TURCK's levelprox series of sensors uses high-frequency ultrasound to achieve this detection. The new T50 sensor has two operating modes to meet a wide range of application needs.
Industrial level detection
Level detection in today's industry is critical to many automation solutions. The choice of sensor is as varied as its application. The key to choosing the right sensor is to consider its interaction with the measured medium. Most level control sensors need to be in contact with the measured medium. This category includes float switches, electrodes, and tuning-fork level sensors. However, in some industrial applications, direct contact of the sensor with the measured medium is not allowed, such as in the food and pharmaceutical industries. In order to meet harsh hygiene standards, the sensor must be completely sealed in a container. In addition, all the parts that come in contact with the medium will encounter the same problems, such as the material of the inner wall of the container and its surface finish. This type of sensor is also affected by the stirrer. In addition, the level sensor that is in contact with the medium also encounters troubles during maintenance and service. When it is necessary to replace the sensor, the container has to be opened and production is interrupted.
Using air as the transmission medium, an ultrasonic sensor for detecting the liquid level directly above the liquid does not need to be in contact with the liquid to be measured, but the ultrasonic transducer still needs to be installed inside the container. Therefore, the materials of such devices are also as difficult to meet the requirements of the food industry as those of contact detection devices.
Capacitance sensors can detect the liquid level through the vessel wall. However, the stainless steel containers often used in the food industry cannot be penetrated by the electric field of the capacitive sensor.
The ideal level detection device for the food and pharmaceutical industries should be able to detect the internal medium through the outer wall of the stainless steel container. In addition, it should also be easily installed on the outer wall of the container for easy maintenance and reliable performance. TURCK's "levelprox" series offers a simple, reliable level detection solution that meets all of these requirements. The unique dual working mode makes its application more extensive.
Principles of Operation There are several ways to use ultrasonic waves to detect the level of liquids on the outside of a container. However, all techniques are based on high-frequency ultrasound pulses, which are coupled to the outer wall of the container by a coupling glue. In reflection mode, the reflected echo of the container wall where the sensor is installed is detected and calculated.
This pulse will propagate within the container wall until it reaches the inner surface of the container wall. If the container is gas, the sound waves are almost completely reflected back to the sensor. At this point it will be reflected again and the pulses will be reflected back to the inner surface of the container, and so on. If the container is filled with liquid, some of the sound waves will be absorbed by the liquid. Absorption of sound waves leads to two consequences: the disappearance of the reflected waves and the propagation of a part of the ultrasonic waves through the liquid to the opposite wall of the container. The new levelprox series sensor LPRE-T50 can use the above two effects to generate switching signals.
Reflection Mode In this mode, the reflection of the supersonic pulse is calculated. The longer the reflection, the less liquid there is in the container. A brief reflection shows that the container is full. In this mode, the reflected echo of the inner surface of the container on which the sensor is installed is also calculated, and the inside of the container is no longer important.
This approach has particular advantages for the detection of heterogeneous media (mixed or containing large bubbles). If a stirrer is installed, this mode is also the best choice. However, the reflection method cannot be applied to those in which residue remains attached to the inner wall of the container in an empty state. Since the reflected echo is weakened by even a thin layer of media, it can cause the sensor to indicate that the container is full.
Echo mode Echo mode calculates the ultrasonic waves propagating in the liquid and the echoes reflected by the inner wall of the opposite container. If the ultrasonic pulse hits the vertical surface of the container, the echo will return along the same path and be detected by the sensor. In this mode, liquids containing large bubbles or the use of stirring devices can affect the detection. If the echo has sufficient intensity when it reaches the sensor, the sensor indicates that the container is full. If the echo is too weak, the sensor indicates an empty state. Even if media is attached to the inner wall of the container, it can be correctly indicated.
Adapting to a specific installation environment Regardless of whether the echo mode or the reflection mode is used, the type of the container, the mounting position of the sensor, and the characteristics of the liquid being measured are all critical factors. Levelprox products must learn the presence/absence of liquid sound waves before detecting the liquid level. Therefore, in the teach mode of the sensor, the empty and full state of the container must be taught by pressing the teach button. Levelprox automatically adapts to the surrounding acoustic environment. Rely on the standard curve detected in teaching mode to give the corresponding output signal. The same method can also be used to detect erroneous or poor coupling with the container wall. This error is indicated by the red LED and the alarm output.
Adjustments The working mode of the LPRE-T50 levelprox sensor can be selected via the DIP switch: reflection mode or echo mode. You can also use the DIP to select the normally open/closed mode of the switch, lock the teach pendant, and set the on/off delay. In the echo mode, the reflected echo of the opposite container's inner wall is calculated.
Installation The three-jaw snap ring allows the sensor to be easily mounted on the outer wall of the container. This method is widely used in the food industry. The snap ring adapter can be welded or affixed to the outer wall of the container. Then insert the sensor into the adapter, place the snap ring gasket, and finally fix it in place with the snap ring. The gasket seals off the sensor and the external environment to ensure its hygienic properties. The ultrasonic transducer head is elastically supported to ensure proper pressure. When properly installed, the sensor should be secured to the outer wall of the container with a certain amount of prestress, regardless of the diameter of the container.
The coupling medium is medically-friendly silicone. Ultrasound can be well coupled to the outer wall of the container, maintaining its viscosity and non-toxicity even at high temperatures.
More Applications Levelprox is an ideal sensor for detecting liquid levels through metal walls. It can be used not only in the food industry but also in systems and mechanical engineering. For example: Used to indicate the empty/full condition of paint containers, waste water, and hydraulic tanks. Due to the availability of paste installation, post-maintenance and adjustment can be easily completed. The sensor can be disassembled and installed in the existing installation position. In addition, the modification of the operating parameters of the switch point can also be achieved by simply relocating the sensor. In the future, there will be more kinds of shape and electrical design to enrich the levelprox product line.