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  • #16
    Re: Fuzzy Control

    Originally posted by mookins link=1178296541/0#14 date=1178708189
    Do you think a shagged and cheap sunbeam machine would be okay to test this stuff on since I could probably shell out for one of those no problems.
    I guess it depends on what sort of a system you want to start experimenting with.... Apart from the cheapest Sunbeam, a Ristretto, all the rest of them use Thermoblocks rather than Boilers so would require a different approach to control, more along the lines of SBs top model, the EM69xx Cafe Series which SB have gotten pretty close to sorting out. A better approach might be to buy an old Single Boiler, non-HX machine of some description that is in need of some TLC and for which components are still available should they be needed, or alternatively, you are able to manufacture.

    Originally posted by mookins link=1178296541/0#14 date=1178708189
    I have been thinking also about pre-heating water, as I found a link on another site. Looks very interesting also.
    Yep, this is indeed a beneficial addition to consider and "Sparky", the CS-er I referred to above, has already made considerable progress along these lines. It would really be worth your while to do a "search" of the forum for Threads/Posts by Sparky to catch up on where hes at. Or, maybe send him a PM and initiate some information exchange. All the best mate,

    Mal.

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    • #17
      Re: Fuzzy Control

      I shall get on it ASAP re: Sparky.

      Re: a machine I think I will just have to be patient and the right machine will present itself on here or eBay. However if anyone happens to read this and knows where I could get one from then please let me know

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      • #18
        Re: Fuzzy Control

        Just a quickie note:

        1. If you use a thermoblock (or whatever) for pre-heat, youll effectively reduce the required control band to close to zero.... which would be nice because:

        2. If you need to pull in 100ml (for easy maths) of water into the boiler, you need (100 * 4.186 * delta-T) J of energy input to keep it constant. If we assume the water in the tank is 20C, and we target 125C, we now need 44kJ (rounded up) of energy whacked in.

        My Silivia (brand new out-of-box only yesterday) has a 1.1kW heating element. So 44kJ requires this on for a fair while! So practically speaking, the control regime is going to have to deal with settling times that stretch out into the O(10s) of seconds. The temperature dropped by the boiler will, of course, not be so big because of the thermal "inertia" of the system, but the nett energy required to bring you back to setpoint doesnt change.

        So I guess if you build a uController solution, one of the first things to do is switch the heater on as soon as the operator hits the pump. You also can figure out how long to leave it on for (on full bore, of course). The lag through the system will ensure any PID/FL system does not "see" the drop until the energy of the system has re-distributed itself and you *know* already youll need to heat.... SO if you have a PID controller - I suspect bypassing it when you brew is probably a way of getting tighter control - PID out of loop, hard on for xx seconds, PID back on.

        In fact, you could probably build a quite accurate control loop from simple thermodynamics - efficiency of heaters is known, specific heats are known, temperature is known - the only nasty things are the quantity of water withdrawn and the heat loss. Be interesting to match a "blind" controller in this application against a PID or FL system...

        Cheers!

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