Rockwell Automation T8842 Trusted Versatile FTA - Manual (Page 14)

Trusted
TM
Versatile FTA T8842
Issue 8 Aug 12 PD-T8842 14
Fire Input Loops
Figure 8 below shows the configuration required to accept input signals from fire input loops. This
configuration may be used for both I.S. and non-I.S. applications.
Figure 8 Fire Inputs
Latching fire detectors are reset by the removal of field power. Using this Fire Input configuration, fire
loops can have their field power supplied from the Trusted
TM
module, using the first channel of a power
group as a power supply, configured as a digital output. This provides control of the field loop from the
application with no added components. The first channel must be wired as shown in Figure 6.
The supply voltage to the field loop is derived from the first channel in each power group and fed via
the 2A fuse located in fuse position C, which acts as a link. Position C is commoned to the remaining
7 channels in the associated power group. Each channel in the power group with a fire input loop
connected requires a 315mA fuse fitted in fuse position A, which provides circuit protection, and a 2A
fuse in position C, to connect to the switched field power. 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. 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.
The maximum switched field supply current is 2 amps in each power group, distributed across
channels 2 to 8. The maximum loop current per channel is 96mA at 24V.
Note that the power supply channel 1 needs to be connected to a load of at least 50mA to protect the
output from no-load shutdown.
For inputs without line monitoring components or using zener diodes, to a Zone Interface or Valve
Monitor module, a 1K 0.6W resistor is required between the Signal connection and the module (in
series with the I/O cable). 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