Electromagnetic flowmeters
The measuring principle
As early as 1832, Michael Faraday tried to determine the speed of the current in the Thames by measuring the voltage induced in flowing water by the earth’s magnetic field. Electromagnetic flow measurement is based on Faraday’s law of induction. According to this law, a voltage is induced when an electric conductive fluid flows through the magnetic field of an electro- magnetic owmeter. This voltage is proportional to the flow velocity of the medium.
Electromagnetic flowmeters
The induced voltage is picked up either by two electrodes in contact with the medium or by capacitive electrodes with no contact to medium and supplied to a signal converter.
A signal converter amplifes the signal and converts it into a standard signal (4…20 mA) as well as to a frequency/pulse signal (e.g. one pulse for every cubic meter of measured medium that ows through the measuring tube).
Electromagnetic flow sensor in sandwich version
- Basic and fully functional flow sensor
- Excellent price performance ratio
- Quick and easy to install and operate
The OPTIFLUX 1000 electromagnetic flow sensor is the economic and ecological solution for various industries, ranging from agriculture to utilities and from fire fighting to machinery.
The instrument is economical due to low investment and maintenance costs; it is ecological due to accurate measurements and no waste.
Highlights
- Minimal or no inlets/outlets
- All KROHNE electromagnetic owmeters are wet-calibrated in a direct comparison of volumes
- Large choice of liner materials suitable for drinking water, wastewater, chemicals, SIP/CIP and solids
- Suitable for use in custody transfer applications
- Measurement is independent of the ow pro le
- Abrasion and corrosion-resistant liners available
- Ceramic measuring tubes and liners available for ange and sandwich versions, also with non-wetted electrodes (capacitives owmeter)
- Speci c models for partially lled pipes
- Virtual reference option: grounding electrodes and grounding rings can be left out
- Electric conductivity of medium can be used for detection of product change
- For high bubble content, high solids content and pulsating ow
- Secure handling of rapid medium changes and pH jumps
- Zero-point stability regardless of changes in medium properties
- Nominal sizes DN 2.5 to 3,000
- 3×100%-diagnostics (application and device diagnostic, out-of-spec-test) exceeds NAMUR requirements
Electromagnetic flow measurement: Increased safety through the use of high-performance ceramics in flange design
The converter is not the only critical factor in the reproducibility of the measured value during electro- magnetic flow measurement. The form stability of the measuring tube under temperature and pressure stresses also plays an important role. To obtain a reliable measurement even with critical media, the measuring tube material, the electrode construction and the process connection must all be taken into account.
The challenge: The new measuring tube material should be highly resistant to caustic, corrosive and abrasive media and show off its superiority to conventional liners made of plastic such as PFA.
KROHNE accepted this challenge and, in close cooperation with FRIATEC AG from Mannheim, Germany, developed a high-performance ceramics for industrial use which can even withstand rapid temperature changes and high mechanical stresses.
When it comes to measuring critical media such as those used in chlorine chemistry, it was also necessary to optimise the electrode construction. The result of these efforts? Using the so-called Cermet electrode has made it possible to develop a 100 % gap-free design. In doing so, the metal of the electrode combines with the material of the ceramic to form an insoluble compound when exposed to high temperatures.
In addition to the sandwiched version, our engineers also developed a flanged version. This version not only guarantees easy installation but also minimises the risk of leakage in case of a fire.
It is no wonder that the fields of application of the ceramic electromagnetic owmeter are so numerous today. They range from measuring acids and alkalis in chemistry to usage in chlorine chemistry, to the volumetric filling of liquids in the beverage, pharmaceutical and cosmetics industries.
KROHNE offers its customers complete application and process diagnostics as well as an accuracy and linearity test (out-of-spec diagnostics) in addition to the usual device diagnostics for the OPTIFLUX line.
With the indicators supplied by OPTIFLUX and knowledge of the process, the user can detect the following application problems with a high degree of certainty:
- Gas bubbles
- Electrode corrosion, deposits on electrodes
- Short-circuit
- Low conductivity of measured medium
- Partial lling of measuring tube
- Liner damage
- External disrupting magnetic elds
- Disrupted flow profileDuring the out-of-spec test, a determination is made, both online and cyclically, as to whether the device is still within its speci cations. In particular, the accura- cy is tested by feeding a test signal. The linearity of the device and the accuracy of the eld current with which the magnetic eld is generated are also checked.
Thanks to the 3×100%-diagnostics, the OPTIFLUX is much more than a simple owmeter: it examines the process and provides the user with valuable infor- mation. In this respect, the OPTIFLUX even exceeds the requirements of VDI/VDE/NAMUR 2650.
Industries
- Agriculture
- Fire-fighting
- Machinery and apparatus construction
- Swimming pools and recreational facilities
Applications
- Precise dosing of liquid fodder, liquid fertilizers, measurement of liquid manure, sprinkler
irrigation systems - Vehicles, fire extinguishing systems: foam mixing, control of sprinkler systems
- Heat counters, energy allocation to buildings and workshops
- Water recirculation and treatment
Cost efficient and reliable flow sensor
The flangeless OPTIFLUX 1000 electromagnetic flow sensor is compact and lightweight. The design is robust with the highly resistant, reinforced PFA liner and Hastelloy® electrodes. This offers an excellent chemical resistance.
The device is a cost-efficient and reliable solution for a wide range of applications. For industries varying from water and wastewater, agriculture, utilities and from fire-fighting to machine building.
