Engineering Expertise

Most automated machines run exactly as well as their PLC program. The mechanical design gets the attention, the fabrication gets photographed, and the robot gets the press release. But the control logic is what determines whether a system starts up cleanly, runs reliably across three shifts, and recovers from a fault in seconds rather than hours. Get the PLC programming right, and the rest of the system gets to perform. Get it wrong, and no amount of mechanical precision or elegant fabrication will save you.

This article covers what PLC programming services actually involve, how platform and protocol decisions affect long-term system performance, and what separates industrial controls work that holds up in production from work that creates ongoing maintenance burdens. It is part of a broader series on custom machine design and automation, and pairs closely with our breakdown of the machine design process from concept to commissioning.

Watch our engineers discuss machine and system design, controls integration, and what it takes to deliver automation that performs. See the full conversation on YouTube.

What Is PLC Programming?

A Programmable Logic Controller (PLC) is an industrial computer designed to control automated machinery and processes in real time. PLC programming is the development of the logic that tells the machine what to do: when to move, when to stop, how to respond to sensor inputs, how to handle fault conditions, and how to communicate with other devices on the production network. It is the software layer that turns a collection of mechanical and electrical components into a coordinated, functional system.

PLC programs are written in one or more of the five standard IEC 61131-3 languages: Ladder Diagram (LD), Structured Text (ST), Function Block Diagram (FBD), Instruction List (IL), and Sequential Function Chart (SFC). Ladder Diagram is the most widely used in North American manufacturing environments and maps closely to the relay logic it replaced. Structured Text is preferred for complex mathematical operations, motion control, and algorithm-heavy applications. Function Block Diagram is common in process control and drive integration work. Experienced controls engineers select the language based on the application, not habit.

PLC programming is a core discipline within Bravo Team’s machine and system design services. It is never subcontracted, which means the engineer writing the PLC code is the same engineer who designed the control architecture and understands the mechanical system it runs.

PLC Platforms: How to Choose the Right One

Platform selection is one of the most consequential decisions in an industrial controls project. The right choice simplifies integration, reduces commissioning time, and makes the system easier to maintain. The wrong choice creates compatibility problems, limits performance, and can saddle a manufacturer with a system that is difficult and expensive to modify as production requirements evolve.

The most widely deployed platforms in industrial automation include Allen-Bradley (Rockwell Automation), Siemens S7, Beckhoff TwinCAT, Phoenix Contact, and Industrial Shields. Each has a different profile of strengths. Allen-Bradley and Siemens dominate large enterprise environments where existing infrastructure, spare parts availability, and familiarity with in-house maintenance drive the decision. Beckhoff TwinCAT with EtherCAT is well-suited to high-speed, multi-axis motion applications where deterministic real-time performance is non-negotiable. Phoenix Contact is a strong choice for modular, distributed I/O architectures. Industrial Shields offers a cost-effective option for lower-complexity applications where budget is the primary constraint.

Safety applications require a separate consideration. Keyence safety PLCs and safety-rated modules from major vendors enable safety logic and standard machine control logic to coexist within a validated architecture without requiring entirely separate hardware. This matters because safety cannot be designed around. As we discuss in both our custom machine design guide and our overview of the machine design process, safety architecture needs to be part of the controls design from day one, and platform selection directly affects how cleanly that architecture can be implemented.

One important note: platform selection should be driven by the application requirements, not by what the controls engineer already knows. The best engineers expand their platform expertise to fit the problem. A controls team that recommends Allen-Bradley for every project, regardless of the requirements, is optimizing for its own convenience rather than the client-partner’s long-term interests.

Industrial Communication Protocols

Industrial communication protocols are the standardized languages that PLCs, drives, sensors, vision systems, and other devices use to exchange data on the automation network. Protocol selection affects system throughput, latency, wiring architecture, and the range of devices that can be integrated. It is a design decision with long-term consequences, not a default setting.

EtherCAT is the highest-performance option for real-time, deterministic communication, and is the preferred protocol for multi-axis motion control and high-speed servo drive integration. It achieves sub-millisecond cycle times, which are critical for applications requiring tight synchronization between axes. Ethernet/IP is the dominant protocol in Allen-Bradley environments and is well-suited to general device communication where EtherCAT-level latency is not required. Modbus TCP is widely used for its simplicity and broad device compatibility, particularly in legacy environments and lower-complexity applications.

IO-Link is increasingly important for intelligent sensor integration, enabling two-way communication with sensors and actuators that previously only provided a digital on/off signal. This allows the PLC to read device diagnostics, adjust sensor parameters remotely, and detect sensor degradation before it causes a fault. CANopen is common in distributed control networks and mobile automation. RS-232 and RS-485 remain relevant for legacy device integration and applications where industrial Ethernet is not practical.

The Bravo Team controls engineering team works fluently across all of these protocols. See our full automation and controls capabilities for more details on our approach to protocol architecture for complex multi-device systems.

HMI Development: The Interface Between Machine and Operator

A Human-Machine Interface (HMI) is the operator-facing display and control system that gives production personnel visibility into machine state, process data, and fault conditions. A well-designed HMI reduces unplanned downtime by providing operators with the information they need to quickly identify and respond to faults. A poorly designed one gets worked around, ignored, or blamed for problems it did not cause.

HMI development at Bravo Team is treated as an engineering discipline, not a cosmetic exercise. Interfaces are built using Qt for cross-platform GUI development or native PLC-based HMI platforms, depending on the application. High-resolution capacitive touch displays enable interfaces tailored to the specific workflows and skill levels of the operators who will use them daily. Alarm management, recipe management, production data logging, and remote monitoring capabilities are designed in as functional requirements, not added as afterthoughts.

