Magnetic and Magnetostrictive Level Meters

Magnetic and magnetostrictive level meters provide continuous liquid level measurement in municipal water and wastewater applications using a magnetostrictive waveguide probe that detects the position of a magnetic float. The system sends ultrasonic pulses down the waveguide, which interact with the magnetic field from the float to generate a return signal whose timing indicates precise level position. These meters typically achieve ±0.5mm accuracy across measurement spans up to 20 feet, making them suitable for critical applications like clearwell monitoring and chemical tank level control. The primary limitation is susceptibility to coating buildup on the float in wastewater applications, which can cause measurement drift and require regular maintenance cleaning.

• Clearwell Storage Tanks (0.5-10 MGD plants): Magnetic level gauges provide continuous level monitoring in 100,000-500,000 gallon clearwells, connecting to SCADA for pump control and regulatory reporting. Selected for reliability in chlorinated water environments and visual verification capability during power outages

• Chemical Feed Tank Monitoring: Magnetostrictive transmitters monitor sodium hypochlorite, ferric chloride, and polymer tanks (500-5,000 gallon capacity). Connected upstream to chemical delivery systems and downstream to feed pumps with low-level alarms. Chosen for accuracy (±0.01% of span) and compatibility with corrosive chemicals

• Wet Well Level Control: Magnetostrictive sensors in 10-50 foot deep wet wells provide pump control signals and high-level alarms. Interface with lift station controls and telemetry systems. Selected for submersible capability and precision in variable flow conditions

• Digester Gas Holder Monitoring: Magnetic gauges track biogas storage levels in 50,000-200,000 cubic foot holders, feeding data to gas utilization systems and safety interlocks

Daily Operations: Operators perform visual checks of magnetic gauge flag positions and verify SCADA readings match local displays. Magnetostrictive units require monitoring of 4-20mA signals and alarm status lights. Typical adjustments include span calibration checks and zero-point verification using portable meters.

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Maintenance: Quarterly cleaning of chamber sight glasses and annual float/waveguide inspection during tank outages. Safety requires confined space entry procedures for wet well units and chemical PPE for feed tank applications. Maintenance technicians need basic electrical skills for transmitter calibration and multimeter operation.

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Troubleshooting: Magnetic gauges fail through float sticking (6-8 year service life) or magnetic coupling degradation. Magnetostrictive units show drift symptoms before electronics failure (10-12 year typical life). Warning signs include erratic 4-20mA signals, display flickering, or discrepancies between redundant level measurements requiring immediate investigation.

• Float Assembly (Magnetic): Permanent magnet enclosed in PTFE or Hastelloy housing, sized 2-6 inches diameter based on specific gravity and tank conditions. Selection depends on process fluid density and temperature range (-40°F to 800°F)

• Waveguide Rod (Magnetostrictive): 316L stainless steel rod (0.125-0.25 inch diameter) extending full measurement range (typically 6-20 feet in municipal applications). Length determines measurement span and accuracy specifications

• Chamber/Bypass Assembly: 2-4 inch diameter stainless steel or PVC chamber with process connections (150-300 PSI rating). Includes isolation valves and drain connections for maintenance access

• Electronics Housing: NEMA 4X or explosion-proof enclosures containing signal processing circuits, 4-20mA output modules, and display units. Temperature rating -40°F to 185°F for outdoor installations

• Magnetic Coupling System: High-strength rare earth magnets providing non-contact level indication through chamber walls, eliminating dynamic seals and potential leak points

• Magnetic Level Meters: Tank height: 2-40 feet typical municipal range, Process pressure: -14.7 to 3,000 psig (most municipal: 0-150 psig), Process temperature: -40°F to +750°F (municipal: 32-180°F), Specific gravity: 0.5-5.0 (water/wastewater: 0.95-1.1), Accuracy: ±5mm (±0.2 inches) standard, Float materials: 316L SS, Hastelloy C, PTFE-coated for corrosive service, Chamber diameter: 2-6 inches (4-inch most common), Flange ratings: 150# ANSI standard, 300# for higher pressures

