Optidrive Eco User Guide Revision 2.01
4.8. Safe Torque Off
Safe,Torque,OFF,will,be,referred,to,as,“STO”,through,the,remainder,of,this,section
4.8.1. Responsibilities
The overall system designer is responsible for defining the requirements of,the,overall,“Safety,Control,System”,within,which,the,drive,will,be,
incorporated; furthermore the system designer is responsible for ensuring that the complete system is risk assessed,and,that,the,“Safety,
Control,System”,requirements,have, been,entirely, met and that the function is fully verified, this must include confirmation testing of the
“STO”,function,before,drive,commissioning
The system designer shall determine the possible risks and hazards within the system by carrying out a thorough risk and hazard analysis, the
outcome of the analysis should provide an estimate of the possible hazards, furthermore determine the risk levels and identify any needs for
risk,reduction,The,“STO”,function,should,be,evaluated,to,ensure,it,can,sufficiently,meet,the,risk level required.
4.8.2. What STO Provides
The,purpose,of,the,“STO“,function,is,to,provide,a,method,of,preventing,the,drive,from,creating,torque,in,the,motor,in,the,absence of the
“STO“,,input,signals,(Terminal,12,with,respect,to,Terminal,13),this,allows,the drive to be incorporated into a complete safety control system
where,“STO“,,requirements,need,to,be,fulfilled
1
The,“STO“ function can typically eliminate the need for electro-mechanical contactors with cross-checking auxiliary contacts as per normally
required to provide safety functions.
2
The,drive,has,the,“STO“ Function built-in,as,standard,and,complies,with,the,definition,of,“Safe,torque,off“,as,defined,by,IEC 61800-5-2:2007.
The,“STO“,Function,also,corresponds,to,an,uncontrolled,stop,in,accordance,with category 0 (Emergency Off), of IEC 60204-1. This means
that,the,motor,will,coast,to,a,stop,when,the,“STO”,function,is,activated,this,method,of,stopping,should,be,confirmed,as,being acceptable to
the system the motor is driving.
The,“STO“,,function,is,recognised,as,a,failsafe,method,even,in,the,case,where,the,“STO“,,signal,is,absent,and,,a,single,fault,within,the,drive,
has occurred, the drive has been proven in respect of this by meeting the following safety standards :
(Probability of dangerous Failures per Hour)
(Safe failure fraction %)
1.23E-09 1/h (0.12 % of SIL 2)
Note : The values achieved above maybe jeopardised if the drive is installed outside of the Environmental limits detailed in section 10.1
“Environmental“
4.8.3. What STO does not provide
Disconnect and ISOLATE the drive before attempting any work on it,The,“STO“,function, does,not,prevent,high, voltages,from,
being present at the drive power terminals.
1
Note,The, “STO“, function, does, not, prevent, the, drive, from, an, unexpected, re-start, ;s, soon, as, the, “STO“ inputs receive the
relevant signal it is possible (subject to parameter settings) to restart automatically, Based on this, the function should not be
used for carrying out short-term non-electrical machinery operations (such as cleaning or maintenance work).
2
Note: In some applications additional,measures,may,be,required,to,fulfil,the,systems,safety,function,needs,the,“STO“,,function,
does not provide motor braking. In the case where motor braking is required a time delay safety relay and/or a mechanical brake
arrangement or similar method should be adopted, consideration should be made over the required safety function when
braking as
When using permanent magnet motors and in the unlikely event of a multiple output power devices failing then the motor could
effectively rotate the motor shaft by 180/p degrees (Where p denotes number of motor pole pairs).
4.8.4. “STO“ Operation
When,the,“STO”,inputs,are,energised,the,“STO”,function,is,in,a,standby,state,if,the,drive,is,then,given,a,“Start,signal/command”,(as,per,the,
start source method selected in P1-13) then the drive will start and operate normally.
When,the,“STO”,inputs,are de-energised,then,the,STO,Function,is,activated,and,stops,the,drive,(Motor,will,coast),the,drive,is,now,in,“Safe,
Torque,Off”,mode
To,get,the,drive,out,of,“Safe,Torque,Off”,mode,then,any,“Fault,messages”,need,to,be,reset,and,the,drive,“STO”,input,needs,to be re-
energised.
4.8.5. “STO” Status and Monitoring
There,are,a,number,of,methods,for,monitoring,the,status,of,the,“STO”,input,these,are,detailed,below
Drive Display
In,Normal,drive,operation,(Mains,;C,power,applied),when,the,drives,“STO”,input,is,de-energised,(“STO”,Function,activated),the,drive,will,
highlight this by displaying “InHibit”,(Note,If,the,drive,is,in,a,tripped,condition,then,the,relevant,trip,will,be,displayed,and,not,“InHibit”)
Drive Output Relay
Drive relay 1: Setting P2-15,to,a,value,of,“13”,will,result,in,relay,opening,when,the,“STO”,function,is,activated
Drive relay 2: Setting P2-18,to,a,value,of,“13”,will,result,in,relay,opening,when,the,“STO”,function,is,activated
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