2 Description of the safety function STO
16 Festo – GDCP-CMMS-ST-G2-S1-EN – 1404NH – English
A plausibility check is performed in the µP between the relay control for the output stage driver supply and
the monitorin g of the driver supply. This serves to pro vi de both error detection of the impulse block and
suppression of the error message E 05-2 (“driv er supply un dervoltage”) occurring in normal operation.
Potential-free acknowledgment contact:
Further, the integrated circuit for “Safe Torque Off” has a potential-free acknowledgment c ontact ([ X3]
pin 5 and 6) for the presence of the driver supply. This is an N/C contact. It must be connected to an
external safety controller or the higher-order controller, for example. Through this controller, the ST O
function must be checked regularly ( e.g. every 24 hours or at the beginning of the shift, if possible at
every S TO request).
If an error occurs in the plausibility check, the control system must prevent further operation, for example, by
switching off the intermediate circuit voltage or breakin g off the output stage enable by the PLC.
The feedback contact has a single channel and may only be used for monitoring.
Tab. A.7 in Appendix A.1.3 describes the electrical data and runtime performance of the
acknowledgment contact.
When the 24 V supply to the basic device is turned on and off, the switching status of the relay
may - due to the internal supply v oltages powering up at a different speed - devi ate briefly
(approx. 100 ms) from the status of the controller for the driver supply relay Rel [X3.2].
Registration of the status of the acknowledgment contact NC1/NC2 is required at every
request of the safety function.
When the safety function has been requested, a c hange in signal must oc c ur at the ac-
knowledgment contact within an application-specific time. A safety-related reaction must
be initiated in the event of a violation.
Aux iliary supply 24 V, 0 V [X1] and [X3]
The motor c ontroller CMMS-ST-...-G2 makes available one 24 V auxiliary supply each at [X1] and [X3].
This can be employed when using the acknowledgment contact NC1/NC2 or to supply external, act ive
sensors.
Tab. A.8 in appendix A.1.3 describes the electrical data for the auxiliary supply.
2.2.3 Runtime perfor mance
The runtime performance for typical applications can be found in the sample circuits:
– Sample circuit for STO in Section 2.3.
– Sample circuit for SS1 Section 2.4.
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