Intelligent electromagnetic flowmeter supports measurement bureau testing

1. OverviewIntelligent electromagnetic flowmeter supports measurement bureau testing

Electromagnetic flowmeter is an electromagnetic induction flow meter designed according to JB/T9248-1999 "Electromagnetic Flowmeters", suitable for flow calculation of conductive liquids with conductivity greater than 5 μ s/cm; The nominal diameter range is 10mm to 3000mm, and it is a series of electromagnetic flowmeter products that integrate intelligence, small and lightweight integration, multifunctionality, high precision, and high reliability. It consists of two parts: sensors and intelligent converters.

Electromagnetic flow meters have a wide range of applications. They can output standard current signals (4-20mA) or pulse signals while meeting on-site monitoring and display requirements. They comply with the HART communication protocol and are used for recording, adjusting, and controlling; Can be widely used for liquid flow measurement of conductive materials in process pipelines in industries such as chemical, environmental protection, textile, metallurgy, mining, pharmaceuticals, papermaking, water supply, food, sugar, brewing, etc; In addition to measuring general conductive liquids, it can also measure the flow rate of conductive liquid-solid two-phase flow, high viscosity liquids, salts, strong acids, strong bases and other liquids according to the special needs of users.

2. Structure

2.1 Sensors

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

(1) 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.

(2) 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.

(3) Excitation coil: The upper and lower excitation coils that generate a magnetic field inside the measuring conduit.

(4) Iron core and magnetic yoke: Introduce the magnetic field generated by the excitation coil into the liquid and form a magnetic circuit.

(5) Shell: Instrument outer packaging.

2.2 Converter:

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

2.3 Product assembly form:

It is divided into two forms: one-piece and split type.

(1) Integrated: The sensor and converter are installed together.

(2) Split type: Sensors and converters are installed separately, forming a flow metering system through connecting cables.

3. Functional Features

Suitable for flow detection of all liquids with conductivity greater than 5 μ s/cm. The change in conductivity does not affect the change in performance.

The flowmeter has long-term high measurement accuracy and is not affected by the physical properties of the fluid. The measurement accuracy can reach 0.5 or 0.3 levels.

The flowmeter has no mechanical movable parts and does not require maintenance during normal operation.

★ Easy to operate, the flow meter is automatically set within the range of 0-10m/s without changing the measurement range.

Due to the excellent corrosion resistance and wear resistance of all components in contact with the tested medium, it has a wide range of applications.

When measuring media containing grease or media that can deposit a non-conductive layer on the electrode surface, interchangeable (scrubbing) electrodes can be used.

The converter and sensor of the flowmeter can be installed in two types: integrated and split.

The converter adopts advanced excitation algorithm.

★ Adopting high-efficiency, high stability, and self-designed wide input range multi group fully isolated switching power supply mode (DC: 18V-36V, AC: 85V-265V)

★ The design has rich output interfaces, making it extremely convenient to use.

a) 4-20mA current output; b) 1K or 2K selectable frequency output;c) Can set pulse output; d) Accumulated threshold output can be set; e) RS485 interface;

★ Equipped with converter native self-test function

★ Large screen Chinese high-definition LCD backlit display

When power is off, EEPROM can protect set parameters and accumulated values;

★ Chinese interface is friendly and easy to operate;

★ Provide non-linear correction function for sensors;

4. Main parameters and technical indicators: The intelligent electromagnetic flowmeter supports testing by the metrology bureau

5Installation of flow meter

5.1 Flow meter installation method

(1) Flow meters are usually installed horizontally, and the axes of the two electrodes should be in the same horizontal plane position.

(2) To prevent negative pressure, the height of the flowmeter should be slightly lower than the height of the pipeline, or a certain pressure should be ensured on the downstream side of the flowmeter:

(3) The inner diameter measured by the flowmeter is inconsistent with the inner diameter of the pipeline. The inner diameter of the pipeline should be greater than the inner diameter of the flowmeter, and a tapered or expanded pipe with a cone angle not greater than 15 ° should be installed between them.

(4) The optimal position for measuring flow meters for liquid-solid two-phase fluids is vertical installation, with the flow direction from bottom to top.

Correctly install the electromagnetic flowmeter as shown in Figure 5.1:

5.2 Precautions for flowmeter installation

5.2.1 Requirements for External Environment

(1) Flow meters should be installed in places with large temperature changes and exposed to high temperature radiation from equipment. If installation is necessary, insulation and ventilation measures must be taken.

(2) It is best to install flow meters indoors. If they must be installed outdoors, they should be protected from rainwater, waterlogging, and direct sunlight. Moisture and sun protection measures should be taken.

(3) Flow meters should be avoided from being installed in environments containing corrosive gases (such as ammonia, acid mist, etc.), and ventilation measures must be taken when installation is necessary.

(4) For the convenience of installation, maintenance, and upkeep, there should be ample installation space around the flowmeter.

