The PLC Pro Method Framework
PLC Pro Methods organize the PLC Pro’s work around each operating condition. The installation’s required behavior is established by its intended function, risk assessment, and applicable safety and functional requirements; PLC Pro Methods provide a consistent approach for coordinating and implementing that behavior. Power Loss Response and Emergency Stop Mode are addressed before Manual Mode, and Manual Mode is established before Auto Mode. This order is deliberate: each method builds on the one before it, creating controls that recover predictably, respond consistently, and give operators a machine they can understand and trust.
Power Loss Response
Mechanical, electrical, controls, and programming decisions must support the same intended power-loss response. Whenever practical, the PLC Pro should be included in this design process because the PLC Pro's understanding of machine operation and control can contribute information that may not be apparent from the hardware design alone.
If electrical power to the PLC is lost, no programmatic response is available until power is restored and the PLC resumes execution.
If the PLC remains powered while electrical power is lost elsewhere in the installation, the PLC must provide an appropriate programmatic response to the affected condition.
Emergency Stop Mode
Emergency Stop (E-Stop) Mode mirrors the installation’s safety-system status in the ordinary control program and provides for the control program’s response to that status. It does not create or invoke the safety-system response. Under PLC Pro Methods, E-Stop Mode is active whenever the mirrored safety-system status indicates that the defined safety response is in effect.
When power is restored after a power loss, E-Stop Mode is expected to be active because the safety-related control system requires deliberate reset before its status indicates that the defined safety response is no longer in effect. The ordinary control program mirrors that status and remains in E-Stop Mode until the safety-system reset is detected.
When the safety-related control system demands the defined safe response, it must place the machine in the safe condition established by risk assessment. E-Stop Mode mirrors that status in the ordinary control program, and the programmatic response must coordinate the ordinary control logic with the safety-system action. The required safety response does not always mean immediately de-energizing every output. Some outputs may remain energized where necessary to reach or maintain the intended safe state.
Achieving the intended response requires coordination across the machine design. The safety-related control system and the actuators, drives, and other hardware it controls must execute the safe response established by risk assessment. The ordinary control logic must recognize that response and coordinate E-Stop Mode with it.
Resetting the safety-related control system does not authorize machine motion. The safety-related control system may be reset only after the conditions required for reset are satisfied. When the ordinary control program detects the successful safety-system reset, E-Stop Mode is no longer active. Under PLC Pro Methods, the machine then enters Manual Mode.
Manual Mode
Operations in Manual Mode place machine actions under deliberate operator direction. This may mean commanding an individual device, positioning equipment, or initiating a limited sequence, but in every case the operator chooses the action and the control system manages how that action is carried out.
Manual Mode does not bypass the machine’s safety systems or equipment protections. Manual commands remain subject to the permissives, interlocks, and conflict checks required for safe and predictable operation while providing the control needed for setup, recovery, and troubleshooting.
Using PLC Pro Methods, the machine always enters Manual Mode when the control program detects that the safety-related control system has been successfully reset and E-Stop Mode is no longer active.
In the machine programming process, Manual Mode is developed and tested before Auto Mode. Manual Mode allows the PLC Pro to establish the equipment-level commands, permissives, interlocks, and Current-State feedback that automatic logic will later use. Once each machine element operates safely and predictably in Manual Mode, automatic sequences can be built on a proven control foundation.
In a PLC Pro machine, every actuator and every device capable of performing work is provided with the controls required to operate it and Current-State feedback in Manual Mode. The operator must be able to command each machine element deliberately, see whether the equipment is responding properly, and understand any condition preventing the requested action.
Auto Mode
Entry into Auto Mode must be deliberately requested by the operator and permitted by the control program. The request is accepted only when the installation meets the conditions required for automatic operation.
Operations in Auto Mode place automatic installation actions under program direction. Rather than commanding individual machine elements, the operator requests that the control program coordinate the actions required to perform the intended work.
Operations in Auto Mode use the equipment-level functions and Current-State feedback developed and verified during Manual Mode. Automatic logic builds on that proven foundation rather than creating a separate path to control the equipment.
On many installations, entering Auto Mode is also the operator’s request to begin or resume automatic operation. When the conditions required for automatic operation are satisfied, sequences may resume, conveyors may start, and other equipment may initiate work immediately.
PLC Pro Methods organize automatic operation around defined sequences of operation. These sequences establish where the installation is in the work being performed and determine which proven equipment-level functions should be requested next. The sequencing methods used to provide that operating context are developed in the following PLC Pro Sequencing discussion.
PLC Pro Sequencing
In Auto Mode, automatic operations are coordinated through ordered sequences. PLC Pros organize automatic operation around these sequences rather than attempting to derive equipment actions from every possible combination of input and output states. This makes machine behavior far more predictable, visible, and easier to troubleshoot.
Each PLC Pro Sequence defines a recognizable machine task with a beginning, ordered steps, completion, and reset. That structure gives the operator a clear view of progress, gives maintenance a direct way to identify what the machine is doing or waiting for, and gives the PLC Pro a repeatable method for coordinating complex machine behavior.