Field-Ready · Lesson 6.3
LON and LonWorks
Peer-to-peer controls from the 1990s that are still running buildings. What to know before you walk in.
What LON Is
LonWorks, developed by Echelon Corporation and released in 1991, was one of the first peer-to-peer control networks designed specifically for building automation. Unlike Modbus (master-slave, one master polls everyone) or early BACnet (supervisor-centric), LON devices can talk directly to each other without a central controller or head end being involved.
At the heart of every LON device is a Neuron chip, a microprocessor manufactured by Echelon and licensed to device manufacturers. The Neuron chip handles all network communication. Every Neuron chip has a unique 48-bit Neuron ID burned in at the factory, similar to a MAC address on a network interface card.
Physical layer: TP/FT-10
The most common LON physical layer is TP/FT-10 (Twisted Pair, Free Topology, 10 Kbps). Unlike RS-485 which requires a strict daisy-chain, TP/FT-10 supports free topology: you can wire devices in a star, bus, ring, or any mix. This made installation significantly easier and is one reason LON was widely adopted. Maximum segment length is 500 meters in free topology; longer runs require a repeater.
Where you will encounter it
LON was heavily adopted between 1995 and 2010, especially in large commercial buildings, universities, and government facilities. Vendors including Echelon, TAC (now Schneider), Siemens, and many VAV box manufacturers shipped LON-native products. Many of these buildings are still running their original LON networks. If you are servicing, upgrading, or integrating a building built in that era, you will likely encounter LON.