Classification advantages and characteristics of electromagnetic flowmeter
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Classification advantages and characteristics of electromagnetic flowmeter
What are the advantages:
1 The electromagnetic flow meter transmitter has a simple structure, no moving parts, and no throttling parts that hinder fluid flow, so it does not cause any additional pressure loss when the fluid passes, and it does not cause such as wear and blockage. Such problems are especially suitable for measuring slurry with solid particles, liquid-solid two-phase fluid such as sewage, and various viscous slurries. Similarly, because it has no moving parts in its structure, it can be made of corrosion-resistant insulating lining and corrosion-resistant materials to achieve excellent corrosion resistance, making it suitable for the measurement of various corrosive media.
2 electromagnetic flow meter is a kind of volume flow measuring instrument, it is not subject to the temperature of the measured medium during the measurement process. The effect of viscosity, density and conductivity (within a certain range). Therefore, the electromagnetic flowmeter can be used to measure the flow of other conductive liquids only after water calibration, without the need for additional corrections.
3 The range of the electromagnetic flow meter is extremely wide, and the range ratio of the same electromagnetic flowmeter can reach 1:100. In addition, the electromagnetic flow meter is only proportional to the average flow velocity of the measured medium, and is independent of the flow state (laminar or turbulent flow) under the axisymmetric distribution.
4 electromagnetic flow meter has no mechanical inertia, sensitive response, can measure instantaneous pulsating flow, and linear. Therefore, the measurement signal can be linearly converted into a standard signal output directly by the converter, which can be indicated locally or remotely.
The measuring principle is Faraday's law of electromagnetic induction. The main components of the sensor are: measuring tube, electrode, excitation coil, iron core and yoke housing. It is mainly used to measure the volumetric flow in conductive liquids and slurries in closed pipes. It includes highly corrosive liquids such as acids, bases, and salts. The product is widely used in petroleum, chemical, metallurgy, textile, food, pharmaceutical, paper and other industries as well as environmental protection, municipal management, water conservancy construction and other fields.
Features:
1. Measurements are not affected by changes in fluid density, viscosity, temperature, pressure, and conductivity;
2. There is no obstructive flow component in the measuring tube, no pressure loss, and the requirements of the straight pipe section are low;
3, series nominal diameter DN15 ~ DN3000. Sensor lining and electrode materials are available in a variety of options;
4. The converter adopts novel excitation mode with low power consumption, stable zero point and high precision. The flow range can reach 1500:1;
5. The converter can be integrated with the sensor or separated;
6. The converter adopts 16-bit high-performance microprocessor, 2x16LCD display, convenient parameter setting and reliable programming;
7. The flowmeter is a two-way measuring system with three totalizers: positive total, reverse total and total difference; can be displayed. Zhuang, anti-flow, and has a variety of outputs: current, pulse, digital communication, HART;
8, the converter uses surface mount technology (SMT), with self-test and self-diagnosis function;
HHLD series electromagnetic flow meter flow range:
The range of the range is confirmed. Generally, the flow rate of the measured medium is 2~4m/s. Under special circumstances, the minimum flow rate should be no less than 0.2m/s, and the highest should be no more than 8m/s. If the medium contains solid particles, the flow rate should be less than 3m/s to prevent excessive lining and electrode friction. For viscous fluids, the flow rate can be selected to be greater than 2m/s. The larger flow rate helps to automatically remove the adhesion on the electrode. The effect of the hysteresis is beneficial to improve the measurement accuracy.
Caliber mm
Flow range m3/h
Caliber mm
Flow range m3/h
Φ15
0.06~6.36
Φ450
57.23~5722.65
Φ20
0.11~11.3
Φ500
70.65～7065.00
Φ25
0.18~17.66
Φ600
101.74～10173.6
Φ40
0.45 to 45.22
Φ700
138.47～13847.4
Φ50
0.71~70.65
Φ800
180.86～18086.4
Φ65
1.19~119.4
Φ900
228.91～22890.6
Φ80
1.81～180.86
Φ1000
406.94～40694.4
Φ100
2.83～282.60
Φ1200
553.90～55389.6
Φ150
6.36～635.85
Φ1600
723.46～72345.6
Φ200
11.3~1130.4
Φ1800
915.62~91562.4
Φ250
17.66~176.25.
