Selection of electromagnetic flowmeter

Selection of electromagnetic flowmeterIt is necessary to comprehensively consider various factors such as the characteristics of the measuring medium, process conditions, installation environment, and functional requirements to ensure measurement accuracy, stability, and economy. The following are the detailed steps and key points for selecting an electromagnetic flowmeter:

1、 Clearly define measurement requirements

Media Type

Liquid/Gas/Steam: Electromagnetic flow meters are only suitable for conductive liquids (conductivity ≥ 5 μ S/cm), such as water, acid-base solutions, mud, etc.

Corrosivity: Choose lining materials (such as PTFE, rubber, ceramics) and electrode materials (such as stainless steel, Hastelloy, titanium) based on the corrosiveness of the medium.

Containing solid particles: If the medium contains impurities such as sediment and fibers, wear-resistant lining (such as rubber) or anti clogging design should be selected.

Viscosity: High viscosity media may affect flow velocity distribution, and it is necessary to confirm whether the flowmeter supports it.

flow range

Determine the normal flow rate, minimum flow rate, and maximum flow rate, and select a range ratio (usually 10:1~150:1) to cover the actual operating conditions.

Avoid long-term flow below the lower range limit (such as<5%), otherwise the diameter needs to be reduced or a low flow rate flowmeter needs to be selected.

Temperature and pressure

Temperature: The regular type is suitable for -20 ℃~+120 ℃, while the high-temperature type can reach+400 ℃ (requiring special lining and electrodes).

Pressure: Select the pressure resistance level based on the pipeline pressure (such as 1.6MPa, 4.0MPa, 6.4MPa).

2、 Key parameter selection

Caliber selection

The diameter should be consistent with the pipeline. If the flow rate approaches the upper or lower limit, the diameter needs to be adjusted through flow rate calculation:

The recommended flow rate for general liquids is 1-3 m/s, and for gases it is 10-30 m/s.

2. Lining material

Polytetrafluoroethylene (PTFE): resistant to strong acids, strong alkalis, and organic solvents, suitable for temperatures ranging from -40 ℃ to+180 ℃, but with poor wear resistance.

Rubber: Strong wear resistance, suitable for temperatures ranging from -20 ℃ to+80 ℃, suitable for water bodies containing sediment and particulate matter.

Ceramics: High temperature resistant, wear-resistant, suitable for temperatures ranging from -20 ℃ to+400 ℃, suitable for high-temperature water or hard particle media.

Polyurethane: It has better wear resistance than rubber and is suitable for temperatures ranging from -10 ℃ to+80 ℃. It is commonly used for measuring slurry and pulp.

electrode material

Stainless steel (316L): suitable for general water and sewage, low cost but limited corrosion resistance.

Hastelloy (HC): resistant to highly corrosive media such as hydrochloric acid and sulfuric acid, with a relatively high price.

Titanium alloy (Ti): resistant to seawater and chloride ion corrosion, suitable for marine environments or chemical industries.

Tantalum (Ta): resistant to strong acids (such as aqua regia), but expensive and only used for special working conditions.

excitation method

Low frequency rectangular wave excitation: Strong anti-interference ability, suitable for industrial wastewater and media containing impurities.

High frequency excitation: Fast response speed, suitable for measuring pulsating flow or rapidly changing flow.

Dual frequency excitation: Combining the advantages of low and high frequencies, balancing accuracy and response speed.

3、 Features and Additional Requirements

output signal

Analog output: 4-20mA current signal, used for PLC/DCS system control.

Digital output: RS485, Modbus, HART protocol, supports remote communication and data acquisition.

Pulse output: used for cumulative flow measurement or connected to a counter.

Display and operation

On site display: The LCD screen displays parameters such as instantaneous flow rate, cumulative flow rate, temperature, etc.

Remote operation: Set parameters and diagnose faults through a mobile app or upper computer software.

Self diagnostic function: detects electrode status and abnormal excitation current, automatically alarms or compensates for zero drift.

Protection level and explosion-proof

Protection level: IP65 (dustproof and waterproof) or IP67 (waterproof), suitable for humid or outdoor environments.

Explosion proof certification: Ex d Ⅱ CT6 (explosion-proof type) or Ex ia Ⅱ CT4 (safety type), used in flammable and explosive places.

special function

Bidirectional measurement: supports forward and reverse flow monitoring, suitable for circulating water systems.

Air traffic control detection: Automatically identify the absence of fluid in the pipeline to avoid erroneous measurements.

Temperature/pressure compensation: Integrated temperature and pressure sensors to improve measurement accuracy (such as steam flow measurement).

4、 Installation and environmental adaptation

Installation method

Pipeline type: standard flange connection, suitable for most industrial pipelines.

Insertion type: suitable for large-diameter pipelines (DN300 and above), with low cost but slightly lower accuracy.

Submersible type: directly installed in open channels or non full pipe culverts, requiring waterproof sealing design.

Requirements for straight pipe sections

Inlet straight pipe section ≥ 5 times the pipe diameter, outlet straight pipe section ≥ 2 times the pipe diameter, to avoid the influence of eddy currents.

If it cannot meet the requirements of the straight pipe section, a rectifier should be installed or an anti-interference flowmeter should be selected.

environmental conditions

Electromagnetic interference: Keep away from strong magnetic fields (such as motors and transformers), and use shielded cables if necessary.

Vibration and shock: Avoid installing near vibration sources or choose anti vibration flow meters.

Temperature changes: High temperature environments require enhanced heat dissipation, while low-temperature environments require insulation measures.

5、 Economy and maintenance costs

Initial investment

Models with high configurations (such as intelligent and explosion-proof) are more expensive, but have better long-term operational stability.

The selection of lining and electrode materials needs to balance corrosion resistance and cost (such as PTFE being 30%~50% more expensive than rubber).

maintenance cost

Non obstructive components: Electromagnetic flow meters have no mechanical wear and have a long maintenance cycle (usually every 2-3 years).

Calibration requirement: Regularly check the electrode status and excitation current, and perform zero point calibration if necessary.

Spare parts cost: The prices of vulnerable parts such as electrodes and liners need to be included in long-term cost considerations.

6、 Selection Example

sceneChemical plant hydrochloric acid delivery pipeline (DN50, flow range 2-10m ³/h, temperature 60 ℃, pressure 1.6MPa)

Selection steps:

Medium: Hydrochloric acid (conductivity of about 30000 μ S/cm), choose Hastelloy electrode+PTFE lining.

Caliber: DN50, flow rate calculation:

Function: Requires 4-20mA output+HART protocol, IP65 protection, Ex d Ⅱ CT6 explosion-proof.

Installation: Pipe type flange connection, inlet straight pipe section ≥ 0.25m (5 × DN50).

Final model: HC electrode+PTFE lined electromagnetic flowmeter, DN50， Range 0-12m ³/h, with HART communication, explosion-proof IP65.

Note: 1. The prices on the system are only reference prices and not actual prices;

2. Flow meters vary in specifications, diameters, and configurations, resulting in different prices. We need to select and quote based on your operating conditions~

After sales and warranty

All products supplied by Duoqin Instrument (Shanghai) Co., Ltd.:

All products come with a 2-year warranty;

Provide free telephone consultation, guidance on installation and debugging services;

Negotiate on-site guidance for installation, debugging, and other matters, and only charge reasonable travel expenses;

Large quantities can provide free on-site guidance for installation and debugging.