Safety circuit / restart lock (STO)
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Safety circuit / restart lock (STO)
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according to EN ISO 13849-1:2008-12, DIN EN 62061:2005 SIL 3
The restart lock is provided for preventing an unintentional start of a speed-variable dri-
ve from the standstill and can, for example, be used in the machine function „Safe stop‟.
It comprises a restart lock tested according to EN ISO 13849-1:2008-12 (VDE 0113)
and a stop function according to EN 60204-1:2007-6, stop category 0. A stop category 1
can be achieved by using a tested, safe emergency stop device with delay or a safe
PLC according to DIN EN 60204-1. The stop functions are defined according to DIN
EN 60204-1 (VDE 0113) paragraphs 9.2.2, 9.2.5.3.
There are three categories of stop functions:
Category 0
Standstill by immediate interruption of the energy supply to the machine drives, i.e.
uncontrolled standstill.
Category 1
The machine is decelerated to standstill without disconnecting the energy supply be-
tween motor and drives (i.e. a controlled standstill). The energy supply is interrupted
at that moment the machine is at a secure standstill.
Category 2
The energy supply between motor and drives is not interrupted (a controlled stand-
still).
Every machine must be equipped with a stop function according to category 0. Stop
functions according to category 1 and/or 2 must be integrated into the machine if they
are necessary for safety and/or operational reasons.
The disadvantages of the disconnection can be eliminated by the consequent use of
electronic elements. The EN 60204-1:2007-6 standard „Safety of machinery - Electri-
cal equipment of machines‟ also allows the use of electronic equipment for the stop
function in case of an emergency, if these – under application of the standards EN ISO
13849-1:2008-12 and/or DIN EN 62061:2005 – meet the same safety requirements as
required according to DIN EN 60204-1.
This checked safety circuit was conceived according to the concept paper by Drivecom
„Technical Guide for Safety Drives‟ from 04/23/2004. The concept paper was checked
by the BIA and the TÜV Rheinland: It was confirmed that the required standards and
regulations were met.
The standstill of the machine must be caused by a high-ranking control before and the
stop function of at least category 2 must be ensured.
The restart lock interrupts the energy supply between drive and motor by deactivating
the output stage control. Thus, any rotation of the motor is made impossible.
The advantage of this circuit is that a single drive can be locked safely in an installation
with several drives while other drives remain in operation. Besides, a drive can be locked
without having to charge the DC link electrolytic capacitor at a new restart.
DANGER
Danger due to electric shock
The restart lock does not galvanically separate the output stages from the
motor. Thus, the restart lock does not protect against electric shock.
→ The complete machine must always be galvanically separated from
the mains by use of the main switch (DIN EN 60204-1 5.3) for any in-
terruptions of the operation, maintenance, repair or cleaning work at
the machine or system.
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Drive Amplifier SD2B plus - 0362171DA1xxxx, 0362171DB1xxxx
