Control System Instrumentation

This article is all about Control system Instrumentation and its integral role with any type of Field Instrumentation.

A Typical Control Room

From our previous article on Field Instrumentation, we know that a field is all about different types of sensors and instruments deployed, to measure & perform critical process oriented tasks. Now, continuing & extending to this, a very popular aspect in all the industries coins is “Automation & Control”. Automation & control activities are together clubbed and grouped under a category called “Control systems”

Any type of field instrumentation used in any type of application always require observation, necessary acknowledgement & control actions. Automation was and is never possible without any manual intervention as far as critical processes are concerned. At least some partial approach of human operators are always or periodically required even in an automated controlled processes to just ensure that whether these processes are running as per desired automational controls or not. For such process’s automation in desired limits as well as their direction and outputs, control system are incorporated as a control layer just above the field instruments layer. In our Instrumentation language, these control layer comprises of PLC, DCS and SCADA systems. All of these items work independently as well in combined package too. These control systems are responsible for monitoring, performing control as well as corrective actions of all the processes & their equipments & instruments tagged with these control systems. The popular proven & running configurations in current running applications are PLC based process, PLC + SCADA based process, DCS + SCADA based process and PLCs + DCS + SCADA based process.

A Typical PLC Panel

PLC (Programmable logic controller), DCS (Distributed control system) and SCADA (Supervisory control and data acquisition) form the pillars of control system instrumentation. Any small process out there or even bulk mega industries, all are running on these systems only, as a control layer, with internal defined layers of authorisational access for defined engineers & operators. Small scale plants can run on PLC based systems. Heavy bulk industries with multiple operations & processing units run on multiple individual PLCs for their individual control with a common DCS as main control as well as monitoring purposes. SCADA provides an interface for instruments and humans. It provides HMI (Human machine interface) screens with GUI (Graphical user interface) based approach on desktop computers with all the processes and their equipments & instruments in terms of graphics and symbols with real time data display for monitoring along with their logs and actions execution. It is a technology through which human operators are able to monitor and intervene in running operations/processes and can even take necessary control and/or corrective actions. SCADA also plays a very vital role with Alarm management of the assigned process. When we talk about alarm management, it consists of multiple small and big tasks like alarm generation, acknowledgement, alarm logs, trends, reports generation and even with some IIOT aspects (Industrial Internet of Things). However IIOT is still in consideration and development phase for our industries and is not deployed with full fledge capacity throughout the industry.

A Typical DCS Panel

All the control systems are configured with multiple desired programs & functions that are supposed to be run continuously 24×7 with or without human operators. However, unmanned stations and processes in our country are followed on a very small scale. Majority of all the applications and processes are always assigned with some human operators to monitor the process in shifts and rotation. Another important aspect is Redundancy. Redundancy is provided at control layer by deploying multiple controllers for dedicated processes in order to prevent complete blackout & lost scenarios in the event of malfunctioning or failure of single or primary controller. There are some applications which are having only single redundancy and even dual redundancy as well. In some applications, redundancies are also done in field level by installing redundant instruments measuring a common process variable of a common equipment. Another important engineering study certifies these control system items with their probability of failure to perform when needed to perform by SIL (Safety Integrity level) studies. These control system components may have some application oriented names like, ESD systems, F&G system, Bottle handling system, ID & FD fan system, HVAC system, Boiler control units, Burner management system, Compressors control systems, Prover systems, Turbine systems and many more. But in all these applications, there is always a micro, small or large I/Os capacity based controller only, which is pre-programmed. Programming languages plays an important role for control system items. PLC based controllers run on Ladder logic which is universally accepted and proven language form last 20 years and still running successfully. DCS system have multiple options based on their OEMs (Original Equipment Manufacturer). However general & most common programming option is FBD (Functional block diagram). Some other languages are SFC (Sequential function chart), IL (Instruction list) and Structured text. SCADA has multiple graphics oriented programming softwares like visual basic, VB.net and many more advanced derivatives of these languages, for creating symbols & graphical representation of processes and their equipments/instruments, with scripting (programming) done in backend.

A Typical SCADA HMI Screen

Designing activities of these control systems is very challenging in terms of sizing, selection, installation, wiring, testing & commissioning. Ideally, based on number of I/Os, nature of process, Human hazards, Process hazards, safety studies and criticalities involved in overall process, sizing, selection, bifurcation, redundancy, response time and architectural interface of these control systems with field instrumentation are to be addressed by an Instrumentation engineer.

Hope the above article might be helpful to you for getting brief & overview information about control systems and their role in overall Instrumentation engineering field. For additional more specific technical information on this topic and sub-topics related & relevant to it, please feel free to write us at [email protected] .Your all doubts & queries will be answered. Also, necessary articles or even training sessions can be arranged & provided for the same, if required by you.

Have a Happy Learning…!

Leave a Reply

Your email address will not be published. Required fields are marked *

Next Post

Analytical Instrumentation

Tue Dec 29 , 2020
This article is all about brief overview of Analytical Instrumentation, dealing with Analysis and Analysers.
error: Content is protected !!