Caution – Siemens 500 NIM User Manual

Page 34

Network Design Considerations

2-16

SIMATIC TIWAY I Series 500 NIM User Manual

LOCAL LINE

END OF LOCAL LINE

BIAS SWITCH OFF

ON ALL OTHER

SECONDARY DEVICES

SWITCH-BIASED

NIM

SWITCH-BIASED

NIM

BIAS SWITCH ON

Figure 2-5

Local Line with Two or More Switch-biased NIMs

CAUTION

Excessive noise can enter the NIM if a switch-biased local line interface port is
unused, for instance in a case where no redundant local line is installed.

Turn on the bias switch on the unused port to prevent the entry of noise into the
NIM.

The Siemens Local Line must be properly terminated at both ends of the
trunk to prevent a possible impedance mismatch which could result in
signal reflections back along the line. Termination is required regardless of
the number or type of devices attached to the network.

NOTE: In the special case of a PM550 using a CIM as its interface to the
network, see Appendix A for detailed line biasing and termination
instructions, which vary from those listed here.

Terminating the
Local Line