Innotech Genesis V4 System - Manual (Page 106)

Installation Instructions for Innotech Genesis Systems
Edition 011100
A-25
A better solution is to use an MPI that has RS485 isolation ICs and to fit a GENII 485I
Isolated RS485 Comms card to the local Digital Controller and earth the screen at the first
Digital Controller in Control Panel No. 2 as shown in Figure A-24.
Figure A-24. Use of GENII MPI, Circuit 2.
A-4.3. CABLE CONNECTION PROCEDURES. This paragraph contains general
procedures for connection of Comms cables and for checks to ensure there are no hazardous
voltages present.
The ideal situation would be that the voltages measured between the data conductors, between
the data conductors and the screen and between the data conductors, the screen and the earthed
parts of a device were 0Vac and 0Vdc. In practice this will not be the case. These
measurements should be made before connecting any Comms cables to ensure that these
voltages are within the specified ratings of the RS485 ICs.
It is important to test all data conductors and the screen because only one conductor may be
faulty if the cable was damaged during installation.
The measured AC voltage is the RMS (effective) value but the ICs are subjected to the peak
value of voltages. Therefore, the AC values in the tests must be less than the DC values.
Switchboard or
Control Panel No. 2
Screen 1 2
Connect Screen
Screen 1 2
Connect Screen
Switchboard or
Control Panel No. 1
Only four outer
links fitted.
Screen is not
earthed.
Only four outer
links fitted.
Screen is not
earthed.
Printer
Modem
MPI
Printer
PC M
C
Screen 1 2
Connect Screen
Six outer links
fitted. Screen is
earthed via
Terminal 2.
Screen 1 2
Connect Screen
Isolated
RS485
GEN4851 Card
isolates Digital
Controller from
cable.
Isolated