AS-LLS Liquid Level Switch

FCI Model AS-LLS is a no moving parts, ultra-reliable level switch which detects the presence or absence of liquid or interface at the sensing location. The AS-LLS level switch is directly installed into tanks, reservoirs, sumps and gearboxes on commercial and military aircraft, as well as spacecraft, vehicles and marine applications. The sensor uses FCI proven thermal dispersion technology to rapidly detect and to signal of a too low level or too high level condition in the installation.  Unlike mechanical level detection, the AS-LLS will not stick, clog or foul and no routine maintenance is required. It is small, compact and lightweight suitable for a broad range of application throughout the aircraft.

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  • Oil Level Sensor
  • Collection Sumps
  • Automation of Sight Gauge Level Detection
  • Waste or Grey Water Reservoirs
  • Hydraulic Reservoirs
  • Coolant Reservoirs
  • Fuel Level Detection
  • Oil / Water Interface Detection
  • Potable Water Reservoirs
  • Backflow Reservoir Detection
  • Condensation Detection in Fuel or Hydraulic Systems


Service: Wet/dry level switch for liquid/air or wet/wet interface

Sensor Element Material: 316 stainless steel all welded construction

Electronics Enclosure: 316 stainless steel; hermetically sealed

Electrical Connection: D38999 or compatible

Process Connection: Flanged with O-ring seal

Insertion Length: Per customer requirement

Signal Output Options
  • Sourcing output: Wet signal: source 240 mA at 28 VDC; dry signal: source Ø VDC
  • Open collector output: Wet signal: closed, sinking up to 100 mA at less than 0.5 VDC; dry signal: open, leakage < 10 µa at 30 VDC

Electrical Power Input: 28 VDC nominal per MIL-STD-704

Power Consumption: 3 watts maximum

Weight: 8 oz [227g] maximum

Proof Pressure: up to 2,000 psig [138 bar (g)] as required by application

Switch Point Adjustment: Factory set at customer specified switch point

Operating Temperature Range
Sensor Element: - 65 °F to 350 °F [- 54 °C to 175 °C]
Specify actual requirement
Electronics: - 40 °F to 257 °F [- 40 °C to 125 °C]
Higher temperatures available optionally

Repeatability: ±1/8 inch [3 mm] of liquid level elevation

Time Response: 5-15 seconds typical, depending on fluid type and switch point

EMI and Lightning Protection: MIL-STD-461 and RTCA/DO-160

Qualifications: MIL-STD-810 and RTCA/DO-160

Quality Systems Approval: ISO 9001, AS9100