Safe Torque Off vacon • 98Service support: find your nearest Vacon service center at www.vacon.com99.4 The principle of STOThe STO functionality, such as the technical principles and data (wiring examples and commission-ing) will be described in this chapter.In VACON ® 20 CP, the STO function is realized by preventing the propagation of the control signalsto the inverter circuit.The inverter power stage is disabled through redundant disabling paths which start from the twoseparated and galvanically isolated STO inputs (S1-G1, S2-G2 in Figure 51). In addition, an isolatedoutput feedback is generated to improve the diagnostics of the STO function and to achieve a bettersafety capability (F+, F- terminals). The values assumed by the STO output feedback are indicatedin the following table:The diagram below is a conceptual schematic diagram and is presented to illustrate the safetyfunction with relevant safety components only shown.Figure 51. STO function principle. (*) Only for MS3.STO inputs Operating conditions STO feedbackoutputTorque at themotor shaftBoth inputs ener-gized with 24V DC Normal operation The feedback mustbe 0Vpresent (motoron)Power removed fromboth inputs STO demand The feedback mustbe 24Vdisabled (motorde-energized)The STO inputs havedifferent valuesFailure in demand ordue to internal faultThe feedback mustbe 0Vdisabled (motorde-energized)(*)Table 44. Values of the STO output feedback (and torque on the motor). (*) Only one channelis preventing the drive from moving.R ReinforcedRR R= 3S1G1S2G2L1L2L3F+F-UVWDC+/R+ R-POWER UNITDC-*
