Rockwell Automation T8423 Trusted 40 Channel 120Vdc Digital Input FTA - Manual (Page 7)

Trusted
TM
120Vdc Digital Input FTA T8821
Issue 6 Feb 08 PD-T8821 7
1. Description
The Trusted TM 40 Channel 120Vdc Digital Input FTA T8821 provides termination for a maximum of 40
input channels from various types of field devices which generate a digital input. Figure 2 below shows
the configuration of a single channel.
Figure 2 Single Channel Schematic
The supply for the field is derived from dual 120V dc feeds which are ‘commoned’ via diodes on the
FTA. Indication of of the presence of the power supply is provided by a green LED. The supply is then
fed to each channel.
The supply voltage to the field is fed via the 50mA fuse. This effectively limits the current in the field
loop. The incoming signal (digital) from the field device is fed directly to the digital input module. Line
monitoring components (if required) provide the necessary thresholds used by the input module to
detect the field loop/device status, i.e. open/short circuit, alarm etc.
The cable linking the 40 channels on the input module to the FTA is terminated at the 96-way socket
SK1. SmartSlot (Version 1) signals from the module are connected to SK1. The SmartSlot connector
is SK2 and is also a 96-way socket. This connector is not used where SmartSlot Version 2 is
employed within the Trusted
TM System. The dual dc field power supplies are connected to the FTA via
a 5-way terminal block PWR TB. The input signals from the field (40-off) are connected by 2-wire
arrangements terminated on 12-off 3-way terminal blocks and 2-off 2-way.