Electromagnetic flow meter has a variety of classification methods, each classification below also have a lot of kinds, the following is an introduction to the electromagnetic flowmeter commonly used six classification methods.
According to the output signal connection and excitation (or power) line system classification
- Four-wire electromagnetic flowmeter
Four-wire system is the traditional electromagnetic flowmeter output signal line and power line (or flow sensor and the sensor between the magnetization wire) by two groups of two wires respectively, is the current main system. - Two-wire electromagnetic flowmeter
Current temperature, pressure / differential pressure, flow and level and other parameters of the field instrumentation tends to output signals and power supply with a common conductor two-wire instrumentation development. Two-wire instrumentation does not require utility power, and electromagnetic flowmeter is often installed in remote places without utility power supply, the use of two-wire system can save utility wiring engineering costs.
Two-wire electromagnetic flowmeter power supply design ideas are 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 flowmeter and electromagnetic water meter adapted to the configuration of the city far from the distribution pool or suburban sewage treatment discharge points and other utility power introduction difficulties in the place. Some models of meters battery life of 1-2 years, some up to 8-10 years.
According to the sensor and converter assembly method classification
- Split electromagnetic flowmeter
Split-type electromagnetic flowmeter is a very common form of application, the sensor into the pipeline, the converter is installed in the instrumentation room or people are easy to access near the sensor, dozens to hundreds of meters apart. In order to prevent the intrusion of external noise, the signal cable is usually double shielded. Measurement of low conductivity liquids and more than 30m together, in order to prevent the cable part of the capacitance caused by signal attenuation, the inner shielding is also required to be connected to the same potential as the core line with a low impedance source of shielding drive. Separate type converter can be far away from the site of harsh environments, electronic parts inspection, adjustment and parameter setting is more convenient. - All-in-one electromagnetic flowmeter
Sensor and converter assembled together directly output DC current (or frequency) standard signals, in fact, electromagnetic flow transmitter. The one-piece type shortens the connection length of the signal line and magnetizing line between the two, and makes it external, hidden inside the instrument, thus reducing signal attenuation and space electromagnetic noise intrusion. The same measurement circuit can be used to measure liquids with lower conductivity than the split type. Eliminate the signal line and magnetizing line wiring, simplify the electrical connection, instrumentation prices and installation costs are relatively inexpensive, more often used in small pipe diameter instrumentation. With the commercialization of two-wire instrumentation development, a body-type instrumentation will have faster development. However, if the pipeline layout restrictions, installed in places that are not easily accessible, it is inconvenient to maintain. In addition, the converter electronic components mounted on the pipe, will be subject to fluid temperature and pipe vibration of the larger limitations.
According to the flow sensor and pipe connection mode classification
- Flange connection
Flange connection is the traditional connection, the sensor has a connecting flange at both ends, and the pipe flange with the bolt between the fixed, can be installed unidirectionally. Large caliber sensors are used in this connection. Volume and weight are larger than the clamped connection. DN15 ~ 600mm electromagnetic flowmeter length between the two flange surface, the International Organization for Standardization has developed standards (ISO 13359; 1998) to be unified. - Flange clamping connection
Flange clamping connection in recent years when the development of the connection, the sensor itself can not Lan, with longer bolts clamped between the two flanges in the pipeline access to the pipe system. This way the sensor is small in size and light in weight, for different pressure specifications and standard pipe system flange hole spacing adaptability; but only applies to smaller pipe diameter (200mm below), to withstand the working pressure of the liquid is low. - Clamp connection
The clamp connection enables quick disassembly and installation, and facilitates frequent daily cleaning. - Threaded connection
This type of instrument is more often used in the pharmaceutical and food industries, and the pharmaceutical proportioning and injection places. Threaded connection is also more often used in petroleum, geological exploration and other high-pressure water injection or cement slurry flow measurement above 16 ~ 25MPa, the shape of the thread is trapezoidal.
According to the flow sensor electrode is in contact with the measured liquid classification
- Contact electrode
Electrodes in contact with the liquid is the traditional structure of the EMF, usually a pair of electrodes, large-diameter instrumentation industry, there are two pairs of electrodes. Non-full tube type EMF is also useful for 3 pairs of motor or strip electrodes. - Non-Contact Electrodes
Large-area electrodes close to the lining (or insulated measuring tube) external surface, capacitive coupling to pick up the flow signal, can be measured than the contact type electrodes capacitive detection method of electromagnetic flowmeter referred to as capacitive electromagnetic flowmeter. Pre-amplifier placed in the sensor only by the electrode, the excitation frequency is higher than the usual EMF, 50/2Hz, there are more than 100Hz. This type of meter will not produce electrode passivation, oxidation and catalytic effects such as electrode surface effect noise, there is no chance of flow noise and slurry noise. The inner surface of the liner covered with grease and other non-conductive layer or a thin insulating structural layer will not affect the measurement; but if the cover layer is a conductive film, the meter will not indicate.
According to the flow sensor structure classification
- Pipeline electromagnetic flowmeter
Pipeline structure that is, such as the structure of the traditional electromagnetic flowmeter, flow sensor with a measuring pipe section connected to the pipeline system. - Insertion type electromagnetic flow meter
Insertion type flow sensor is essentially electromagnetic flow rate sensor, magnetizing coil and electrode assembled into a rod, from the pipe to be measured on the hole inserted, the measured flow rate and converter preset coefficients such as the area of the pipeline multiplied by hydrochloric acid to obtain the flow rate. In addition to single-point “point flow rate”, there are side multi-point “runoff speed”. This type of instrument is suitable for large pipelines, because it is the measurement of local flow rate deduction of fluid flow, measurement accuracy is lower than the short pipe type, usually only used for process control, is not suitable for application in trade accounting measurement, but the price is relatively inexpensive.
Classification by use
- General purpose
In metallurgy, petrochemical, paper, printing and dyeing, textile, water supply, sewage treatment and other industries generally use more split type in large diameter flange connection; pharmaceutical, biological, fine chemical and other industries commonly used in small caliber, small caliber instrumentation, one-piece clamping connection or threaded connection is more suitable for the place. - Explosion-proof
Explosion-proof electromagnetic flowmeter is used in places with flammable atmosphere. Because most of the electromagnetic flowmeter several times the current energy is large, usually designed as explosion-proof, sand-filled, pouring sealing type and gas-tight type, etc. But now some electromagnetic flowmeter excitation energy. But now some electromagnetic flowmeter excitation power is greatly reduced, there is also an intrinsically safe type that is previously known as the safety of spark type, flow sensor part and the conversion part of the conditions of the composition of a whole, all installed in the hazardous area. - Hygienic type
Cheese, food, medicine, biochemistry and other industrial requirements of regular steam sterilization, the sensor should be easy to dismantle and clean, and pipeline connection part of the requirements of rapid loading and unloading of the sanitary provisions of the structure, and the liquid contact material should be non-toxic and harmless. Sanitary electromagnetic flowmeter is developed to meet the above requirements. - Diving-resistant type
Used in manholes installed under the ground, can withstand short-term water intrusion, equivalent to the shell protection class IP67 or NEMA6; there are also equivalent to the protection class IP68, can withstand long-term diving. - Submersible
Used to measure the flow of waterways, such as industrial drainage and sewerage, under the natural flow of free water in open channels or non-full pipe culverts. The sensor is installed in the lower part of the cut-off baffle of the nullah and is immersed underwater for a long period of time. Used for high flow moments to install multiple diversion models with the same shape as the sensor to expand the flow.
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