Φ2000
1130.4～113040.00
Φ300
25.43～2543.40
Φ2200
1367.78～136778.4
Φ350
34.62~3461.85
Φ2400
1627.78～162777.6
Φ400
45.22~4521.6
Φ2600
1910.38～191037.6
HHLDE series intelligent selection table:
model
caliber
HHLD
15~2600
Code
Installation form
Y
One-piece
F
Split type
Code
Converter model
ZA
Round
ZB
Square
Code
output signal
I.4
4~20mA
f
Frequency 1KHz
Rs
Serial communication (485)
C
Control output
Code
Explosion protection requirements
N
No explosion protection
EX
Explosion-proof (only for split type)
Code
Medium temperature
T1
≤65°C
T2
≤120°C
T3
≤180°C (only for split type)
Code
Lining material
NE
Neoprene (≤65°C)
PTFE
Polytetrafluoroethylene (≤189°C)
PVC
Polyvinyl chloride (≤70 °C)
Code
Electrode material
316L
stainless steel
HC
Hastelloy C
HB
Hastelloy B
Ti
titanium
Ta
é’½
classification:
Electromagnetic classification according to excitation: DC excitation; AC excitation; low frequency square wave excitation
To produce a uniform and constant magnetic field, you need to choose a suitable excitation method. According to the excitation current mode, there are DC excitation, AC (power frequency or other frequency) excitation, low frequency rectangular wave excitation and dual-frequency rectangular wave excitation.
1. DC excitation: DC excitation uses DC or a permanent magnet to produce a constant uniform magnetic field. The biggest advantage of this DC excitation transmitter is that it is less affected by AC electromagnetic field interference, so the influence of self-inductance in the liquid can be ignored. However, the use of a DC magnetic field tends to cause the electrolyte liquid passing through the measuring pipe to be polarized, that is, the electrolyte is electrolyzed in the electric field to generate positive and negative ions. Under the action of the electric field force, the negative ions run to the positive electrode, and the positive ions run to the negative electrode, which will result in positive The negative electrodes are surrounded by ions of opposite polarity, which seriously affects the normal operation of the meter. Therefore, DC excitation is generally only used to measure non-electrolyte liquids, such as liquid metal flow (mercury at normal temperature and liquid steel at high temperatures, lithium, potassium).
2. AC excitation: Electromagnetic flow meters used in industry mostly use AC frequency excitation mode of power frequency (50Hz) power source to generate alternating magnetic field, avoiding polarization interference on the surface of DC excitation electrode. However, AC excitation brings a series of electromagnetic interference problems (such as orthogonal interference, in-phase interference, zero drift, etc.). AC excitation is now being replaced by low frequency square wave excitation.
3. Low-frequency square wave excitation: The low-frequency square wave excitation waveform has two values ​​(positive-negative) and three-valued (positive-zero-negative-zero), and its frequency is usually 1/2~1/32 of the power frequency. The low-frequency square wave excitation can avoid the orthogonal electromagnetic interference of the AC magnetic field, eliminate the power frequency interference caused by the distributed capacitance, suppress the eddy current caused by the AC magnetic field in the pipe wall and the fluid, and eliminate the polarization phenomenon of the DC excitation.
The measurement principle is based on Faraday's law of electromagnetic induction. The split type electromagnetic flowmeter consists of a sensor and a transducer. The sensor is mounted on the measuring pipe. The converter is installed within 30 meters or within 100 meters of the sensor. The two are connected by shielded cables. . The main components of the split type electromagnetic flowmeter sensor are: measuring tube, electrode, excitation coil, iron core and yoke housing. It is mainly used to measure the volume flow in conductive liquids and slurries in closed pipes. Such as water, sewage, mud, pulp, various acids, alkalis, salt solutions, food slurry, etc., widely used in petroleum, chemical, metallurgy, textile, food, pharmaceutical, paper and other industries as well as environmental protection, municipal management, water conservancy construction and other fields High temperature, high humidity, inconvenient observation environment. 
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