The Liquiphant FTL31 is a point level switch designed for detecting liquid level (or the presence/absence of liquid) at a specific point (as opposed to continuous level measurement).
It uses the vibronic / tuning fork principle: a fork vibrates at a given resonance frequency; when the fork is immersed in a liquid, that resonance frequency shifts, which is detected by the electronics.

Key Technical Specifications

Here are some of its main specs & capabilities:

Spec	Value / Range
Process temperature	−40 °C to +150 °C
Process pressure	Vacuum up to +40 bar (≈ 580 psi)
Minimum density of medium	Standard >0.7 g/cm³; optionally >0.5 g/cm³
Wetted materials	Stainless steel 316L (for all parts in contact with process liquid)
Process connections	Various threaded connections: G½, G¾, G1, NPT etc.
Electrical / Output options	3-wire DC-PNP (10-30 V DC), or 2-wire AC/DC (20-253 V)
Communication / Features	Some versions have IO-Link; continuous self-monitoring; LED indicators; plug-and-play, no calibration needed.

Applications / Use Cases

Overfill protection: to detect when liquid reaches a certain high level to prevent spillovers.
Dry-run protection: detecting when a pump’s liquid level drops too low.
Lower level detection: as a safety / control switch in tanks, vessels, pipes.
Industrial machinery, cleaning systems, anywhere a simple reliable point-level detection is needed.

Key Advantages

Reliability & Safety: It has built-in continuous self-monitoring, meaning if power is lost or there's a fault, the sensor gives a safe (fail) signal.
Insensitive to many disturbances: Turbulence, flows, air bubbles, conductivity, foam-build-up or changing media properties have little to no effect. The resonance-based tuning fork is fairly robust in these conditions.
No calibration needed: Reduces setup time and maintenance.
Compact and rugged design: Stainless steel housing; various mounting and connection options; high pressure/temperature capability.
Multiple output / electrical versions: Good flexibility to match with different control systems (DC, AC, PNP, etc.).

Things to Consider / Limitations

Minimum density requirement: Standard versions require medium density >0.7 g/cm³. If your liquid is lighter, you’ll need the optional version (>0.5 g/cm³).
Not suitable for all hazardous-area use: The FTL31 is not suited for some hazardous area classifications; for hygienic or especially demanding environments, other models (e.g. FTL33) might be more appropriate.
Switching point location depends on installation: Orientation, mounting, distance from walls, etc., can affect the exact switch point. Proper installation is important (vertical, horizontal, ensuring fork drains off etc.).
Response time / hysteresis: There is some delay when the fork is covered vs uncovered, and hysteresis (difference between on/off switching) to be considered in tight control loops.

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