7.4 Example 3: Two-hand controlThis example describes a machine where a two-hand control initiates the dangerous movement as long asboth push buttons on the two-hand control are pressed and the process provides an enabling signal.The dangerous movement is initiated by the closing of two subsequent contactors, which are monitored via afeedback loop.7.4.1 Functional description of safety functionsThis example uses the following safety functions:n By pushing an emergency stop button all hazardous movements must be stopped (via SF_Emergency-Stop). Emergency stop has the highest priority. After releasing the EStop push button, a reset viaS0_Reset is required.n By pressing both push buttons of the two-hand control, the safety output is activated. The release of anyof the two-hand push buttons disables the safety output and stops the dangerous motion via the contac-tors K1 and K2 (via SF_TwoHandControlTypeII).n The initial state and the operational state of the connected contactors K1 and K2 are monitored and if anerror is detected, the safety output cannot become operational (via SF_EDM).n After power on of the safety or functional application, or after an emergency stop condition, the two-handcontrol must be released and re-operated in order to activate the safety output again (via SF_OutCon-trol). In order to guarantee this for the functional application restart, the Process signal from the func-tional application is connected to the Activate input of the two hand control function block THC_S2_S3 (Ifthe application process is restarted while the two hand control is activated, the FB goes to the state C003signalling an error that both buttons are pressed at the activation, prohibiting a restart.).In this example, only one operation mode exists.Safety application examplesExample 3: Two-hand control > Functional description of safety functions30.03.2017 AC500-S 437
