How soon is too soon

I will expand on this a little bit, because it may not have been clear from the ancient presentation that I referred to before.
In the early stages what is important is what you want to do, not how you do it.
Suppliers are solution focused and in the early stages, many will look at a project with only a simplistic understanding the requirements and decide that it is just like one they did before and then propose a similar solution.
A good example that I observed recently involved a large and well known supplier who looked briefly at an application and decided that it needed a batch manager. As the detailed functional requirements were developed it became quite clear that standard batch manager’s just did not fit. I won’t go into the details here, but suffice it to say that in the end it was removed. Time was wasted because of the supplier’s incorrect assumptions.
Francis
www.controldraw.co.uk

In my experience asking the automation vendor to start creating any type of design (valve sequencing, etc.) before the P&IDs and Process Description are set proves to be a wasted effort. However, I think it would be useful to have the some automation architects discuss high-level project requirements (e.g. MES considerations) at the initial planning stage.

I have to keep my reputation for challenging! So here is a 10 year old presentation explaining how it is possible to delay the vendor's involvement as long a possible so ensuring that you retain control and ensure that the vendors have to compete.
Follow the link to
Platform Independent Functional Specifications
on http://www.controldraw.co.uk/presentations/Presentations.htm

I think there is not possible to apply it for all projects. It depends on customer. For customer with sophisticated staff there is not necessary to invite vendor so early, because they know what exactly need. On the other side, cusomer without vision and staff need to help from us ( it should be sometimes challenge :-) ). From our side ( producers, vendors )is necessary to inform customers what is new in business ( new products, trends, how to save they money and so on .... ).