Fluid level measurement system and method

A transport refrigeration system for a transportable temperature controlled space, the transport refrigeration system comprising:

• a compressor, a condenser and an evaporator fluidly connected to one another;
• an engine operatively connected to the compressor;
• and
• a fuel tank assembly fluidly connected to the engine, wherein the fuel tank assembly is subjected to vibrations from movement of the temperature controlled space as the temperature controlled space is transported, the fuel tank assembly including:
• a fuel tank configured to contain a fuel, a fuel vapor and air, the fuel tank having a maximum fuel level and an interior and an exterior;
• an ultrasonic fluid level sensor configured to be directed toward a surface of the fuel such that sound from the fluid level sensor is reflected from the surface of the fuel for sensing a level of fuel, the fluid level sensor coupled to the fuel tank and spaced from the maximum fuel level;
• and
• a tubular spacer having a first end and a second end and a length between the first end and the second end, wherein the first end is positioned adjacent the ultrasonic fluid level sensor and the second end is positioned in communication with the interior of the tank;
• wherein the fluid level sensor includes a transducer having a ring period and wherein the length of the spacer is at least half the distance that the sound travels through the fuel vapor and air toward the surface of the fuel during the ring period of the transducer.