The test of a good HMI is whether an operator who has never seen the machine before can identify a fault, understand its cause, and take the correct corrective action without calling for engineering support. If that test fails, the HMI needs to be redesigned. Our engineering team brings the same rigor to HMI design that it applies to every other element of the controls architecture.

Safety PLCs and Functional Safety in Industrial Controls

Functional safety is the engineering discipline of ensuring that a control system behaves correctly in response to its inputs and, critically, fails safely when something goes wrong. In industrial automation, functional safety governs how the control system handles E-Stop events, guarding bypasses, door interlock faults, and any condition that could expose a person to a hazard.

The key standards are ISO 13849, which defines Performance Levels (PL a through e) for safety functions, and IEC 62061, which defines Safety Integrity Levels (SIL 1 through 3). These standards require that safety functions be implemented in validated, safety-rated hardware and software, separately from the standard machine control logic. A safety relay or safety PLC performs continuous self-diagnostics, and any detected fault causes the system to enter a defined safe state rather than an undefined one.

Keyence safety PLCs are a common choice for applications where safety logic and standard control logic need to coexist without fully separate hardware. They provide the diagnostic coverage required by ISO 13849 while integrating cleanly with the broader PLC architecture. For OEMs selling equipment into regulated markets, the safety PLC program and the associated risk assessment documentation are deliverables that need to be part of the project from the start, not bolted on during final inspection.

For a deeper look at machine safety standards and their application to custom automation systems, see our complete guide to custom machine design and automation.

Where PLC Programming Projects Go Wrong

PLC programming failures in production rarely look like software bugs. They look like unexplained faults, intermittent stops, slow fault recovery, and machines that require experienced technicians to keep running. The root causes are almost always in how the program was written and documented, not in the hardware it runs on.

Underdocumented code. PLC programs that lack comments, consistent naming conventions, and clear structure become unmaintainable. When the controls engineer who wrote the program leaves the project, the system becomes a black box. Troubleshooting requires reverse-engineering the logic rather than reading it. This is not a minor inconvenience; it directly increases downtime and maintenance costs over the life of the system.

Poor alarm management. Systems with hundreds of alarms, many of which fire simultaneously during a fault cascade, leave operators unable to identify the root cause fault from the downstream effects. Good alarm management means defining alarm priorities, eliminating nuisance alarms, and structuring fault logic so that the first fault is clearly identified and the cascade is suppressed until it is resolved.

No version control. PLC programs modified in the field without version tracking can result in the program running on the machine not matching any documented version. When a problem occurs, there is no baseline to return to and no record of what changed. Version control for PLC code is not optional on any professionally managed automation project.

Platform selection driven by familiarity. Recommending the same PLC platform for every project, regardless of application requirements, is a red flag. A controls team that defaults to one platform is optimizing for their own learning curve, not for the performance and maintainability of your system. As noted in our overview of the machine design process, the right engineering approach starts from requirements, not from the tools the team already knows.

Want to see how Bravo Team engineers approach machine and system design in practice? Watch our team walk through the work on YouTube.

Frequently Asked Questions

What does a PLC programmer do?

A PLC programmer develops the control logic that governs how an automated machine operates: machine sequences, I/O management, fault handling, safety interlocks, and communication with other devices on the automation network. On complex projects, PLC programming also involves control architecture design, protocol selection, HMI development, and integration testing with mechanical and software systems. A skilled PLC programmer understands not just the language they are writing in but also the mechanical and electrical systems the program controls.

What is the difference between PLC and DCS?

A Programmable Logic Controller (PLC) is optimized for discrete, event-driven control of machinery and production equipment. A Distributed Control System (DCS) is designed for continuous process control in industries like oil and gas, chemical processing, and power generation. PLCs respond to discrete inputs and execute sequences. DCS systems manage continuous variables like flow, temperature, and pressure across large, geographically distributed plant infrastructure. In advanced manufacturing and custom machine design, PLCs are almost always the right choice.

How long does PLC programming take for a custom machine?

PLC programming for a custom machine typically runs in parallel with the latter stages of mechanical and electrical design and through system integration. For a straightforward single-axis system, controls development might take two to four weeks. For a multi-robot cell with vision guidance, safety logic, motion control, and full HMI development, controls work can span several months. The full timeline is established during the scoping process. Talk to our controls engineers to scope your project.

What PLC platforms does Bravo Team work with?

Bravo Team’s controls engineering team works across Allen-Bradley, Siemens S7, Beckhoff TwinCAT, Phoenix Contact, Industrial Shields, Keyence safety PLCs, Raspberry Pi, and Nvidia Jetson platforms. Platform selection is driven by application requirements, not familiarity. See our automation and controls capabilities for the full list of supported platforms and protocols.

Industrial Controls Done Right

PLC programming is the layer of a custom automation system that most directly determines how it behaves in production. Platform selection, protocol architecture, HMI design, and safety logic are all engineering decisions with long-term consequences. They deserve the same rigor applied to the mechanical and electrical design, and they require engineers who understand the full system, not just the controls layer in isolation.

At Bravo Team, controls engineering is fully in-house and fully integrated with our mechanical, electrical, software, and fabrication capabilities. The engineer writing your PLC code understands the machine it is running. That integration is what makes the difference between controls that work on the bench and controls that hold up in production.

Explore our machine and system design services, learn more about our Engineering as a Service model, or contact us to start a conversation about your controls project.