Electromagnetic Flow Meter Selection Guide

Electromagnetic Flow Meter Selection Guide

1. First Step: Core Prerequisite Verification

1. Conductivity Requirement

- General electromagnetic flow meter: conductivity ≥ 5 μS/cm.

- Pure water, deionized water, oil, organic solvents and gas cannot be measured.

- Low-conductivity media (softened water, high-purity water): special low-conductivity electrodes required.

2. Flow Conditions

- Must be full pipe flow.

- Not suitable for vacuum conditions (may cause lining peeling).

- Applicable media: water, sewage, acid & alkali solutions, slurry, pulp, food slurries and other conductive liquids.

2. Second Step: Diameter and Range Selection

2.1 Recommended Velocity

表格

Medium Type Recommended Economic Velocity Minimum Measurable Velocity Maximum Velocity
Clean water, tap water 1.5~3 m/s 0.3 m/s 5 m/s
Wastewater, sewage 2~3 m/s 0.5 m/s 5 m/s
Slurry, ore pulp 2~3 m/s 0.8 m/s 3 m/s
High viscosity, easy crystallizing 1~2 m/s 0.5 m/s 3 m/s

2.2 Range Selection Rules

- Normal operating flow should be within 20%~80% of full scale.

- Minimum flow should not be lower than 5% of full scale.

- For pulsating flow, select models with digital filtering and pulsation compensation.

3. Third Step: Lining Material Selection

表格

Lining Material Advantages Temp Range Typical Applications Not Suitable For
PTFE Excellent corrosion resistance -40~180℃ Strong acids, alkalis, food Vacuum, high abrasion
FEP Good corrosion & vacuum resistance -40~120℃ Corrosive liquids High abrasion
Polyurethane (PU) Excellent wear resistance -20~80℃ Slurry, ore pulp Acids, alkalis, high temp
Hard Rubber Low cost, good abrasion 0~80℃ Tap water, sewage Strong oxidants
Neoprene Good elasticity & abrasion -20~70℃ Wastewater, river water Strong chemicals, oil

4. Fourth Step: Electrode Material Selection

表格

Electrode Material Typical Applications
316L Stainless Steel Tap water, circulating water, general sewage
Hastelloy C Seawater, chloride-containing wastewater
Hastelloy B Reducing acids, hydrochloric acid, sulfuric acid
Titanium Seawater, brine, oxidizing acids
Tantalum Concentrated nitric acid, strong corrosive media
Platinum Low conductivity, high-purity, food & pharma

- For scaling media: use scraper electrodes, capacitive electrodes.

- For food & pharma: hygienic grade with 3A / EHEDG certification.

5. Fifth Step: Electrical & Functional Selection

1. Power Supply

- 220V AC: general industrial use

- 24V DC: explosion-proof, DCS systems

- Battery-powered: field, no power supply

2. Output Signals

- Standard: 4–20mA, pulse output

- Communication: HART, MODBUS-RTU, RS485, PROFINET

- Optional: empty pipe detection, alarm, wireless transmission (GPRS/4G/NB-IoT)

3. Accuracy Class

- Custody transfer: 0.2 class

- Process control: 0.5 class (most common)

- Municipal water supply: 1.0 class

6. Sixth Step: Installation & Structure Selection

1. Environmental Requirements

- Protection:

- Indoor: IP65

- Outdoor, well, submerged: IP68

- Avoid strong electromagnetic interference (inverter, motor).

2. Structure Type

- Integral type: simple wiring, low cost

- Split type: sensor & converter separated, suitable for wells, high temp, vibration

- Flanged type: standard for most pipelines

- Wafer type: compact, small diameter

7. Key Selection Mistakes to Avoid

- Do NOT use for media with insufficient conductivity (pure water, oil).

- Do NOT use standard type in vacuum (lining damage risk).

- Do NOT select too low velocity (large error, zero drift).

- Do NOT mismatch lining/electrode with corrosive or abrasive media.

- Must be properly grounded (resistance ≤10Ω).

- Install with sufficient straight pipe: upstream 5D, downstream 3D.

- Do NOT install at pump suction, highest point, or close to valves.