There are several industries that rely on liquid level sensors, particularly for safety reasons, process optimization, or leak detection. These include the medical, chemical, water and sanitation, food and beverage, transportation, and petrochemical industries. Over the decades, several techniques and technologies have been employed to obtain accuracy and reliability. These have come at varying expenses, durabilities, and applications. This article focuses on magnetostrictive level transmitters. Specifically, how they work, their application, and stand-out features in contrast to other forms of liquid level detection.
An Overview of Industrial Liquid Level Sensors
There are two broad types of liquid level sensors. Point level sensors detect when a liquid reaches a specific level. These are usually employed to raise alarm when a fluid reaches a concerning level. The level could be too high, thus, indicating the potential of a spillage or pressure build-up or it could be too low, which could be the result of leakage. Continuous level sensors are useful for processes during which the levels of a liquid fluctuate and accurate measurement of volume is necessary or required. There are several factors to consider when selecting an appropriate method to track the levels of liquids beyond whether point or continuous level detection is required. Factors include the chemical composition, density, viscosity, and other properties of the liquid measured, including its propensity to foam, the characteristics of vapors produced by the liquid, if any, and the surrounding atmosphere or environment.
Magnetostrictive level transmitters are continuous float level sensors that provide near real-time level measurements by creating competing magnetic fields to generate a signal corresponding to liquid level. Other types of continuous level sensors include radar transmitters, ultrasonic sensors, and submersible pressure transducers. Each of these has unique features that make them suitable or inappropriate for different applications.
How Magnetostrictive Level Transmitters Work
Magnetostriction is a property exclusively found in ferromagnetic materials, i.e. materials attracted to or capable of forming permanent magnets. It refers to how the ferromagnetic molecules in such elements or compounds cause these substances to expand or contract in response to the introduction of a magnetic field. Essentially, they can convert electromagnetic energy into vibrations or mechanical energy.
Magnetostrictive float level measurement sensors are composed of three main components. A hollow stem containing a waveguide made from ferromagnetic material is suspended in the liquid being measured. A hollow float moves with the surface of the liquid up and down the stem. Inside this float is a permanent magnet. As the float moves, its magnetic field changes the alignment of the magnetic molecules of the waveguide in the stem. The third component is the device electronics. The electronics produces an electromagnetic pulse at predetermined intervals. This pulse travels down the waveguide, creating its own magnetic field. When this pulse reaches the float, the conflicting magnetic fields create vibrations in the waveguide, causing a torsional stress wave, or strain pulse, to propagate back up the waveguide at a known speed. The strain pulse is detected by a component of the electronics that converts the mechanical energy into an electronic signal. Last, an electronic chip measures the time lapse between the initial pulse and the returning strain pulse, thus, determining the distance between the device electronics and the float with a high degree of accuracy.
Advantages of Magnetostrictive Level Transmitters
As previously mentioned, magnetostrictive transmitters are very accurate. They can report the levels of a liquid to within 0.04 inches (1.00 mm). In addition to this accuracy, their design, components, and mechanics mean this technology has low installation and maintenance costs, requires minimal effort in calibration, and results in lower downtimes and longer life spans. Further, magnetostrictive level sensors have capabilities that cannot be matched by competing technologies, such as radar transmitters, ultrasonic sensors, and submersible pressure transducers.
Like magnetostrictive probes both radar and ultrasonic sensors are time of flight instruments that determine levels based on the time lapse between the initial transmission and the reflected return signal. Radar level transmitters use electromagnetic radiation to detect the levels of liquid. They emit low-energy, high-frequency impulses that reflect off the surface of the liquid measured. Also like magnetostrictive transmitters, high-quality radar transmitters, such as those which utilize True Echo™ technology, should not have their accuracy adversely affected by the presence of foam, vapors, or other environmental factors. The radar sensors’ electromagnetic waves travel through all kinds of media at the speed of light; as such, they are accurate as long as they are reflecting off the correct surface. Ultrasonic level sensors utilize soundwaves that are imperceptible to humans to detect the liquid level. Unlike magnetostrictive probes and radar sensors, ultrasonic sensors can have inaccurate readings due to excessive heavy vapor build-up, foam, thick dust, or aerosols that could create a false surface.
