Capacitive Level Sensors for Fuel, Oil & Hydraulics

High-precision, drift-free liquid level measurement with no moving parts. Engineered for vehicle fleets, telematics, heavy machinery, hydraulic units, and demanding industrial process tanks.

Longvista capacitive level sensors (SFLS500 Series and SLS605 Series) represent the modern standard for continuous level monitoring. Built to overcome the limitations of mechanical float switches that jam with sludge and ultrasonic sensors that fail in fuel vapors or heavy foam, our probes deliver linear, high-resolution measurement across non-conductive hydrocarbons, viscous oils, wastewater, and aggressive chemical solutions.

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Optimized for Complex Media & Harsh Environments

  • Hydrocarbons & Industrial Liquids: High-sensitivity detection for diesel, gasoline, biofuel, hydraulic oils, lubricants, and industrial wastewater.

  • Solid-State Reliability: Zero moving parts guarantees maintenance-free operation under intense vibration, sloshing, and mechanical stress.

  • Advanced Systems Integration: Standardized industrial outputs (4–20 mA, 0–5V, 0–10V, RS485 Modbus, CAN bus) for seamless connection to GPS telematics, PLCs, and SCADA networks.

Quick Comparison: SFLS500 vs. SLS605 Series

Feature SFLS500 Series SLS605 Series
Primary Focus Fleet Fuel & Mobile Asset Management Industrial Process Tanks & Heavy Operations
Target Media Diesel, Gasoline, Biodiesel, Kerosene, Light Oils Hydraulic Oils, Viscous Liquids, Sewage, Chemicals
Key Advantage Auto-calibration & Field-truncatable probe rods RF Anti-coating & Anti-adhesion technology
Temperature Range -50°C to +125°C -40°C to +150°C
Max Process Pressure Up to 0.6 MPa Up to 2.5 MPa
Protection Rating IP68 IP68 / IP67

Selection Guide

1. Auto-Calibration vs. RF Anti-Coating Technology

  • For Clean Fuels & Fleet Tanks (SFLS500 Series): Utilizes multi-layer tomographic scanning to auto-calibrate against dielectric variations caused by temperature shifts or changing fuel blends.

  • For Viscous, Sticky, or Conductive Fluids (SLS605 Series): Utilizes Radio Frequency (RF) capacitance technology. By analyzing both resistive and capacitive impedance, the sensor ignores thin liquid films, crystallization, or heavy condensation adhering to the probe rod, measuring only the true bulk liquid level.

2. Tank Material Considerations: Metal vs. Plastic/Fiberglass

  • Metal Tanks: The conductive metal wall acts naturally as the ground reference electrode. Standard rod probes operate at maximum precision.

  • Plastic, Composite, or Underground Tanks: Non-conductive tanks lack a ground reference. For these installations, select a Coaxial Probe (a rod enclosed inside an outer reference tube) or an auxiliary ground line to ensure a stable electric field.

3. Avoiding Volume Measurement Errors in Irregular Tanks

For non-rectangular tanks (e.g., horizontal cylindrical fuel tanks or baffled mobile reservoirs), liquid height does not scale linearly with volume.

  • The Solution: Choose our RS485 Modbus models. These support multi-point calibration tables directly within the sensor memory, outputting true volumetric data directly to your telematics or control platform.

Technical Features & Material Resilience

Material / Feature Engineering Advantage Practical Benefit
Aluminum Alloy Rods Lightweight & High Rigidity Allows field-cutting (SFLS500S) without probe bending
304 / 316L Stainless Steel Corrosion & Chemical Resistance Long service life in contaminated fuels, marine, & industrial sumps
PTFE Coating (SLS6054) Hydrophobic & Anti-Corrosive Essential for strong acids, raw chemical liquids, & sticky media
Encapsulated Electronics Vibration & Shock Isolation Prevents component failure on diesel generators & heavy machinery

Practical Installation & Maintenance Best Practices

  • Bottom Clearance Gap: Always leave a 5–10 mm clearance between the probe tip and the bottom of the tank. This prevents false readings caused by accumulated water or heavy sediment at the bottom.

  • Avoid Turbulent Inlets: Do not position probes directly beneath fuel return lines, pump inlets, or high-velocity discharge pipes. Turbulence and entrained air bubbles destabilize capacitance readings.

  • Cable Shielding: In high Electromagnetic Interference (EMI) environments (near alternators, heavy motors, or Variable Frequency Drives), use shielded twisted-pair cables grounded at the receiver end only.

Troubleshooting Guide

Symptom Likely Cause Professional Solution
Erratic Signal Fluctuations Heavy sloshing or electrical noise (EMI) Enable internal digital damping; verify cable shield grounding.
Sudden “100% Full” Reading Water accumulation touching the probe base Drain water from the tank sump; maintain the 5–10 mm bottom gap.
Gradual Measurement Drift Heavy wax, sludge, or chemical coating buildup Clean probe with solvent; upgrade to the SLS605 series with RF anti-coating technology.
Inaccuracy After Refueling Shift in fuel blend (e.g., standard diesel to biodiesel) SFLS500 auto-calibrates automatically; for legacy units, execute a quick 2-point recalibration.

Technology Comparison: Why Choose Capacitive?

Technology Ideal Application Key Advantage Key Limitation
Capacitive Fuel, Oils, Hydraulics, Process Tanks No moving parts, highly stable, anti-coating models Requires dielectric matching
Ultrasonic Water, Open Chemical Tanks Non-contact measurement Affected by heavy vapors, foam, & pressure
Float Switch Basic High/Low Level Alarms Simple, low initial cost Mechanical wear; easily jammed by sludge
Radar Large Bulk Storage & Harsh Vapors Extreme precision, non-contact Higher initial equipment investment
Hydrostatic Deep Wells, Water Reservoirs Submersible, easy installation Sensitive to density changes

Frequently Asked Questions (FAQ)

Q: Can I cut the probe length during installation?

A: Yes, the SFLS500S model is specifically designed to be cut to length directly in the field using a standard saw. The internal microprocessor automatically recalibrates to the new length without complex tools.

Q: How do these sensors assist in fuel theft prevention?

A: When integrated with a telematics terminal via RS485 Modbus, the SFLS500 detects rapid drops in fuel level in real-time—even when the vehicle ignition is switched off—triggering instant alerts for unauthorized siphoning.

Q: Are capacitive sensors suitable for high-temperature industrial oil applications?

A: Yes. While standard fleet fuel sensors are rated for ambient temperatures, the SLS605 Series handles high-temperature industrial oils and process media up to +150°C and pressures up to 2.5 MPa.

Ready to eliminate measurement drift in your liquid storage systems?

[Request a Technical Quote] — Contact our team with your tank dimensions and fluid properties for a custom-tailored probe configuration.

Related Sensing Technologies

If you are evaluating alternative measurement principles for your facility, explore our complementary instrumentation categories:

  • [Level Sensors Overview]: Explore our complete range of point level and continuous measurement solutions.

  • [Submersible Level Sensors]: Reliable hydrostatic pressure transmitters for deep wells, water tanks, and wastewater sumps.

  • [Ultrasonic Level Sensors]: Non-contact continuous monitoring for open channels, water treatment, and chemical storage.

  • [Radar Level Sensors]: High-frequency non-contact transmitters for extreme temperatures, high pressure, and bulk solids.

  • [Pressure Sensors] & [Flow Meters]: Complete process control instrumentation for industrial pipelines and automation systems.

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