There are many classification methods for electromagnetic flow meters, and there are also many types of products corresponding to each classification. When selecting products, it is necessary to have a basic understanding in order to make a good selection and ensure the correct use of the product. This article provides the following six conventional classifications for electromagnetic flow meters.

Classification of electromagnetic flow meters

1、 Classification by sensor and converter assembly method

Split type electromagnetic flowmeter: Split type is the most commonly used form of electromagnetic flowmeter, with sensors connected to pipelines and converters installed in the instrument room or near sensors that are easily accessible to people, with distances of tens to hundreds of meters. To prevent external noise intrusion, signal cables are usually shielded with double layers. When measuring liquids with low conductivity and converging for more than 30m, in order to prevent signal attenuation caused by partial capacitance of the cable, it is also required to connect the inner shielding to a shielding drive with a low impedance source of the same potential as the core wire. The separated type converter can be far away from harsh on-site environments, making electronic component inspection, adjustment, and parameter setting more convenient.

Integrated electromagnetic flow meter: The sensor and converter are assembled together to directly output a standard DC current (or frequency) signal, which in fact becomes an electromagnetic flow transmitter. The integrated system shortens the connection length of the signal line and excitation line between the two, and makes them externally connected and concealed inside the instrument, thereby reducing signal attenuation and spatial electromagnetic wave noise intrusion. Similarly, the measuring circuit can measure liquids with lower conductivity compared to the split type. The wiring of signal and excitation lines has been eliminated, simplifying electrical connections. The instrument prices and installation costs are relatively cheap, and small diameter instruments are more commonly used. With the commercialization of second line instruments, there will be rapid development of integrated instruments. However, if installed in inaccessible locations due to pipeline layout limitations, maintenance is inconvenient. In addition, the electronic components of the converter installed on the pipeline will be greatly limited by fluid temperature and pipe vibration.

2、 Classification based on whether the flow sensor electrode is in contact with the measured liquid

Contact type electrode - The electrode in contact with liquid is the traditional structure of EMF, usually consisting of one pair of electrodes. Large caliber electromagnetic flow meters use two pairs of electrodes. Non full tube EMFs also have 3 pairs of motors or strip electrodes.

Non contact electrodes - Large area electrodes are tightly attached to the outer surface of the lining (or insulated measuring tube), and flow signals are monitored through capacitive coupling. Electromagnetic flow meters that can measure capacitance detection compared to contact electrodes are referred to as capacitive electromagnetic flow meters. The preamplifier is placed inside the sensor, only relying on the electrode, and the excitation frequency is higher than the usual EMF, which is 50/2Hz, with some exceeding 100Hz. This type of instrument will not generate electrode surface effect noise such as electrode passivation, oxidation, and catalyst action, and there may also be no flow noise or slurry noise. The inner surface of the lining is covered with non conductive layers such as grease or thin insulation structural layers, which 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 electrodeless electromagnetic flowmeter.

3、 Classification by flow sensor and pipeline connection method

Flange connection - Flange connection is a traditional connection method, where the sensor has connecting flanges at both ends and is bolted to the pipeline flange for one-way installation. The large-diameter sensors of electromagnetic flow meters adopt this connection method. The volume and weight are both larger than the clamping connection method. The length between two flange faces of DN15-600mm electromagnetic flow meters has been standardized by the International Organization for Standardization (ISO13359-1998).

Flange clamp connection: The flange clamp connection is a connection method developed in recent years. The sensor of the electromagnetic flow meter itself does not have a 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 has strong adaptability to different pressure specifications and standard pipe flange hole spacing; But it is only suitable for smaller pipe diameters (below 200mm) and can withstand lower liquid working pressure.

Clamp connection: The clamp type connection can achieve rapid disassembly and installation of electromagnetic flow meters, making it convenient for frequent daily cleaning.

Thread connection: This type of electromagnetic flow meter is widely used in industries such as medicine and food, as well as in scenarios such as pharmaceutical proportioning injection. Threaded connections are also widely used for high-pressure water injection or cement slurry flow measurement above 16~25MPa in petroleum, geological exploration, and other fields. The shape of the thread is trapezoidal.

4、 Classification based on output signal connection and excitation (or power supply) wiring system

Four wire electromagnetic flow meter - The four wire system is the main current system of traditional electromagnetic flow meters, which consists of two sets of four wire systems with two wires each for the output signal line and power line (or the excitation wire between the flow sensor and the sensor).

Two wire electromagnetic flow meters - Currently, field instruments for parameters such as temperature, pressure/differential pressure, flow rate, and material level tend to develop two wire instruments that share wires for output signals and power supply. Two wire instruments do not require mains power, and electromagnetic flow meters are often installed in remote places without mains power supply. Adopting a two wire system can save on the cost of mains wiring engineering. The design concept of the power supply for the two-wire electromagnetic flowmeter can be divided into zero signal output current (i.e. 4mA) supply, greater than zero signal output supply, and battery (or solar cell) supply. Battery powered electromagnetic flow meters and electromagnetic water meters are suitable for configuration in places far away from urban distribution pools or suburban sewage treatment discharge points where it is difficult to introduce electricity. Some models of instrument batteries have a lifespan of 1-2 years, while others can last up to 8-10 years.

5、 Classification by flow sensor structure

Pipeline type electromagnetic flow meter: The pipeline type structure is similar to the structure of traditional electromagnetic flow meters, and the flow sensor is connected to the pipeline system with a measuring pipe section.
Insertion type electromagnetic flow meter: The insertion type flow sensor is essentially an electromagnetic flow rate sensor. The excitation coil and electrode are assembled into a rod shape, inserted into a hole on the pipeline to be tested, and the measured flow rate is multiplied by the coefficient of the pipeline area preset by the converter to obtain the flow rate. In addition to the single point "point velocity", there are also multi point "radial velocity" on the side. This type of instrument is suitable for large pipelines because it measures local flow velocity to calculate fluid flow rate, with lower measurement accuracy than short pipe types. It is usually only used for process control and is not suitable for trade accounting measurement, but its price is relatively cheap.

6、 Classification by purpose

Universal type: In industries such as metallurgy, petrochemicals, papermaking, printing and dyeing, textiles, water supply, sewage treatment, etc., split type medium and large diameter flange connections are commonly used; Micro and small caliber instruments are commonly used in industries such as medicine, biology, and fine chemicals. Electromagnetic flow meters with integrated clamp connection or threaded connection are widely used in various places.

Explosion proof: Explosion proof electromagnetic flow meters are used in places with flammable gases. Due to the high current energy of most electromagnetic flow meters, they are usually designed as explosion-proof, sand filled, sealed, and airtight types. But now some electromagnetic flow meters have significantly reduced their excitation power, and there are also intrinsically safe types, formerly known as safety spark types. The flow sensor and conversion parts are conditionally integrated and all are installed in hazardous areas.

Hygienic: Industries such as cheese, food, medicine, and biochemistry require regular steam sterilization. Sensors should be easy to disassemble and clean, and the connection to pipelines should use a fast loading and unloading hygienic structure. Materials in contact with liquids should be non-toxic and harmless. The sanitary electromagnetic flowmeter is developed to meet the above requirements.

Submersible resistant - suitable for underground inspection wells, capable of withstanding short periods of water immersion, equivalent to an enclosure protection level of IP67 or NEMA6; There are also electromagnetic flow meters with a protection level equivalent to IP68, which can withstand long-term diving.