IMAC2B009 V2
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Ampcontrol Pty Ltd
– ABN 28 000 915 542
iMAC System User Manual
iMAC2B009 V4
– 10/18
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1.4.2 3-Wire System
3-Wire systems are typically used for emergency stop systems where constant monitoring of all modules is
required, regardless of whether an emergency stop has been activated.
In a 2-Wire system, when an emergency stop is activated, all modules downstream of the activated switch
go offline and cannot be monitored. The 3-Wire system addresses this shortcoming of the 2-wire system by
using separate signal and monitoring lines.
The Signal Line (or A-line) is fed through all of the emergency stop contacts and terminated into the EOL
module. The Monitoring Line (or B-line) is terminated into an MEOL module. All iMAC fieldbus modules are
connected to and communicate across the Monitoring Line.
The A-line and B-line are separated using a resistor, the resistor value is typically 47 ohms and allows faults
to be detected. Monitoring and comparing the EOL and MEOL module resistance readings allows the
system to detect short circuit cabling faults between the A and B lines.
Figure 1.2: 3-Wire iMAC Fieldbus System Configuration
1.4.3 Intrinsically Safe Systems
If the iMAC fieldbus is required to be intrinsically safe, a Master Line Barrier (MLB) is required. The MLB
barrier provides I.S. protection and incorporates the A-line resistor for three wire systems (i.e. there is no
need for an additional external A-line resistor; the MLB provides this via its A-line connection).
Figure 1.3: MLB Intrinsic Safety Barrier (Provides both 2-Wire and 3-Wire Terminal Connections)
WARNING!
The MLB barrier must be installed in the safe area.
For full intrinsic safety requirements, please refer to the I.S.
documentation.
1oo1 Safety Output
CR
IMAC
CONTROLLER
Stop Switches
MEOL
EOL
iMAC
Input Module
Resistor
Stop Switches
A
B
C
iMAC
Input Module
IMAC
CONTROLLER
Resistor
A
B
C
I.S.
Protection
MLB
(Master Line Barrier)
