Liquicap M FTI51

Summary

Product identification

The Liquicap M FTI51 and FTI52 are capacitance point level switches for liquids, designed for point level detection.

Application

The device is suitable for:

• Detection of highly viscous liquids and pastes that tend to form buildup.
• Interface detection of different liquids (e.g., oil on water).
• Two-point control (e.g., pump control) using a single process connection.
• Foam detection of conductive liquids.

It can operate under vacuum and pressures up to 100 bar, with material options supporting temperatures from –80 °C to +200 °C.

Key Features and Benefits

• Active buildup compensation for viscous media.
• Simple commissioning with a single button press.
• Versatile application with a range of certificates and approvals.
• Corrosion-resistant materials in contact with the process, which are FDA-listed.
• Two-stage overvoltage protection.
• Short reaction times.
• No recalibration needed after replacing electronics.
• Suitable for safety systems requiring SIL2/SIL3 compliance.
• Automatic monitoring of electronics.

Measuring Principle

The device operates on the principle of capacitance point level detection. The probe and container wall form a capacitor. The capacitance changes as the probe becomes covered by liquid. A specific switching capacitance, set during calibration, triggers the switch. Active buildup compensation is included to counteract influences from buildup on the probe. For non-conductive containers, a ground tube acts as a counterelectrode.

Measuring System

The measuring system can consist of:

• The Liquicap M FTI51 or FTI52 point level switch and an electronic insert (FEI51, FEI52, FEI54) for a compact system.
• The Liquicap M FTI51 or FTI52 point level switch, an electronic insert (FEI53, FEI57S, FEI58), and a separate transmitter power supply unit for systems requiring external switching units.
• The Liquicap M FTI51 or FTI52 point level switch, the FEI55 electronic insert, and a transmitter power supply unit for 8/16 mA signal transmission.

Electronic Inserts

Various electronic inserts are available, offering different functionalities:

• FEI51: Two-wire AC connection, load switched directly into the power supply circuit.
• FEI52: Three-wire DC version with PNP output, load switched via transistor.
• FEI53: Three-wire DC version with 3 to 12 V signal output, for separate switching units.
• FEI54: Universal current version with relay output (2 floating changeover contacts).
• FEI55: 8/16 mA signal transmission, SIL2/SIL3 hardware/software approval, for separate switching units.
• FEI57S: PFM signal transmission, for separate switching units with PFM signal.
• FEI58: NAMUR standard (H-L edge 2.2 to 3.5 / 0.6 to 1.0 mA), for separate switching units.

Operating Conditions: Installation

• FTI51 (rod probe): Can be installed from above, below, or the side.
• FTI52 (rope probe): Can be installed vertically from above.
• General: Probe must not touch the container wall. Recommended distance from the container floor is ≥ 10 mm. Probes should not be installed in the filling curtain area or too close to agitators. A minimum distance of 500 mm is recommended between adjacent probes.

Operating Conditions: Environment

• Ambient temperature range: –50 to +70 °C (–40 to +70 °C with F16 housing).
• Storage temperature: –50 to +85 °C.
• Climate class: DIN EN 60068-2-38/IEC 68-2-38: test Z/AD.
• Vibration resistance: DIN EN 60068-2-64/IEC 68-2-64: 20 Hz– 2000 Hz; 0.01 g²/Hz.
• Shock resistance: DIN EN 60068-2-27/IEC 68-2-27: 30 g acceleration.
• Degree of protection: IP66, IP67, IP68, NEMA4X depending on housing type.
• Electromagnetic compatibility (EMC): Interference emission to EN 61326 (Class B); interference immunity in accordance with EN 61326 (Industrial) and NAMUR Recommendation NE 21.

Operating Conditions: Process

• Process temperature range: The operating temperature is limited by ambient temperature and housing type. For example, the polyester housing F16 restricts the temperature to –40 °C. The diagrams show the interplay between ambient (Ta) and process (TP) temperatures, ranging up to +200 °C for the process temperature under certain conditions.
• Process pressure limits:
  • Probe ø10 mm, ø14 mm: –1 to 25 bar.
  • Probe ø16 mm: –1 to 100 bar. With inactive length, maximum is 63 bar (or 32 bar with CRN approval).
  • Probe ø22 mm: –1 to 50 bar.
  • Pressure values at higher temperatures must be determined considering relevant standards (EN 1092-1, ASME B 16.5a, JIS B 2220).
• Pressure and temperature derating: Diagrams illustrate pressure derating curves based on process temperature for various probe sizes and process connections.

Mechanical Construction

Various housing materials and types are available, including Polyester (F16), Stainless Steel (F15, F27), and Aluminum (F17, F13, T13). Different process connections are offered, such as threads (G, NPT), Tri-Clamp, and flanges (EN, ANSI, JIS). Probe types include rod (FTI51) and rope (FTI52), with options for fully insulated, partially insulated, inactive lengths, and active buildup compensation.

Technical Data: Probe

• Capacitance values:
  • Basic capacitance: approx. 18 pF.
  • Additional capacitance in air: approx. 1.3 pF/100 mm (rod) and 1.0 pF/100 mm (rope).
  • Capacitance in water: varies by probe type and diameter.
• Material: Materials in contact with the process are typically 316L (1.4435) or 316 (1.4401) for metallic parts, and PFA or PTFE/FEP for insulation. Materials not in contact with the process include PA, PBT-FR, silicone, and aluminum alloys.

Input

• Measured variable: Change in capacitance between the probe rod and the tank wall or ground tube, which correlates to the liquid level.
• Measuring range:
  • Measuring frequency: 500 kHz.
  • Span (ΔC): 5 to 1600 pF (or 5 to 500 pF with FEI58).
  • Final capacitance (CE): max. 1600 pF.
  • Adjustable initial capacitance (CA): 5 to 500 pF (range 1) or 5 to 1600 pF (range 2, not with FEI58).
  • Minimum capacitance change for detection: ≥ 5 pF.
• Measuring conditions: Notes on using inactive length for nozzles, active buildup compensation for viscous liquids, and fully insulated probes for pump control. Formulas and examples are provided for calculating minimum probe length and maximum probe length based on capacitance.

Output

• Switch behavior: Binary or Δs operation (pump control, not with FEI58).
• Fail-safe mode: Minimum/maximum quiescent current safety is switchable at the electronic insert (FEI53, FEI57S with Nivotester).
  • MIN: Switches when probe is uncovered (dry running protection).
  • MAX: Switches when probe is covered (overfill protection).
• Switching delay: Adjustable from 0.3 to 10 s (FEI51, FEI52, FEI54, FEI55), dependent on the Nivotester (FEI53, FEI57S), or selectable between 1 s / 5 s (FEI58).
• Galvanic isolation: Provided between the probe and power supply for FEI51, FEI52; between probe, power supply, and load for FEI54. For FEI53, FEI55, FEI57S, FEI58, refer to the connected switching device.

Certificates and Approvals

The device is compliant with CE, RoHS, RCM-Tick, EAC, and may have Ex approvals. Additional approvals like CRN and compliance with Pressure Equipment Directive 2014/68/EU (PED) are available.

Accessories

Available accessories include protective covers, shortening kits, overvoltage protection units, and weld-in adapters.

---

Disclaimer: This extraction may miss figures, footnotes, or revisions. Contractual data must match the OEM PDF revision used on the project.

Official datasheet (PDF)

Lenntech datasheet mirror