SMAC CBC-EIP, User Manual, Page: 8 / 42

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2.1.2 STO
The STO (Safe Torque Off) is a safety system that prevents motor from delivering torque in
an emergency event
while the CBC-EIP remains connected to the power supply. When STO
is activated, the drive’s power stage is disabled regardless of what the CBC- EIP is doing and
the motor shaft will slow down until it stops under its own inertia and frictional forces.
The STO of CBC- EIP has been designed to be compliant with Safety Integrity Level 3 (SIL3)
according to IED 61800-5-2. To meet the requirements, the STO reliability has been
increased by means of the following characteristics:
•
2x fully independent STO channels
•
STO feedback output for external diagnostics. Note that by default this is not available
in the CBC- EIP, please ask SMAC to have this enabled when required.
•
Detection of abnormal STO operation
Figure 2.2 depicts the schematic of the STO circuit in the CBC- EIP. The STO works with
negative logic: power stage is deactivated by default and in this state, a software fault (error
code 0xFF60) with will be generated if there is an attempt to activate the power stage. To
allow the activation of the power stage (by turning on the power stage transistors), STO
inputs 1 and 2 must be energized by supplying them with a DC voltage (see
Figure. 2.7 for
the detailed electrical schematic). Alternatively, the STO inputs can be disabled by applying
jumper connections as described in section 2.1.4.
Figure 2.2. STO circuit schematic.
Figure 2.3 shows the behavior of STO_FB in relation to one of the STO inputs. The objective
of STO_FB is to provide external diagnostics of the STO circuit, to allow an increased system
reliability. A common practice in the diagnostics is to delay the stop of the power stage from
the deactivation of STO_FB and the STO inputs. This way, short pulses can be applied for
testing the STO circuit without stopping the system operation.
When only one of the STO input channels is energized, the STO operation is viewed as
abnormal. If only one channel is energized for more than the latching time (0.6 s < T
latching
<
2.6 s), a dangerous failure in the system is considered and the STO is activated in latching
STO1
STO2
STO_FB
Feedback
Logic
+12 V
DC/DC
+SUPPLY
PH. U
PH. V
PH. W
Power stage