The Incredible Expanding Spec'

This is why I always specify 25-50% more I/O than what is presently required.

Also make sure there's some spare space in the control box for the inevitable feature creep and size the power supply 20-40% over what you need now. The extra cost is negligible compared to laying out a new control panel and having to buy new parts.

It also shows your boss/client that you put some forethought into the project to accommodate expansion should it be needed. And it's almost always needed.

As for a PLC vendor, these guys have always done good by me:

http://web2.automationdirect.com/adc/Shopping/Catalog/PLC_Hardware

(If you get the WinCE based CPU you can even program the thing using flowcharts)

Best of luck.

We're going head first into PLC's. All our furnaces are being changed over with new panels, PLC's and HID's. I've been spearheading this changeover.

I took this online course here:

http://www.online-tech-training.com/

It's George Brown College, in Toronto.

The company paid for it, about $1600.

There is a simulator with the course.

http://web2.automationdirect.com

I buy a lot of stuff from them.

Ya, worm hole, that would be cool, then I could get a proper pint.

I like the Allen-Bradley.

Ahhh a common cry!!... I hate it when people are told an instrument has a computer in it, as then they think they can program it to do virtually what they want!!!

Luckily, since I've run my own business I now insist on a full specification agreed by both parties, before I quote... and then when they start asking for extras I tell them how much they each cost, until they give up and shut up!!!

It worked well, even with a multinational giant company, they let me design a prototype instrument and I demonstrated it to them after 3 months work... They then all sat around and said we will need this adding we want extra this... what about adding a display for this?.... etc... etc...

I just turned to them told them I could do it but it would cost extra, about double the price... Then they all started complaining and I pointed out the agreed specification at the centre of the contract and that shut them up!!!

John.

Yeh..I call it the WIBNI (Wouldn't it be nice if...) syndrome.

Yeh and WIBNI they'd worked out WTF they wanted at trickone.
We'd carefully explained that we could give 'em a quick turnaround by writing new software for an existing product...but the down side was there wouldn't be any expansion room.... These were the same oiks that took 6 months to tell us that some pump tubes were only lasting 3 weeks.

If they are reading this...they are very nice blokes and the tea was lovely.

Del

The Allen-Bradley MicroLogix 1100 is pretty good for small jobs, skid packages... Ethernet, serial comms, and modbus RTU built-in, and online programmable. Not bad cost either, last one I bought (1 year ago) was $425 USD. The programming software cost is another "kettle of fish" however. No idea of the cost on that.

Maybe you need to start giving them the Lt. Colombo treatment. He was a fictional LAPD homicide detective portrayed by Peter Falk in a TV series and a series of made-for-TV movies. He would investigate every detail of the crime, and often he would hound the murderer with incessant questions. At the end of an encounter, the suspect would think that this man in the trench coat was going to leave him alone for a while, but Colombo would come back for "Just one more question.." Sometimes the criminal was glad to get caught, because that meant the end of the investigation!

During the initial negotiations, keep asking them if they know of anything else they want added as far as devices, programming, capabilities, etc. Maybe even suggest a few. Maybe allow a set period where they can add additional features. Then have the company lawyers put a clause in the contract that after that period ends, they have to renegotiate and start over from scratch.
I know, lawyers have a bad reputation, but even a shark has a purpose in the ecosystem.

Nice Kitty.

Del, We always write a memorandum of understanding ( MOU) when we start one of these jobs to define what sucess is. Mission creep is a poor way to run awar and a pisspoor way to do engineering. Cuz we don't seem to get paid any more for the "oh by the way...'s"

ANything above and beyond the MOU We quote as an additional job. So that we can properly bill for the Given away consulting resources of our talented and expensive engineers, dont you know.

Can't help you on the plc.

But do you think we could wire up my old commodore 64 to handle this job-

milo

Yes..this is all true.
Most customers are pretty good at sitting down with us, and I think we got caught out having come off the back of a 'Perfect job' ... clearly defined, brainstormed a new inovative solution with the customer... sensible development time, plenty of field trials. Don't s'pose I'll see another one of those for a looooooooooooooong time .
We are generally dealing with small companies who rely on our tecnical expertise...this bad job is in a newish area for us and the guys involved are just awful at communicating.... we hear now't for 6 months then they want something tommorrow. (I'd have kicked 'em into touch ages ago but there may be a bit of busines there at the end of the day...)

yep. been there myself. thats how/why we developed the MOU approach.

Hopefully a mouse family will be tendered as aresult from all your hard work.

milo

It doesn't help that it's done piecemeal. We did the first offs as agreed...and got paid.
The customer is effectively 'starting from scratch' with a new spec' and we'll get paid for the new work... so it's not really a problem as such..

Just a bloody irritation as it wastes a lot of time and effort... but hey ...calm...calm..I am getting paid for this so why should I give a toss?
(answer 'cos I like doing things in a sensible way ..._{oh no you don't...} who said that?)

Ah yes, I've been having a shufti on the web and Wiki gives a good explaanation of 'ladder programming' and I found a free down load PLC programing/simulation site.

Del

The guy that said What doesn't kill me makes me stronger." obviously failed to account for the time wasted and going over the dam as we go through one of these "Love ins."

It sounds like you are on the right track, and learning new stuff will be a great payoff.

milo

There are lots of PLC vendors all making a good product. People generally recommend the type they are most familiar with. But the problem always comes down to the total cost (hardware, software, cables, upgrades & support).

