Cable Line Topology
What are the requirements for cable line topology with RS-485 and CAN interfaces?
When designing a cable line with RS-485 and CAN interfaces it is necessary to remember that each measuring line starts from interface converter and has a linear structure (no star-type connections are allowed).
Length of the cable line branches for connecting digital modules must be as short as possible. When connecting laboratory modules with connector tees, branch length must not exceed 0.5 m. In constructing measuring network with industrial version digital modules, the smallest length of the branches is ensured, since the couplers are embedded into the module’s package.
Typical measuring line topology is shown in the figure below:
Thus, the measuring networks RS 485 and CAN 2.0 enable connection of up to 60 and 32 ZETSENSOR modules respectively.
So, what are the limitations regarding digital modules compatibility within the structure of a single measuring line?
The particular interface type (RS-485 or CAN) to be used within the measuring line depends on the type of the interface converter installed at the beginning of the measuring line. ZET 7070 and ZET 7076 are designed for RS-485 interface, while ZET 7174 and ZET 7176 – for CAN interface.
Digital module’s interface type should correspond to that of the interface converter within a particular measuring line. It is not allowed to use digital modules with different interface types in one and the same measuring line.
Note: it is not allowed to use two interface converters within a single measuring line but for the cases when telemetric system ZET 7172 is installed at the end of CAN cable line. ZET 7172 has an interface converter of ZET 7172M model, which is used to form galvanically isolated radio channel. In this case ZET 7172S will be used as a measuring line continuation.