AC Fuel Probes

The LMS Carbon Composite Fuel Quantity Probes with AC Systems are made with lightweight and durable carbon composite. They are the lightest fuel probe available in the industry and virtually immune to corrosion, cracking, dents or other field maltreatment. In fact, LMS has delivered over 7,000 carbon composite fuel quantity probes to the field, operating with no field failures in a wide variety of both commercial and military aircraft.

Carbon Composite Construction

The LMS Carbon Composite Fuel Probe weighs up to 40%  lighter than aluminum of a similar metal probe. For example, a 38” long LMS composite probe now in production (with cable) weighs less than 10 ounces.

Electrical Connections

All electrical connections to the capacitance probe, from the interface connector to the actual probe tubes, make use of soldered or composite bonded electrical connections. There is no friction or riveted electrical connections on the LMS Carbon Composite Fuel Probe and all electrical terminations are sealed from the fuel environment.


Fatigue cracking of aluminum fuel probes, although infrequent, does occur around flood holes or riveted connections especially with a relatively long flange mounted cantilevered unit. The LMS Carbon Composite Probe with carbon composite tubing is inherently resistant to fatigue because the material does not “work harden” as aluminum does. Since the composite tubes weighs up to 40% lighter than aluminum and are generally stiffer, the resonance amplitudes are significantly less.

AC Fuel Probe Features

  • Robust composite two-tube design
  • Won’t dent, scratch or absorb hand oils
  • Low level capability
  • AC system is not susceptible to EMI
  • No electrical components on probe
  • No friction or riveted electrical connections
  • No fatigue or cracking under high vibration or slosh loads
  • Weighs up to 40% lighter than aluminum of a similar metal probe

DC Fuel Probes

LMS’ DC Fuel Probe is compatible with a 200v/m EMI environment. The probe utilizes two carbon composite tubes as the capacitive elements. The outer tube is grounded to the airframe which provides a Faraday cage shield around the probe components. This design shields the diodes from the 200v/m EMI levels. The two tubes are structurally joined by a nickel-plated cap or flange, and linked to the system with an EMI connector. The design protects the probe elements from arcing. The weight reduction benefit is especially noticeable when compared with metal two tube and three-tube designs.

Fuel Density Measurement

The LMS DC Fuel Probes are density compensated by measuring temperature and using a proprietary LMS design for correcting the variation of dielectric constant to fuel density.

DC Fuel Probe Features

  • Robust two composite tube design with EMI compatible outer tube
  • Won’t dent, scratch or absorb hand oils
  • Low level capability
  • Full density compensated probe
  • No coaxial shielding (over-braid only)
  • Lowest cabling complexity
  • No outer tube shorts to ground
  • More accurate pre-calibrated system
  • No friction or riveted electrical connections
  • No fatigue or cracking under high vibration or slosh loads

Fuel Dielectric Compensator

Increase system accuracy without additional part numbers

LMS’ compensators can be added to AC carbon composite fuel probes.  The compensator directly measures the dielectric of the fuel which allows for fuel quantity compensation across variations in temperature and fuel type.  Not all fuel gauging systems require a compensator, but it is an option for aircraft that frequently switch between fuel types and demand a high level of accuracy.  

The compensator is made from stainless steel tubes bonded to a plastic end cap and is built-in to the bottom of a fuel quantity probe. The compensator has three concentric tubes to increase its capacitance range while remaining short to ensure it stays submerged in fuel as long as possible.

  • Increased accuracy across fuel types
  • Environmental MIL-STD and DO-160 Testing
  • Corrosion-resistant stainless steel
  • Integrates into a carbon composite fuel probe

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