HIMax Safety Manual - Tuv-fs.com

9 Software HIMaxExample: A key switch is connected to a digital input. The digital input is assigned to aglobal variable associated with the system variable "Read only in Run“. The owner of a keycan thus activate or deactivate the operating actions "stop", "start" and "download".9.5 ForcingForcing is the procedure for replacing a variable's current value with a force value. Thevariable receives its current value from a physical input, communication or a logicoperation. If the variable is forced, its value does no longer depend on the process, but isdefined by the user.Forcing is used for the following purposes:• Testing the user program; especially under special circumstances or conditions thatcannot otherwise be tested.• Simulating unavailable sensors in cases where the initial values are not appropriate.WARNINGUse of forced values can disrupt the safety integrity!Forcing is only permitted after receiving consent from the test authority responsiblefor the final system acceptance test.When forcing values, the person in charge must take further technical and organizationalmeasures to ensure that the process is sufficiently monitored in terms of safety aspects.HIMA recommends to set a time limit for the forcing procedure, see 9.5.1.Forcing can operate on two levels:• Global forcing: Global variables are forced for all applications.• Local forcing: Values of local variables are forced for an individual user program.9.5.1 Time LimitsTime limits can be set both for global and local forcing. Once the defined time has expired,the controller stops forcing values.It is also possible to define how the HIMax system behaves on completion of the forcingprocedure:• With global forcing, the resource is stopped or continues to run.• With local forcing, the user program is stopped or continues to run.It is also possible to use forcing without time limit. In this case, the forcing procedure mustbe stopped manually.The person responsible for forcing must clarify what effects stopping forcing have on theentire system!9.5.2 Restricting the Use of ForcingThe following measures can be configured to limit the use of forcing and thus avoidpotential faults in the safety functionality due to improper use of forcing:• Configuring different user profiles with or without forcing authorization• Prohibit global forcing for a resource• Prohibit local forcing• Forcing can also be stopped immediately using a key switch.To do so, the system variable "Force deactivation“ must be linked to a digital inputconnected to a key switch.Page 50 of 70HI 801 003 D Rev.2.0