Innotech Device Network Cabling - Manual (Page 19)

Innotech Device Network Cabling Installation Instructions
© Mass Electronics Pty Ltd 2007 Chapter 2 – Primary Networks Page 19
2-2 Management of other devices on the Primary Network
When other controllers such as Viewports or converters are added to the primary network they must
be installed in a manner that does not interrupt the integrity of the primary network. A lot of current
devices will have the soft earth option and are fully isolated from the factory. There is no issue mixing
the current style earth connection with previous models of hardware on the primary network if the
following rules are applied.
These HMIs and converters will be referred to as soft earth devices with respect to comms screen
termination.
For any soft earth type device connected to a primary network there are some general rules for
connection.
• Do not break the continuity of the screen
• Use the ‘S1’ terminal for both the entering and leaving screen termination
• You must earth the system at a single bonded earth point. This is regardless of the number of soft
earth points connected
• Attempt to ensure the net and global networks are the same length and follow the same path
2-2.1 HMIs and Converters
Typically all converters or HMIs will connect to the NET network and do not connect to the Global
network. This will present a few variations in how this device could be connected to the network. It is
important to ensure that the screen is kept continuous.
The below connection is wrong because it breaks the continuity of the screen creating a situation
where potential differences in earth current between Device 1 and Device 2 can occur, therefore the
reliability of the comms connection may be compromised.


In the correct example, notice that the NET comms screen is in ‘S1’ terminal only. If you were to
use the ‘S1’ and ‘S2’ terminals you would break the continuity of the NET screen. This could cause
a potential difference between each side of the HMI or converter and possibly introduce network
reliability issues.
The HMI or converter must have the Earth terminal or the 24V neutral, connected to earth where
available. This will provide the path for the soft earth.
Device Device
HMI / ConV
Figure 2-3: Incorrect HMI or Converter Comms Connection
Figure 2-4: Correct HMI or Converter Comms Connection