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QAY220 All Terrain Crane Operation Manual
8-1
Chapter 8 Safety devices
LMI consists of a CPU, a display, a length
/ angle sensor, a pressure sensor, a height
limiter and connecting cable. The system will
act after comparing the actual moment and
the rated moment. In the microprocessor the
actual moment value detected by the sensor are
compared with the rated moment value stored
in the memory device of central control unit. If
the limit value is reached, the overload signal
can be seen on the display. Meanwhile, the CPU
outputs the control signals, and after combined
with the other control devices, the dangerous
operation will be stopped automatically. Crane
performance and structure data are stored in the
CPU, based on which operation condition data
can be calculated. The cord reel installed on
the boom can measure boom angle and length.
Length sensor can also transmit the signal of
the height limiter. The actual load is detected by
pressure sensor installed in the rod chamber and
no rod chamber of the elevating cylinder and
stored in the microprocessor after conversion.
Combined with the crane structure parameter
the microprocessor will get the actual load valve
through sophisticated calculation. According
t o t h e s i g n a l s o f b oo m l e n g t h a n d b o o m
angle input by related sensors, and the signal
input by pressure sensor, the computer in the
controller calculates the crane working radius
and the load of elevating cylinder, and then
calculates the crane load moment. Comparing
the value calculated with the max. value of
load capacity in the data base, finally displays
the corresponding information for crane lifting
operation.
8-1 Load moment indicator (LMI)
8-1-1 Working principle
When an overload occurs, the load moment
limiter will automatically cut the crane motions
which will increase the load moment (boom
extending, boom lowering and hoist up) and
only reserve those operations that will decrease
the load moment (boom retracting, boom raising
and hoist down).
8-1-2 Safety function
During lifting operation the controller will
monitor the crane
’
s working condition. If the
automatic mode is set, the crane will perform
the operation depending on signals input by
control lever according to the working mode set.
8-1-3 Logic control function
When hook block approaches boom head
sheave (approx. 800 mm), the hoist limit switch
turns on, i.e. the motion of extending boom and
winding hook block are stopped. At the same
time, the warning lamp comes on.
8-1-4 Hoist height limit function
Safety devices
Chapter 8
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