Rockwell Automation TDI16EIA 16-Channel Digital Input Termination Card - Manual (Page 7)

TDI16EIA October 2005 – Issue 3 7
Triguard SC300E TDI16EIA 16-Channel D/I Termination Card
THEORY OF OPERATION
Figure 2-3 is a circuit diagram showing a typical digital input channel.
Power supplies for the termination cards are normally provided by a Power Distribution Panel
PDD24 which performs diode auctioneering of its dual redundant power supplies.
Power for the digital input circuits (normally from the PDD24) is fed to input FS1 or FS2. Where
the PDD24 is not used and dual supplies are required, these are connected to FS1 and FS2
respectively and auctioneered on the termination card by D17 and D18.
Each digital input channel is powered via an indicating fuse from a common +ve bus. The ‘fuse
failed’ output from each fuse is connected to a common alarm bus. If any fuse fails, local
indication is provided by the illumination of Fuse blown LED LD1. A signal to operate a remote
alarm is available at Alarm output PL1.
The PDD24 has a Fuse blown alarm indicator with provision for multiple inputs. This facility can be
wired to provide fuse blown indication for an entire cabinet.
The -ve bus may be grounded via TS1 if required, preventing the power supplies from ‘floating’
when the chassis cable is disconnected.