Rockwell Automation T8842 Trusted Versatile FTA - Manual (Page 10)

Trusted
TM
Versatile FTA T8842
Issue 8 Aug 12 PD-T8842 10
Digital Inputs (Powered)
Figure 4 shows a channel configured to accept digital input signals from the field from devices which
require power from the loop, e.g. fire input devices.
Figure 4 Digital Inputs (with power)
The configuration shown above enables powered digital input devices to be interfaced to the Trusted
TM
TMR Zone Interface module. The channel is configured by fitting a 315mA fuse in position A, which
provides circuit protection. Power for the field loop is derived from the dual 24Vdc source via the 2A
fuse in position D, which acts as a link. The 250R resistor (7W 1%) allows the field device status to be
monitored via the resistor voltage drop. It also acts as a field current limiter (96mA at 24V). The
voltage at the field side of the resistor is detected by the module and used to determine the
healthy/alarm state from the field device.
For inputs which directly short the input or apply a fixed voltage (e.g. zener diode line monitoring), to a
Zone Interface or Valve Monitor module, a 1k 0.6W resistor is required in position A. This is because
the module requires an impedance to allow internal testing. Note that this will change the voltages seen
by the module.
Field
Power
TBFPn
0V
Channel 1
B
Precision Resistor
Signal
A
0V
Field
Terminals
TBn
Signal
TBGn
Power Resistor
C
D
F
E
Fuse Field Power
3
2
1 1
2
3
4
m
2
2A
315 mA