Several classification methods for electromagnetic flow meters

Electromagnetic flow meters are classified based on whether the flow sensor is in contact with the measured liquid or not:

(1) Contact type electricity

The electricity in contact with liquids is the traditional structure of EMF, usually consisting of one pair of electricity, while the large-diameter instrument industry uses two pairs of electricity. Non full tube EMF also uses 3 pairs of motors or strip electrodes.

(2) Non contact electrical

The electromagnetic flowmeter with a large area of electricity closely attached to the outer surface of the lining (or insulated measuring tube) can detect the flow signal by capacitive coupling, and can measure the capacitance detection method of contact type electricity. The principle is shown in the diagram above. The preamplifier is placed inside the sensor and relies solely on electricity. The excitation frequency is higher than the usual EMF, at 50/2Hz, and there are also those that exceed 100Hz. This type of instrument does not generate electrical surface effect noise such as passivation, oxidation, and catalytic effects, and there may be no flow noise or slurry noise. Covering the inner surface of the lining with non-conductive layers such as grease or thin insulation structures will not affect the measurement; But if the covering layer is a conductive film, the instrument will have no indication.

Some foreign instrument manufacturers refer to this type of instrument as an electromagnetic flowmeter without electricity.

Electromagnetic flow meters are classified according to the structure of flow sensors:

(1) Short tube type

The short tube structure is similar to the structure of traditional electromagnetic flow meters, where the flow sensor is connected to the pipeline system with a measuring pipe section.

(2) Insertion type

The plug-in electromagnetic flowmeter sensor is essentially an electromagnetic flow velocity sensor, which is assembled into a rod shape with an excitation coil and electricity. It is inserted into an opening on the pipeline to be measured, and the measured flow velocity is multiplied by a coefficient equal to the pipeline area preset by the converter to obtain the flow rate. In addition to the single point "point flow velocity", there are also side multi-point "radial flow velocities".

This type of instrument is suitable for large pipelines because it measures local flow velocity to calculate fluid flow rate, with measurement accuracy much lower than short pipe types. It is usually only used for process control and is not suitable for trade accounting and measurement. But relatively cheap. The application features can also be found in the plug-in flowmeter.

Classified by the connection method between flow sensors and pipelines:

(1) Flange connection

The traditional connection method for flange connection involves connecting flanges at both ends of the sensor, which are fixed to the pipeline flange with bolts and can be installed unidirectionally. Large caliber sensors all use this connection method. The volume and weight are both larger than the clamping connection method.

The length between the two flange faces of DN15-600mm electromagnetic flow meters has been standardized by the International Organization for Standardization (ISO 13359; 1998).

(2) Clamp on connection

Clamp on connection is a connection method developed in recent years. The sensor itself has no flange and is clamped between the two flanges of the pipeline with longer bolts to connect to the pipeline system. This sensor has a small volume and light weight, and is highly adaptable to different pressure specifications and standard pipe flange hole distances; But it is only suitable for smaller diameters (below 200mm) and can withstand lower liquid working pressures.

Several classification methods for electromagnetic flow meters

(3) Sanitary Connection

An example of a Chinese sanitary connection in the right picture, connected to the IDF support component of the International Dairy Federation, enables quick disassembly and installation, facilitating frequent daily cleaning.

Several classification methods for electromagnetic flow meters

(4) Threaded connection

The threaded connection method of the Chinese instrument in the following figure. This type of instrument is commonly used in industries such as pharmaceuticals, food, and pharmaceutical injection systems. Threaded connections are also widely used for high-pressure water injection or cement slurry flow measurement above 16-25MPa in petroleum, geological exploration, etc. The thread shape is trapezoidal.