Commissioning: the order that finds problems early
A sequence that surfaces the expensive faults while they are still cheap to fix.
Short answer
Prove things in an order where each step depends only on what is already proven: power and safety circuits first, then I/O point by point with the program stopped, then individual devices in manual, then sequences, then the full cycle. Skipping straight to running the sequence is what turns a wiring fault into two days of debugging logic.
The order matters more than the thoroughness, because a fault found in the wrong order is diagnosed against the wrong assumptions.
The sequence
1. Power and safety. E-stops drop the contactors. Prove this before anything can move.
2. I/O, point by point. Program stopped or in a state that commands nothing. Actuate each input in the field and watch the bit. Force each output and watch the device.
3. Devices in manual. Each motor, each valve, individually, with somebody watching the actual equipment.
4. Sequences. One at a time, dry where possible.
5. Full cycle. Dry, then with material.
Every step depends only on what the previous step proved. That is the whole design of the sequence, and it is why skipping ahead costs so much time.
The I/O check is not optional
It is boring and it is where the faults are. A crossed pair of inputs behaves perfectly until the one condition that distinguishes them, which is usually a fault condition during production.
Write down what you changed
Commissioning is when a program diverges most from its documentation. An hour capturing changes at the end saves a week eighteen months later.
Common questions
- How do you check PLC I/O during commissioning?
- Point by point, with the program in a state where it cannot command anything. Actuate each input at the field device and confirm the correct bit changes in the program. Force each output individually and confirm the correct device responds. Two people and a radio is faster than one person walking back and forth.
- What is the difference between a FAT and a SAT?
- A Factory Acceptance Test runs at the builder's works, often with simulated I/O, to prove the system before it ships. A Site Acceptance Test runs on site with real equipment and real material. The FAT catches logic problems cheaply; the SAT catches everything the simulation could not represent.
Keep reading
- Safety
SIL or PL: which one does your machine need?
Two standards, two scales, and one machine. Which one applies, how they map to each other, and why the answer is usually ISO 13849.
- Safety
Categories B, 1, 2, 3 and 4, in plain terms
Five architectures, what a single fault does to each, and the practical wiring that goes with them.
- Safety
Safety relay or safety PLC: how to decide
One is a wiring decision, the other is a programming one. The count of safety functions, not the size of the machine, is what settles it.