Magnetic and Magnetostrictive Level Meters

Magnetic and magnetostrictive level meters measure liquid level in tanks and wet wells using a float containing a magnet that travels along a vertical probe. As the float moves with changing liquid level, the magnet triggers either mechanical flags (magnetic) or electronic pulses (magnetostrictive) to indicate position. Magnetostrictive versions send timed electrical pulses down a wire, and the magnet's position determines pulse return time, providing continuous level readings with accuracy typically within ±0.04 inches. These meters work well in clean water clearwells, chemical storage tanks, and digesters where contact measurement is acceptable. The key trade-off: both types require the float to move freely, so they struggle with heavy buildup, turbulence, or debris that can jam the float or coat the probe.

• 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

Misconception 1: Magnetic and magnetostrictive level meters are the same technology with different names.

​

Reality: Magnetic meters use mechanical flag indicators for local reading only; magnetostrictive meters use electronic pulse timing for remote digital signals and continuous measurement.

​

Action: Clarify whether you need local visual indication, remote monitoring, or both before requesting quotes.

​

Misconception 2: These meters work in any liquid because the float doesn't touch electronics.

​

Reality: Floats can jam from grease buildup, get stuck on foam layers, or fail if specific gravity changes significantly from calibration conditions.

​

Action: Ask manufacturers about float material compatibility and minimum specific gravity requirements for your application.

Magnetostrictive waveguide is a thin wire housed inside the probe tube that transmits ultrasonic pulses when energized by the electronics. The waveguide is typically nickel-iron alloy protected by a stainless steel tube rated for submersion in water or wastewater. This wire must remain straight and untensioned—any bending from impact or debris accumulation causes false readings or complete failure.

​

Position magnet float rides on the liquid surface and contains permanent magnets that interact with the waveguide's magnetic field. The float is sealed foam or hollow stainless steel, sized to match the specific gravity of water or wastewater applications. Float sizing directly affects accuracy in turbulent conditions—undersized floats bounce excessively while oversized floats respond slowly to level changes.

​

Process connection housing anchors the probe assembly to the tank or wet well and provides electrical conduit access. Common materials include 316 stainless steel flanges or threaded NPT connections, with NEMA 4X or IP68-rated junction boxes for electronics. This connection point is where most installation errors occur—misalignment causes the float to bind on the probe tube.

​

Electronics module generates the interrogation pulse, measures time-of-flight, and converts the signal to a 4-20 mA output or digital protocol. The module is typically housed in a weatherproof enclosure with DIN-rail mounting and requires 24 VDC loop power. This component determines resolution and update rate—faster sampling catches rapid level changes but may require more signal filtering in turbulent wells.

​

Probe tube surrounds and protects the waveguide while guiding the float through its travel range. Tubes are 316 stainless steel or coated aluminum, with lengths from 2 to 30 feet depending on measurement span. Tube straightness and internal smoothness matter because any roughness or bow creates friction that prevents the float from tracking true level accurately.

Daily Operations: You'll monitor level readings on your SCADA system and compare them to visual observation during rounds—discrepancies of more than 2 inches warrant investigation. Normal operation shows smooth, responsive tracking as pumps cycle or flow changes. Notify maintenance if readings freeze, jump erratically, or drift slowly away from visual level over several days.

​

Maintenance: Monthly visual inspections check for float damage, debris accumulation on the probe, and secure mounting hardware—this takes 10 minutes and requires no special tools. Annual removal and cleaning prevents buildup that binds the float, typically a two-person job requiring confined space entry in wet wells. Most plants handle routine maintenance in-house, but electronics troubleshooting or waveguide replacement requires manufacturer support and costs $800-2000 depending on probe length.

​

Troubleshooting: Erratic readings usually indicate float binding from debris or a damaged probe tube—pull the assembly and inspect for grease, rags, or bent sections. Frozen readings suggest electronics failure or a cracked waveguide, which requires manufacturer diagnostics using specialized software. Floats last 5-10 years in clean water but degrade faster in grit-laden wastewater—replace immediately if you see cracks or waterlogging that changes buoyancy.

Selecting magnetic and magnetostrictive level meters requires balancing measurement range, accuracy needs, process conditions, and installation constraints—each variable influences the others and affects both initial cost and long-term reliability.

​

Measurement Range (feet) determines the physical length of the float chamber or probe assembly you'll need to accommodate. Municipal magnetic and magnetostrictive level meters commonly measure between 2 and 30 feet of level span. Shorter ranges suit clarifier weirs and filter underdrain monitoring, while longer ranges handle wet wells, storage tanks, and digester applications where you're tracking significant depth changes across the full vessel height.

