Walk into any factory in Morbi, Rajkot or Ahmedabad, ask the maintenance team why they chose their PLC, and you'll usually get one of three answers: "because the OEM specified it," "because we always buy this brand," or "because it was cheapest." None of these are good reasons. Choosing a PLC well is about matching the right processor to your I/O count, communication requirements, scan time, future expansion, and lifetime support.
This guide walks through the actual decision steps we use when sizing a PLC for ceramic factories, foundries, pharmaceutical lines, and packaging machines — with honest opinions on the major brands available in India.
1. Count Your I/O (Realistically, with Margin)
The first — and most overlooked — step is counting digital inputs, digital outputs, analog inputs and analog outputs. Then add 20–30% spare for future expansion. Cramming a system into a CPU at 100% utilisation always backfires within 18 months.
| I/O Range | PLC Class | Typical Application |
|---|---|---|
| Up to 32 I/O | Micro / Nano PLC | Single machine, simple sequencing |
| 32–128 I/O | Compact PLC | Small process line, batching |
| 128–512 I/O | Modular PLC | Medium line, multi-machine cell |
| 512–2,048 I/O | Mid-range PLC | Full factory section, SCADA-integrated |
| 2,048+ I/O | High-end / Distributed PLC | Plant-wide, redundant systems |
2. Decide What It Must Talk To
Communication requirements often dictate the PLC choice more than I/O count. Make a list of every device the PLC must communicate with: HMIs, VFDs, servo drives, remote I/O, weighing indicators, SCADA, MES/ERP, IoT gateway.
- Modbus RTU/TCP — supported by every brand; cheapest for connecting drives, meters, scales
- Profinet / Profibus DP — Siemens-native; needed if your VFDs/HMIs are Siemens
- EtherNet/IP — Allen-Bradley standard; used heavily in automotive, food & beverage
- CC-Link / CC-Link IE — Mitsubishi networks; common in CNC and packaging
- CANopen / EtherCAT — required for high-speed motion (servo systems)
- OPC UA / MQTT — for industry 4.0, cloud, Power BI dashboards
3. Estimate Scan Time & Performance Needs
Scan time = the time the PLC needs to read inputs, run logic, and update outputs. For most factory machines, 10–50 ms is fine. But certain applications demand much faster:
- Press machines, bottling lines, packaging: 5–10 ms required for crisp registration
- Motion / Servo control: 1–2 ms required — needs a motion CPU or dedicated motion module
- Batching / level control: 50–100 ms is fine — cheapest CPU works
- Safety functions: need a separate safety PLC or safety I/O module (TUV/SIL-rated)
4. Brand Comparison — Honest View from the Field
Siemens (S7-1200 / S7-1500)
The gold standard for medium to large industrial automation. Excellent engineering tools (TIA Portal), best-in-class Profinet/Profibus support, huge ecosystem, strong factory acceptance worldwide. Higher cost, but Siemens-trained engineers are easy to find in Gujarat. Best for: ceramic factories, pharma, chemical, large process plants.
Delta (DVP / AS / AH Series)
Excellent value for money. Strong in micro and compact range, with HMI, VFD, and servo ecosystem all from the same brand — easy integration. ISPSoft programming software is free. Local support in India is good. Best for: small/medium machines, OEM applications, ceramic press machines, packaging.
Mitsubishi (FX5U / Q / iQ-R)
Industry standard for CNC, machine tools, and Japanese-style OEM machines. Outstanding motion control. GX Works programming is highly capable. Tightly integrated with Mitsubishi VFDs and servos. Best for: textiles, printing, packaging, CNC retrofit.
Allen-Bradley (MicroLogix / CompactLogix / ControlLogix)
Dominant in automotive and food & beverage. Studio 5000 software is excellent. Premium pricing — usually only chosen when end-customer specifies it. Spare parts and engineering support cost more in India. Best for: US-spec export machines, automotive Tier-1, beverage lines.
Schneider (Modicon M221 / M241 / M340)
Strong in process automation and infrastructure (water, HVAC). EcoStruxure Machine Expert is solid. Good value in the mid-range. Best for: water/ETP plants, HVAC controls, infrastructure projects.
Omron (CP1 / CJ2 / NJ / NX)
Excellent for compact machines and motion control. Sysmac Studio is one of the best programming environments. Strong vision-system integration. Best for: packaging, pick-and-place, vision-guided machines.
5. Don't Ignore After-Sales Support
The cheapest PLC is worthless if you can't get a replacement card within 24 hours when it fails at 2am. Before finalising a brand, ask:
- Is there an authorised distributor within 100 km?
- Are common I/O cards available off-the-shelf, or imported on request?
- Are programming tools free, or behind a license wall?
- Are there qualified engineers locally who can troubleshoot?
- Is there an active community/forum for the brand in India?
For most Morbi-area factories we recommend Delta or Siemens: Delta for small/medium budget-sensitive applications; Siemens when scale, networking, or future SCADA expansion is involved. Both have strong local support, fast availability of spares, and trained engineers across Gujarat.
6. A Practical Sizing Example
A Morbi ceramic press machine needs to control: 24 digital inputs (limit switches, pressure switches), 16 digital outputs (solenoid valves, contactors), 4 analog inputs (pressure transducers), 1 HMI, and 2 VFDs. Communication: Modbus to VFDs, Ethernet to HMI.
Recommendation: Delta DVP-12SA2 + DVP-16SP expansion + DVP04AD analog module or Siemens S7-1200 CPU 1214C + SM 1231 analog input. Both fit comfortably with 30% spare I/O, both support Modbus and Ethernet, both have HMIs in the same family. Choice comes down to ecosystem and budget.
Tell us your I/O list, the devices it must talk to, and the budget — we'll specify a PLC, BOM, panel design, and program the logic too. View PLC services or WhatsApp us.