Two integrators quote the same production line and the numbers land 40% apart. Almost never because one is gouging. Usually because the two quotes describe different projects. Here is what actually moves the number, and how to make your RFQ comparable.
1. How well the scope is defined
Scope definition is the single biggest cost driver, and it is the one you control. "Upgrade the palletiser controls" can mean a like-for-like PLC swap, or it can mean a full rewrite with new safety, new HMI screens, recipe handling and a data link to your MES. Those are not the same project, and the engineering hours differ by an order of magnitude.
A quote built on a one-line description has to carry contingency. A quote built on a machine survey, an I/O list and an agreed functional description does not. Expect the second one to be cheaper per unit of actual work, even if the number looks higher on paper.
2. Whether the hardware is specified or discovered
Controls hardware is often 30-45% of a retrofit budget. The difference between a quote you can trust and one you cannot is usually whether someone opened the panel. Existing drives, safety relays, power supplies and enclosure space drive replacement decisions that are invisible from a description.
Practical consequence: a site visit before quoting is not sales theatre. It is the difference between a firm price and an allowance.
3. Engineering hours: the part nobody itemises
Engineering is where projects quietly overrun. The work splits into roughly these buckets:
- Functional design - sequence of operation, interlocks, alarm philosophy, recipe structure.
- Code - PLC logic, HMI screens, motion, safety configuration, communications.
- Panel build - layout, drilling, wiring, tagging, point-to-point checks.
- Commissioning - dry runs, I/O verification, tuning, operator trials, production ramp.
- Documentation - as-built drawings, backups, tag lists, training notes.
Commissioning is the classic underestimate. A panel that is built correctly can still take days on site because a sensor is 4 mm out of position or a safety door interlock does not satisfy the risk assessment. Budget for site time as its own line, not as a rounding error.
4. Legacy reality: what is already in the cabinet
Older lines carry hidden cost: undocumented modifications, jumpers around interlocks, obsolete processors with no spare parts, and drawings that stopped matching the machine a decade ago. Every one of those adds reverse-engineering time.
If the existing controller is end-of-life, the honest options are usually migrate now or carry spares risk. A quote that ignores this is not cheaper, it just moves the cost to the first breakdown.
5. Uptime requirements and when the work can happen
Work performed during a two-week shutdown is priced differently from work squeezed into a six-hour Saturday window. Night shifts, weekend premiums, parallel staging and cutover rehearsals all buy risk reduction, and all cost money.
Tell the integrator your real production constraint up front. A plant that can run at 70% capacity for a week often saves more than it spends by avoiding a compressed cutover.
Four project shapes, four very different budgets
- Panel build only. Drawings and hardware are defined; the cost is materials, labour and test. Predictable, quick to quote.
- Controls retrofit. New PLC/HMI on existing mechanicals. Moderate engineering, heavy commissioning, real discovery risk.
- Machine integration. New equipment tied into an existing line, with safety, handshakes and line coordination. The interfaces are where the hours go.
- SCADA and reporting layer. Little field work, a lot of data modelling, tag structuring and screens. Cheap on hardware, expensive on definition.
If your project mixes two of these, say so. Mixed scope is the most common reason a "simple" job turns into a change order.
What to put in an RFQ so the quotes are comparable
- Machine or line description, with photos of the existing panel interior.
- Existing hardware: PLC model, HMI model, drives, safety devices, network.
- Functional requirements: what the machine must do that it does not do today.
- Constraints: shutdown windows, production targets, operator training needs.
- Deliverables: drawings, backups, source code ownership, warranty period.
- Who supplies hardware, and whether spares are included.
Source code ownership deserves its own line. Ask for it in writing. If a supplier will not hand over commented source and backups at handover, that is a lifecycle cost you are accepting.
Red flags in a low quote
No site visit, no I/O count, no commissioning line, no mention of documentation, and a delivery date that ignores your shutdown calendar. Any one of those is survivable. Three together usually means the number is a placeholder.
Getting a number you can plan against
Send the machine details, a photo of the panel interior, and the outcome you need. We will tell you which of the four project shapes you are actually in, what has to be verified on site, and where the risk sits - before anyone signs anything.