Installation/Cabling
Installation/Cabling
3
Termination resistors
–
120
Ω
Tx
Rx
+
+
–
+
–
+
–
Tx
Rx
+
–
+
–
Tx
Rx
+
–
+
–
Tx
Rx
120
Ω
Instrument 1
Instrument 2
Instrument ‘N’
Each
RS485
interface has specific connection and
termination biasing requirements which will be detailed in
their installation instructions. The general principles are as
follows.
Terminations
Because each wire is a transmission line, it
must be properly terminated to prevent reflections. Where
multiple instruments are daisy-chained together, a 120 ohm
terminating resistor should be fitted at the connection to
the PC and to the last instrument in the chain.
