Corrosion resistant high-frequency electromagnetic flowmeter

Corrosion resistant high-frequency electromagnetic flowmeter can not only meet on-site display requirements, but also output 4-20mA current signals for recording, regulation and control. It has been widely used in industrial technology and management departments such as chemical, environmental protection, metallurgy, medicine, papermaking, water supply and drainage.

1Corrosion resistant high-frequency electromagnetic flowmeterInstrument Introduction:

The measurement accuracy of high-frequency electromagnetic flowmeter is not affected by changes in fluid density, viscosity, temperature, pressure, and conductivity. The sensor induced voltage signal is linearly related to the average flow rate, resulting in high measurement accuracy. There is no obstruction in the measuring pipeline, so there is no additional pressure loss; There are no movable parts inside the measuring pipeline, so the sensor has an extremely long lifespan. Due to the fact that the induced voltage signal is formed in the entire space filled with a magnetic field and is the average value on the surface of the pipeline, the sensor requires a shorter straight pipe section, with a length of 5 times the diameter of the pipeline. The sensor part only has the inner lining and electrodes in contact with the measured liquid. As long as the electrode and inner lining materials are selected reasonably, they can be corrosion-resistant and wear-resistant.

2、 Working principle:

The high-frequency electromagnetic flowmeter, based on Faraday's principle of electromagnetic induction, installs a pair of detection electrodes on the pipe wall perpendicular to the axis of the measuring tube and the magnetic field lines. When the conductive liquid moves along the axis of the measuring tube, it cuts the magnetic field lines and generates an induced potential. This induced potential is detected by the two detection electrodes, and its value is proportional to the flow rate. Its value is E=KBVD equation:

E - Induced potential;

K - coefficient related to magnetic field distribution and axial length;

B - Magnetic induction intensity;

V - average flow velocity of conductive liquid;

D - electrode spacing; (Measuring the inner diameter of the tube)

The sensor uses the induced potential E as a flow signal, which is transmitted to the converter. After amplification, transformation, filtering, and a series of digital processing, the instantaneous and cumulative flow rates are displayed on a backlit dot matrix LCD. The converter has 4-20mA output, alarm output and frequency output, and is equipped with communication interfaces such as RS-485, and supports HART and MODBUS protocols.

IIICorrosion resistant high-frequency electromagnetic flowmeterMain components:

A high-frequency electromagnetic flowmeter consists of a sensor and a converter. The sensor is installed on the measuring pipeline, and the converter can be combined with the sensor to form an integrated electromagnetic flowmeter. The converter is installed within 30 meters or 100 meters of the sensor, and is connected by a shielded cable to form a separate electromagnetic flowmeter. The main components of the anti-corrosion electromagnetic flowmeter sensor are: measuring tube, electrode, excitation coil, iron core, and magnetic yoke housing.

4、 Application scope:

High frequency electromagnetic flow meters can not only meet on-site display requirements, but also output 4-20mA current signals for recording, regulation, and control purposes. They have been widely used in industrial technology and management departments such as chemical, environmental protection, metallurgy, medicine, papermaking, and water supply and drainage. In addition to measuring the flow rate of general conductive liquids, electromagnetic flow meters can also measure the volumetric flow rate of liquid-solid two-phase flow, high viscosity liquid flow, and salt, strong acid, and strong alkali liquids.

5、 Advantages:

1. The instrument structure is simple, reliable, without moving parts, and has a long working life.

2. No flow blocking components, no pressure loss or fluid blockage.

3. No mechanical inertia, fast response, good stability, can be applied to automatic detection, adjustment, and program control systems.

4. The measurement accuracy is not affected by the type of measured medium and its physical parameters such as temperature, viscosity, density, pressure, etc.

5. Different combinations of PTFE or rubber lining materials and electrode materials such as Hc, Hb, 316L, Ti can adapt to the needs of different media.

