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2.4.4. STO Diagnostics
Activation of STO means removing power from the XC2’s STO inputs. This is typically done by pressing
the emergency stop switch. The XC2 initiates a diagnostic check every time the STO is activated after the
Diagnostic Test Delay Time has elapsed. The diagnostic check verifies that each channel has entered the
safe state. The XC2 is held in the safe state if it determines that one of the channels has not properly
entered the safe state. An open circuit or short to 24 V in either STO channel will result in this condition
(refer to
Section 2.4.3. ). The Status Utility screen can be used to verify the levels of the STO input signals
while trouble shooting.
In order to meet the listed SIL level, the STO circuit must be activated (power removed from both inputs)
according to the interval specified in
Table 2-27 .
Table 2-30: STO Timing
Time Description Value
T1 STO Delay Time (STO input active to motor power off) 450-550 msec
T2
STO deactivated to motor power on (the software is typically
configured so that the motor does not automatically re-energize).
< 1 msec
T3 Diagnostic Test Delay Time 550-610 msec
Figure 2-26: STO Timing
The software is typically configured to execute a controlled stop when the STO state is first detected. If
power is reapplied to the STO inputs before the STO Delay Time, an STO hardware shutdown will not
occur but a software stop may, depending on the width of the STO pulse. The controller will ignore STO
active pulses shorter in length than the STOPulseFilter parameter setting.
2.4. Safe Torque Off Input (STO) XC2 Hardware Manual
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