Device Instance Number
The Device Instance Number must be unique across the
entire BACnet system network because it is used to
uniquely identify the BACnet devices. It may be used to
conveniently identify the BACnet device from other
devices during installation. The Spyder BACnet
Controllers Device Instance Number is automatically set
when it is added to a WEBStation-AX project. The Device
Instance Number can be changed by the user, which may
be necessary when integrating with a third party or when
attempting to replace an existing controller and it is
desired to maintain the existing Device Instance Number.
NOTE: For complete instructions on how to set the
MS/TP MAC address or set the Device Instance
Number refer to the Installation Instructions,
form 62-0310.
Termination Resistors
Matched terminating resistors are required at each end of
a segment bus wired across (+) and (-). Use matched
precision resistors rated 1/4W ±1% / 80 - 130 Ohms.
Ideally, the value of the terminating resistors should
match the rated characteristic impedance of the installed
cable. For example, if the installed MS/TP cable has a a
listed characteristic impedance of 120 Ohm, install 120
Ohm matched precision resistors.
NOTE: The controller does not provide any network biasing.
Shield Terminating
Following proper MS/TP cabling shield grounding
procedures is important to minimize the risk of
communication problems and equipment damage caused
by capacitive coupling. Capacitive coupling is caused by
placing MS/TP cabling close to lines carrying higher
voltage. The shield should be grounded on only one end of
the MS/TP segment (typically the router end). Tie the
shield through using the SHLD (terminal 4) on the Spyder
BACnet Controller.
