A successful centralized control system and its implementation.

In order to identify the term "successful", we need to understand first why do we need a centralized control system?

to answer this question, we need to imagine that we have a project that is distributed to a very large area, and this project is divided into several zones and every zone has its own specification and requirements, so every zone is isolated from the other zones, and we need to connect all the isolated zones together in a central place where all the operations for all the zones are held, managed, controlled, and supervised together at the same time this is the concept of centralized control.

So, a successful centralized control systems are capable of connecting several isolated subsystems together at the same time, and still able to monitor, and control all the zones at the same time with high reliability, availability, and maintainability.

the centralized control system is based on the concept of multi-tier architecture as described in the figure below:

The Client Tier: represents the presentation level where the business process is being supervised, monitored, and actions are being taken from the operator like Human Machine Interface (HMI).

Processing Tier: represents the middle level where the system application being installed, and system functions are running like a run time servers, maybe Alarms server, or a Trend server.

Data Tier: represents the field level or where the data is being stored and managed whether it's a database like SQL database or data source like Programmable Logic Controllers (PLC).

What is so special about Multi-Tier Architecture?

The most powerful advantage of multi-Tier architecture is the high scalability where you can expand the system according to your need, for example if you have a small application, you can merge the three tiers into one computer, or if you have a quite bigger application, you can use a computer in every tier, and for mega projects where the application is very complex and the data frequency is very high you might have multiple computers in every tier, so it's better to identify your need carefully.

Another powerful advantage is the operation reliability, and it's achieved by considering modes of degradation, and the modes of degradation are defined as switching over to lower-level mode when a higher-level mode is out of service, so there's no down time under all the circumstances.

Centralized Control Modes

Modes of operation in any CC system shall have degraded modes,

mainly, the Centralized Control Center has most of the features and has the higher level of automation.

The local degraded mode is achieved when the centralized level is out of service, and the operation is being held by every local operator and every local operator is responsible only for his own territory or his own isolated zone.

The field degraded mode is achieved when the local mode is out of service and this mode is the most basic mode where the operation is being held by the main field controllers, and most of the functions in CC and local modes cannot be achieved but the very basic functions are running to keep the system safe.

things to be considered carefully in any centralized control system.

• you have to identify carefully the data flow where all the process variables are assigned to groups, and every group is assigned to its dedicated client.
• you have to identify the interfaces carefully by identifying a compatible application in every device within every device in every tier.
• you have to identify the communication protocols between the systems and subsystems, because every communication protocol has its own limitations, so it's required to identify these limitations in order to overcome data loss.
• to plan for integration test between all the systems and subsystems, the integration test is mandatory if many vendors are involved in the same project.

• A client validation for every part of the system is required to avoid any conflict with the client during The Factory Acceptance test or Site Acceptance Test.

In general, by following the project V-Model by identifying the client requirements, then designing the required system, and then going to verification and validation, with a successful installation and implementation, and after that a successful testing and commissioning, and a good plan for warranty and Maintenace after the project delivery.