--- title: "Case study: new system vs existing (cost, manpower)" subject: "Instrumentation II" chapter: 10 key: "semester_5/instrumentation_ii:cs-cost-manpower-automation" source: https://www.bctengineer.com/q/semester_5/instrumentation_ii/cs-cost-manpower-automation site: BCT Engineering --- # Case study: new system vs existing (cost, manpower) Instrumentation II · Chapter 10: Case Study - Asked in: 2071 Chaitra, 12 marks; 2070 Chaitra, 12 marks; 2078 Kartik, 12 marks; 2078 Bhadra, 12 marks (asked 4 times) - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/instrumentation_ii/cs-cost-manpower-automation - Whole chapter: https://www.bctengineer.com/md/semester_5/instrumentation_ii/chapter-10 ## Question Draw the complete block diagram of industrial process control system involved in your case study. Explain why you want to implement this control system over existing one in terms of cost, manpower and plant automation. What problems you might face after implementing this control system. ## Short answer A microcontroller-based closed-loop system with PT100 sensor, steam valve control and SCADA cuts steam, rejects and manpower; investment Rs 12 lakh recovers in ~10.4 months (monthly saving Rs 1.15 lakh). Post-implementation issues: operator training, power quality, sensor maintenance, EMI and single-point failure risk. ## Answer **Assumed case study:** a milk pasteurisation and packaging section of a dairy plant (HTST process: raw milk tank, heat exchanger, steam-heated holding tube, cooling, filling). The existing system uses analog panel indicators, bimetal thermostats, a manual steam valve and operator logging. (If your own visit was to another plant, replace the process names; the structure of the answer stays the same.) #### Block diagram of the process control system (existing) ```text Raw milk tank --> pump --> heat exch. --> holding tube (level sw) (motor (steam valve (72 C, 15 s) starter) manual) | cooling --> filling Panel meters / thermostats <-- operator reads, adjusts ``` The proposed closed-loop control: ```text PT100 --> Amp/SigCond --+ Level sensor ----------+--> MUX/ADC (12-bit) Flow sensor ---(pulse)-+ | Keypad ----------------+---> [Microcontroller] <--> LCD 16x2 | ARM/AVR + flash | Opto + SSR/relay <----------+ watchdog, timers +--> RS-485 | | (Modbus) Pump / steam valve / alarm +--> EEPROM log PC / SCADA Power supply: 24 V + 5 V + UPS ``` #### Why implement it (cost, manpower, automation) - **Cost:** accurate temperature control (±0.5 C) saves steam and avoids over- or under-pasteurisation, so fewer batches are rejected and there are fewer quality complaints. Automatic logging saves the cost of paper records and avoids logging mistakes. Maintenance is cheaper because of the diagnostics. - **Manpower:** one operator supervises the whole line from the panel/PC instead of one operator per section, and fewer operators are needed for manual valve control and gauge reading. - **Plant automation:** automatic sequencing (start-up, CIP, filling), alarms and interlocks, remote monitoring, trend and production reports, traceability, and an easy path to later expansion. **Cost-benefit (assumed figures):** investment Rs 12,00,000 (controller panel, sensors, valves, SCADA PC, installation, training). Monthly savings: manpower Rs 60,000, steam/energy Rs 35,000, reduced rejection Rs 20,000 = Rs 1,15,000. Payback = 12,00,000 / 1,15,000 ≈ **10.4 months**; yearly return = 13.8 lakh on 12 lakh, about 115 percent. #### Problems after implementation 1. Initial investment and the need for training; operators may resist change. 2. Dependence on supply quality: power cuts and voltage fluctuation (use a UPS/stabiliser). 3. Noise and EMI from motors and ground loops affect the sensors (shielding and grounding are needed). 4. Sensor drift and calibration, and steam and moisture damage; periodic maintenance is required. 5. Software bugs, the need for skilled support or spares, and cyber and data security. 6. Single point of failure (reduced by a watchdog, manual override and redundancy). ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Payback period given Rs 12,00,000 investment and Rs 1,15,000 monthly savings? A. About 10.4 months B. About 5 months C. About 24 months D. About 1.04 months Answer: A. 12,00,000/1,15,000 = 10.43. (Key point: Payback) 2. How does manpower benefit? A. More operators needed B. One operator supervises the whole line from the panel/PC C. No operator needed ever D. Operators per valve Answer: B. Fewer operators. (Key point: Manpower) 3. Which is a post-implementation problem? A. Perfect accuracy forever B. No maintenance C. Noise/EMI and sensor drift needing calibration D. No training Answer: C. Needs shielding and calibration. (Key point: Problems) 4. Mitigation of single point of failure? A. Remove alarms B. Remove backup C. Ignore D. Watchdog, manual override and redundancy Answer: D. Provides safe fallback. 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