KB1461 - LonWorks Channel Twisted-Pair Terminators
- Michael Wytyshyn (Unlicensed)
Problem
Do I need to use Terminators on a LonWorks Twisted-Pair Network
Solution
Termination: What is it?
Termination, is essential on your twisted pair networks (FT-10 and TP-1250).
Termination absorbs unwanted signal reflections (resonance of date signal) which would interfere with communications causing packet errors.
Absence of terminators can cause packet corruptions.
Terminator values must match the channel transceiver type and topology.
Free topology uses one 52.3 ohm terminator anywhere on segment
Bus topology uses two 105 ohm terminators one at each end of segment
Verifying Termination
All LonWorks terminators are AC coupled resistors or RC-combinations and present complex impedance to the network. DC-based multi-meter devices are, therefore, not appropriate to measure or verify the correct termination of a LonWorks network. The complex impedance “Z” must be measured using an AC bridge.
It is imperative, in the case of a link power channel, that the link power supply is turned off and fully discharged before any measurements are taken. In the case of power line transceiver based networks, any supply voltage must also be removed.
Measure the impedance between the network cable pair at any point on a channel. Given a measurement at 1 kHz, the readings should be in the magnitude indicated by the following table:
The values for Z in the table do not take into account cable loop resistance and other factors such as the input impedance of any devices on the channel. However, a reading in the indicated area should be sufficient as an indicator for correct termination in most cases.
Terminator Placement:
Free Topology: usually placed at SmartServer.
Bus Topology: one placed at SmartServer and the other at the far end of the bus
Lab and Manufacturing Testing:
Always use termination
In most cases you only need the resistor and not the capacitors.
Related Products
FT-10 channels
TP-1250 channels
Power line channels