6. There are various flow meter models available, including pipeline type and plug-in type.

7. Using EEPROM memory, the storage of measurement and operation data ensures safety and reliability.

8. It has two types: integrated and separated.

9. High definition LCD backlit display.

6、 Performance indicators:

1. Instrument accuracy: pipeline type 0.5 level, 1.0 level; Insertion type 2.5 level.

2. Measurement medium: various liquid and liquid-solid two-phase fluids with conductivity greater than 5 μ S/cm.

3. Flow velocity range: 0.2-8m/s.

4. Work pressure: 1.6MPa.

5. Environmental temperature: -40 ℃ to+50 ℃.

6. Medium temperature: PTFE lining ≤ 180 ℃; Rubber material lining ≤ 65 ℃.

7. Explosion proof mark: Exmibd Ⅱ BT4.

8. Explosion proof certificate number: GYB01349.

9. External magnetic interference: ≤ 400A/m.

10. Shell protection: integrated type: IP65;

Detached type: Sensor IP68 (5 meters underwater, with rubber lining); Converter IP65.

11. Output signal: 4-20mA.DC, load resistance 0-750 Ω

12. Communication output: RS485 or CAN bus

13. Electrical connection: M20 × 1.5 internal thread, φ 10 cable hole

14. Power supply voltage: 90-220V.AC, 24 ± 10% V.DC

15. Maximum power consumption: ≤ 10VA

7、 Range confirmation:

The flow rate of the medium measured by the general industrial electromagnetic flowmeter should be 2-4m/s. In special circumstances, the minimum flow rate should not be less than 0.2m/s, and the maximum flow rate should not be greater than 8m/s. If the medium contains solid particles, the commonly used flow rate should be less than 3m/s to prevent excessive friction between the lining and the electrode; For viscous fluids, the flow velocity can be chosen to be greater than 2m/s. A higher flow velocity helps to automatically eliminate the effect of viscous substances attached to the electrode, which is beneficial for improving measurement accuracy.

Under the condition that the range Q has been determined, the size of the flowmeter diameter D can be determined based on the range of flow velocity V mentioned above, and its value can be calculated by the following formula:

Q=πD2V/4

Q: Flow rate (㎡/h) D: Inner diameter of pipeline V: Flow rate (m/h)

The range Q of the electromagnetic flowmeter should be greater than the expected maximum flow value, while the normal flow value should be slightly greater than 50% of the flowmeter's full range scale.

8、 Structural form of electromagnetic flowmeter:

1. Sensor:

The sensor mainly consists of a measuring conduit, measuring electrodes, excitation coils, iron cores, magnetic yokes, and a housing.

a、 Measurement catheter: composed of stainless steel catheter, lining, and connecting flange, it is a carrier for measuring the on-site working conditions of the measured liquid.

b、 Measurement electrode: a pair of electrodes installed on the inner wall of the measurement catheter, perpendicular to the axial flow direction, to generate signals for the measured liquid.

c、 Excitation coil: The upper and lower excitation coils that generate a magnetic field inside the measuring conduit.

d、 Iron core and magnetic yoke: Introduce the magnetic field generated by the excitation coil into the liquid and form a magnetic circuit.

e、 Shell: Instrument outer packaging.

2. Converter: It is an intelligent secondary meter that amplifies and processes flow signals. After being operated by a microcontroller, it can display flow and cumulative measurement, and output signals such as pulses and analog currents for measuring or controlling fluid flow.

3. Product assembly form: It is divided into two forms: integrated and split.

a、 Integrated: The sensor and converter are installed together.

b、 Split type: Sensors and converters are installed separately, forming a flow metering system through connecting cables.

c、 To meet the requirements of measuring different media, there are multiple choices for the lining and electrode materials of sensors.

9、 Classified by excitation method:

To generate a uniform and constant magnetic field, it is necessary to choose a suitable excitation method. According to the excitation current method, there are DC excitation, AC (power frequency or other frequencies) excitation, low-frequency rectangular wave excitation, and dual frequency rectangular wave excitation.