(5) The installation site of the flowmeter should avoid strong magnetic fields (such as large transformers, welding machines) and strong vibration sources. If the pipeline vibrates greatly, there should be fixed pipe supports on both sides of the flowmeter.

(6) The pipeline for installing flow meters should not have significant leakage current, and there should be good grounding conditions nearby.

(7) The flow direction of the fluid is consistent with the direction of the flow mark.

(8) The installed pipeline should be filled with the measured medium to prevent empty pipes.

(9) Do not install flow meters in pipelines with negative pressure to prevent lining detachment.

5.2.2. Requirements for straight pipe sections

In order to improve the effects of eddy currents and flow field distortions, there are certain requirements for the length of the straight pipe sections before and after the installation of the flowmeter, otherwise it will affect the measurement accuracy (rectifiers can also be installed, avoiding installation near the regulating valve and half open valve as much as possible) (see Figure 5.2 and the table below)

5.3 Requirements for piping

The flowmeter has certain requirements for the upstream and downstream piping of the installation point, otherwise it will affect the measurement accuracy.

(a) The inner diameter of the upstream and downstream piping should be the same as that of the sensor, and should meet the requirement of 0.98DN ≤ D ≤ 1.05DN (where DN represents the inner diameter of the sensor and D represents the inner diameter of the piping)

(b) Optional reducer

(c) The piping and sensors must be concentric, with a coaxial deviation of no more than 0.05DN

5.4 Requirements for bypass pipes

In order to facilitate the maintenance of the flowmeter, it is best to install a bypass pipe for the flowmeter. In addition, if the fluid on the pipeline that needs to be cleaned for heavily polluted fluids and the flowmeter cannot be stopped, a bypass pipe must be installed (see Figure 5.3).

Figure 5.3 Requirements for installing bypass pipes for flow meters

The installation requirements for flow meters on pipelines are shown in Figure 5.4.

Figure 5.4Installation requirements for flow meters on pipelines

5.6 Installation of PTFE and F46 lined sensors

Polytetrafluoroethylene (PTFE) and F46The installation of lining sensors will deform under pressure. During installation, the flange connection screws should be tightened evenly. If the force is not uniform, the PTFE pipe may become deformed·The edge is easily crushed, so it is best to use a torque wrench to evenly tighten the connecting bolts during installation.

Fusible molded PFA or F46

The temperature resistance and corrosion resistance of this lining are similar to PTFE, and it is made by compression molding. Stainless steel wire mesh can be added inside the measuring tube, which enhances the bonding force between the lining and the metal tube, reduces the thermal expansion coefficient of the lining, and overcomes the disadvantages of PTFE lining damage caused by high temperature thermal expansion and negative pressure.

5.7 Precautions for installation and construction of flow meters

(1) The installation size must be calculated accurately, otherwise it is easy to leak or fail to install.

(2) The fluid flow direction must be consistent with the flow arrow on the sensor body.

(3) The electrode axis of the flowmeter must be approximately horizontal, otherwise it will affect the measurement accuracy.

(4) The flanges on both sides of the sensor must be kept level, otherwise it is easy to leak.

(5) To avoid the formation of vortex flow after installation, it is necessary to ensure that the coaxial connections of process piping, seals, and flow meters are not staggered.

(6) When installing a flowmeter, it is strictly prohibited to weld and match it tightly against the flowmeter flange to avoid burning the flowmeter lining.

(7) For installation pipelines of different properties, corresponding grounding methods should be adopted (see sensor grounding)

(8) For corrosive media, it is best to install them vertically and allow the tested medium to flow from bottom to top. This can prevent solid particles from depositing in the flow tube, ensure uniform corrosion of the lining, and extend the service life.

(9) For large-sized measuring pipe diameters (DN>200mm), expansion heads can be used for easy installation.

5.8 Grounding of flowmeter

The grounding method of the casing of an electromagnetic flowmeter is directly related to measurement accuracy and stability. The signal size of the two electrodes of the electromagnetic flowmeter is relative to the potential of the fluid inside the pipeline, so it is necessary to ensure that the pipeline and flowmeter themselves have good grounding.

Generally, metal pipelines are well grounded and the grounding wire can be omitted, but the screws that fix the flange must ensure that the pipeline and flow meter are fully connected. If there is strong electromagnetic interference in the environment, an independent grounding wire can be used.

If insulated pipelines are used, metal short pipes or grounding rings must be installed between the flowmeter and the pipeline, and then connected to the flowmeter with wires before grounding. There are three types of grounding rings: general grounding ring, necked grounding ring, and protective grounding ring, as shown in the figureAs shown in 5.5.

(1) General grounding ring

Grounding rings must be installed on both sides of the sensor on plastic and cathodic protection tubes.

(2) Neck grounding ring

If the medium has strong wear resistance, use a neck grounding ring to protect the lining.

(3) Protective grounding ring

PTFE lined sensors should use protective grounding rings. It can be fixed on the flange with screws to protect PTFEofThe edge is not damaged.

Figure 5.5