Rockwell Automation T8824 Trusted 40 Channel 120V ac Digital Input FTA - Manual (Page 6)

Trusted
TM
120Vac Digital Input FTA T8824
Issue 4 Sep 11 PD-T8824 6
1. Description
The Trusted TM 40 Channel 120Vac Digital Input FTA T8824 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 a 120V ac feed which is connected to AC Input terminal block
TB1. 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 to the digital input module via a resistive
divider. This divides the voltage down to levels suitable for an analogue measurement.
Revision E T8824 FTAs use two power resistors in series, as shown in the circuit diagram in Figure 2.
Earlier revisions used 4x4 resistor arrays. The resistor arrays on the top half are 68K and the bottom
resistor arrays are 1K.
Line monitoring is limited to voltage detection on the module. Refer to PD-T8424 for details.
The cable linking the 40 channels on the input module to the FTA is terminated at five 10-way
connectors (TBG1 to TBG5). The input signals from the field (40-off) are connected by 2-wire
arrangements terminated on 5-off 16-way terminal blocks.