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| Beijer BFI-P2 User Guide |
Version 3.04
www.beijerelectronics.com
4.14.2. What STO Provides
The purpose of the “STO“ function is to provide a method of preventing the drive from creating torque in the motor in the absence
of the “STO“ input signals (Terminal 12 with respect to Terminal 13), this allows the drive to be incorporated into a complete safety
control system where “STO“ requirements need to be fulfilled.
1
The “STO“ function can typically eliminate the need for electro-mechanical contactors with cross-checking auxiliary contacts as per
normally required to provide safety functions.
2
The drive has the “STO“ function built-in as standard and complies with the definition of “Safe torque off“ as defined by IEC 61800-5-
2:2007.
The “STO“ function also corresponds to an uncontrolled stop in accordance with category 0 (Emergency Off), of IEC 60204-1. This
means that the motor will coast to a stop when the “STO” function is activated, this method of stopping should be confirmed as being
acceptable to the system the motor is driving.
The “STO“ function is recognised as a fail-safe method even in the case where the “STO“ signal is absent and a single fault within the
drive has occurred, the drive has been proven in respect of this by meeting the following safety standards:
SIL
(Safety Integrity
Level)
PFHD
(Probability of dangerous
Failures per Hour)
SFF
(Safe failure
fraction %)
Lifetime
assumed
EN 61800-5-2
2
1.23E-09 1/h (0.12 % of SIL 2)
50
20 Yrs
PL
(Performance Level)
CCF (%)
(Common Cause Failure)
MTTFd
Category
EN ISO 13849-1
PL d
1
4525a
3
SILCL
EN 62061
SILCL 2
NOTE
The values achieved above maybe jeopardised if the drive is installed outside of the Environmental limits detailed in section
4.14.3. What STO Does Not Provide
Disconnect and ISOLATE the drive before attempting any work on it. The “STO“ function does not prevent high voltages
from being present at the drive power terminals.
1
NOTE
The “STO“ function does not prevent the drive from an unexpected re-start. As soon as the “STO“inputs receive the
relevant signal it is possible (subject to parameter settings) to restart automatically, Based on this, the function should not be
used for carrying out short-term non-electrical machinery operations (such as cleaning or maintenance work).
2
NOTE
In some applications additional measures may be required to fulfil the systems safety function needs: the “STO“
function does not provide motor braking. In the case where motor braking is required a time delay safety relay and/or a
mechanical brake arrangement or similar method should be adopted, consideration should be made over the required
safety function when braking as the drive braking circuit alone cannot be relied upon as a fail safe method.
When using permanent magnet motors and in the unlikely event of multiple output power devices failing then the motor
could effectively rotate the motor shaft by 180/p degrees (Where p denotes number of motor pole pairs).
4.14.4. “STO“ Operation
When the “STO” inputs are energised, the “STO” function is in a standby state, if the drive is then given a “Start signal/command” (as
per the start source method selected in P1-13) then the drive will start and operate normally.
When the “STO” inputs are de-energised then the STO Function is activated and stops the drive (Motor will coast), the drive is now in
“Safe Torque Off” mode.
To get the drive out of “Safe Torque Off” mode then any “Fault messages” need to be reset and the drive “STO” input needs to be
re-energised.
4.14.5. “STO” Status and Monitoring
There are a number of methods for monitoring the status of the “STO” input, these are detailed below:
Drive Display
In Normal drive operation (Mains AC power applied), when the drives “STO” input is de-energised (“STO” Function activated) the
drive will highlight this by displaying “
Inhibit
”.
NOTE
If the drive is in a tripped condition then the relevant trip will be displayed and not “Inhibit”.
4
Elec
trical Installation
