Control System Specification

Yes....a very large subject and often quite a bit of wrangling goes on over this. The customer knows what he wants a system to do. (Functional Design) However, he hires a company to build his system and the actual system designer and PLC programmer knows how what he produced to customer specs does. (Functional Design) The customer is not sure how the produced design actually functions, and the producer is probably not sure exactly how the customer intends to use it in a larger system. So who does this specification? We have had some interesting meetings on this subject.

...tells the programmer how the system is expected to deliver the required results stared in the User Requirement Specification. It is used alongside the Valve Sequence Chart, the Instrument Scedule, the Alarm Schedule and the I/O Schedule to give the programmer all the needed information.

Site Acceptance Testing will use the Functional Design Specification as guidance. Anything that the system does not do that is stated in the Funcrional Design Specification goes down on the Snagging List until it is fixed.

Yes - this is exactly how it is to be.

The point I was making was in the real world we find customers who are not sure of this and try to tell the programmer to develop this. Only the end user knows how he expects things to function.

Quite. Commercial chaos can reign when it isn't written down.

Reigns supreme!

Our company has a very details FDS process, and we charge for it separately in our proposals. This puts a lot of customers off when they first see it, they seem to think this should be part of the bidding process, i.e. BEFORE a contract is written. We insist otherwise, but we don't just roll the hours it takes into the generalized "Engineering" charges. The reason is, we WILL NOT proceed until the customer has signed off on the FDS document, and many times in the past we had people stall, waste our time, give us bogus information etc. etc. and refuse to pay for the extra time. So now we quote a price to create the FDS as a "not to exceed" value, which shows them the value of cooperating. We sometimes don't get the contracts because of this, but in probably 50% of the cases, we get called back in later to fix the mess created by the low bidder who left it all undefined.

And or "mulligan" price is always a little higher...