Special electromagnetic flowmeter for wastewater measurement

Principle of operation

The measurement principle of the electromagnetic flowmeter is based on Faraday’s law of electromagnetic induction. The measuring tube of the flowmeter is a non-magnetic alloy short tube lined with insulating material. Two electrodes are fixed on the measuring tube, penetrating the tube wall along the diameter direction, with the electrode tips essentially flush with the inner surface of the liner. When the excitation coil is energized by bidirectional square wave pulses, it generates a working magnetic field with a magnetic flux density B in a direction perpendicular to the axis of the measuring tube. At this time, if a fluid with a certain conductivity flows through the measuring tube, it cuts the magnetic field lines and induces an electromotive force E. The electromotive force E is proportional to the product of the magnetic flux density B, the inner diameter d of the measuring tube, and the average flow velocity v. The electromotive force E (flow signal) is detected by the electrodes and sent to the converter via a cable. The converter amplifies and processes the flow signal, then displays the fluid flow rate, and can output signals such as pulses and analog current for flow control and regulation.

Main Technical Parameters

Parameter	Specification
Nominal diameter series DN (mm)	PTFE lined (flow-through type): 10, 15, 20, 25, 32, 40, 50, 65, 80, 100, 125, 150, 200, 250, 300, 350, 400, 450, 500, 600 Rubber lined (flow-through type): 40, 50, 65, 80, 100, 125, 150, 200, 300, 350, 400, 500, 600, 800, 1000, 1200 Note: Special specifications can be customized.
Flow direction	Forward, reverse, net flow
Turndown ratio	150:1
Repeatability error	±0.1% of measured value
Accuracy class	Flow-through type: Class 0.5, Class 1.0
Medium temperature	Ordinary rubber lining: -20 ~ +60 °C High-temperature rubber lining: -20 ~ +90 °C PTFE lining: -30 ~ +100 °C High-temperature PTFE lining: -30 ~ +180 °C
Rated working pressure	Flow-through type: DN10 – DN65: ≤2.5 MPa DN80 – DN150: ≤1.6 MPa DN200 – DN1200: ≤1.0 MPa
Flow measurement range	Velocity range: 0.3 – 15 m/s
Conductivity range	Conductivity of measured fluid ≥5 μs/cm (Most water-based media have conductivity in the range 200–800 μs/cm and are suitable for electromagnetic flowmeters.)
Output current and load resistance	4–20 mA fully isolated, load resistance <750 Ω Pulse frequency 0–1 kHz, photoelectric isolated OCT, external power supply ≤35 V, max collector current 25 mA when conducting
Electrode material	Molybdenum-containing stainless steel, Titanium (Ti), Tantalum (Ta), Hastelloy (H), Platinum (Pt), or other special electrode materials
Protection class	Submersible type: IP68 Other types: IP65
Power supply	85–265 V, 45–63 Hz
Straight pipe length	Flow-through type: upstream ≥5 DN, downstream ≥2 DN
Connection type	Flange connection between flowmeter and piping; flange dimensions conform to GB9119-88
Explosion-proof mark	mdllBT4
Ambient temperature	-25 °C ~ +60 °C
Relative humidity	5% ~ 95%
Total power consumption	<20 W

Selection of materials for electrodes and grounding rings

Material	Corrosion Resistance
Molybdenum-containing stainless steel (OCr18Ni12Mo2Ti)	Nitric acid, <5% sulfuric acid at room temperature, boiling phosphoric acid, formic acid, alkaline solutions, sulfurous acid under certain pressure, seawater, acetic acid
Hastelloy C / Hastelloy B (HC, HB)	Resistant to oxidizing acids, oxidizing salts, seawater, non-oxidizing acids, non-oxidizing salts, alkalis, and sulfuric acid at room temperature
Titanium (Ti)	Seawater, various chlorides and hypochlorites, oxidizing acids (including fuming nitric acid), organic acids, alkalis
Tantalum (Ta)	All chemical media except hydrofluoric acid, fuming sulfuric acid, and alkalis, including boiling hydrochloric acid, nitric acid, and sulfuric acid below 175°C
Platinum (Pt)	Resistant to various acids, alkalis, and salts, except aqua regia

Instructions for the selection of lining materials

Lining Material	Name	Symbol	Performance	Max Operating Temperature	Applicable Liquids
Rubber	Chloroprene rubber	–	Moderate wear resistance; resistant to low concentrations of acids, alkalis, and salts	< 80°C	Tap water, industrial water, seawater
Rubber	Polyurethane rubber	–	Excellent wear resistance; poor acid and alkali resistance	< 60°C	Pulp, slurry, etc.
Fluoroplastic	Polytetrafluoroethylene	F4 or PTFE	Very stable chemically; resistant to boiling hydrochloric acid, sulfuric acid, aqua regia, and concentrated alkalis	< 180°C	Highly corrosive acid, alkali, and salt liquids
Fluoroplastic	Tetrafluoroethylene and hexafluoropropylene (Teflon FEP)	F46 or FEP	Slightly inferior chemical performance compared to PTFE	–	Corrosive acid, alkali, and salt liquids
Plastic	Tetrafluoroethylene and ethylene (ETFE)	F4 or ETFE*	Slightly inferior chemical performance compared to PTFE	–	Corrosive acid, alkali, and salt liquids
Plastic	Polyethylene	PO	Chemically stable	< 60°C	Sewage
Plastic	Polyphenylene sulfide	PPS	–	< 150°C	Hot water