Case study: revamping MBI system for CEO

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.)

Proposed design (blueprint for the board)

 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

Hardware solution

A microcontroller board (12-bit ADC, UART, timers, watchdog), PT100 sensors with an amplifier, level and flow sensors, optocoupler plus SSR/relay drivers for the pumps and steam valve, a 16x2 LCD and keypad, an RS-485 link to a PC, a 24 V/5 V power supply with UPS, and an enclosure (IP54) with grounding and surge protection.

Software requirements

Firmware in C: ADC acquisition and filtering, PID/hysteresis control, alarm and interlock logic, keypad/LCD menu, Modbus RTU communication, data logging and watchdog. PC side: SCADA/HMI screens with trends, alarms and reports (for example an open-source or vendor package).

Key figures (calculated): a PT100 amplifier scaled 0-150 C to 0-5 V and a 12-bit ADC give a resolution of 150/4096 = 0.037 C per count (1.22 mV per count at 5 V), enough for the ±0.5 C pasteurisation limit. An 8-byte Modbus-style frame at 9600 baud takes 8 × 10 bits / 9600 = 8.3 ms, so every point can be updated several times per second.

Advantages

Accurate and stable temperature, quality and traceability, savings in steam, labour and rejects, remote monitoring, and easy expansion.

Disadvantages

Upfront cost, the need for training, sensitivity to electrical noise and power quality, software maintenance, and dependence on spares.

Gain in efficiency (assumed)

The temperature swing reduces from ±3 C to ±0.5 C; steam saving is about 8 percent; rejects fall from 1.5 percent to 0.5 percent; and labour is reduced from 4 to 2 operators per shift.

Cost breakdown (assumed, Rs)

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.