Belden Hirschmann HC4900, User Manual

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acoustic alarm sounds and load-moment-increasing machine
movements are switched off at the same time.
An A2B (hoist limit) situation occurs when the hook block comes into contact
with the boom head. The danger exists in such situations that the hoist rope
will break, causing the load to fall. A hoist limit situation could arise from the
load being pulled against the boom head or from the boom being extended or
lowered without the hoist rope having been allowed to slacken.
Test method as below
：
 Manually lifting the weight attached to the A2B switches, then the audible
alarm sound and the A2B alarm light will light.
 Slowly raise the hook or lower the boom or extend (telescope) the boom to
create a potential two-block condition, when the hook lifts the weight, the
audible alarm sound, the A2B alarm light will light and the crane movement
such as hoist up, luffing down, telescopic out will be stopped.
 If the light and audible alarm does not function as described and the crane
movements are not stopped, the system is not working properly. The
malfunction shall be corrected before operating the crane.