PLC and HMI programming, written to be maintained
Most industrial code outlives the person who wrote it. The difference between a machine that can be modified in an afternoon and one that has to be rewritten is entirely down to how the original was structured.
Structure matters more than cleverness
Plant code gets read far more often than it gets written — usually at 3am by somebody who didn't write it and needs the line running. Consistent naming, sequences that map onto how the machine actually operates, and comments that explain why rather than restating what. Clever code that only its author understands is a liability dressed up as an asset.
Working on plant that's already running
Modifying a live system is a different discipline from writing a new one. It means understanding the existing logic before changing it, knowing what's safe to alter online and what needs a shutdown, and having a way back if the change doesn't behave. Plenty of the work is on machines whose documentation was lost years ago, where the first job is reading the code to work out what it actually does.
Platforms
CODESYS, Rockwell Automation and Siemens TIA Portal, with CANopen and ifm devices on the fieldbus side. Where a platform isn't one that's been worked with before, it's better to say so than to learn it at your expense — though the concepts transfer more than vendors like to admit.
HMIs people can actually use
An operator interface is a safety and productivity component, not decoration. Alarms that say what's wrong and what to do about it, screens laid out around the task rather than the I/O list, and diagnostics that let a fitter find a fault without a laptop. A good HMI reduces the number of times anyone needs to call you.
Common questions
Can you work on a machine somebody else programmed?
Yes, and it's a lot of the work. Machines outlive their original integrators and the documentation usually goes with them. The first stage is reading the existing code and establishing what it does before changing anything.
Which platforms do you work with?
CODESYS, Rockwell Automation and Siemens TIA Portal, plus CANopen and ifm on the device side. If your plant runs something else, it's worth asking rather than assuming either way.
Do you do the electrical work too?
The control and low-voltage side, yes. Licensed electrical work — supply termination, motor installation and anything else requiring an electrical licence — is carried out by licensed electricians.
Talk through the scope
Grouped technical hours or a fixed-scope project, depending on how defined the work is.