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Sunbeam Intuitive issues

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  • #16
    Re: Sunbeam Intuitive issues

    Sorry I failed to reply - Im not getting notifications for this thread for some reason...

    Anyway, just be careful with the "cheaper" options. If youre going to have a coffee machine for the next 10 years (quite likely?) then cheaper is usually more expensive, and produces worse coffee! I know the initial outlay is larger, but you get a longer lasting machine (and a better taste!)

    Once you get out of the hardly normal stock into the Silvias, Lelits, etc you usually (not an expert here) gain the ability to replace parts more easily, hence cheaply, and parts are descendant from the semi-commercial machines, hence they last longer. This "middle range" has some complexities which vary with each manufacturer, such as temperature stability, flow control, noise, features, etc but these can be overcome by technique.

    Once you push through to the "prosumer" or "semi-commercial" range like Diadema, Giotto, etc. youll probably overcome those issues as well. This is a good spot (IMHO) to save up for in 2 or 5 or x years.

    Originally posted by 010C050314600 link=1312202818/13#13 date=1312440564
    I keep reading about "PID" - what is that?
    Barry explained the acronym, but "PID" is commonly used to mean "PID Controller". To explain it, I would explain the alternative - a thermostat. A thermostat controlled machine will switch on at (for example, depending on boiler/block/design etc.) 96 degrees and off at 105 degrees. I actually have no idea of the numbers, but that doesnt matter... This is a typical ON/OFF control (just like your oven temp control, note the oven lamp cycling on/off. This on/off time is called the duty cycle).

    A PID controller is more like an analog control, say in a cars cruise control. Image if your cars cruise control, when set for 100km/h, opened the throttle fully at 95km/h and closed it off completely at 105km/h - not a very comfortable ride! The reason you can do this with an oven is because of two things - "thermal inertia", and "your chicken dinner doesnt care"! So a PID uses funky maths (there are multiple types of PID controllers - non-decoupled, bumpless, anti-windup, teryaki chicken, not to mention PI, and P controllers) to find the right amount of fuel to maintain the car at 100km/h.

    Your chicken dinner doesnt care, but your coffee grinds do They care in the order of +/- 1 degree celcius around 94 degrees (although true snobs will vary this temperature depending on the particular roast...) When you extract from a thermostat controlled boiler direct to the grouphead (no heat exchanger or HX) then hot water going out at 90 - 99 degrees will be replaced by cold water coming in. So if you start extracting when the water is 95 degrees, you may finish when the water is 93 degrees, IF youre lucky enough to be able to tell what temp it is, which is why you hear words like "temperature surfing" and "duty cycle". If you have a PID, then the boiler is always trying to keep the water at 9x degrees, and so long as the boiler can put more heat in than is being lost by the temperature of the replacement water, youre a happy chappy!

    Thats all well and good, but I can hear you all asking "but my heating element isnt variable, so how does the PID controller vary it?". You were all asking that right? Its quite simple - a PID controller then passes the analog value (eg 0 - 100%) to a pulse width modulator (PWM). The PWM takes, say, 80%, and varies a fast switch on and off hundreds of times per second. (At work we would deal with PWMs at 8000Hz, I dont actually know what a boiler switches at, but I guess its in the order of 10-100Hz). So for a 80% load on a 10Hz switching frequency you would be on for 0.8s and off for 0.2 seconds.

    I would stress that a PID needs to be programmed well. PID control programming is part science and part magic - Ive spoken to engineers whove been using PIDs for decades and dont know how to set them up properly to minimise overshoot and instability (where you keep chasing the temp up and down like a yo-yo). I dont know who/how sets up your coffee machine PID but if you were purchasing one you would want to make sure it was set up well, or you could download some specs to set it up yourself.

    Just another reason (again, In My Humble Opinion) for going for a more expensive machine with a boiler, heat exchanger, and even an E61 style heated grouphead...

    Hm, that post ended up pretty long - probably because Im not doing so much control systems lately Hope it helps you, and others Everyone, please pick at my mistakes as usual.

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    • #17
      Re: Sunbeam Intuitive issues

      This PID Vs Thermostat discussion sounds awefully like the Positive Vs Negative feedback control systems we learnt in electrical engineering.
      Quite fascinating and worth Wikiing.
      Negative feedback, as I recall, approaches its target logarithmically (inverse of exponentially) slowing down as it approaches - this way it never turns "off".
      Positive feedback barrell-rolls to its target, overshoots it, shuts off, under-shoots it, turns on, etc, etc until it hits the target at some sort of equilibrium.

      I think thats how it goes.........

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      • #18
        Re: Sunbeam Intuitive issues

        yes and no... you can have feedback or feedforward feeding a PID controlled system, and in either case it can be set up well or not. Too much overshoot and undershoot is a sign of bad PID setup.

        The difference with a thermostat is it is TRYING to overshoot and undershoot by a massive margin on purpose! sometimes 10 degrees and hence if youre using that output directly to the group head youre in for a roller coaster ride!

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        • #19
          Re: Sunbeam Intuitive issues

          My head is aching....I just want a decent cup of coffee!! ;D

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          • #20
            Re: Sunbeam Intuitive issues

            Originally posted by 133229020D382F3B383E295D0 link=1312202818/18#18 date=1312695819
            My head is aching....I just want a decent cup of coffee!!
            I hear that! The details can get... well, detailed! But its understanding things like this that can help you choose machine A over machine B.

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            • #21
              Re: Sunbeam Intuitive issues

              so I just won an ebay auction for a used Sylvia for$354....... very excited - need to arrange for pickup.

              description said that it is in good working order - wha should I be looking for when I pick it up to ensure I dont end up with a Lemon?

              where would be the closest service place for a rancillio in bayside Melbourne?

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