SIEMENS
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Siemens D 21.4 · 2017
Safety Integrated
Safety Integrated
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Function
Safely-Limited Speed (SLS)
The SLS function monitors the drive to ensure that it does not
exceed a preset speed or velocity limit.
Effect
The SLS function monitors the drive against a parameterized
speed limit. Four different limit values can be selected. As in the
case of SOS, the speed setpoint is not influenced independently.
After SLS has been selected, the higher-level control must bring
the drive down below the selected speed limit within a parame-
terizable time. If the speed limit is exceeded, a customizable
drive-integrated fault reaction occurs.
The SLS limit stage 1 can be multiplied by a factor that is trans-
ferred in 16-bit resolution via PROFIsafe. This allows an almost
unlimited number of limits to be specified.
Application
The SLS function is used if people are in the danger zone of a
machine and their safety can only be guaranteed by reduced
speed. Typical application cases include those in which an
operator must enter the danger zone of the machine for the
purposes of maintenance or setting up, such as a winder in
which the material is manually threaded by the operator. To
prevent injury to the operator, the roller may only spin at a safely
reduced speed. SLS is often also used as part of a two-stage
safety concept. While a person is in a less critical zone, the SLS
function is activated, and the drives are only stopped in a smaller
area with higher potential risk. SLS can be used not only for
operator protection, but also for machinery protection, e.g. if a
maximum speed must not be exceeded.
Customer benefits
The SLS function can contribute to a significant reduction in
downtime, or greatly simplify or even accelerate setup. The
overall effect achieved is a higher availability of the machine.
Moreover, external components such as speed monitors can
be omitted.
Safe Speed Monitor (SSM)
The SSM function warns when a drive is working below an
adjustable speed limit. As long as it remains below the threshold,
the function issues a safety-related signal.
Effect
If a speed value drops below a parameterized limit, a safety-
related signal is generated. This can, for example, be processed
in a safety controller to respond to the event by programming,
depending on the situation.
Application
With the SSM function, in the simplest case, a safety door can be
unlocked if the speed drops below a non-critical level. Another
typical example is that of a centrifuge that may be filled only
when it is operating below a configured speed limit.
Customer benefits
Unlike SLS, there is no drive-integrated fault reaction when the
speed limit is exceeded. The safe feedback can be evaluated in
a safety control unit, allowing the user to respond appropriately
to the situation.
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© Siemens AG 2017