Safe Torque Off (Sto) - Danfoss VLT Midi Drive FC 280 Instruction 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 SIL 2
•
IEC/EN 61800-5-2: 2007 SIL2
6 6
•
IEC/EN 62061: 2012 SILCL of SIL2
•
EN ISO 13849-1: 2008 Category 3 PL d
To achieve the desired 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 adjustable frequency drive 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 are cut off. Figure 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
37
55
PELV
Figure 6.1 STO Architecture
32
®
VLT Midi Drive FC 280
+UDC
IGBT
X3
high-side
gate driving
circuit
17 V X3
diagnostic
circuit
IGBT
X3
low-side
gate driving
circuit
Danfoss A/S © 11/2015 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 adjustable frequency drive 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
Figure 6.2.
Test pulse Test pulse STO demanded
T37/38
5ms max.
STO request
state
STO valid
STO invalid
Figure 6.2 Test Pulse Filtering
Asynchronous input tolerance
The input signals at the two terminals are not always
synchronous. If the discrepancy between the two signals is
longer than 12 ms, the STO fault alarm (alarm 188, STO
Function Fault) occurs.
Valid signals
To activate STO, the two signals must be both at low level
for at least 80 ms. To terminate STO, the two signals must
be both at high level for at least 20 ms. Refer to
Torque Warning or
alarm
No warnings or
2)
Yes
alarms.
No Warning/alarm
68: Safe Stop.
No Alarm 188: STO
Function Fault.
No Alarm 188: STO
Function Fault.
± 1.5 V, with
Time
Debounce time
Time
MG07A122