budgetary quotes for PLC programming

g.robert

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Join Date
Aug 2003
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texas
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Hello everyone. I have been getting bogged down with some quotations I need to get out. My question is if anyone has a example or "rule of thumb" for estimating programming cost for a project? I am not talking about software cost, cables, hardware,start-up, documentation or anything else you could think of, just the estimate for a ladder type program.

Right now I go by "day rate" which I have set up in a spread sheet. I "guess" (based on past experiences) how many days, or fractions of, it would take to sit down and create program. It seems to me that maybe I could just have a budgetary price for each I/O.

Keep in mind that I have also in the quotation materials,skid wiring, panel shop assembly, documentation along with appropriate profit margin mark ups on the entire project. So the program cost is not the make or break item of the entire project.

I am just looking for something a little more specific to base quote on than the "I think it will take this long" method. Thanks in advance for any input.
 
Very difficult indeed.

To quote a programming job is hard. One quiz for the End-user is to ask for a detailed machine operation flow chart.

Not to scare them you just say that you want them to just write down the basic operation of the machine... in sequence.

If they give you a Grafcet type of chart then your in business. If they fail to write anything down but prefer just talking about it your in trouble.

End-users seldom hunderstand there system in the level of details needed to write a program. Although they know all of those details individually, they lack the global vision and analysys grid a programmer needs.

Soooooo, for a rule of thumb:

1. They have a poor hunderstanding, Hardware cost x 5
2. They have a very good hunderstanding and make the effort to write it down, Hardware cost x 2

Hey! Mind you, this is a rule of thumb. This thumb which was hit by a hammer many time before :)
 
Thats what I was looking for.
Does 5 X hardware for program with scetchy operational layout from user and 2 X hardware for well documented layout sound reasonable to others?

The goal is to not waste alot of time fretting over a guess and expedite the quoation, but still be in line with what other professionals come up with dollar wise.

Does anybody go by I/O. ie; 16 di + 6 do x $100.00 = cost???
 
I would go with panic mode on this one. Try to think in terms of tasks more than I/O. I/O count can be mighty misleading depending on your mix of process versus permissives.
Pierre makes a good case, assuming you used the process description to define your hardware costs. This seems to assume that the same people that can't give you a good idea of the process also cannot give you a good idea of the hardware required. I don't necessarily know that this is true.
In my case I always seem to come up short on time when I do what I consider an honest estimate. I usually try to look at it in terms of processes or tasks that plc needs to do. So I now tend to fudge my estimates accordingly. Which brings us back to the experience thing. Until you do several jobs and really know your capability, both in programming speed and process definition, make sure you bid high in terms of hours. And try to track your actual timer against your estimates so you can compensate in the future.
I'm sorry I don't have any real good suggestions. For lack of anything better I would start with Pierre's idea and go from there.

Keith
 
Robert

I would not go by the hardware price, sometime the cost of the hardware
is nothing with the amount of work.
Take the cost of hardware and add your profit.
If you have detail flow chart you can estimate the job by day rate
then add 15% for "surprises"
If you dont have detailed flow chart make it by your self and send it to your customer for approval, if he is not respond or he hesitate
or asking things which is not logical add 50% on your estimate.
The most importent rule dont start to work with out flow chart
that the customer sign on.In that case you have the right to ask for evry major change.
If you have HMI share the customer with what you doing, in the end he might not to except to what you made (last week I spend half night to change all my touch screen)You will have to do it again.

All the Best
 
HI All
Robert
We are here in egypt goes to calaculate programming cost as a function of the number of I/O's taking the into cosideration the hours needed for programming .As a role of thumb for me i multiply the no of I/O's with a factor compare the result with the result of multiplaying the expected working hours and the daily rate and of course i chose the bigger figure to offer to my client .
i never calculate as a multiple of hardware prices but some compatitor multiply by 3 as minimum.

I hope that could help.
thx
 
Thanks guys. As stated originally I, up until this point, just estimated the number of days I thought I would spend to program based on previous experiences. This method allways leaves me wondering.. I would love to have a mathmatic formula to use that would stop my constant wondering.

It should be stated that I , at this time, deal with pretty straight forward programs. Little or no math, no sub routines and very few analog signals. This is the main reason I think I may be able to utilize a I/O X $ method.

Arik, can you (or anyone else) provide sample of your flow chart? I have allways used a text logic layout to confirm program function.
Here is a small example:

Pump A in Hand
1. press start button and pump will start.
2. pump will stop if level is low
3. pump will require press of start button to restart after level has been restored.
4. press stop button to stop pump
5. pressing E-stop will stop all function

Pump A in Auto
1. Pump will start once high level is reached in tank
2. pump will stop at low level
3. pump will restart once high level is reached and repeat cycle
4. pressing E-stop will stop all function
 
Ya might get burned..........

Trying to quote based on I/O count x hardware cost is totally impossible especially as cheap as PLC hardware is becoming. As stated in an earlier post funtionality is what you have to base your price on. Simple machines require simple programs. Complex equipment may require much more sophisticated programming with little or no increase in I/O count to speak of.

There are so many time consuming things that can be incorporated that have nothing to do with I/0 count. Does it have to interface with an HMI or SCADA? Does it involve discrete control, process control, or data handling features?
Extra safety features, function interlocking, alternate functions, Emergency/start up/shut down routines etc. could be added just to name a few.
Let the customer spell out what he wants in writing. It will probably be very simple. Provide his basic machine operation. You can always add features after installation "for a small nominal fee". I have never had a customer refuse to pay for additional features if presented correctly and they usually will pay hourly for the extra programming.

If you do it right you may get hired as a permanent consultant!
Works for me! :p

Dave
 

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