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3.8 Anti-Two-Block Function Overview
This section describes fault diagnoses of the Anti-Two-Block detection circuit.
The computer supplies a protected positive feed to the Anti-Two-Block switches at the boom/jib head
via the Reeling Drum Signal Cable, slip-ring, and Reeling Drum cable. With the Anti-Two-Block weight
hanging freely on the switch(es), the switch contact is closed and the signal return to the computer is
high (6.25 volts). When the weight is lifted by the hook block, the switch contact is opened, and the
computer will sense a low signal input (0 volts) from the ATB signal return.
Since the computer checks the protected feed voltage internally, the system is capable of detecting a
short circuit of the feed (or the ATB signal return when the switch is closed) to the crane chassis. Fault
codes are defined in
SECTION 3.3 FAULT REPORTING AND FAULT CODES
.
Most problems with the ATB circuit may be identified through inspection of cables, switches, and the
Reeling Drum. Damage to these parts may result in continuous or intermittent ATB alarms.
FIGURE 3.8 ANTI-TWO-BLOCK FUNCTION SCHEMATIC
CRANE WIRING HARNESS
BROWN
BLACK
8-WAY
CONNECTOR
REELING DRUM
SIGNAL CABLE
BLACK
BROWN
TB1
BLACK
BROWN
SLIP-RING
REELING DRUM CABLE
ATB SWITCH(ES) & CONNECTOR
AT BOOM/JIB HEAD
REELING DRUM
D
A
MG500 COMPUTER UNIT
+10V
0V
470R
1K
ATB
INPUT
ATB
FEED
TEST
G1
G2
BULKHEAD
CONNECTOR
6
5
2
1
TB2
