Establish a usable baseline.
Confirm the exact hardware, programming software and current project files. Ask whether the original project can be opened and whether the organisation has permission to modify it. A file named latest is not enough to establish that it matches the running system.
Record the agreed backup and restoration responsibilities before development. This is a planning step, not an instruction to connect to or overwrite a live PLC. The site team should decide when the equipment can be inspected and which checks can be carried out without affecting production.
Write down the functions that must be preserved.
List current manual and automatic modes, startup and shutdown behaviour, key interlocks, alarm handling and operator permissions. Add any interfaces to upstream equipment, downstream equipment or another supplier’s system. The new requirement should be described alongside this preservation list.
An apparently small change may alter what happens after a stop, communication interruption or mode switch. These behaviours should be reviewed explicitly rather than left to inference from a new button or parameter field. Review examples with the people who operate and maintain the equipment.
Review communication changes as a separate interface.
When adding an HMI or SCADA connection, identify data ownership, available addresses, types, units and read/write permissions. A new monitoring interface may read existing information without taking over control, but that distinction needs to be designed and checked for the actual system.
For third-party equipment, confirm a responsible contact and a testable point list. Do not assume that another supplier’s internal program, network changes or licence work is included in an interface-development assignment. List those dependencies before estimating commissioning effort.
Plan verification and a controlled handover.
Agree which changes can be reviewed offline and which require the physical machine. Identify the authorised onsite person, the available test conditions and the checks that show both the new function and retained functions behave as intended. Any production intervention needs the site’s approval.
Keep a record of outstanding observations and the final files delivered. Specify the change scope, backups, explanatory notes and subsequent support responsibilities. The purpose is to make the modification reviewable and recoverable, not to imply that remote connectivity alone makes live-machine work safe.
Bring your equipment into the discussion.
Use the blank checklist to describe the required behaviour, available hardware and the boundary of the work. An initial non-confidential summary is enough to start; do not include passwords or proprietary source files.
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