01 · Application
What does the machine do?
Packaging, conveyors, assembly, pumps, robotics and process systems each have different control demands.
Industrial automation field guide · 01
How to Choose the Right PLC for an Industrial Machine
A practical engineering framework for turning machine requirements into a reliable PLC specification.
PLC selection frameworkReady to specify
01Machine applicationDefine
02I/O and CPU loadSize
03Network and motionConnect
04Safety and expansionVerify
Inputs · architecture · modelIndustrial control
Start with the application
Six questions define the right PLC
The best PLC is not always the most powerful or the least expensive. Start with the real machine requirements and size the complete control system around them.
02 · I/O
How many signals are required?
Count DI, DO, AI, AQ, temperature, encoder, high-speed and safety signals. Reserve 20–30% for growth.
03 · Performance
How much CPU power is needed?
Check scan time, memory, data handling, recipe management, PID loops and diagnostic requirements.
04 · Network
Which devices must connect?
List HMI, drives, remote I/O, robots, barcode readers, SCADA and the required industrial protocols.
05 · Motion
Is synchronized motion required?
Confirm axes, positioning accuracy, encoder feedback, servo communication and cycle-time targets.
06 · Safety
What safety level is required?
Emergency stops, doors and light curtains may require a fail-safe PLC and safety-rated I/O.
Engineering considerations
Build the control architecture around the machine
Standard machine control
• Compact CPU with integrated I/O\n• Basic sequence control and diagnostics\n• Local HMI and drive communication\n• Limited but predictable expansion
Advanced machine control
• Modular CPU with distributed I/O\n• High-speed motion and technology objects\n• Multiple networks and SCADA connectivity\n• System-wide diagnostics and future expansion
Engineering PC
PLC CPUProgram + diagnostics
HMI / SCADA
Industrial Ethernet / PROFINET
Remote I/O
Drives / Robots
Detailed engineering factors
Move from process requirements to a PLC specification
PLC selection starts with the process flow, equipment locations, instrument types, control-room position and site conditions. The architecture should then be checked against expansion, spare capacity, communication ports, grounding, shielding and redundancy requirements.
01 · Site environment
Check temperature, humidity, dust, condensation, salt mist, chemically active substances, biological contamination, vibration and electromagnetic interference. In cold areas, cabinet heating may be required; in hot areas, ventilation or climate control may be necessary. The published operating range is only one part of the design decision.
02 · Rack and remote I/O expansion
Large systems may exceed the module capacity of one cabinet. Select the expansion architecture according to cabinet locations, distance, diagnostic needs and service strategy. Ethernet-based remote I/O, PROFIBUS DP or other supported networks may each be suitable in different projects.
03 · Grounding and shielding
Analog signals, encoder cables and industrial networks can be affected by electrical noise. Plan cable routing, shield termination, protective earth, equipotential bonding and cabinet separation together with the PLC and I/O design.
04 · CPU redundancy
For processes where a single CPU failure would cause unacceptable downtime, evaluate redundant CPUs, redundant networks, redundant power supplies and the required failover behavior. Redundancy must be designed at system level, not added only by changing the CPU.
| Communication planning point | Engineering guidance | Design check |
|---|---|---|
| Short copper Ethernet runs | Use suitable industrial Cat5e/Cat6 cabling within the permitted channel length. | EMC, connector quality and switch placement |
| Long cabinet-to-cabinet links | Consider PROFIBUS DP, industrial Ethernet with fiber, or a qualified remote-I/O solution. | Distance, topology, diagnostics and service access |
| 100 m to 2 km links | Multimode fiber may be economical when supported by the selected network devices. | Transceiver type, bandwidth and optical budget |
| Links beyond 2 km | Single-mode fiber or a dedicated industrial communications solution may be required. | Fiber specification, redundancy and lightning protection |
| Inter-vendor equipment | Modbus TCP/RTU or a protocol gateway can simplify data exchange between different PLC brands and instruments. | Register map, byte order, update rate and fault handling |
05 · Communication interfaces
Count every external device that must exchange data: packaged skids, instruments, drives, HMIs, robots, SCADA, MES and cloud or cellular gateways. Check the number and type of integrated ports, expansion communication modules, connection limits and whether an OPC UA, Modbus, PROFINET, PROFIBUS or TCP/IP interface is required.
06 · PLC size and project scale
Point count can provide an initial direction, but it is not the only sizing method. Small PLCs may suit compact skids or systems below roughly 200 points; medium systems may fall around 200–2,000 points; larger systems may need a modular high-performance platform. The actual CPU, scan time, memory, network load and architecture must be verified.
07 · I/O allowance
Use the real signal list as the baseline and add practical spare capacity. A 10–15% allowance is a common starting point, but the right margin depends on project size, signal type, future modifications and module granularity. Rounding to the manufacturer’s available module sizes is part of the final order calculation.
