Rockwell Automation T8842 Trusted Versatile FTA - Manual (Page 13)

Trusted
TM
Versatile FTA T8842
Issue 8 Aug 12 PD-T8842 13
Analogue inputs (4-20mA)
Figure 7 below shows the configurations required to accept input signals from current sourcing
analogue field devices.
Figure 7 Current Sourcing Analogue Inputs
The (optional) field power for each channel configured for analogue inputs is derived from the dual
24Vdc supplies via a 315mA fuse fitted in fuse position B, which provides circuit protection.
Current sourcing analogue field devices may be interfaced to the VFTA by fitting a 2A fuse in fuse
position E, which acts as a link, and a 50mA fuse in fuse position A, for circuit protection. This enables
current detection through the 250R resistor (high precision 0.1%). The fuse in fuse position A limits the
signal current to 50mA.
Current sinking analogue field devices may only be interfaced to the VFTA using a current mirror
interface. This interface may also include I.S. protection, e.g. MTL5040.
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
50 mA
2A
315 mA