New instrument diagnostic concepts offer interesting approaches for process optimisation due to high reliability and accuracy, low maintenance requirements, low power consumption and insignificant pressure loss, electromagnetic flowmeters (magmeters) are among the process industries’ preferred flow measuring devices. The diagnostic options offered by magmeters like the OPTIFLUX are especially interesting. These options not only provide users with insight into the device status but also into the process itself.

Electromagnetic flowmeters (magmeters) presently make up 30% of the European flowmeter market. Even though the measuring principle has been in use for more than 30 years, industry experts still figure there is annual growth of more than 2%. This can be attributed to the versatility and largely independent nature of viscosity, density, pressure and temperature of the flowing medium. In addition, there are no built-in components in the flow cross section of the measuring sensor. To cover the widest possible spectrum of applications, KROHNE developed a complete series of measuring technology sensors, all belonging to the OPTIFLUX line.

The measuring technology was further optimized in conjunction with the newly developed an economical IFC 100 converter a successor to IFC 300, the high-end model. For example, the sensors were fitted with highly effective shielding measures, resulting in accuracy of 0.15% and a reproducibility of 0.06% for the ceramic sensor. Thanks to improvements in data processing, the OPTIFLUX achieves very high application reliability, even with media containing a high degree of air bubbles or suspended solid content or those with pulsing flows. And thanks to its superior accuracy and comprehensive diagnostic possibilities, it is also suitable for custody transfer applications.

Due to the integrated conductivity measurement, application areas not previously options for conventional magmeters have been opened up to the OPTIFLUX, including, media change detection, for example. So in many cases there is no need for an additional conductivity measuring device. Further, the OPTIFLUX features a series of approvals, whether it’s for custody transfer (OIML,KIWA),Hazardous area applications (ATEX,FM,CSA,SAA,…) or hygienic applications (3A, EHEDG). That means that it is not just an all-purpose device, but one that can be used around the world as well.

Always a solution

Nevertheless, some special measuring situations call for somewhat modified series. One example is volumetric filling in the beverage industry, such as PET bottles. Here, in addition to the usual hygienic requirements in the food and beverage industries, there are dynamic requirements of the flow meters. Precise filling is particularly difficult with carbonated contents as the bottles stretch while being filled. The flowmeter must feature extremely high reproducibility for volumes filled within a few seconds. In conjunction with leading system manufacturers, KROHNE developed the BATCHFLUX for these applications. It has since become the industry standard for use in filling machines. Thanks to its extreme form stability, the high-tech ceramic measuring tube guarantees unrivalled long-term stability and thus no change in the reproducibility of the filling volume for years.

TIDALFLUX flow meters feature a capacitive filling height measuring system behind the liner, providing precise and reliable flow measurement in partially filled pipelines. This applies regardless of whether the pipeline is filled to 10 or 100% of the pipeline cross section. That makes them predominantly suitable for measurements in the wastewater industry, in gravity fed networks (_2°), transfer stations, in the outlet of rain spillway basins and water treatment plant inlets and outlets. The device guarantees that data is displayed calmly, even when the surface of the medium is rough, or when there are waves or foam in the measuring tube. The fill level sensors do not come into contact with the liquid. This eliminates the possibility of interference caused by oils and fats floating on the surface. The OPTIFLUX 2000 and ENVIROMAG series have also excelled equally as a water and wastewater specialists, standing out mainly due to their long-term stability and reliability. The series possesses all international drinking water approvals, meets OIML R-49, ISO 4064, DVGW and ISO installation lengths and is also available in sizes up to DN 3000. Therefore they are used for drinking water but also for ground water, wastewater, cooling water and leak detection.

If a magmeter is exposed to extraordinary strains such as corrosive or abrasive media or high operating pressures, users rely on the OPTIFLUX 5000 with ceramic measuring cell. Typical examples include measuring acids and bases in the chemical industry or measuring products with highly abrasive materials in the mining industry or on dredgers. This device model is available in a sandwich version and now as a flange version.

