Safe Torque Off (Sto) - Danfoss VLT Midi Drive FC 280 Operating Manual

Safe Torque Off (STO)

6 Safe Torque Off (STO)
The Safe Torque Off (STO) function is a component in a
safety control system. STO prevents the unit from
generating the energy that is required to rotate the motor,
thus ensuring safety in emergency situations.
The STO function is designed and approved suitable for
the requirements of:
•
IEC/EN 61508: 2010 SIL2
•
IEC/EN 61800-5-2: 2007 SIL2
•
IEC/EN 62061: 2012 SILCL of SIL2
•
EN ISO 13849-1: 2008 Category 3 PL d
To achieve the required level of operational safety, select
and apply the components in the safety control system
appropriately. Before using STO, carry out a thorough risk
analysis on the installation to determine whether the STO
function and safety levels are appropriate and sufficient.
The STO function in the frequency converter is controlled
via control terminals 37 and 38. When STO is activated, the
power supply on the high side and low side of the IGBT
gate driving circuits is cut off. Illustration 6.1 shows the STO
architecture. Table 6.1 shows STO statuses based on
whether terminals 37 and 38 are energized.
24 V
24 V
12
voltage
source
38
17 V
diagnostic
37
55
PELV
Illustration 6.1 STO Architecture
MG07A402
Operating Guide
+UDC
IGBT
X3
high-side
gate driving
circuit
X3
circuit
IGBT
X3
low-side
gate driving
circuit
Danfoss A/S © 10/2017 All rights reserved.
Terminal 37 Terminal 38
Energized
1)
Energized
De-energized
De-energized 3)
De-energized Energized
Energized De-energized
Table 6.1 STO Status
± 5 V, with terminal 55 as the reference
1) Voltage range is 24 V
terminal.
2) Torque is present only when the frequency converter is operating.
3) Open circuit, or the voltage within the range of 0 V
terminal 55 as the reference terminal.
Test pulse filtering
For safety devices that generate test pulses on the STO
control lines: If the pulse signals stay at low level (≤1.8 V)
for no longer than 5 ms, they are ignored, as shown in
Illustration 6.2.
5 ms max. Test pulse
T37/38
STO request
state
STO valid
STO invalid
Illustration 6.2 Test Pulse Filtering
Asynchronous input tolerance
The input signals at the 2 terminals are not always
synchronous. If the discrepancy between the 2 signals is
longer than 12 ms, the STO fault alarm (alarm 188, STO
Function Fault) occurs.
Valid signals
To activate STO, the 2 signals must both be at low level for
at least 80 ms. To terminate STO, the 2 signals must both
be at high level for at least 20 ms. Refer to
chapter 9.6 Control Input/Output and Control Data for the
voltage levels and input current of STO terminals.
Torque Warning or
alarm
No warnings or
2)
Yes
alarms.
No Warning/alarm
68: Safe Torque
Off.
No Alarm 188: STO
Function Fault.
No Alarm 188: STO
Function Fault.
± 1.5 V, with
STO demanded
Time
Debounce time
Time
37
6 6