AC Fuel Probes

The LMS Composite Fuel Quantity Probes with AC Systems are made with lightweight and durable graphite 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 6,200 graphite composite fuel quantity probes to the field, operating with no field failures in a wide variety of both commercial and military aircraft.

Graphite Composite Construction

The LMS Composite Fuel Probe weighs approximately half that 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 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 Composite Probe with graphite composite tubing is inherently resistant to fatigue because the material does not “work harden” as aluminum does. Since the composite tubes are roughly half the weight of 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
  • Half the weight of aluminum probes

DC Fuel Probes

LMS’ DC Fuel Probe is compatible with a 200v/m EMI environment. The probe utilizes two graphite 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
  • Half the weight of three-tube aluminum EMI probes


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