​

Accuracy (inches or percent of span) affects your ability to control processes tightly and avoid nuisance alarms. Municipal installations typically achieve accuracy between ±0.1 and ±0.5 inches for magnetostrictive units, or ±0.25 to ±1.0 inches for magnetic float designs. Magnetostrictive technology delivers tighter accuracy across the full span, which matters for inventory management and precise pump control, while magnetic floats offer adequate performance for alarm functions and general level indication where slight variations don't impact operations.

​

Process Temperature (°F) influences float material selection and seal integrity throughout the measuring chamber. Municipal water and wastewater level meters commonly handle process temperatures between 32°F and 180°F. Higher temperatures—found in digester supernatant or heated process tanks—require high-temperature seals and specialized float materials, while ambient-temperature applications in wet wells and clearwells allow standard materials that reduce cost and simplify maintenance.

​

Process Pressure (psig) dictates chamber wall thickness and flange ratings for the float tube assembly. Most municipal magnetic level meters operate between atmospheric pressure and 150 psig. Pressurized applications like hydropneumatic tanks and pressure filters demand thicker-walled chambers with higher-rated flanges, while atmospheric tanks and open channels allow lighter construction that's easier to install and less expensive to procure.

​

Specific Gravity Range (dimensionless) determines float buoyancy calibration and whether a single instrument can handle varying process conditions. Municipal level meters commonly accommodate specific gravities between 0.7 and 1.5. Applications with consistent fluid properties—like potable water or final effluent—use floats calibrated to a narrow range, while sludge blanket monitoring or chemical feed tanks with varying concentrations require wider-range floats or field-adjustable designs to maintain accurate tracking across process changes.

​

All values are typical ranges—actual selection requires manufacturer consultation and site-specific analysis.

Should you use magnetic float or magnetostrictive measurement technology?

​

• Why it matters: Technology choice affects accuracy, complexity, and maintenance requirements for your application.
• What you need to know: Required accuracy, budget constraints, and whether you need continuous or point-level measurement.
• Typical considerations: Magnetic float switches work well for simple alarm points and are easier for operators to troubleshoot. Magnetostrictive transmitters provide continuous analog signals with higher accuracy but require more sophisticated calibration and electronics knowledge from your maintenance team.
• Ask manufacturer reps: How does temperature stratification in the chamber affect float stability and measurement reliability?
• Ask senior engineers: When has float binding or coating buildup caused false alarms at similar facilities?
• Ask operations team: Can your technicians calibrate magnetostrictive electronics or will you need vendor service contracts?

​

How will you handle interface mounting and chamber configuration?

​

• Why it matters: Mounting configuration determines accessibility, reliability, and integration with existing structures and piping.
• What you need to know: Chamber diameter, process connections available, and whether retrofit or new construction dictates constraints.
• Typical considerations: Side-mounted chambers offer easier maintenance access but require adequate clearance and structural support. Top-mounted installations save floor space and work better in retrofit situations but complicate float replacement and cleaning procedures.
• Ask manufacturer reps: What minimum chamber diameter prevents turbulence from affecting float movement in your specific design?
• Ask senior engineers: Have you seen installation orientations that created access problems during routine maintenance activities?
• Ask operations team: How often do you need to remove floats for cleaning or inspection?

​

What level of redundancy and failsafe design do you need?

​

• Why it matters: Redundancy decisions affect system reliability, capital cost, and operational complexity during equipment failures.
• What you need to know: Consequences of measurement failure, process criticality, and whether backup systems already exist downstream.
• Typical considerations: Critical applications like pump control or overflow prevention often justify dual transmitters with independent power supplies. Less critical monitoring points may rely on single instruments with alarm-on-failure outputs to alert operators.
• Ask manufacturer reps: How does your transmitter signal a sensor failure versus an out-of-range condition?
• Ask senior engineers: What measurement failures have caused process upsets and how was redundancy designed?
• Ask operations team: Can you operate manually if this measurement fails during off-hours?

Lead Times: Standard units ship in 4-8 weeks; custom lengths or exotic materials extend to 10-14 weeks, comparable to other process instruments. Important for project scheduling—confirm early.

​

Installation Requirements: Vertical clearance above tank for probe removal during maintenance; process connection must align with vessel nozzle (threaded, flanged, or hygienic). Electrical conduit routing to transmitter head; some models require separate junction box. No special rigging equipment for standard probes under 10 feet.

​

Coordination Needs: Coordinate with structural for nozzle location and reinforcement pads on new tanks. Electrical provides power and signal wiring to control panel or PLC. Controls integrator configures 4-20mA scaling, alarms, and failsafe states in SCADA.

Magnetrol – Eclipse guided wave radar and magnetic level indicators; strong in municipal water treatment applications with hazardous area approvals.

​

AMETEK Drexelbrook – Magnetostrictive and RF admittance level transmitters; specializes in challenging water/wastewater applications with foam or turbulence.

​

ABB – Magnetic level switches and continuous transmitters; broad product range with integration into municipal SCADA systems.

​

This is not an exhaustive list—consult regional representatives and project specifications.

• 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