Safely-Limited Speed (SLS)
The SLS function monitors the drive to ensure that it does notexceed a preset speed or velocity limit.
Effect
The SLS function monitors the drive against a parameterized speedlimit. Four different limit values can be selected. The speedsetpoint is not influenced independently. After SLS has beenselected, the higher-level control must bring the drive down belowthe selected speed limit within a parameterizable time. If thespeed limit is exceeded, a customizable drive-integrated faultreaction occurs.
The SLS limit stage 1 can be multiplied by a factor that istransferred in 16-bit resolution via PROFIsafe. This allows analmost unlimited number of limits to be specified.
Application
The SLS function is used if people are in the danger zone of amachine and their safety can only be guaranteed by reduced speed.Typical application cases include those in which an operator mustenter the danger zone of the machine for the purposes ofmaintenance or setting up, such as a winder in which the materialis manually threaded by the operator. To prevent injury to theoperator, the roller may only spin at a safely reduced speed. SLSis often also used as part of a two-stage safety concept. While aperson is in a less critical zone, the SLS function is activated,and the drives are only stopped in a smaller area with higherpotential risk. SLS can be used not only for operator protection,but also for machinery protection, e.g. if a maximum speed must notbe exceeded.
Customer benefits
The SLS function can contribute to a significant reduction indowntime, or greatly simplify or even accelerate setup. The overalleffect achieved is a higher availability of the machine. Moreover,external components such as speed monitors can be omitted.
The SLT function monitors the current/torque of a motor.
The SLT function allows the torque to be reduced within a definedperiod of time. If the torque exceeds the SLT monitoring limit, thedrive responds with a "Safe Stop". The stop responses STO or SS1can be specified via parameters.
In the simplest case, this function is used for force limiting whenopening and closing a protective door on a machine.
The SLT function avoids the use of external hardware for measuringand limiting the force and the associated wiring effort.
The SSM function warns when a drive is working below an adjustablespeed limit. As long as it remains below the threshold, thefunction issues a safety-related signal.
If a speed value drops below a parameterized limit, asafety-related signal is generated. This can, for example, beprocessed in a safety controller to respond to the event byprogramming, depending on the situation.
With the SSM function, in the simplest case, a safety door can beunlocked if the speed drops below a non-critical level. Anothertypical example is that of a centrifuge that may be filled onlywhen it is operating below a configured speed limit.
Unlike SLS, there is no drive-integrated fault reaction when thespeed limit is exceeded. The safe feedback can be evaluated in asafety control unit, allowing the user to respond appropriately tothe situation.
The STO safety function for SIMATIC MICRO-DRIVE can be activatedvia terminals, e.g. for use of a conventional safety circuit.
For standalone safety solutions for small to medium sizedapplications, it is frequently sufficient that the various sensingcomponents are directly hardwired to the drive.
For integrated safety solutions, the safety-relevant sequences aregenerally processed and coordinated in the fail-safe SIMATICcontroller. In this case, the system components communicate via thePROFINET fieldbus. The safety functions are controlled via the safePROFIsafe communication protocol.
The SIMATIC MICRO-DRIVE drives can be easily integrated into theplant or system topology.
PROFIsafe (only for the failsafe variants, e.g. PDC100F)SIMATIC MICRO-DRIVE drives support the PROFIsafe profile based onPROFINET.
PROFIsafe is an open communications standard that supports standardand safety-related communication over the same communication path(wired or wireless). A second, separate bus system is therefore notnecessary. The telegrams that are sent are continually monitored toensure safety-relevant communication.
Possible errors such as telegrams that have been lost, repeated orreceived in the incorrect sequence are avoided. This is done byconsecutively numbering the telegrams in a safety-relevant fashion,monitoring their reception within a defined time and transferringan ID for transmitter and receiver of a telegram. A CRC (cyclicredundancy check) data security mechanism is also used.
The operating principle of Safety IntegratedTwo independent switch-offsignal paths
Two independent switch-off signal paths are available. Allswitch-off signal paths are low active. This ensures that thesystem is always switched to a safe state if a component fails orin the event of cable breakage. If a fault is discovered in theswitch-off signal paths, the STO or SS1 function (depending onparameter settings) is activated and a system restartinhibited.
Two-channel monitoringstructure
All the main hardware and software functions for Safety Integratedare implemented in two independent monitoring channels (e.g.switch-off signal paths, data management, data comparison). Acyclic crosswise comparison of the safety-relevant data in the twomonitoring channels is carried out.
The monitoring functions in each monitoring channel work on theprinciple that a defined state must prevail before each action iscarried out and a specific acknowledgement must be made after eachaction. If these expectations of a monitoring channel are notfulfilled, the drive coasts to a standstill (two channel) and anappropriate message is output.
Safe actual value sensing with encoderThe safe actual value sensing is based on the redundant evaluationof the differential incremental tracks A/B that supply HTL/TTL andthe three Hall-effect sensors integrated in the motor.
All EC motors of the Siemens Product Partners with IQ encoder andHall-effect sensors can be used for all of the safety functions ofthe SIMATIC MICRO-DRIVE drive system.
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