I use Allen Bradley a lot but it's very expensive (especially the software and endless upgrades). I prefer Omron, it's cheap, scalable and very reliable.

An old PC is a handy source of PCL inputs and outputs.

A game-card has 4 inputs and 4 analogue inputs. Although not very trustworthy it provides for a cheap method of input and testing.

A RS232 has at least 2 input and 2 output lines. It is accessed by direct reading or writing to the registers.

A parallel port has at least 11 outputs and 4 inputs which also come in handy. It can also be multiplexed to provide for 64 outputs.

Del,

Check this. price is available online to decide. Omron is also a comparatively cheaper and reliable option.

Thanks,

fandel (fan-of-'del the cat')(friend from india)

That's not a change in spec, it is merely marketing!

I hope you had a contract with a clause that specified what was ordered, a change process and a re-quote once the changes are signed off on.

I've got a guy who wants a simple light measurement - the contract has taken longer than the work as they keep changing things and going into another round of signatures. We don't have a signed contract yet, but he still wants the results on Friday. Like, tomorrow. Assuming I get the signed contract today, of course....

Presumably the project has an approved Control Philosophy document to which all the kittens () are working?

The answer to all the questions is along the lines of, 'yes, and this organisation will provide them when the currently-approved Control Philosophy document has been updated and a purchase order raised for the additional costs that this organisation will advise that it will incur in carrying them out'.

I just had this email turn up explaining some facts of life...

Does the statement, "We've always done it like that" ring any bells? Read this email to the end; you'll love it!!

The US standard railroad gauge (distance between the rails) is 4 feet, 8.5 inches.
That's an exceedingly odd number. Why was that gauge used?

Because that's the way they built them in England , and English expatriates built
the US Railroads.

Why did the English build them like that?

Because the first rail lines were built by the same people who built the
pre-railroad tramways, and that's the gauge they used.

Why did "they" use that gauge then?

Because the people who built the tramways used the same jigs and tools
that they used for building wagons, which used that wheel spacing.

Okay! Why did the wagons have that particular odd wheel spacing?

Well, if they tried to use any other spacing, the wagon wheels would
break on some of the old, long distance roads in England , because
that's the spacing of the wheel ruts.

So who built those old rutted roads?

Imperial Rome built the first long distance roads in Europe (and England)
for their legions. The roads have been used ever since.

And the ruts in the roads?

Roman war chariots formed the initial ruts, which everyone else had to match for fear of destroying their wagon wheels. Since the chariots were made for Imperial Rome, they
were all alike in the matter of wheel spacing.
The United States standard railroad gauge of 4 feet, 8.5 inches is derived from the original specifications for an Imperial Roman war chariot. And bureaucracies live forever.

So the next time you are handed a specification and wonder what horse's ass came up with it, you may

be exactly right, because the Imperial Roman army

chariots were made just wide enough to accommodate the back ends of two war horses.
!

Now, the twist to the story

When you see a Space Shuttle sitting on its launch pad, there are two big booster rockets attached to the sides of the main fuel tank. These are solid rocket boosters, or SRBs.
The SRBs are made by Thiokol at their factory at Utah. The engineers who designed the SRBs would have preferred to make them a bit fatter, but the SRBs had to be shipped by train from the factory to the launch site.

The railroad line from the factory happens to run through a tunnel in the mountains.

The SRBs had to fit through that tunnel.

The tunnel is slightly wider than the railroad track, and the railroad track,
as you now know, is about as wide as two horses' behinds.

So, a major Space Shuttle design feature of what is arguably the world's most advanced transportation system was determined over two thousand years ago by the width of a horse's ass.

- And -
You thought being a HORSE'S ASS wasn't important

I worked at the Promontory facility last year designing tooling and handling for several programs.

There are no tunnels between the 'factory' and railroad, but I am certain there tunnels between Utah and Florida.

Interesting note: The boosters are not transported by rail until they are 30 miles outside of the facility. They go in special two ended trucks and take up most of the road getting there.

An opposing view:

http://www.snopes.com/history/american/gauge.asp

Hey, just tell 'em what we tell ours - you can have any added features you want - may we now have whatever more money WE want?

Look on the bright side Del, at least it sounds like you were aggravated on your home turf. The first Engineering company I worked for sent me on a one day meeting with the customer to answer some questions they had about somebody esle's "skid package". They wanted to change things so it would talk to the DCS system we were installing. Five days later...

No change of clothes, no company credit card to pay for the motel, or meals. The only way I got out of being arrested for the hotel bill, was someone else from the company got there the last day and payed it. When I got back, I put in an expense report for $24.99 for every meal for every day (Yep! You guessed it, anything less than $25/meal didn't need a reciept.). The Project manager mangler refused to sign it, so I took it to the Controls manager. When he questioned it , I told him that was the "pound of flesh" I charged for starving. He signed it, and then told accounting to issue me a company credit card. I never got "caught with my pants down" like that again.

Handled well. RAH would be so proud.

milo

Hi Del

We also use Allen Bradley quite a lot, but it is quite expensive. Because of the wide range of stuff that AB manufacture, there are different cables and communication protocols. They have tried to incorporate all the variants in their comms software so it is sometimes a mission to connect and go online with a PC or Laptop.

We have recently acquired some equipment with Delta PLC's. These appear to be quite powerful and relatively inexpensive. The software is also freely available for download from their website.

Brgds, Maurice