2 Engineering
2.5 Safety-related switch off
Electronic motor starter EMS-...-SWD
12/18 MN034002ZU-DE/EN
www.eaton.com
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2.5 Safety-related switch off
The section below shows the simplest way to integrate an EMS-DOS/ROS-
SWD electronic motor starter into an controlled stop circuit. In it, the 24 V DC
supply voltage from the power output stage is cut off at ter
(24 V DC), - (0 V DC), EN+ (24 V DC enable signal), and EN- (0 V DC
reference potential for enable signal) and with a safety relay as soon as the
emergency-stop button is pressed.
The motor voltage is guaranteed to be cut off 25 ms after the rated control
voltage is cut off. The power output stage‘s supply voltage can either be
supplied using an external 24 V DC power supply unit or tapped from
ter (24 V DC) and – (0 V DC) directly on the electronic motor starter.
The power output stage‘s supply voltage can also be supplied via a safety
24 V DC control output. In this case, it is necessary to take into account that
enable inputs EN+ and EN- are suitable for unblanking pulses with a duration
of up to 8 ms and blanking pulses with a duration of up to 3 ms.
Since the power output stage‘s supply voltage is cut off using a single
channel only, this type of installation is only permissible in accordance with
SIL 3 (category 3, category 4) if a fault exclusion for cross fault short-circuits
is permissible.
This will be the case, for example, when the electronic motor starter and the
safety relay are installed in the same control panel. If this type of fault
exclusion is not permissible, however, the voltage must be cut off with two
channels or two poles.
The following circuit examples, which show how to implement a safety
shutdown mechanism for electronic motor starters, are designed to cut off
the supply voltage for the electronic motor starter‘s power output stage.
When using this approach, it is always necessary to bear in mind that cutting
off the supply voltage while the motor is being driven will always result in
additional wear to the electronic motor starter. Because of this, these two
circuits should only be used if a maximum of 10,000 shutdown operations
are expected throughout the system's entire service life!
