System Design; Introduction; Step 1: Planning Your System; Step 2: Determining I/O Requirements - GE 90-30 PLC Series Installation And Hardware Manual

System Design

Chapter
12

Introduction

This chapter is not intended to cover every possible aspect of designing a Series 90-30 system, but
it does provide you with basic product selection guidelines and with help in finding the information
you need.

Step 1: Planning Your System

Planning is an important part of designing a system. The better you plan the system, the less
trouble you will have installing and implementing it. The following list discusses some basic
things to know or have when planning your system:

Step 2: Determining I/O Requirements

This step comes next because other Series 90-30 component choices are dependent on the number
of I/O points required. In particular, the number of modules required, and their locations,
determines what type and how many baseplates are needed and also is a major factor in CPU
selection. Note that there are some restrictions on the maximum number of certain types of
modules (Analog I/O and Option) that can be supported in one PLC system. See the table
"Maximum Number of Modules Per System" for data.
GFK-0356Q
Expectations. If a new system, what is it expected to do? If retrofitting an existing system,
what does it do now, and what is it expected to do after it is retrofitted.
Specifications (preferably in writing). These include such things as operating environment
information, speed, accuracy, repeatability, size, conformance to standards, cost restrictions,
time requirements, etc.
Documentation. If retrofitting existing equipment, you can refer to its documentation (layout
drawings, schematics, etc.). If the documentation is lost, perhaps a copy is available from the
manufacturer. Additional information may be gathered from discussions with the equipment
operators and maintenance technicians. For a new design, there are probably mechanical or
process drawings of the equipment.
To start, determine how many I/O points, both analog and discrete, are needed for your system.
If retrofitting an existing system, use the schematic diagrams for the system. If designing a
new system, use the mechanical drawings or specifications to determine what inputs and
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