Ultrasonic and radar level gauges operate on different principles, which makes them suitable for different applications. Radar level gauges rely on the dielectric constant of the material being measured, while ultrasonic gauges depend on the density of the substance. As a result, radar may not perform well with materials that have a low dielectric constant, making ultrasonic the preferred choice for solid materials. Additionally, radar uses electromagnetic waves, which can travel through air without needing a medium, whereas ultrasonic waves are sound waves that require a physical medium to propagate.
Radar systems also have different emission modes compared to ultrasonic ones. Ultrasonic devices use piezoelectric crystals that vibrate to generate sound waves, which limits their use in high-pressure or vacuum environments. They are typically used in atmospheric pressure tanks. In contrast, radar systems can be used in high-pressure process vessels. Radar has a wider beam angle than ultrasonic, so non-contact radar is not ideal for small or elongated containers—guided wave radar is often recommended instead.
In terms of accuracy, radar level gauges generally offer higher precision than ultrasonic ones. High-accuracy radar is commonly used in storage tanks, while ultrasonic is more suitable for less critical applications. Cost-wise, ultrasonic level gauges are usually more affordable. However, long-range ultrasonic models, such as those covering 6 to 70 meters, can be expensive. In such cases, radar may not be feasible, and ultrasonic becomes the only viable option.
Ultrasonic level gauges are non-contact, reliable, and cost-effective, offering maintenance-free operation. They eliminate issues like clogging, leakage, and contact with industrial media that are common in other methods such as pressure transmitters, capacitive sensors, or float systems. These advantages make them ideal for most open or closed containers.
With advancements in electronics, ultrasonic level gauges can now measure distances from a few centimeters up to tens of centimeters, even under harsh conditions. Their simplicity lies in their working principle: an ultrasonic probe at the top of the container emits a pulse, which reflects off the surface of the medium and returns to the probe. The time difference between the transmitted signal and the echo determines the distance to the surface.
Several factors affect the performance of ultrasonic level gauges. First, the speed of sound plays a crucial role in calculations. The formula D = t1 × C / 2 is used, where D is the distance, t1 is the time, and C is the speed of sound. Since the speed of sound varies with the medium, modern systems allow users to set different sound velocities for various materials to improve accuracy.
Temperature changes also impact the speed of sound. A temperature change of 1°C can alter the speed by about 0.17%. To compensate, many systems include temperature sensors and software to adjust measurements automatically. It's important to place the temperature sensor correctly, either separately from the probe or integrated into the system, to ensure accurate readings.
Pressure changes indirectly affect sound speed through temperature variations. While pressure itself doesn’t directly influence the speed of sound, it affects temperature, which in turn influences sound propagation. This relationship is described by the equation ln(T1/T2) = 1.4 × ln(P1/P2).
The transmission and reception of ultrasonic signals occur via piezoelectric crystals inside the probe. When an electrical signal is applied, the crystal vibrates, emitting sound waves. The same crystal then detects the returning echo. However, during the initial resonance phase, the probe may not accurately detect echoes, creating a "blind zone" where measurements are unreliable. This blind zone corresponds to a distance of about 1.7 meters for a 10ms delay.
Echo strength is another key factor. Stronger echoes lead to better detection, but they depend on the transmitted signal strength, the properties of the medium, and the reflectivity of the surface. In dusty environments, dust causes significant signal attenuation, though it has minimal effect on sound speed. Using low-frequency probes or special foam-coated surfaces can help mitigate this issue.
Airflow in open spaces can slightly affect the path of sound waves, but the impact is generally minor. The surface characteristics of the medium being measured also play a role. Liquid surfaces tend to produce stronger echoes than solid surfaces, which may scatter the signal in different directions, reducing the strength of the returned signal.
Despite these challenges, many manufacturers incorporate features like temperature compensation and echo tracking to enhance reliability. As a result, ultrasonic level gauges have become one of the most widely used non-contact measurement technologies in industries ranging from liquid level monitoring to solid material detection and open channel flow measurement.
Standing Desk Frame, High quality, primum
Suzhou Herstar Medical Technology Co., Ltd. , https://www.hosunherstar.com