Network Design Considerations
2-16
TIWAY 1 TI505 NIM User Manual
2.4
LOCAL LINE BIASING
In certain network configurations, the Local Line must be biased to raise its noise immu-
nity and to prevent oscillations of receivers connected to the line.
The need to apply a bias voltage to the Local Line depends on the interface configuration
of your network.
2.4.1
Biasing Configurations
It is very likely that you will have a mixture of TI505, SIMATIC TI500, and PM550 P/Cs
on your network. Three different Local Line media biasing combinations exist, based on
the number and type of interface devices used with the P/Cs. Possible combinations are
Installations consisting solely of self-biased devices.
Installations consisting of both switch-biased and self-biased devices. (Some
older TIWAY I devices have Bias Switches.)
Installations with PM550 CIMs.
This section covers self-biased and switch-biased configurations only. (All TI505 NIMs
are self-biasing.) Appendix A discusses biasing and terminating a Local Line having all
three types of devices.
CAUTION
If a switch-biased Local Line interface port is unused (i.e., in a
case where no redundant Local Line is installed) the Bias
Switch on the unused port must be turned ON to prevent the
entry of spurious noise into the NIM.
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