Rockwell Automation T8800 Trusted 40 Channel 24V dc Digital Input FTA - Manual (Page 7)

Trusted
TM
24Vdc Digital Input FTA T8800
Issue 5 Sep 05 PD-T8800 7
1. Description
The Trusted TM 40 Channel 24Vdc Digital Input Field Termination Assembly T8800 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 24V 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.