3
General description, function
10.2013
11
B
A
_S
LE
22
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N
.D
O
C
X
3.6
Safety functions
3.6.1
Overload cut-off
The overload cut-off is designed in accordance with performance level d, category 2, to
EN 13849-1:2006. As shown in the simplified circuit diagram,
UBS
supplies the first load
sensor
Load1
. The load sensor current is fed into
l1+
and the bridge from
I1-
to
GD
closes the circuit.
The second load sensor
Load2
is supplied by
UB
. The load sensor current is fed into
l2+
and the circuit is closed internally.
The overload cut-off disconnects in the following cases:
•
If the load sensor current exceeds the set cut-off threshold while
S↑
is active, the
SLE22 recognises
"Overload"
and disconnects
K↑ and K↑↑
. The outputs are dis-
abled until the overload is no longer detected.
•
If the load sensor current exceeds the set cut-off threshold while outputs
K↓, K↓↓
are
active or at standstill, the SLE22 recognises
"Overload"
after 800 ms and disables
outputs
K↑
and
K↑↑
, until the overload is no longer detected.
Due to an internal filter function the maximum reaction time for cut-off when lifting a load
from the ground is 500 ms. The elasticity of the crane system must be taken into account
to obtain the total reaction time.
"
Overload
" is acknowledged when the load on the hook is less than 82,5% of maximum
working load and safety input
S
↑ is active for 2 seconds or the load (minimum load)
corresponds to a current value of 6 mA for 2 seconds.
Outputs K↓ and K↓↓ can be switched after an overload has been detected!
3.6.2
Sensor errors
The SLE22 constantly monitors and compares the values of sensor channels 1 and 2.
The following three types of sensor error are detected:
Differential error
if the difference between the sensor currents is > 6,7%,
related to the set overload
cut-off point
(see page 16 for definition)
•
Broken cable:
If the sensor current in one or both sensor channels is < 3.3mA
•
Short circuit:
if the load sensor current in one or both sensor channels is >24.5 mA
In all three cases of sensor error output relays K↑ and K↑↑ are disabled dependent on
activation of safety inputs S↑ and S↕↕ and the incident is displayed by the device LEDs.
The maximum reaction time for disabling the outputs is:
if input
S↑
is active = 950 ms
if input
S↑
is not active = 1950 ms
A sensor error is acknowledged if:
•
The difference between the sensor currents is <6.6%, related to the overload cut-off
point
1,
and
•
the load sensor current is within the function limits
and
•
up
S↑
is not activated.
Definition:
The basis for calculation is the hoist sensor current, i.e. the cut-off sensor current (at
110% load) minus the zero point current (at 0%) load.
Example: cut-off current = 13 mA; zero point current = 4.0 mA; permissible current
difference between the sensor channels <= 0.6 mA