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Principle, Selection And Installation Requirements Of Electromagnetic Flowmeter

Author:vacorda    Source:www.vacorda.com    Date: 2020-05-07 10:43:33
Principle of electromagnetic flowmeter

The electromagnetic flowmeter is made according to Faraday's law of electromagnetic induction. The electromagnetic flowmeter is used to measure the volume flow of conductive liquids. The electromagnetic flowmeter is composed of an electromagnetic flow sensor and a converter. Due to its unique advantages, electromagnetic flowmeters have been widely used in the flow measurement of various conductive liquids in industrial processes, such as various acids, alkalis, salts and other corrosive media;

Product features of electromagnetic flowmeter
▲ There are no moving parts and no choke parts in the pipeline, and there is almost no additional pressure loss in the measurement.
▲ The measurement results are related to the physical parameters such as flow velocity distribution, fluid pressure, temperature, density, and viscosity.
▲ At the scene, the range can be modified online according to the actual needs of the user.
▲ High-definition backlit ICD display, full Chinese menu operation, easy to use, simple operation, easy to learn and understand.
▲ SMD device and surface mount (high reliability of SMT circuit)
▲ 16-bit embedded microprocessor, fast operation speed, high precision, programmable frequency and low frequency rectangular wave excitation, which improves the stability of fluid measurement and low power consumption.
▲ Full digital processing, strong anti-interference ability, reliable measurement, high accuracy, flow measurement range up to 150: 1
▲ Ultra-low EMI switching power supply, using a wide range of power supply voltage.
▲ There are three totalizers in it, which can display the forward cumulative amount and the difference totalized amount respectively. There is no power-down clock inside, which can record 16 power-down times.
▲ Digital communication signal output such as RS485, RS232, Hart and Modbus.
▲ With self-inspection and self-introduction function

Technical parameters of electromagnetic flowmeter
▲ Nominal diameter series DN (mm), special specifications can be customized
▲ Flow direction: positive, negative, net flow
▲ Range ratio: 150: 1
▲ Repeatability error: ± 0.1% of measured value
▲ Accuracy grade: pipeline type: 0.5 grade, 1.0 grade
▲ Temperature of measured medium: ordinary rubber lining: -20 ~ + 60 ℃
▲ High temperature rubber lining: -20 ~ + 90 ℃
▲ Teflon lining: -30 ~ + 100 ℃
▲ High temperature vinyl lining: -30 ~ + 180 ℃
▲ Rated working pressure: pipeline type: DN10 ~ DN65: ≤2.5MPa;
                                                DN80 ~ DN150: ≤1.6MPa;
                                                DN200 ~ DN1200: ≤1.0MPa
▲ Flow measurement range: The flow velocity range corresponding to the flow measurement range is 0.3 to 15m / s.
▲ Conductivity of measured fluid: ≥5μs / cm (Most media with water as its component, whose conductivity is in the range of 200-800μs / cm, can use electromagnetic flowmeter)
▲ Output: Current: 4-20mADC (fully isolated); pulse frequency 0 ~ 1KHz, photoelectric isolation OCT, external power supply ≤35VDC, maximum current of collector when turning on is 25mA
▲ Electrode material: 316L, titanium (Ti), tantalum (Ta), Hastelloy (H), platinum (Pt) or other special electrode materials
▲ Protection level: ordinary type: IP65, diving type: IP68
▲ Working power: 85~265VAC, 45~63HZ
▲ Straight pipe length: pipeline type: upstream ≥5DN, downstream ≥2DN
▲ Connection method: Both the flow meter and the piping are flanged. The flange connection size should meet the requirements of GB9119-88.
▲ Explosion-proof: mdIIBT4
▲ Ambient temperature: -25 ℃ ~ + 60 ℃
▲ Relative temperature: 5% ~ 95%
electromagnetic flowmeter (3)
Selection of electromagnetic flowmeter

Selecting the type, specifications, and installation method of the flowmeter according to the measurement object, measurement medium parameters, and working conditions is the most important part in the selection of the electromagnetic flowmeter. For the end-use unit, the selection points are as follows:

1. Precision levels and functions

Select the accuracy of the electromagnetic flowmeter according to the measurement requirements and the application. For example, in the case of trade settlement, product transfer and energy measurement, you should choose high precision (such as 1.0, 0.5 or higher).

2. Test medium flow rate, meter range and caliber

When measuring general media, the full-scale flow of the electromagnetic flowmeter can be in a wide range of 0.5-12m / s for the flow rate of the measurement medium. The selection of instrument specifications (caliber) is not necessarily the same as the process pipeline, and it should be determined according to whether the measurement flow range is within the flow rate range. That is, when the flow velocity of the pipeline is too low to meet the requirements of the flow instrument, the diameter of the instrument needs to be reduced to increase the flow velocity in the tube and obtain satisfactory measurement results. For liquids with good conductivity, the maximum flow rate does not exceed 5m / s, and the economic flow rate ranges from 1.5m / s to 3m / s.

3. Electrode material and ground ring material

The corrosion resistance of the electrode to the measurement medium determines which electrode material is selected, and at the same time, the surface level of the electrical level is not required. In other words, the corrosion resistance of the electrode is an important basis for selecting the material.

The material of the grounding ring should be the same as that of the electrode, otherwise it is easy to generate electrochemical polarization potential. Generally, 316L or Hastelloy is used. From economic considerations, noble metals such as tantalum and platinum are rarely used.

Metal process pipes are in direct contact with the medium, and the ground wire is directly connected to the metal pipe or flange, so no ground ring is required.

Electromagnetic flowmeter sensor installation environment installation environment requirements

The protection level of the electromagnetic flow sensor housing is generally IP65 (International GB4208 housing protection level-dustproof and water-proof). For the choice of the installation place, please refer to Chapter 5, Section 5. The main requirements of the installation environment are:
(1) The sensor should be installed in a dry and ventilated place, avoiding humid and easily flooded places, and avoid direct sunlight and rain directly.
(2) Avoid installing in places where the ambient temperature is too high. The integrated structure of the electromagnetic flowmeter is also subject to the ambient temperature of the electronic components, which should be lower.
3 (3) There should be no strong leakage current on the pipeline where the sensor is installed, and it should be as far away as possible from equipment with strong electromagnetic fields, such as large electromechanicals and large transformers, so as not to cause electromagnetic field interference;
(4) The pipeline or ground on which the sensor is installed should not have strong vibration, especially the integrated instrument;
(5) The place where the sensor is installed should consider the space for maintenance on site.

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