08 · Programming language
LAD is often clear for discrete machine logic; FBD can suit function-oriented control; SCL is efficient for algorithms, data handling and reusable logic; SFC is useful for clearly defined sequences where the platform supports it. Select a language strategy that matches the process, team skills, diagnostics and long-term maintenance plan.
Memory and resources
Do not size the CPU by I/O count alone
Modern PLC projects use several memory areas and technology resources. A program that fits the I/O count may still exceed code memory, data memory, retentive memory, connection resources or motion capacity.
Load memory
Project and configuration data
Stores program blocks, hardware configuration, technology objects and project data. Some platforms use removable memory or a memory card for this area.
Work memory
Runtime code and data
CPU-integrated RAM is used while the program runs. Code and data capacity are model-dependent and should be checked against the completed project.
System memory
Runtime process areas
Includes process images, bit memory, timers, counters, local data and peripheral access areas used by the CPU during operation.
Retentive memory
Data retained after power loss
Selected variables and data blocks can be configured as retentive, depending on the CPU and project settings. Confirm the available capacity and behavior.
Resource limits
Connections and technology
Check communication connections, motion objects, PID loops, diagnostic buffers, web functions and module-specific resource limits.
Best practice
Test the actual program
When possible, select a candidate CPU in the engineering software, configure representative hardware and compile a realistic program before purchase.
ProcessI/O + devices
CPU resourcesCode · data · system / Retentive · connections
ProgramLAD · SCL · FBD
VerifyCompile + test
Choose by machine type
Practical PLC selection examples
Use these examples as a first planning reference. The final model still depends on the complete I/O list, communication architecture and safety design.
| Machine | Typical requirements | PLC direction | Important checks |
|---|---|---|---|
| Small conveyor | Basic DI/DO, one drive, local HMI | Compact PLC | Integrated I/O and Ethernet |
| Packaging machine | Recipe control, sensors, drives, safety | Compact or mid-range PLC | Motion, cycle time and safety I/O |
| Water treatment | Pumps, valves, analog process signals, SCADA | PLC with remote I/O | Analog accuracy and communication |
| Large production line | Multiple stations, robots, distributed I/O | Modular high-performance PLC | Network load, diagnostics and expansion |
Before ordering
PLC selection checklist
Prepare this information before requesting a quotation or confirming a complete MLFB/order number.
01 · I/O
DI, DO, AI, AQ and special signals
02 · Network
HMI, drives, remote I/O and protocols
03 · Motion
Axes, encoders, accuracy and cycle time
04 · Safety
Emergency stops, guards and safety level
05 · Environment
Temperature, dust, vibration and noise
06 · Expansion
Spare I/O, modules and future upgrades
07 · Software
Engineering platform and firmware compatibility
08 · Cost
Hardware, software, commissioning and spares
Questions buyers ask
Frequently asked questions
Is a larger PLC always better?
How much spare I/O should be reserved?
When is a fail-safe PLC required?
What should I send to a PLC supplier?
Recommended model shortlist
50 recommended industrial automation models
Use this shortlist as a starting point for application planning and product discovery. The model column uses complete manufacturer designations or catalog references; confirm the final electrical variant, firmware, lifecycle status and regional availability before purchase.
| # | Brand | Full model / catalog number | Product type | Typical application |
|---|---|---|---|---|
| 1 | Siemens | 6ES7214-1AG40-0XB0SIMATIC S7-1200 CPU 1214C DC/DC/DC | Compact PLC | Packaging, conveyors and compact machines |
| 2 | Siemens | 6ES7215-1AG40-0XB0SIMATIC S7-1200 CPU 1215C DC/DC/DC | Compact PLC | Medium machines with additional communication |
| 3 | Siemens | 6ES7513-1AM03-0AB0SIMATIC S7-1500 CPU 1513-1 PN | Modular PLC | Medium production systems and distributed I/O |
| 4 | Siemens | 6ES7515-2AN03-0AB0SIMATIC S7-1500 CPU 1515-2 PN | High-performance PLC | Complex machines and multi-station lines |
| 5 | Siemens | 6ES7155-6AU01-0CN0SIMATIC ET 200SP IM 155-6 PN | Remote I/O interface | Distributed I/O in compact control panels |
| 6 | ABB | AC500 PM595-4ETH | High-performance PLC | Large machines and process automation |
| 7 | ABB | AC500-eCo PM5032-T-ETH | Compact PLC | Small machines and cost-sensitive systems |