1. DC excitation

The direct current excitation method uses direct current or a magnet to generate a constant and uniform magnetic field. The biggest advantage of this DC excitation transmitter is that it is less affected by AC electromagnetic field interference, so the effect of self inductance in the liquid can be ignored. However, using a direct current magnetic field can easily polarize the electrolyte liquid passing through the measurement pipeline, that is, the electrolyte is electrolyzed in an electric field, producing positive and negative ions. Under the action of the electric field force, negative ions run towards the positive electrode and positive ions run towards the negative electrode, which will cause the positive and negative electrodes to be surrounded by ions of opposite polarity, seriously affecting the normal operation of the instrument. So, DC excitation is generally only used to measure non electrolyte liquids, such as liquid metal flow (mercury at room temperature and liquid steel, lithium, potassium at high temperature), etc.

2. Communication excitation

Most electromagnetic flow meters used in industry use AC excitation with a power frequency of 50Hz to generate an alternating magnetic field, avoiding polarization interference on the surface of the DC excitation electrode. However, using AC excitation can bring a series of electromagnetic interference problems (such as orthogonal interference, in-phase interference, zero drift, etc.). Nowadays, AC excitation is being replaced by low-frequency square wave excitation.

3. Low frequency square wave excitation

There are two types of low-frequency square wave excitation waveforms: binary (positive negative) and ternary (positive zero negative zero), with frequencies typically ranging from 1/2 to 1/32 of the power frequency. Low frequency square wave excitation can avoid orthogonal electromagnetic interference caused by AC magnetic fields, eliminate power frequency interference caused by distributed capacitance, suppress eddy currents caused by AC magnetic fields on pipe walls and inside fluids, and eliminate polarization phenomena caused by DC excitation.

10、 Precautions during installation:

1. The axis of the non measuring electrode must be approximately horizontal;

2. The measuring pipeline must be filled with liquid;

3. There should be at least a 5 * D (D is the inner diameter of the flow meter) straight pipe section in front of the flow meter, and at least a 3 * D (D is the inner diameter of the flow meter) straight pipe section in the back;

4. The direction of fluid flow and the arrow direction of the flowmeter *;

5. Vacuum inside the pipeline can damage the lining of the flowmeter, so special attention should be paid;

6. There should be no strong electromagnetic field near the flowmeter;

7. There should be ample space near the flowmeter for installation and maintenance;

8. If there is vibration in the measuring pipeline, there should be fixed supports on both sides of the flowmeter. When measuring mixed liquids of different media, the distance between the mixing point and the flowmeter should be at least 30 × D (D is the inner diameter of the flowmeter). To facilitate the cleaning and maintenance of the flowmeter in the future, a bypass pipeline should be installed.

11、 When grounding protection, the following points must be noted:

1. Sensors and converters should be grounded separately and not connected to motors or process pipelines. The grounding resistance should be less than 10 ohms.

2. The measuring tube, housing, shielding wire, converter, and secondary instrument of the sensor must be grounded.

3. The grounding of sensors and converters should be done on site, and the shielding layer of secondary instruments should be grounded on the control room side. Do not connect multiple terminals to avoid interference caused by different potentials.

4. The sensor is installed on a metal pipeline, and the grounding wire of the sensor can be connected to the pipeline flange according to the manufacturer's requirements to form a reliable grounding circuit. The grounding point of the instrument should be an independent grounding point and cannot be shared with other electrical equipment.

12、 Installation requirements for straight pipe sections:

The electromagnetic flowmeter sensor has certain requirements for the upstream and downstream straight pipe sections of the installation point, otherwise it will affect the measurement accuracy.

1. If there is a tapered pipe upstream of the sensor installation point, there should be an equal diameter straight pipe section of not less than 15D upstream of the sensor and an equal diameter straight pipe section of not less than 5D downstream.

2. If there is a gradually expanding pipe upstream of the sensor installation point, there should be an equal diameter straight pipe section of not less than 18D upstream of the sensor, and an equal diameter straight pipe section of not less than 5D downstream.

3. If there is a 90 ° elbow or lower joint upstream of the sensor installation point, there should be an equal diameter straight pipe section of not less than 20D upstream of the sensor, and an equal diameter straight pipe section of not less than 5D downstream.

