Supply Conception - Siemens SIMATIC PCS 7 Manual

3.2

Supply conception

Overview
Buffer conception
Connecting TM I/O to PCS 7
C79000-G8076-C710-04
The PLC system draws its power from a 24 VDC or 230 VAC power supply.
On startup (after power is returned or after a reset) the application is always
loaded from buffered CPU memory module.
The FM456-4 configuration is backed up on a Flash ROM Memory Card.
The lithium cell in the PS buffers the date and time-of-day as well as data on
the CPU's memory module.
In order to resume with the last states and selected steps free of surge after a
voltage drop and when power is returned, we recommend a redundant supply
in the central PLC area. Even after load power loss, including the supply of
DP stations and/or TM I/O units, the buffered PLC can communicate with the
OS, generate process control failure messages and specifically apply configu-
red failure and resume strategies.
We differentiate:
a) Redundant 24 VDC power supply by means of two diodes
wired in parallelism, switched in series to the PLC module rack of the 24
VDC version;
The redundant power supply busbar is arranged centrally on this system.
b) Uninterruptible power supply with distributed buffered operation;
A low-cost SITOP power DC-UPS 40 A is available.
Refer to Catalog KT 10, Power supply SITOP power, System wiring
SITOP connection.
This UPS system allows an uninterrupted supply/buffer operation transition.
The buffer units can be switched in parallel in order to adapt power to system
requirements. When the UPS is designed to operate on the basic unit, for ex-
ample, you can use the smallest 7 Ah backup battery module to buffer power
loss times of approx. 4.5 h (with PCS7/TM) and approx. 1,6 h (with migra-
tion and TM I/O busses).
On power loss the lithium cell buffers the programs in the PS. After power is
returned, restart is always executed with system and user data stored on the
system's Memory Card.
In order to avoid a restart after voltage drops on supply side, the PLC can be
supplied redundant from two supply circuits with the help of two diodes, e.g.
once from a battery.
This buffers all power drops, independent of the supply for I/O peripherals,
and saves the respectively last system/operating states, thus allowing to re-
sume operation.
Commissioning
3-7