Knowing the causes of errors

The broad range of the magmeters, as described, has resulted in more than three million of these flow meters in use today. However, as before, many devices still only feature simple diagnostic options, only providing information about the device status, while neglecting other aspects such as the specific process environment or whether the device is operating outside its specifications. In this respect, modern magmeters can do much more. Users and manufacturers have pooled their experience about the most common error modes of field devices and their wishes in terms of diagnosis and have come up with a NAMUR guideline. Due to their importance when it comes to process measuring technology, electromagnetic flow meters (magmeters) were also described. Typical application errors include gas bubbles in the product, electrode corrosion, too low conductivity, liner damage, deposits on electrodes, external magnetic fields, electrode short-circuit or partial filling. Errors in signal processing as well as non-linearity can also lead to data errors. The OPTIFLUX series diagnostic concept detects all of these error states. They can lead to measuring errors, fluctuating displays or even to long-term destruction of the magmeters. The OPTIFLUX 3×100% diagnosis comprises three different series of tests – testing of device functions, testing for adherence to specifications (out-of-spec-diagnosis) and the application test. When checking the device functions, for example, the microcontroller, the memory and the outputs are checked. With out-of-spec testing, online and cyclical tests are run to determine whether the device is still within its specifications in terms of accuracy and linearity. What is of interest is the information the measuring device provides about the process. When it comes to application testing, the device detects whether, for example, there are gas bubbles in the product. It is particularly useful where containers are filled or emptied in batches and as a consequence, gas bubbles and partial filling of the lines have previously resulted in erroneous measurements. Thanks to the variety of tests included in the 3×100% diagnostic concept, the user is assured of the smooth functioning of the measuring point in difficult applications and environmental conditions. This is made possible by the combination of the sensor from the OPTIFLUX magmeters series and the IFC 300 converter. Three examples demonstrate the performance of the diagnostic concept:

Monitoring the measuring electrodes

The converter injects an alternating current IEP into the process liquid by way of the magmeters electrodes. This current generates a voltage drop URE, which depends on the resistance RE, in other words the electrical conductivity of the product. From this, errors like electrode contamination short-circuit and interruption of electrode line (important for magmeters with separate converters) can be deduced:

The measured resistance REl enables the indication of the conductivity s and e.g. the following statements:

• Conductivity outside of the permitted limits of the magmeters or medium

• Change in medium (e.g. transition from process to cleaning liquid or vice versa in CIP processes)

• Quality of cleaning processes (e.g. wastewater)

Further, status outputs with adjustable switching points or bus connections signalize an overstepping or under-running of associated conductivity values.

Checking linearity of magnetic circuit and signal processing

This patented magmeters linearity test is based on the EMF equation U =v • B • k • D where

U = induced signal voltage,

v = average flow rate,

B = induction in the measuring tube,

k = proportionality constant,

D = pipe diameter

Normally, induction B and signal voltage U are proportional to field current IF, used by the converter to feed the field coils. For the linearity test, the amplitude of the rectangular field current IF is intermittently switched to 50% of the nominal value. As long as everything is linear, B, U and the output of the primary signal processing must be reset to 50% of the value present at full current IF (100%). When the magnetic circuit or electronic system is non-linear, this setpoint of 50% is not adhered to. This is detected and reported by the converter.

Detection of external magnetic fields

Among other things, magmeters are used in electrolysis plants or on electric furnaces in strong external magnetic fields. Such fields can saturate the ferromagnetic yoke of the magmeters magnetic circuit. This yoke is supposed to provide the magmeters useful field with low magnetic resistance on its return on the outside of the measuring tube. When saturated, the resistance increases. The induction B in the measuring tube and signal voltage U become smaller. This can result in errors when displaying the flow. Without an external field, rectangular current IF generates a field strength stroke H via the magnetic coils and an induction stroke B. This determines the signal voltage U. When switched to 50% of the field current, B and U are reset linearly to 50% of the previous values. A strong external field with field strength H0 moves the working point of the magnetic circuit to the nonlinear saturation area of the magnetization curve B = f(H). The relationship of the induction and the signal voltage values with a field current of 100% and of 50% then deviates from the set point. This is a clear indication that the accuracy of the magmeters is being influenced by the external magnetic field and leads to a message.

Conclusion

The combination of electromagnetic sensors and the intelligent IFC 300 converter sets new standards in device and process diagnostics. The IFC 100, a new member of the KROHNE flowmeter family available since the beginning of 2008, also benefits from this. While the IFC 300 converter is used more in critical applications such as measuring media with a high degree of suspended solid content, right down to highly accurate custody transfer applications, the new converter was developed for both simple applications in the water industry as well as for demanding standard applications in chemistry.The converter has already proven its reliability in a comprehensive field test. In addition to the chemical and water industry, the device is also used in the food industry, environmental technology as well as mechanical engineering and power plants. With the most complete and most innovative range of magmeters devices on the market, there is hardly an application that is not covered. Even when other standard devices can no longer be used,KROHNE is almost always ready with an answer. The KROHNE Magmeters show that they can handle almost any measuring situation, not only providing reliable data but also supporting the user in process optimization.

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