4. If there are two 90 ° elbows on the same plane upstream of the sensor installation point, there should be an equal diameter straight pipe section of not less than 25D upstream of the sensor and an equal diameter straight pipe section of not less than 5D downstream.

5. If there are two 90 ° elbows on different planes upstream of the sensor installation point, there should be an equal diameter straight pipe section of not less than 40D upstream of the sensor and an equal diameter straight pipe section of not less than 5D downstream.

6. The flow regulating valve or pressure regulating valve should be installed as much as possible outside 5D downstream of the sensor. If it must be installed upstream of the sensor, there should be an equal diameter straight pipe section of not less than 50D upstream and an equal diameter straight pipe section of not less than 5D downstream.

Special attention

1. If a valve is installed near the upstream of the sensor installation point, constantly opening and closing the valve will have a great impact on the service life of the sensor, and it is very easy to cause * damage to the sensor.

2. Sensors should be avoided as much as possible from being installed on very long overhead pipelines. Over time, the sagging of the sensor can easily cause sealing leakage between the sensor and the flange. If installation is necessary, pipeline fastening devices must be installed at 2D positions upstream and downstream of the sensor.

13、 Main technical data:

1. Technical data of the whole machine and sensors

2. Converter technology data

3. Selection of lining

4. Selection of imported protective flanges and grounding flanges (or grounding rings)

5. Selection of electrodes

14、 Correct selection:

The selection of instruments is a very important task in instrument applications. Relevant data shows that 2/3 of instrument failures in practical applications are caused by incorrect selection or installation of instruments. Please pay special attention.

1. Collect data:

The composition of the fluid being tested;

Zui high traffic, Zui low traffic;

The highest work pressure;

Zui high temperature, Zui low temperature;

2. Range confirmation:

The flow rate of the measured medium in general industrial flow meters should be between 2-4m/s. In special cases, the minimum flow rate should not be less than 0.2m/s, and the maximum flow rate should not be greater than 8m/s. If the medium contains solid particles, the commonly used flow rate should be less than 3m/s to prevent excessive friction between the lining and the electrode; For viscous fluids, the flow velocity can be chosen to be greater than 2m/s. A higher flow velocity helps to automatically eliminate the effect of viscous substances attached to the electrode, which is beneficial for improving measurement accuracy.

Under the condition that the range Q has been determined, the size of the flowmeter diameter D can be determined based on the range of flow velocity V mentioned above, and its value can be calculated by the following formula:

Q=πD2V/4

Q: Flow rate (㎡/h) D: Inner diameter of pipeline V: Flow rate (m/h)

The electromagnetic range Q should be greater than the expected maximum flow rate value, while the normal flow rate value should be slightly greater than 50 times the full scale of the flowmeter.

3. Reference flow range:

15、 Selection Table:

16、 Ordering Notice:

1. Product: If there are model standards, please call directly to inquire about prices and learn more details!

2. If there are no product model specifications, please send the operating requirements, design drawings, and technical specifications to our company.

3. Product ordering requires parameters such as diameter (DN), nominal pressure (Mpa), temperature (℃), flow range (m3/h), medium name (such as water), connection method (clamp type, threaded type, flange type, clamping type, split type, insertion type, etc.).

4. Quotation confirmation: Our company provides a quotation list and technical standard specifications to the customer for confirmation. After both parties confirm the technical aspects, the contract will be drafted.

5. Quality requirements, quality standards, and conditions for suppliers to be responsible for quality: in accordance with relevant national quality standards.

After-sales service

1. From the date of contract signing, our company provides free maintenance and upkeep services for the products provided, and promises lifelong repair services;

2. Jiangsu Desen Instrument Co., Ltd. will regularly communicate with customers to understand the usage of the product and solve any problems that arise during their use, providing free services;

3. During the warranty period, if there is any man-made damage, our company is responsible for repairing it and collecting the repair costs incurred;

4. If there are quality problems or dissatisfaction with the product, users can choose to return or exchange it unconditionally. The company does not charge any handling fees. If there are quality problems, the company will bear the round-trip shipping costs.