Process automation

Discussion in 'Embedded Systems and Microcontrollers' started by sedanprod, Jan 18, 2009.

  1. sedanprod

    Thread Starter New Member

    Jan 18, 2009
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    Hi Guys ,its my first time doing such a project. Im in Africa and really dont have any experience practically, but the theoreticalm aspect is well covered.
    im dealing with a water treatment plant and my job is to automate the whole process. After studying it, i realized it would be feasible if a designed a batch process, with valves and pumps as intermidiaries to each stage. each holding tank would need sensors to study its xteristics at any time(t).

    i think the first stage would be to automate the opening and closing of the valves, switching on and off the pumps (coreespondingly).
    second would be to create an interface whereby it could be controlled maybe from a PDA or a simple computer.most likey a GUI.

    the problem is that i think i have to choices ,
    using micro controllers to do the job , (( unfortunately i didn't learn them yet))
    or by using analog parts like op-amp ( as integrator , Differentiator ,and so on )
    pertaining the GUI interface...i have no ideas at all.i know about PLDs and PICs but as i said earlier on...in my part of the world i have no hands-on-experience..atleast engineering wise.

    HELP!!!...PLEASE...
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    What is the general operation of the plan? At what circumstances the valves have to be opened/closed? Describe it a bit.
     
  3. loosewire

    AAC Fanatic!

    Apr 25, 2008
    1,584
    435
    Are you going to be working with fresh potent water,will the source
    be well.Are you building the plant,do you have c- license.more infomation
    will be useful.do have a working plant,or are doing irrigation. I am trying
    to q-factor your location,salt water by sea or land location. More info
    please.
     
  4. davebee

    Well-Known Member

    Oct 22, 2008
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  5. sedanprod

    Thread Starter New Member

    Jan 18, 2009
    8
    0
    More info: its a water treatment plant. I'll be needing to build a small prototype of the whole system, something that can later be integrated into the real plant.

    The system is divide into 3 main parts:

    Water is first pumped into the holding tank from a defined source, usually a lake or river. in my school;a dam. When the water first comes into the plant it is typically screened to remove sticks, trash or other large pieces of contaminants.

    the water is then pumped from the holding tank to another tank (ehere coagulation, flocculation, and sedimentation takes place) using low lift pumps. chemicals (alum and lime) are added to the flowing water before it reaches this next stage, perhaps through a dozzing pump or something.

    coagulation: Alum and other chemicals are added to water to form tiny sticky particles, called floc, that attract dirt particles.

    Flocculation: The water is stirred slowly with paddles to mix the alum with the dirty water.

    Sedimentation: The water is no longer stirred and is allowed to settle. The heavy particles (floc) settle to the bottom and clear water is then pumped out & into the filtration chamber.

    Filtration: Water passes through filters that help remove even smaller particles. Our filters consist of gravel, sand, garnet and charcoal. Each layer filters out a smaller and smaller particle. The charcoal not only acts as a filter but neutralizes taste and odor.

    Disinfection: After filtration, the water is pumped again into a clean water tank (or storage chamber)before which it is mixed with chlorine to adjust its ph (neutralizing point). A small amount of chlorine is added to kill any bacteria or microorganisms that may be in the water. It is at this step that we also add a small amount of fluoride for dental health.

    Storage: Water is then pumped from this clean water tank to elevated tanks and booster tanks through high-lift pumps. using gravity, the water is distibuted through pipes to halls of residence, departments and staff quaters in the school.

    NOTE: a compressor is employed from time time for back-washing, whereby water in the clean water tank is pumped back to the filteration tank to wash it.
     
  6. sedanprod

    Thread Starter New Member

    Jan 18, 2009
    8
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    Thanx for the response...im not to familiar with this site, so im not sure i posted my reply at the right place. but pls check out the general wall under my topic (process automation) for my reply to your post.
    thanx
     
  7. sedanprod

    Thread Starter New Member

    Jan 18, 2009
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    0
    Hey, thanx a bunch for the response. ive done my research on PLCs and it seems like a messiah to my issues. im not just too sure of the economic implications as i have no experience with PLCs. pls comment on this? is this really the most economical and efficient method?
     
  8. davebee

    Well-Known Member

    Oct 22, 2008
    539
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    Why don't you also research SCADA systems, GUI software products designed to interact with PLCs for monitoring and controlling projects.

    http://en.wikipedia.org/wiki/SCADA

    About the only alternative I know of to a PLC is an RTU, a slightly different instrument.

    http://en.wikipedia.org/wiki/Remote_Terminal_Unit

    Many projects I've worked on have many of both PLCs and RTUs all connecting to the master SCADA system.

