Rockwell Automation T8805 Trusted 60 Channel 24V dc Digital Input FTA Non-Incendive - Manual (Page 7)

Trusted
TM
24Vdc Digital Input FTA Non-Incendive T8805
Issue 1 Aug 08 PD-T8805 7
1. Description
The Trusted TM 60 Channel 24Vdc Digital Input T8805 provides termination for a maximum of 60 input
channels from various types of field devices which generate a digital input. Figure 1 below shows the
configuration of a single channel.
Figure 1 Single Channel Schematic
The field supply is derived from dual 24V dc feeds which are ‘commoned’ via diodes on the FTA. 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 developed across the 5kB resistor, then connected to the appropriate
input circuit on the Input Module. Electro-static discharge (ESD) transients are suppressed by D3. 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 connector linking the 60 channels on the input module to the FTA is terminated at SK2 which is a
96-way socket. The SmartSlot connector is SK1 and is a 96-way socket (this socket is no longer
used). The dual 24V dc power supplies are connected to the FTA via a single 4-way connector (PL1).
Ten 12-way connectors are used for the field loops (PL2 to PL9, PL11 and PL12). PL10 is an auxiliary
2-way plug provided for power monitoring purposes (future use).
FIELD
TERMINATION
DUAL 24Vdc
FIELD
SUPPLIES
TO DUAL
DIGITAL INPUT
MODULE 8402
D3 5K
220R
REMAINING CHANNELS
0V