--- title: "Making the case for digital control" subject: "Digital Control System" chapter: 1 key: "semester_6/digital_control_system:case-for-digital-control" source: https://www.bctengineer.com/q/semester_6/digital_control_system/case-for-digital-control site: BCT Engineering --- # Making the case for digital control Digital Control System · Chapter 1: Introduction to Discrete Time Control System - Asked in: 2082 Chaitra, 4 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/digital_control_system/case-for-digital-control - Whole chapter: https://www.bctengineer.com/md/semester_6/digital_control_system/chapter-1 ## Question As a manager of an industrial plant, you want to digitalize the control system. How would you make your case for digital control system to the company board? ## Short answer Present problems of the existing analog system: drif, recalibration, no data tracing. Digital control bring better quality, flexibility, lower cost per loop, advanced control, data logging, and industry 4.0 readiness. Support with payback calculation and a risk mitigation plan using a pilot and phased change-over. ## Answer To convince the board, the case should be presented in terms of **cost, production, quality and risk**, supported by data from the plant. #### 1. Present problems with the existing analog system - Drift and frequent recalibration of analog controllers; old parts hard to find. - No record of process data, so faults and quality losses are hard to trace. - Each loop needs its own controller and panel space. #### 2. Benefits of digital control - **Better product quality:** accurate, repeatable control with no drift; less scrap and rework. - **Higher productivity:** advanced control (cascade, feed-forward, adaptive) gives faster start-up and less downtime. - **Flexibility:** recipes, set points and control laws changed by software for new products, without new hardware. - **Lower cost per loop:** one PLC/DCS handles many loops; less wiring and panel space. - **Data and monitoring:** logging, trends, alarms, remote monitoring (SCADA), and energy reporting. - **Predictive maintenance and diagnostics:** fewer unplanned shutdowns. - **Safety:** interlocks and emergency shutdown logic in software. - **Future readiness:** integration with ERP, Industry 4.0 and IoT. #### 3. Financial justification - Give the capital cost (hardware, software, installation, training). - Estimate yearly savings (energy, scrap, labour, maintenance, downtime). - Show the **payback period** and return on investment, e.g. a cost of Rs 50 lakh saving Rs 20 lakh a year pays back in 2.5 years. #### 4. Plan to manage risk - Pilot project on one line before full roll-out. - Phased change-over during planned shutdowns; keep manual back-up. - Train operators and maintenance staff; choose a vendor with local support. A short presentation with these points, supported by figures from a pilot study, makes a strong case. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. In what terms should the case be presented to the board? A. Cost, production, quality and risk, supported by plant data B. Only technical features of microcontrollers C. Only the vendor's brochure D. Personal preference of engineers Answer: A. A board decision needs business terms backed by data from the plant. (Key point: Framing the case) 2. A project costs Rs 50 lakh and saves Rs 20 lakh a year. What is the payback period? A. 2 years B. 2.5 years C. 4 years D. 0.4 years Answer: B. 50 / 20 = 2.5 years. (Key point: Payback period) 3. Which is part of the plan to manage risk in changing over? A. Replace all lines at once without a back-up B. Pilot on one line, phased change-over during planned shutdowns, and manual back-up C. Remove operator training to save cost D. Avoid vendor support Answer: B. A pilot, phased roll-out, back-up and training reduce risk. (Key point: Risk management) 4. Which is a problem with the existing analog system that supports the case? A. It records too much data B. It requires no calibration C. Drift and frequent recalibration, hard-to-find parts and no process data record D. It has too few loops Answer: C. Drift, obsolete parts and lack of data are the pain points that digital control addresses. 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