A customer may ask for a “PLC controller” when the actual requirement is a programmable device that monitors inputs, executes control logic, communicates with other electronic devices, and controls outputs.
A conventional programmable logic controller, or PLC, may be appropriate for a stationary industrial process. A mobile machine controller can perform many of the same basic functions, but it must operate within a different electrical system, environment, network architecture, and equipment lifecycle.
For OEM engineers, the better question is not simply, “Do we need a PLC?”
It is: What type of programmable controller fits the machine and its complete control architecture?
What Does a PLC Controller Do?
PLC stands for programmable logic controller. Although “PLC controller” is technically redundant, it is a commonly used search term.
A PLC or programmable controller typically:
- Receives signals from sensors, switches, operator controls, or other devices
- Evaluates those signals using programmed logic
- Commands valves, relays, actuators, lighting, motors, or other outputs
- Repeats the process as operating conditions change
This input-process-output model also applies to many mobile machine controllers. The differences become clear when the controller is evaluated within the application.
PLC vs. Mobile Machine Controller
Both controller types may monitor inputs, execute logic, control outputs, communicate with other devices, and support diagnostics.
A controller used on a vocational vehicle, construction machine, military platform, or other mobile application may also need to:
- Operate within a battery-powered electrical system
- Withstand shock, vibration, moisture, dust, and temperature extremes
- Communicate over CAN or SAE J1939 networks
- Control hydraulic valves and other high-current loads
- Fit restricted installation spaces
- Support different machine models and option packages
- Provide diagnostics for production and field service
The distinction is not simply terminology. It is a question of whether the controller fits the machine’s electrical, environmental, communication, and functional requirements.
Key Controller Selection Considerations
Operating Environment
Industrial PLCs are often installed inside protected enclosures. A mobile controller may be mounted directly on the machine and exposed to vibration, shock, moisture, contamination, temperature changes, and electrical disturbances. Engineers should compare documented controller specifications with the actual mounting location and operating conditions.
Power and I/O
A controller must be compatible with the machine’s supply voltage, grounding, power distribution, circuit protection, startup conditions, and shutdown behavior. I/O selection should also go beyond the total point count. Evaluate the required:
- Digital and analog inputs
- Frequency or resistive sensor inputs
- High-side or low-side outputs
- Output current capacity
- Proportional hydraulic outputs
- Feedback and fault detection
- Protection requirements
- Future expansion capacity
Two controllers with similar I/O counts may support very different signal types and electrical loads.
CAN and J1939 Communication
Mobile equipment commonly uses CAN-based networks to connect controllers, displays, keypads, sensors, drivetrain interfaces, telematics devices, and distributed I/O. Controller selection should account for:
- Number of required networks
- Supported communication protocols
- Connected devices
- Required messages
- Fault and network diagnostics
- Gateway requirements
- Future network expansion
A CAN port alone does not establish that a controller is the right fit. Communication must be evaluated as part of the complete system architecture.
Diagnostics and Serviceability
A well-planned control system should help technicians distinguish among faults involving:
- Sensors and input signals
- Outputs and electrical loads
- Wiring and connectors
- Power and ground
- Network communication
- Application logic
- Configuration or calibration
Controller diagnostics are only one part of serviceability. Displays, fault codes, service tools, machine-state visibility, and wiring documentation also affect how quickly a problem can be isolated.
Platform Scalability
A controller may meet the needs of one machine while creating limitations for the next model, attachment, option package, or controlled function. Before selecting hardware, consider:
- Expected machine variants
- Credible future I/O requirements
- Additional network devices
- Software reuse
- Harness implications
- Configuration management
- Validation requirements
Scalability does not mean adding unused capacity without analysis. It means establishing a practical path for known and credible future requirements.
For example, HED’s CL-4000 series offers scalable machine controllers with a shared architecture to support expanded I/O requirements.
For a closer look at managing model and option growth, explore how a scalable control platform can support machine variants without multiplying complexity.
When Should an OEM Consider a Mobile Machine Controller?
A mobile machine controller should be evaluated when the application involves:
- Construction or earthmoving equipment
- Vocational trucks and work vehicles
- Lifting or access equipment
- Forestry and road-building machines
- Emergency or rescue vehicles
- Military and mobile-support platforms
The machine category alone does not determine the correct hardware. Controller selection should be based on the operating environment, power system, I/O, communication, software, diagnostics, packaging, and long-term platform strategy.
Select the Controller as Part of the System
A controller does not operate in isolation. It must work with operator interfaces, sensors, valves, actuators, power-distribution devices, wiring harnesses, communication networks, application software, and diagnostic systems.
Before committing to hardware, define:
- Which functions the controller will manage
- Where the application logic will reside
- Which device owns each function
- How information will move through the system
- How faults will be detected and communicated
- How the architecture will support future configurations
The objective is not simply to find a programmable device. It is to establish a control platform that operates reliably, integrates cleanly, and supports the machine roadmap.
Build the Architecture Around the Machine
“PLC controller” may be the phrase that starts the search, but it should not determine the final architecture.
HED works with OEM engineering teams to evaluate controllers as part of the complete mobile machine control system, including I/O, operator interfaces, power distribution, CAN communication, diagnostics, application software, and controlled functions.
Selecting a Controller for a Mobile Equipment Application?
Evaluate the I/O, communication, environmental, software, and scalability requirements before committing the architecture.
Request a control architecture review to help with your evaluation. Not ready for an evaluation just yet? Explore HED Controllers