| 8 | ABB | AC500-XC PM595-4ETH | Extreme-condition PLC | Outdoor and harsh industrial environments |
| 9 | Allen-Bradley | CompactLogix 5380 5069-L306ER | Compact controller | Machine control and EtherNet/IP systems |
| 10 | Allen-Bradley | ControlLogix 5580 1756-L85E | High-end controller | Large production lines and plant control |
| 11 | Allen-Bradley | Micro850 2080-L50E-24QBB | Micro PLC | Small standalone machines |
| 12 | Honeywell | ControlEdge PLC CPE400 | Process controller | Process skids and industrial control |
| 13 | Honeywell | ControlEdge PLC CPE800 | Process controller | Distributed process and plant applications |
| 14 | Honeywell | Experion C300 Controller | Process control module | Continuous process control and DCS systems |
| 15 | Schneider Electric | Modicon M221 TM221CE24R | Compact PLC | Small machines and basic Ethernet control |
| 16 | Schneider Electric | Modicon M241 TM241CE40R | Compact PLC | Motion-ready machine automation |
| 17 | Schneider Electric | Modicon M262 | Motion controller | Multi-axis machines and robotics |
| 18 | Schneider Electric | Modicon M580 BMEP582040 | Process PLC | Large process systems and remote I/O |
| 19 | Omron | CP2E-N40DR-A | Compact PLC | Small machines and equipment control |
| 20 | Omron | CJ2M-CPU33 | Modular PLC | General machine automation and legacy upgrades |
| 21 | Omron | NX1P2-1140DT | Compact machine controller | EtherCAT machines and integrated motion |
| 22 | Omron | NJ501-1300 | Machine controller | Advanced motion and robotics |
| 23 | GE / Emerson | PACSystems RX3i CPU315 | Modular PLC CPU | Process and factory automation |
| 24 | GE / Emerson | PACSystems RX3i CPU320 | High-performance PLC CPU | Large I/O systems and plant control |
| 25 | GE / Emerson | RSTi-EP CPU | Remote I/O controller | Distributed I/O and modular machines |
| 26 | Mitsubishi Electric | FX5U-32MT/ES | Compact PLC | Small machines and positioning |
| 27 | Mitsubishi Electric | iQ-F FX5UC | Compact PLC | Space-limited control cabinets |
| 28 | Mitsubishi Electric | iQ-R R04ENCPU | Modular PLC CPU | Large systems and high-speed control |
| 29 | Mitsubishi Electric | iQ-R R16MTCPU | Motion CPU | Multi-axis motion applications |
| 30 | Danfoss | VLT AutomationDrive FC 302 | Variable-frequency drive | Motors, pumps, fans and conveyors |
| 31 | Danfoss | VLT Midi Drive FC 280 | Compact drive | Compact machinery and motor control |
| 32 | Danfoss | VLT AQUA Drive FC 202 | Process drive | Water, wastewater and pump systems |
| 33 | Eaton | XC-152-E8-11 | Compact PLC/HMI | Small machine control with visualization |
| 34 | Eaton | XC-303 | Modular PLC | Machine and building automation |
| 35 | B&R | X20CP1586 | Machine controller | High-performance automation and motion |
| 36 | B&R | X20CP0484 | Compact controller | Modular machine control |
| 37 | Phoenix Contact | PLCnext Control AXC F 2152 | Open PLC controller | Connected machines and edge applications |
| 38 | Phoenix Contact | PLCnext Control AXC F 3152 | High-performance controller | Large automation and data applications |
| 39 | Phoenix Contact | Inline ILC 2050 BI | Modular controller | Distributed I/O and building systems |
| 40 | Bosch Rexroth | ctrlX CORE | Industrial controller | Connected automation and robotics |
| 41 | Bosch Rexroth | IndraControl XM22 | PLC controller | Modular machines and motion systems |
| 42 | Bosch Rexroth | IndraControl XM42 | High-performance PLC | Complex automation and multi-axis control |
| 43 | ICS Triplex | Trusted TMR Processor T8100 | Triple-modular-redundant controller | Critical process and safety systems |
| 44 | ICS Triplex | Trusted TMR Interface T8311 | Safety interface module | High-integrity I/O and safety architectures |
| 45 | ProSoft | PLX30-EIP-MBTCP | Protocol gateway | EtherNet/IP and Modbus TCP integration |
| 46 | ProSoft | MVI56E-MNET | Communication module | Modbus TCP with ControlLogix systems |
| 47 | ABB | AC500 CM579-PNIO | Communication module | PROFINET integration and remote devices |
| 48 | Siemens | CP 1543-1 | Communication processor | SCADA, Ethernet and plant networks |
| 49 | Schneider Electric | Modicon X80 BMXP342020 | PLC CPU | Modular control and distributed I/O |
| 50 | Omron | NX102-9000 | Machine controller | Integrated PLC, motion and EtherCAT |
Note: the list includes PLCs, machine controllers, process controllers, drives and protocol modules because the brands shown cover the wider industrial automation ecosystem. Verify the exact manufacturer article number and current availability before quoting.
Need help selecting a PLC?
Send your machine type, I/O count, drive quantity, communication protocols and safety requirements. We can help prepare a practical PLC configuration for quotation.