Sections: Parts: | Input | Processor | Output | Selection
Major
Considerations in Selection
1. Control Process. Know the process to be controlled.
2. Type of Control. Determine the type of control, such as
a. Distributed. One central controller coordinating different process controllers.
b. Centralized. All processes and systems are controlled by a single controller.
c. Individualized/Machine Control. One controller controls only one segment of the process.
3. I/O Interface. Determine the I/O Interface requirements, such as:
a. Estimated number of digital / analog I/Os.
b. Specifications of the I/Os.
c. Determine if remote I/O is required.
d. Provide allowances for future expansion.
4. Language Functions. Determine the language of the controller, to include boolean, or high-level and the construction of the basic instructions, such as:
a. Statement List, a list of logic statements using either the assembly language, also called the Instruction List, or Standardized Text.
b. Function Box/Blocks uses logic gates and follows the format of Step -- Actions--Transactions. Also known as the Sequential Function Chart, a graphical description of the sequential behavior of a control program.
c. System Flowcharts contains Action/Input blocks, Decision/Comparison blocks.
d. Ladder Diagram or the Relay Ladder Logic, a representation of the boolean logic drawn in rungs containing representations of contacts, coils plus special function blocks.
5. Memory. Determine the type of memory, whether:
a. Volatile, variable or erasable, also know as the
RAM, or random-access memory, to include DRAM, SRAM.
b. Non-Volatile, fixed or non-erasable, also known as the ROM, or the read-only memory, to include PROM, EPROM, EEPROM.
c. Combination of RAM and ROM.
6. Memory Capacity. to include the estimate memory usage based on memory utilization per instructions plus an extra memory for complex programming and for future expansion.
7. Scan Time. Evaluate the processor scan time requirement.
8. Programming and Storage Devices. Define the programming and storage devices requirements, to include:
a. Cathode Ray Tube, the monitor, screen.
b. Disk Storage including disk: hard or floppy disks, compact, video, or digital disks, cassette, chip packs or memory packs.
c. Programmer
to include the keyboard, punch board, pointing devices: electronic pen, touch screen, or mouse.
9. Peripheral Devices. Including:
a. Graphic Display, the GUI - graphic user interface as opposed to the monitor.
b. Operator Interface consisting of the switches and other components for the use of the operator as opposed to that of the programmer.
c. Line Printers - serial or parallel, using dot-matrix or jet-technology.
d. Documentation Systems - including programming manuals: help, tutorial, trouble shooting guide, installation and maintenance manual, specifications, user guide, etc.
e. Report Generation System - the software or mechanism of which reports are generated.
10. Price. Consider the affordability, purchasability, the rate-of return, etc.
Introduction
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