Plug in intelligent electromagnetic flowmeter

1. OverviewPlug in intelligent electromagnetic flowmeter

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. Working principle: Plug in intelligent electromagnetic flowmeter

The working principle of electromagnetic flowmeter is based on the law of electromagnetic induction of flange. When a conductor moves in a magnetic field, an induced electromotive force is generated at both ends of the conductor perpendicular to the direction of the magnetic field and the direction of motion. The magnitude of electromotive force is directly proportional to the speed of conductor motion and the magnetic induction intensity of the magnetic field.

As shown in Figure 4.1, when a conductive fluid flows through an insulated conduit with an inner diameter of D (m) and a pair of measuring electrodes at an average flow velocity of V (m/s), the conduit is in a uniform magnetic field with a magnetic induction intensity of B (T), and an induced electromotive force E (V) is generated on the pair of electrodes, which is perpendicular to the direction of the magnetic field and the fluid.

The Faraday law of electromagnetic induction is: E=B • D • V (1)

The volumetric flow rate of the flow rate is:（2）

From formulas (1) and (2), we can obtain:（m3/h) （3）

Therefore, the electromotive force can be expressed as:（4）

When B is a constant, it is also a known number for a fixed aperture D, as shown in formula (3)=K (constant), then formula (3) can be rewritten as: QV=K • E (m3/h) (5)

From formula (5), it can be seen that the flow rate QV is directly proportional to the electromotive force E.

In the above formula: E induced potential; D Measure the inner diameter of the tube; B magnetic induction intensity; V average flow velocity; K is a coefficient related to magnetic field distribution and axial length.

Figure 4.1 Working principle of electromagnetic flowmeter

5. Main parameters and technical indicators

6. Converter structure circuit

The electromagnetic flowmeter converter provides stable excitation current to the excitation coil of the electromagnetic flow sensor. The preamplifier amplifies and converts the electromotive force induced by the sensor into standard current or frequency signals, which facilitates the display, control, and adjustment of flow. The converter circuit structure is shown in Figure 6.1.

6.1 Converter Circuit Structure