Unlike magnetostrictive probes, both radar and ultrasonic sensor technologies are non-contact level sensors that rely on the beam of electromagnetic waves and soundwaves, respectively, to reach the surface being measured and return to the sensor. This means these sensors can encounter beam angle complications. Because level transmitters are contact level sensors, they save the user from dealing with beam angle complications that are present when using non-contact level sensors such as radar and ultrasonic sensors.
Submersible pressure transducers, on the other hand, are contact level sensors that determine the levels of liquids by measuring the pressure applied to a given surface area, and, given the known density of the liquid above, the level can be calculated. Obviously, this relies on having consistent liquid densities, and any chemical variations result in inaccurate measurements. Magnetostrictive level transmitters are advantageous over submersible pressure transducers because they only require the stem of the instrument to be submersed in the liquid being measured rather than the entire instrument and cables. Because the cable isn’t exposed to the liquid being measured, the magnetostrictive probe can be used in harsher environments and is more chemically compatible than the submersible pressure transducer.
Magnetostrictive level transmitters also excel at measuring interface level. There are several industrial and commercial operations that store liquids that separate into two distinct layers because of different densities of liquids. With these immiscible liquids, such as a water solution and an organic compound like oil, it is possible for a single magnetostrictive level sensor to provide the separate levels of each liquid. More than one float can be attached to a single stem. The bottom float can be precisely weighted such that it sinks in the lighter fluid but floats on the denser bottom layer.
Applications of Magnetostrictive Level Transmitters
There are several applications to consider. In the current globalized economic environment, competitive pressures can arise from anywhere in the world. Lean practices, which focus on minimizing waste and getting precise measurements of inputs required in production just in time when they are needed, are no longer just a competitive advantage. They may be the difference between survival and loss of customers due to price incompetence.
Additionally, consumers are more demanding with regards to quality and less patient with underperforming products and companies, in general. If products vary in quality due to fluctuating chemical compositions, consumers will notice this as a weakness. As a result, most businesses involved in chemically complex processes often employ a quality assurance team which checks that each batch meets their standards. The work required from this department can be significantly reduced by the ability to take precise measurements during any given process in real-time. This reduces the number of bad batches produced and limits waste. Further, early detection of erroneous processes can limit downtime during production. Magnetostrictive level transmitters enable a business to measure exactly how much their production cycles require in terms of input material, predict when refills will be needed, and reduce the chances of overstocking and incurring needless storage costs
Furthermore, magnetostrictive level sensors can be built with temperature sensors along the inside of the stem. As such, whether there is more than one liquid or not, this technology can be used to measure temperature differences at several levels. These features, and the materials used to make these sensors, make magnetostrictive level sensors quite suitable in industries that work with hazardous materials, such as the petrochemical industries. Leaks of corrosive liquids or other pollutants come at a high cost for any business. There may be many strategies employed to prevent leakage. However, it is crucial to detect leaks early as the longer leaks go undetected, the more significant the damage done to the external environment and, potentially, to equipment used.
Magnetostrictive level transmitters can detect slight changes in the levels of liquid in an operational container, in storage, or being transported in near real-time should those levels deviate from expected volumes. On the other hand, processes that require a constant flow of liquid as it is blended with other ingredients, for example in the water purification process or the manufacture of certain beverages, could be vulnerable to contamination or variation in quality if the flow rate is too fast or too slow. With these applications, magnetostrictive transmitters should come equipped with several features. Among the best designs of level sensors are those which are made from a resilient material. Depending on the purpose, the stem material used could range from general purpose stainless steel to chemically-resistant titanium. Sensors can also be made with electronic components that make the sensor explosion proof or intrinsically safe. These variations can be customized to maximize the sensors safety compatibility for the application it is used in.
APG manufactures a range of transmitters for various industries and purposes. Because different businesses and industries use a diverse collection of containers, APG offers a range of magnetostrictive level sensors suited for various tank or container sizes. Further, the sensors manufactured by APG can be customized according to your specific business needs. Customizable features include probe length, stem type, float type, specific gravity, and outputs. One of the vital features incorporated in these sensors is Tank Cloud compatibility. In a digital and information age, businesses need not rely on the availability of an individual on-site to check readings off a meter. Tank Cloud enables sensors to relay information via the internet, enabling the significant reduction in time required between the discovery of adverse events and a course of action being reached by decision-makers.