    I think these are the best tools for your job, but then, I don't know everything.
     
  9. sedanprod

    Thread Starter New Member

    Jan 18, 2009
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    0
    Hey, davebee...u're a badguy (thats actually a compliment where im from!). Thanx a bunch for your help.would research as you've advised.
    but pls still advise on economics of these systems!
    aite....1
     
  10. davebee

    Well-Known Member

    Oct 22, 2008
    539
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    I really can't help with the economics. I'm a database guy; my job is installing datawarehouses at job sites to store several years of water quality data, as some of our laws require. I'm not involved with either buying PLCs or budgeting the overall project. Besides, the projects I worked on are huge, multimillion dollar projects, where the price of a PLC is a drop in the bucket as compared to the overall engineering costs, so I don't think I could compare the economics of the projects I worked on to your project. Here are a couple of sites where I installed data warehouses:

    http://sfwater.org/Project.cfm/MC_ID/35/MSC_ID/393/MTO_ID/649/PRJ_ID/244

    http://sfwater.org/Project.cfm/MC_ID/35/MSC_ID/393/MTO_ID/649/PRJ_ID/203

    But I would guess that for you, also, the cost of SCADA software and PLC systems would be small as compared to the rest of the hardware and engineering.

    It is possible to buy PLCs in a great many price ranges; you can get a small but functional unit for less than US $200. Buying a small unit like that might be a great way to get started learning the technology.
     
  11. sedanprod

    Thread Starter New Member

    Jan 18, 2009
    8
    0
    ...couldnt thank u enough for all ur support. would hola at you again once ive gotten a strong headway. i'll also check up on the links posted.
    Nice 1
     
  12. sedanprod

    Thread Starter New Member

    Jan 18, 2009
    8
    0
    Hey, whatsup.op things are going aite with u...long time though!
    I really do appreciate your help so far, its been really valuable. My input sensors so far are basically Float switches and Flow siwtches (rotameter); for indicating when to turn on/ off my transfer pumps. and the output sensors are solenoid valves, dozing pumps and regular pumps. im also going to be using relays (normally opened time closed).
    I need futher advise from you to get me to the next step; how do i connect or interface these sensors to my plc? i dont think its feasible to connect them directly, or is it? i've been doing some studying on the material i downloadd and im seeing stuffs on npn/pnp connections, sinking and sourcing ouputs/ inputs?...thses are not so so strange,but a lil help from you will speed things up for bearing in mind i have a due date for submission.
    i also read something about a CE123 PLC trainer and the Digital Logic circuit trainer...how handy and applicable do u think these are?
    pls anything u say is golden, believe me.

    thanx for ur continual and anticipated support!
    Dee.
     
  13. davebee

    Well-Known Member

    Oct 22, 2008
    539
    46
    Hi Dee,

    I got your PM; but can't give much advice on this - I really don't have any personal practical experience in real-life sensor to PLC connectivity. From what I've seen at my company, most analog sensors use 4-20 mA current loops to physically wire the sensors to the PLCs, and digital switches are simply wired to the PLC digital inputs.

    You may need to look at the potential noise or voltage spike probability for any particular switch and use different conditioning for each switch - a nearby switch in an electrically quiet environment may need no more conditioning that the PLC already provides, but a switch located hundreds of feet away, or that runs past big motors or other electrical noise sources may need shielded wire or an optical fibre line or a radio link or something like that.

    You don't always know what to expect when you first do the design. My company recently installed a radio link on a water job to connect a remote site to the main office over about 30 miles, but had endless problems with signal dropout, even though all the theoretical calculations and even measured signal strengths were within specification. They finally solved the signal loss problems by simply raising the antennas another 20 feet.

    But I'm really not the best guy to ask about this - you'd be better off asking someone who has some actual experience.

    The CE123 trainer looks pretty nice. It is supposed to be paired with the CE111, a little unit with a pair of liquid tanks, valves and fluid level sensors that the CE123 can operate. Together they look like they would be a great introduction to PLC process control.

    A digital logic trainer seems to me to be less useful for someone studying a water system project.

    If this is coursework, you might need to know about stuff like NPN/PNP source/sink external connectivity, but that seems like the sort of low-level detail that you houldn't spend too much time on.

    David
     
  14. sedanprod

    Thread Starter New Member

    Jan 18, 2009
    8
    0
    As i said...anythingh you say is golden, you've been quite helpful...again!
    Thanx
     
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