Input/Output Controller

DOE-HDBK-1132-99

modified, or serviced without affecting any other drop (except from loss of data

from the drop being serviced). Modularity also allows easy expansion from a

small system to a large system and reduces spare inventory.

Input/Output Controller . Input/output controllers consist of intelligent modules,

4.2.2

each performing a dedicated function. Modules are chosen to meet the specific

function including input/output mix, redundancy, geographic distribution, and

process requirements. Capability should be provided in the controller to perform

logic functions that will eliminate the need for separate programmable logic

controllers (PLCs). On critical processes, the use of backup power supplies,

redundant controller, and input/output cards should be considered. Also, these

controllers should be located as near as possible to the process to reduce the

cost of cable installation.

Communications . Communication networks in the system provide high-speed,

4.2.3

secure controller information exchange, as well as an open network for standard

computing hardware access where appropriate. Communications between

individual modules should be via local, independent buses that allow complete

integration of the family of modules. Open system capabilities may also allow

third-party software to be an integral part of the system.

Data Highways. For critical applications, redundant data highways should be

4.2.4

considered. Failure of one data highway should be transparent to the system

and should not affect system performance. An alarm message that would

activate upon failure of a redundant highway should be considered at the

operations station. Fiber optics may be useful in this application for its immunity

to noise and electrical fault isolation. Wide band width, high reliability, and noise

resistance should make fiber optic networks an attractive component of many

complex control systems. Redundant computer controls and uninterruptible

power sources should make these new technology control systems much more

accurate and reliable than traditional analog systems.

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