Mettler Toledo IND560 PDX Guide D'installation page 50

IND560 PDX Installation Manual
Some examples of connecting external equipment are shown in Figure 2-32.
RS-485 Transmission Line Termination
The RS-485 network should include a terminating resistor, installed between the
two lines at or on the last node. The terminating resistor should match the
characteristic impedance of the transmission line, approximately 120 ohms. This
terminating resistor is required when connecting ARM100 modules to the port.
2-20
Figure 2-32: Sample COM1 Connections