Rockwell Automation T8801 Trusted 40 Channel 24V dc Digital Input FTA Non Incendive - Manual (Page 7)

Trusted
TM
24Vdc Digital Input FTA T8801
Issue 7 Jul 12 PD-T8801 7
1. Description
The Trusted TM 40 Channel 24Vdc Digital Input FTA Non Incendive T8801 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 220R resistor. This effectively limits the current in the field
loop allowing inputs from nonincendive field devices located in hazardous areas. 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. 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.