From time to time, LonWorks® devices like the WattNode® meter stop communicating or exhibit unreliable communication. This can occur for a variety of reason:

  • Electromagnetic interference
  • Loose, intermittent, or broken wiring
  • Defective or damaged WattNode meter
  • Excessive bus length
  • Bus needs termination
  • Too many nodes on the bus

Electromagnetic Interference

This can be difficult to diagnose, because it is hard to measure interference. The best evidence for interference is when the communication failures seem to occur when a particular device or load (motor, pump, or other equipment) is running. Another test is to try moving the WattNode away from a source of possible interference, such as a variable speed drive, inverter, etc.

Echelon recommends running network wiring away from power mains and other high voltage wiring to prevent interference.

The WNB series WattNode for LonWorks models were somewhat more susceptible to electromagnetic interference. Our new WNC series models have improved isolation and immunity.

Loose, Intermittent, or Broken Wiring

This is a very common cause of intermittent communication. The most common cases are:

  • A wire that is loose in a screw terminal
  • A loose junction where a cable has been spliced or extended

We sometimes also see a break inside a cable, but this normally only happens with cables that are repeatedly flexed.

The LonWorks FTT10A communication media will sometimes work, even with a loose connection or one of the two wires not making contact, but the reliability will be poor in this case.

The easiest way to troubleshoot this is to try connecting directly to the WattNode with the bad or unreliable communication to see if the direct connection works reliably.

Defective or Damaged WattNode Meter

In rare cases, the internal circuitry of the WattNode may be defective or damaged, leading to unreliable communication. A good test for this is to try swapping two WattNode meters: one with reliable communications and one with unreliable communications. If the problem moves with the WattNode, then it’s probably a problem with the WattNode. If the problem stays with the circuit being monitored, then it’s more likely interference, bad wiring, or a related problem.

Excessive Bus Length

Long buses are more prone to unreliable communication, especially if the wiring doesn’t meet Echelon’s recommendations. See LonWorks FTT10 Cables for recommended cables and recommended network lengths.

Bus Termination

Echelon recommends double termination for any network using more than 500m (1640 feet). Even shorter networks will be more reliable and more resistant to interference with terminators.

Too Many Nodes on the Bus

Echelon allows for up to 64 nodes per network segment. There are cases when a lower number is recommended, particularly if there is a lot of network traffic resulting in excessive collisions. Also, if the bus is long, the combination of a long bus and many nodes increases the risk of communications problems.

See Also