Step 5: Selecting Baseplates - GE 90-30 PLC Series Installation And Hardware Manual

Step 5: Selecting Baseplates

The requirements determined in the previous steps will largely dictate what baseplates to select.
Please refer to the "Baseplates" chapter for additional details.
GFK-0356Q Chapter 12 System Design
data storage. This is not available in some of the other CPUs. See the "CPU Firmware and
PROM Configurations" table in the "CPUs" chapter for details.
Expansion and Upgrade - The Embedded CPUs do not support Expansion or Remote racks
and do not allow changing CPU type. Therefore, they have limited options for expansion or
upgrade. Modular CPUs can usually be upgraded to more powerful CPUs. The type of
modular CPU determines whether a system can have a total of 5 or 8 baseplates, which can
have a direct bearing on the future expansion capabilities of a system. For example, if you
only need 49 total Option and I/O Modules, you could use one of the CPU331-341 CPUs.
However, you would be at the maximum module limit and would not be able to add any more
to the system without changing the CPU. If you used, instead, one of the CPU360-364 CPUs,
you could later add up to 30 more modules while keeping the same CPU.
Cost - If some of the other factors such as performance or extended features are not major
issues, one of the lower cost CPUs can be applied. However, sometimes purchasing a more
expensive CPU with extended features can be less costly than purchasing a lower cost CPU
and an additional Option module to cover the feature needed. Besides the direct cost of the
modules, using the single CPU would save a PLC slot, which could help avoid the need for,
and cost of, an extra Baseplate, Power Supply, I/O Bus Expansion Cable, etc. Since prices are
subject to change, it would not be practical to give an example of this. Please check with your
distributor for current pricing information.
Display requirements - The CPU351, CPU352, CPU363, and CMM311 have serial ports that
are often used to communicate with HMI or Operator Interface (OI) devices.
Time of day (TOD) clock requirements - The Embedded CPUs do not have one, the Modular
CPUs do.
System size limitation - If you are close to the maximum number of modules limit of your
system, you can use modules that have dual functions to conserve rack slots. For example, the
CPU364 has CPU and Ethernet communications capability in one module. The CPUs 351,
352, and 363 have CPU and Serial Communications capability in one module. There are
discrete and analog combination I/O modules that provide a limited number of both inputs and
outputs in one module. Also, the 32-point discrete I/O modules conserve rack slots compared
with lower density (16-point and less) I/O modules. You may also be able to use Genius
Blocks or Field Control distributed I/O to accommodate the need for additional I/O, since these
do not require a PLC slot; they communicate with the PLC over a communications bus.
Protection against unauthorized changes. CPUs 360—364 have a keylock switch that can
be locked to protect against unauthorized changes to the PLC. CPUs 311—341 do not have a
keylock switch. However, all CPUs have the capability of password protection for the
application program.
Embedded CPU baseplate - If the previous selections dictate the use of an Embedded CPU,
you have three choices. The CPU311 and CPU313 are 5-slot sizes, and the CPU323 is a 10-
slot size. The CPU311 has 6K Bytes of memory and the CPU313 has 12K Bytes.
Modular CPU Baseplate - If you need a modular CPU, you must use a Modular CPU
baseplate. There can be only one CPU baseplate per system. There are two types, 5-slot and
System Design and Layout
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