Many plants run mechanically sound machines with control systems that are ten, twenty or more years old. Spares are getting scarce, the people who understood the original logic have moved on, and every breakdown takes longer to fix. A controls retrofit can address all of this — if it is planned well.
Why retrofit instead of replace?
Replacing a complete machine is expensive and disruptive. If the mechanical equipment is in good condition, upgrading the controls — PLC, drives, HMI, panel — can restore reliability, add features such as data logging and remove obsolescence risk for a fraction of the cost.
1. Survey what you actually have
Retrofits go wrong when the starting point is unclear. A survey should cover:
- Existing controllers, drives, HMIs and their models
- Panel condition and available space
- Field devices — which can be reused and which need replacing
- Existing drawings, and whether they match what is installed
- Availability of the existing PLC program and documentation
If the drawings are out of date, producing as-built drawings is usually the first deliverable.
2. Define what success looks like
Be specific about goals. Examples:
- Remove dependence on obsolete parts
- Reduce breakdown frequency or diagnosis time
- Add monitoring, alarms or reports
- Standardise on one PLC platform across the plant
- Improve energy performance with VFDs
Clear goals make it possible to compare options and justify the investment. Be cautious of generic promises about savings — benefits depend entirely on the starting condition.
3. Decide the scope: full or phased
A full retrofit replaces everything in one shutdown. A phased approach — for example, PLC first, then HMI/SCADA, then drives — spreads cost and risk across several shutdowns. Phasing works well when shutdown windows are short or budgets are annual.
4. Preserve the process knowledge
The existing program contains years of process knowledge: sequences, interlocks, timers and workarounds. Before migrating:
- Back up the existing program and drive parameters
- Review and document how the machine actually behaves
- Agree which behaviours must stay the same and which should change
Program conversion tools can help, but a converted program should always be reviewed and tested rather than trusted blindly.
5. Prepare as much as possible off-site
Shutdown time is the most expensive time. Minimise it by:
- Building and testing new panels before the shutdown
- Developing and simulating PLC and HMI software in advance
- Pre-labelling field cables and preparing termination schedules
- Staging spares for anything that might fail when disturbed
6. Plan the cut-over in detail
A cut-over plan lists every step, who does it and how long it should take. It should include:
- Isolation and safety procedures
- Removal of old equipment and installation of new
- I/O checks and functional tests
- Acceptance criteria for restarting production
- A fallback plan if something unexpected happens
7. Commission and document
After start-up, update drawings to as-built, store final program backups and walk your maintenance team through the new system. A retrofit that leaves you with undocumented equipment simply resets the obsolescence clock.
Retrofit planning checklist
- Survey completed and drawings verified
- Goals and success criteria agreed
- Full vs phased scope decided
- Existing programs and parameters backed up
- Off-site build and testing scheduled
- Cut-over plan and fallback agreed
- Documentation and handover included in scope
Work with Sparsh Automation
We plan and deliver industrial retrofits and upgrades, supported by obsolete product support and system design and engineering. Tell us about your equipment to start with a survey.
This article provides general technical information. Always follow equipment manufacturers' instructions, applicable standards and your site's safety procedures.