【Weekly Question 20090720】Experience in Selecting Magnetostrictive Level Gauges

1# wwxxss_1 is mainly used for level measurement. The data includes the names of the two media, the density of the media, the operating pressure and operating temperature under specific conditions, the center distance between the flanges, the tag numbers, and so on. For maintenance, the main focus is on proper configuration and avoiding various interferences. Product: Magnetrol

1. Magnetostrictive level gauges are used for measuring the liquid level in oil tanks, and their advantages include: 1. High reliability: Since magnetostrictive level gauges operate on the principle of waveguides and have no mechanical moving parts, there is no friction or wear. The entire converter is enclosed in a stainless steel tube, remaining in non-contact with the medium being measured; as a result, the sensor operates reliably and has a long service life. 　　2. High precision: Since the magnetostrictive level gauge operates using guided pulses, it determines the measured displacement by measuring the time between the starting pulse and the ending pulse, which results in high measurement precision. Its resolution is better than 0.01% FS, a precision that is difficult to achieve with other sensors. 　　3. Good safety: The magnetostrictive level gauge has high explosion-proof capabilities, featuring intrinsically safe design, which ensures safe use; it is particularly suitable for measuring chemical raw materials and flammable liquids. There is no need to open the tank lid during measurement, thereby avoiding the safety risks associated with manual measurement. 　　4. Magnetostrictive level gauges are easy to install and simple to maintain: They are generally installed through existing pipe openings at the top of the tank, making them particularly suitable for installation in underground tanks and those that are already in use, without disrupting normal production during installation. 　　5. Facilitates automated system operation: The secondary instruments of magnetostrictive level gauges use standard output signals, which makes it easy for microcomputers to process these signals. This facilitates networked operation and enhances the degree of automation of the entire measurement system. 　　Working principle: The magnetostrictive level gauge consists of three parts: a probe rod, a circuit unit, and a float. During measurement, the circuit unit generates a current pulse, which travels downward along the magnetostrictive wire and creates a circular magnetic field. A float is attached to the probe rod, and this float moves up and down along the probe rod as the liquid level changes. Since the float is equipped with a set of permanent magnets, it generates a magnetic field as well. When the current magnetic field meets the float’s magnetic field, a “twist” pulse, or “return” pulse, is generated. The time difference between the \"return\" pulse and the current pulse is converted into a pulse signal, thereby determining the actual position of the float and measuring the liquid level. 2. We have not used magnetostrictive level gauges, but we believe that the medium being measured by such gauges should not contain too many particles or impurities; this is an aspect to keep in mind when selecting one!

1. Advantages such as high reliability, precision, good safety, ease of installation and maintenance, and suitability for system automation enable the business philosophy that \"there is no best, only better.\" 2. Selection data: measurement range, medium temperature, operating pressure, material of the float and magnetostrictive wire, specifications of the mounting flange, and sealing type ； Operating voltage, wiring system, output signal, communication protocol, protection rating, explosion protection rating, etc. When selecting, attention should be paid to the viscosity and the allowable range of the dielectric constant of the medium. 3. This device requires minimal maintenance; only proper sealing of the transmitter and regular cleaning of the float are necessary. The K-TEK AT100 series is really good!

Magnetostrictive level gauges are generally chosen when integrated local and remote monitoring is required. It has high precision and is easy to maintain. Their measurement ranges do not need to be the same as the flange spacing; it is sufficient that the remote measurement range matches the local measurement range. The parameters that need to be provided during selection are the measurement range, medium temperature, density, viscosity, operating pressure, material of the float and magnetostrictive wire, installation flange specifications, and sealing type ； Operating voltage, output signal, protection rating, explosion-proof rating, etc.

For magnetostrictive effects, I recommend Emerson; I chose it in previous designs, and it has performed very well so far – it’s stable and offers high precision.

In storage tanks equipped with internal floating disks, the instrumentation and equipment teams must pay special attention to the positioning of the openings in the magnetostrictive level gauge equipment, in order to avoid problems such as collisions between the float well and the internal struts of the floating disk during installation, as well as significant damage to those internal struts. The diameter of the openings in the floating disk should be larger than the diameter of the float (and weight).

A magnetostrictive level (interface) gauge is mainly composed of a non-magnetic probe rod (stainless steel tube), a magnetostrictive wire (waveguide), a float, as well as amplification circuits, signal processing circuits, conversion and transmission circuits, etc； Magnetostrictive level gauges feature extremely high measurement accuracy, simple and easy installation and calibration, a long service life, and can also measure interface levels ； The data that need to be provided during selection include: measurement range, operating temperature, operating pressure, density, viscosity, material of the float, specifications of the mounting flanges and type of sealing surface, output signal, protection rating, explosion protection rating, etc. If measuring liquid level, a guided-wave radar level gauge can also be used ； If measuring the boundary condition, radio frequency admittance can be used.

Mainly, the price of magnetostrictive materials is relatively high, so they are used less often. It meets all standard measurement conditions, offers wide adaptability, and boasts high precision!

Our company uses it quite a lot. However, the brand is relatively limited to Tianjin K-TEK; in my opinion, its stability is poor. This is evident in two main aspects: first, the threshold voltage of the transmitter section needs to be adjusted frequently; second, the detection section is prone to faults such as open circuits, and once it gets damaged, the device is essentially unusable. For example, although the level gauge on the storage tank wasn’t vibrating, it started to malfunction after the detection rod was cleaned once – it’s quite fragile. However, this type of level gauge has significant advantages in measuring interface levels, as it only requires setting the density of the float; moreover, its calibration is simple. In particular, level gauges for levels up to 2 meters are quite stable, while those for levels above 3 meters require more maintenance.

Our unit also uses a large amount of such devices; there are tanks with position sensors, as well as devices for detecting changes in position – such as the position of the stationary blades in fans and turbines, or the opening degree of valves. The devices that were installed two years ago have hardly been maintained at all. What’s most surprising is that there’s a blower produced by Sulzer in Switzerland back in 1987, which uses magnetostrictive position transmitters to monitor the angle of its stationary blades. I checked it again yesterday without needing to adjust the zero point or range settings. It’s likely that the manufacturer no longer exists. Most of the devices we use now are from Beijing Kangyutongda, and their performance is very stable; foreign brands like Schaevitz offer even greater reliability.