Technical Characteristics and Advanced Measurement
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Capacitance Principle: The probe and the vessel wall (or a ground tube) form a capacitor. As the level rises, the capacitance changes. The FMI51 converts this change into a proportional 4 to 20 mA signal.
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Independence from Medium Changes: In conductive liquids ($> 100 \mu S/cm$), the probe is factory-calibrated so that it provides accurate readings regardless of the dielectric constant. This means you can switch from water to a different conductive chemical without recalibrating the device.
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Build-up Immunity: The high-quality insulation and sophisticated electronics ensure that even if a sticky or viscous medium coats the rod, the measurement remains accurate, reflecting the actual level rather than the coating.
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Extreme Environment Tolerance: Engineered for durability, the FMI51 operates reliably from cryogenic temperatures (-80 °C) up to high-heat industrial processes (+200 °C), and can withstand pressures up to 100 bar.
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Safety and Reliability: The device is certified for use in safety-related systems up to SIL2. It also features two-stage overvoltage protection to safeguard against power surges or lightning strikes.
Technical Specification Matrix
| Feature | Technical Details |
| Measuring Principle | Capacitance (Continuous) |
| Probe Length | 0.1 to 4.0 m (0.3 to 13 ft) |
| Medium Conductivity | Independent of dc if > 100 μS/cm |
| Process Temperature | -80 to +200 °C (-112 to +392 °F) |
| Process Pressure | Vacuum to 100 bar (1,450 psi) |
| Materials (In-process) | 316L, PFA, PTFE (FDA-listed) |
| Output | 4…20mA HART |
Primary Applications
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Aggressive Chemical Processing: Level monitoring in acids, alkalis, and solvents where corrosion resistance is mandatory.
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High-Pressure Vessels: Ideal for reactors and steam applications where structural integrity is a priority.
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Inventory Management: When paired with Fieldgate technology, it provides real-time data for remote monitoring and automated supply chain replenishment.
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Food and Life Sciences: Thanks to FDA-listed materials and hygienic certificates, it is suited for monitoring ingredients and final products in sanitary tanks.
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Marine and Offshore: Certified for use on ships and offshore platforms, providing reliable level data for fuel, oil, or ballast tanks.
