Maretron NMEA 2000 Gasoline Tank Level Monitor (24 inch Depth Gasoline Tanks) TLM150-01Maretron NMEA 2000 Gasoline Tank Level Monitor (24 inch Depth Gasoline Tanks) TLM150 01 Maretrons TLM150 is used to sense gasoline fluid levels of tanks using ultrasonic technology. Ultrasonic, or sound waves, are transmitted via the TLM150 mounted at the top of the tank and the flight times of the sound waves to and from the fluid are measured much like a depth sensor. What this means for you is that there are no difficult to handle long probes