• Magnetostrictive Level Meters: Measurement range: 6 inches to 28 feet, Resolution: ±0.01 inches (±0.25mm), Repeatability: ±0.005 inches typical, Process connections: ¾-inch to 4-inch NPT/flanged, Supply voltage: 12-42 VDC or 85-265 VAC, Output signals: 4-20mA, HART, Modbus, Foundation Fieldbus, Probe materials: 316L SS standard, exotic alloys available, Operating temperature: -40°F to +300°F process, electronics to +185°F, Pressure rating: Up to 5,000 psig (municipal typically <300 psig)

• What is the required measurement accuracy and does the application justify magnetostrictive over magnetic? Magnetostrictive offers ±0.01-inch accuracy vs. ±0.2-inch for magnetic indicators. Critical for chemical feed tank dosing (alum, polymer) where ±1% accuracy affects treatment costs. Standard clearwell or wet well applications typically accept magnetic accuracy. Wrong choice wastes $3,000-8,000 on unnecessary precision or compromises process control

• What are the specific gravity, viscosity, and coating tendencies of the measured fluid? Float selection critical - standard 316L SS floats work for SG 0.7-1.4. Lower SG requires larger floats, higher SG needs tungsten-weighted floats. Polymer solutions, biosolids, or high-solids streams may coat probes/floats, requiring air purge systems or ultrasonic cleaning. Wrong float sizing causes measurement drift within 6 months

• Does the installation require local indication, remote monitoring, or both? Magnetic indicators provide inherent local readout but need separate transmitters for SCADA integration ($2,500 additional cost). Magnetostrictive units include integral electronics but may need local displays ($800-1,200). Tank accessibility and operator rounds frequency determine optimal configuration

• What are the process connection requirements and tank construction constraints? Side-mount magnetic requires external chamber with upper/lower process connections - needs 18-inch minimum clearance. Top-mount magnetostrictive needs only single

• Tank height: 2-40 feet typical municipal range

• Process pressure: -14.7 to 3,000 psig (most municipal: 0-150 psig)

• Process temperature: -40°F to +750°F (municipal: 32-180°F)

• Accuracy: ±5mm (±0.2 inches) standard for magnetic, ±0.01 inches (±0.25mm) for magnetostrictive

• Float materials: 316L SS, Hastelloy C, PTFE-coated for corrosive service

• Output signals: 4-20mA, HART, Modbus, Foundation Fieldbus

• Supply voltage: 12-42 VDC or 85-265 VAC

• Enclosure ratings: NEMA 4X or explosion-proof

• Material/Equipment Verification: Verify probe material compatibility with process fluid chemistry, Confirm temperature/pressure ratings match vessel conditions, Check explosion-proof ratings for methane environments

• Installation Requirements: Minimum 6-inch clearance from tank walls and internal structures, Dedicated 2-inch NPT or flanged connection required, 120/240V power supply within 100 feet of transmitter

• Field Challenges: Foam interference requires programming adjustments, Turbulence near inlet pipes affects readings

• Coordination Issues: Lead times typically 8-12 weeks for municipal-grade units

• Endress+Hauser - Levelflex FMP50 series, widely used in municipal clarifiers and chemical storage tanks

• VEGA - VEGAFLEX 80 series, popular for lift station wet wells and process tanks

• Magnetrol - Eclipse 700 series, common in smaller municipal facilities for chemical feed systems

• Siemens - SITRANS LG200, frequently specified for larger treatment plants with integrated automation systems

• Ultrasonic level transmitters - Better for open channels, 30-40% lower cost, but struggle with foam and vapor

• Pressure transmitters - Most economical for simple level measurement, 50-60% cost savings, but require specific gravity compensation

• Float switches - Reliable for simple on/off control in lift stations, 80% cost reduction, but limited to discrete level points rather than continuous measurement

Establish direct relationships with manufacturer field service representatives - they provide invaluable commissioning support and troubleshooting expertise that local distributors often lack. Consider purchasing spare probe assemblies for critical applications; replacement typically costs 60-70% of complete unit price. Negotiate extended warranties beyond standard 2-year coverage, especially for harsh chemical environments where probe degradation accelerates.