It was the day before Christmas...

Some months ago a customer mooted the idea of making some changes to an installation we did 20 years ago. We didn't really encourage further discussion as it was something we really didn't want to get involved in. Apart from anything else, all drawings and notes had been put in their possession as per in the original contract. Guess what. They lost them. Everyone in the industry advised us not to touch a thing and to walk away from the job.

However, at the beginning of last week, they got back to us and said they wanted to go ahead with the project and were installing the necessary hardware, oh, and could we get it wired up and the software changes in and tested before Christmas - after all, it was only one valve being added to the system. A less than really sharp manager agreed.

So...
Up until Wednesday I was going flat out trying to get my head round a program written by a novice programmer, for an ancient logic controller in a horribly arcane language. Then yesterday myself and a colleague went on site to do the installation. By the way, did I mention that we couldn't do any preliminary tests because they wouldn't shut down the system till Wednesday night.

Initially we couldn't get the laptop to talk to the old controller. It took us several hours to work out that not only was the connecting cable non-standard, but so was the serial communications. Eventually we got the software on, and started making cautious tests - we hadn't wired the new valve in at this point just in case there were problems. Well there indeed were!

First, the control sequence was not the same as what we'd been told, so that involved rewriting the program on site to take this into account.

Next, the original programmer liked to do 'clever' tricks with his programs. These always come back to bite you years later - and indeed we were seriously puzzled as to why values were apparently changing themselves and screwing up our corrections (remember I said we couldn't do any early tests). We eventually discovered the guy (bless his cotton socks) had discovered a way of bulk updating large blocks of data, which he'd preceded to use enthusiastically, blissfully unaware that this also corrupted values in the 'gaps' that he wasn't using but we were!

After this was sorted we started to wire in the new valve only to discover that the 'telltale' that was supposed to tell us which way the valve was positioned wasn't changing, so we went to examine the valve itself. This was along way up narrow metal stairs and gantries. When we got there my colleague came out with a burst of the most interesting invective. You see, this valve was driven by compressed air, and our electronics just supplied a trigger. This normally works fine, but you do actually have to pipe in an air supply - there was none! We then had our only short break while the factory maintenance crew frantically rigged up a temporary air supply.

Back to work, and yes the valve was switching over correctly. Wonderful. Well, no actually. being a bit cynical about these things we decided to double check which pipe went where, only do discover they'd done the plumbing in reverse. Once again we dived into the program to make it reflect what was actually happening as opposed to what they told us would happen. Only that wasn't the whole story, because now the telltale was the wrong way round, so we had to climb all the way up again. Swap the air pipes from the valve actuator, climb back down agin, and modify the program yet again.

Nearly done, time to start wrapping things up, only the display for the control system decides to die (20 years is a damn good live for a monitor!). Probably all the switching off and on finally killed it. However we had to deliver a working system, so snatched a flat screen monitor from their stores and bolted it in place behind the original safety screen.

All packed up and ready to go. Final test and a main divert valve (nothing to do with us) sticks, so we have to hang around and wait for them to clear it before we can complete the test.

We started at 9am and worked through until 10pm without stopping, except one time for a cup of tea and some crisps (supplied by considerate shop-floor staff).

Today they did a pilot run and it seems they are happy, but we won't know for sure until they run the whole system again next year.