Functions
5.12 Safety-related applications
Frequency inverter
204
Operating Instructions, 08.10. 2008, t.b.d.
Testing the shutdown paths
Shutdown paths are circuits used to shut down a motor in a safety-relevant fashion. The
shutdown paths must be checked regularly to ensure that the fail-safe frequency inverter
complies with certification requirements.
In the factory setting, the frequency inverter always checks its shutdown path if the STO
function is deselected.
The shutdown path test takes approximately three seconds. The frequency converter cannot
be switched on during the test. The frequency converter signals this status as "switching on
inhibited" in the status word (r0052, bit 6). A higher-level controller must evaluate this bit to
ensure that the frequency converter accepts its ON command.
To minimize the waiting time whenever an STO request is issued, this function can be
deactivated by making the relevant settings on the STO screen (P9601, bit 1 and P9801,
bit 1).
Figure 5-45 Testing the shutdown paths
A timer monitors the regular shutdown path test. The monitoring time (P9659) can be
extended up to a maximum of one year. When the timer has expired, this is signaled via
status word r9772, bit 15. A higher-level controller must monitor this bit to ensure that the
STO safety function is tested on a regular basis.
Figure 5-46 Test period for shutdown paths
Debouncing and filtering the signals from the fail-safe input
As soon as a fail-safe input has been assigned to a safety function, the frequency converter
checks the consistency of the input signal. Consistent signals at both terminals always
assume the same signal state (high or low).