Checking The Operating Limit Switch Actuator - DEMAG DC-Com 1 Operating Instructions Manual

The chain hoist slipping clutch provides the emergency limit position limiter function for chain hoists that are not
fitted with an operating limit switch or which have a defective operating limit switch. This emergency limit position
limiter may only be approached in exceptional cases, i.e. it must not be approached in normal operation. High
additional loads occur in the chain when the slipping clutch is tripped.
For this reason, the "operating limit switch for lifting" function must be checked every day.
If an operating limit switch is defective, the hoist motor is switched off when the electronic speed monitoring func‐
tion of the slipping clutch is tripped. For this reason, cut-off in the upper hook position is not a reliable indicator for
correct operation of the operating limit switch. If cut-off by the operating limit switch fails, a warning message is
output, see  "Warning messages", Page 98.
Fig. 39 Buffer with limit switch not actuated (A),
buffer with limit switch actuated (B), defective
buffer with limit switch actuated (C).
If the buffer or cut-off springs are strongly compressed, it may be assumed that the hoist motor will not be
switched off by the limit switch, but by the speed-monitoring function of the slipping clutch. This may cause the
chain to break if the limit position is frequently approached.
Checking the operating limit switch for lowering
The "Operating limit switch for lowering" must be checked at least once per year.
Proceed as follows:
● Remove the chain collector box  "Removing the chain collector box", Page 71
● Check as described above for the "Operating limit switch for lifting".
Optional geared limit switch
If an optional geared limit switch is fitted, the hoist unit must be switched off before the bottom block or hook as‐
sembly come into contact with the chain hoist guide plate. To check this function, the upper hook position must be
approached at high lifting speed (without a load). When the hoist unit has been switched off, there must be a mini‐
mum distance of at least 20 mm between the bottom block or hook assembly and the chain hoist guide plate.
8.5.4.2

Checking the operating limit switch actuator

The operating limit switch actuator must be checked for any external damage, e.g. a bent actuator plate.
72
Checking the operating limit switch for lifting: raise the hook assembly
or bottom block until it is approximately 10 cm below the highest hook
position. Then raise it to the highest hook position at creep lifting speed
until the chain hoist automatically switches off.
● 1/1 reeving:
It must only be possible to compress the buffer or cut-off springs on
the hook assembly by a small amount after the unit has switched off.
● 2/1 reeving:
It must only be possible to compress the upper part of a bottom
block with internal cut-off springs onto the lower part by a small
amount so that approx. 20 mm of the black part of the bottom block
remains visible.
It must also only be possible to compress the springs on a bottom
block with external cut-off springs by a small amount after the unit
has switched off.