium, thereby changing the speed of sound and leading to inaccurate distance calculations. Furthermore, the accumulation of significant condensation on the sensor probe can severely attenuate the ultrasonic signal. For such environments, it is necessary to select sensors equipped with built-in temperature compensation and anti-condensation designs.

Q8: What types of output signals do industrial ultrasonic level sensors typically provide to facilitate automation integration?

A8: They typically offer three main types of output signals to meet the requirements of PLC/DCS control systems: discrete outputs (PNP/NPN), used for simple high/low level alarms or position detection; analog outputs (4–20mA / 0–10V), used for continuous monitoring of liquid or material levels; and digital communication outputs (RS485 / Modbus), used for multi-point networking and the integration of smart devices.

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