Stahl SLE22 - Safety Functions

3 General description, function
10.2013 11
BA_SLE22_EN.DOCX
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 S
LE
22 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