Innotech Genesis II Digital Controller (v5) - Manual (Page 113)

Page 113
Genesis II Installation Instructions
© Mass Electronics Pty Ltd 2010 Chapter 5 – Network Installation
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.
1. Do not break the continuity of the screen.
2. Use the ‘S1’ terminal for both the entering and leaving screen termination.
3. You must earth the system at a single bonded earth point. This is regardless of the number of
soft earth points connected.
4. Attempt to ensure the net and global networks are the same length and follow the same path.
Regardless of the type of isolation used in either the current model devices (all now standard with
fully isolated soft earth) or older series controllers (plug-in optional isolation card), there is no effect
on the Primary Network earth requirements. The isolation is not on the Primary Network, but
between the Primary Network and the power supply of only that respective controller. All network
rules apply as stated.
There are three types of Earth referred to in this document:
1. Bonded, hard or clean.
2. Soft.
3. Floating.
These definitions are listed below in relation to the Innotech networks.
1. A bonded, hard or clean earth is defined as a low impedance earth point with little or no chance
of conducted noise either already present or likely to be created when bonded to a circuit. For
Innotech’s reference we also explicitly mean there is no potential difference to true earth.
2. A soft earth is where there is a path to earth via a circuit. This provides a tie to earth so
potential differences are minimised. This path has higher impedance than a bonded earth.
This does force strong earth currents, i.e. leakage currents from large AC motors, to remain on
the proper heavy gauge earth wires, while leaving the soft earth paths unaffected. So whilst
having multiple earth connections we have not created any effective earth loops. Soft earth
is often used in 24V supplied devices. The ‘tie to earth’ is in fact a ‘tie to 0V’ because there is
no dedicated earth terminal available. It is therefore expected that the 0V is earthed near the
supply transformer.
3. Floating simply means that there is no path to an Earth point at all provided by the device, not
even a soft earth path. A floating device has no earth.