Endress Hauser FTL51 Level Transmitter with HART Protocol

Liquiphant FTL50 – Detailed Overview

1. Working Principle (Vibronic / Tuning Fork)

• The FTL50 has a metal tuning fork that is continuously excited to vibrate at its natural resonance (~85 Hz).
• In air (or gas): the fork vibrates freely at a higher frequency.
• When liquid covers the fork: the vibration is damped → frequency decreases → electronics detect the shift.
• The switch changes state (relay or electronic output).
• This principle is independent of:
• Conductivity (works in non-conductive oils or conductive water)
• Dielectric constant (not affected by media change)
• Density (works down to ~0.5 g/cm³)
• Viscosity (works up to ~10,000 mm²/s)

2. Key Features

• Compact design → ideal for installation in tight spaces, pipes, and small tanks.
• No calibration required → plug-and-play solution.
• Failsafe mode selectable → High (overfill protection) / Low (pump dry-run protection).
• Self-monitoring electronics → diagnostic function with NAMUR NE 107 status signal.
• Wide media compatibility → from water to oils and aggressive chemicals.
• Maintenance-free (no moving parts, no wear).
• Safety rated → SIL2/3 certified according to IEC 61508.

3. Technical Specifications

• Measuring task: Point level detection in liquids
• Process temperature:
• Standard: –40 °C … +150 °C
• Special versions: up to 280 °C
• Process pressure: up to 40 bar (580 psi)
• Density limit: ≥0.5 g/cm³ (can be used with light hydrocarbons, solvents)
• Viscosity range: up to 10,000 mm²/s
• Pipe diameter: ≥25 mm
• Output options:
• Relay (SPDT)
• PNP/NPN transistor
• 2-wire AC/DC
• NAMUR signal
• Fieldbus (PROFIBUS PA, FOUNDATION Fieldbus)
• Ingress protection: IP66/67, NEMA 4X
• Explosion protection: ATEX, IECEx, FM, CSA, NEPSI (gas and dust applications)

4. Applications

• Overfill protection in tanks and vessels (safe shutdown).
• Dry-run protection for pumps (avoiding damage).
• Leak detection in pipelines and containment.
• Safety-critical loops (SIL-rated shutdown).
• Suitable for:
• Water & Wastewater
• Chemical and Petrochemical
• Oil & Gas
• Food & Beverage (hygienic versions available)
• Power Plants

5. Variants & Comparison

6. Certifications & Standards

• Functional Safety: SIL2/3 (IEC 61508)
• Explosion Protection: ATEX, IECEx, FM, CSA, NEPSI
• Marine approvals: ABS, BV, DNV GL, LR (for shipbuilding)
• Hygienic standards (for FTL51C): EHEDG, 3A, FDA-compliant materials
• Process safety compliance: WHG (German Water Resources Act)