What it is

The Soliphant FTM51 is a vibronic point level switch designed for bulk solids (especially fine-grained or powdery materials) in silos or containers.

• “Point level” means it detects that the level has reached a specific point (e.g., high level or low level), rather than continuously measuring level.
• “Vibronic” indicates the measuring principle is based on vibration (mechanical oscillation) of a fork probe.
• The FTM51 version is the one with an extension tube (i.e., can reach deeper into the vessel) among the Soliphant M series (FTM50, FTM51, FTM52) for fine-grained bulk solids.

How it works (measuring principle)

• The fork (two prongs) of the probe vibrates at a certain frequency when free (i.e., when the prongs are not covered with material).
• When the medium (bulk solid) covers the fork, the vibration amplitude (or frequency) changes (typically damped). The electronics detect this change and trigger the switching output.
• Because there are no mechanical moving parts (other than the vibratory element itself) the device is essentially maintenance-free and robust.
• The device offers diagnostics (e.g., build-up on the probe, abrasion, and density setting) to ensure reliable detection in challenging bulk-solid applications.

Key Specifications & Features

Some of the main technical data for the FTM51:

• Process temperature: –50 °C to +280 °C (-60 °F to +540 °F)
• Process pressure: vacuum up to +25 bar (vacuum to ~360 psi)
• Minimum bulk density (for detection): Standard fork ≈ 10 g/L; short fork ≈ 50 g/L.
• Grain size allowed: ≤ 10 mm (≈0.39 in) for typical bulk solids.
• Materials and finishes: Wetted parts selectable (316L stainless steel with surface finish options, PTFE or ETFE coatings for build-up or corrosion protection)
• Electronics and outputs: Various insert-electronics options (relay, thyristor, NAMUR, PFM signals) to suit different control systems.
• Certification / Safety: Supports SIL 2 per IEC 61508, has versions suitable for hazardous atmospheres (dust/gas).

Applications / Where to Use

• The FTM51 is intended for silos, containers or hoppers storing fine-grained bulk solids or powders — e.g., cereals, flour, sugar, cocoa, animal feed, detergent powders, chalk, etc.
• Because of its robustness and design for low-density media, it is suitable for materials with low bulk density (e.g., very light powders) where detection is more challenging.
• It is also used where vibration, dust or build-up would hamper other types of sensors — because the vibronic principle is largely insensitive to external vibration and build-up (depending on version/coating).

Advantages & Benefits

• Maintenance-free (no moving mechanical parts) → less downtime.
• Reliable even with low bulk density materials.
• Not significantly affected by external vibration of vessel or build-up on sensor (with proper coating/selection) — which is often a problem in bulk solids applications.
• Flexible sensor lengths (FTM51 supports extension tubes up to 4 000 mm) so can be mounted in tall silos.
• Many options for electronics and approvals (hazardous area, SIL) to suit industrial environments.

Considerations / What to Check

• Ensure the minimum bulk density of your material is above the detection threshold for the selected fork (standard vs short fork). If your material has extremely low density, you must verify compatibility.
• Confirm the grain size and physical characteristics (flow, bridging, dustness) are compatible with this sensor — the specification lists ≤ 10 mm grain size for FTM51.
• Check the environmental/operating conditions: temperature, pressure, dust/hazardous area classification, coating needed for build-up/corrosion.
• Mounting: Because it is a point-level switch, you need to install it at the correct height corresponding to the event you want to detect (e.g., high level, low level) and ensure correct orientation and clearance for the vibrating fork.
• Sensor length and extension tube: For tall silos you’ll need the correct extension version. FTM51 supports up to 4 000 mm sensor length.
• Build-up on the probe: While the device is designed with coatings and diagnostics, heavy build-up environments may still require cleaning or alternative designs.
• Calibration / settings: Although the principle is simple, you may need to set density switch, switching delay, and density setting for accurate detection.