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Operating Manual: PSS SB ACTIVE JUNCTION BASIS
Bus structure with PSS SB ACTIVE JUNCTION BASIS
Rules for incorporation
The Active Junction (base unit and expansion module) is transparent for all
telegrams on the main branch and sub branches. If a signal error occurs within a
sub branch (permanent dominant signal level), the sub branch will be ignored.
Please note the following rules:
• The physical arrangement of the Active Junction on the main branch can be
freely selected. However, bear in mind that run time delays on the signals must
be considered when using an Active Junction. These run time delays can be
expressed as constant virtual cable runs (see section entitled “Determining the
bus cable runs and transmission rate”).
• Using the Active Junction allows you to build a star or tree structure, rather than
the linear topology specified for SafetyBUS p. This reduces the effective
electrical cable runs (no return line needed).
• The relationship of the cable runs to the transmission rate should be
maintained.
• Where possible, plan to use only complete I/O-Groups in a sub branch. This
increases the availability if an error occurs.
Rules for bus termination
Each branch (main branch and sub branches) must be fitted with terminating
resistors.
• The signal lines (CAN_L and CAN_H) on the first and last bus subscribers on
the main branch should be fitted with terminating resistors (120 Ohm).
• The Active Junction is the first bus subscriber on a sub branch. The device has
an integral terminating resistor for each sub branch. The signal lines (CAN_L
and CAN_H) on the last bus subscriber on each sub branch should therefore
be fitted with a terminating resistor (120 Ohm). If necessary use special IP67
terminators.
