Siemens ISI EN 50295 Brochure page 135

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Overview
General design of the AS-Interface power supplies
Note:
The "ground" connection to the system earth must always be as
short as possible.
AS-Interface power supplies are part of the necessary and most
important components of an AS-Interface system.
AS-Interface power supplies generate a stabilized DC voltage of
30 V DC with a high constancy and low residual ripple. They
work in the same way as primary switched-mode regulators.
Data and power are always transmitted simultaneously via the
AS-Interface two-wire cable. For this reason, AS-Interface power
supplies must also ensure data decoupling in addition to supply-
ing the AS-Interface system.
For this reason, standard power supplies must not be used for
the supply of an AS-Interface system.
AS-Interface power supplies supply the electronics of the sys-
tem (AS-Interface master, AS-Interface modules) and all con-
nected sensors. Depending on the power requirements of the
AS-Interface system, graduated power supplies from 2.4 to 7 A
are available.
Please note that there are different power supplies for the sen-
sors and actuators.
The power for the actuators (outputs) is usually not supplied by
the AS-Interface cable. This must be done by a separate load
power supply unit which must be connected via a separate
cable (e.g. black AS-Interface flat cable). It can also be used to
implement corresponding emergency stop circuits.
If an auxiliary power supply is required in addition to the
AS-Interface voltage, the very compact combination power
supply unit with 1 x 30 V DC and 1 x 24 V DC can be used.
AS-Interface Power Supply Units
If so-called double masters are used, the dual power supply unit
with 2 x 30 V can be used.
Performance characteristics:
• high efficiency
• low residual ripple
• short-circuit proof and stable at no load
• overvoltage protection at input
• small dimensions
• low weight
• simple and fast assembly
All AS-Interface power supplies have an AS-Interface certificate.
Power supplies with UL, CSA, and ship construction approba-
tion are available for worldwide use.
Note:
An additional external infeed (AUX POWER) of 20 to 30 V DC is
required for the supply of the output circuits. The additional
infeed must comply with VDE 0106 (PELV), protection class I.
Earth fault detection
"... earth faults in control circuits must not result in unintended
startup or dangerous movements of the machine nor must they
prevent the machine from stopping (EN 60 204, Part 1 or
DIN VDE 0113)".
To fulfill these requirements, the AS-Interface earth fault detec-
tion module or power supplies with earth fault detection are
used. These modules permit earth faults in AS-Interface systems
to be safely detected and signaled.
The following earth faults are recognized:
• AS-i "+" earth fault
• AS-i "-" earth fault
• Earth faults of sensors and actuators which are supplied by the
AS-Interface voltage.
One module for each AS-Interface system is sufficient.
Introduction
Siemens IK PI · 2004 6/135
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