Terminal Resistance

What are the requirements for terminal resistance at the end points of a measuring line?

In constructing a measuring line with CAN or RS-485 interfaces, it’s necessary to set terminal resistance at its ends.

All the ZETLAB interface converters (except for the ZET 7177 module) are equipped with integrated terminal resistances, thus the measuring line at interface converter side is equipped with terminal resistance.

There are third-party industrial devices (interface converters) with and without integrated terminal resistance. When using interface converters without integrated terminal resistance, it is necessary to set external terminal resistance. The measuring line side which is opposite to the side connected to the interface converter must be equipped with terminal resistance, rate of which is to be chosen depending on the measuring line length:

  • line length up to 40 m — 120 Ohm;
  • line length 40 to 1000 m — 150…300 Ohm.