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.
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.
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
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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