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Thread: PID explanation please?

  1. #1
    blunt
    Guest

    PID explanation please?

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    from what ive read i believe it to be a more precise way of maintaining constant temp and i believe it replaces the box with the points in my cimbali jr d. please forgive the lack of technical terms as im learning as i go. i dont understand all the abbreviations like PID itself. my temps fluctuate on my JR D by several degrees and im wondering if this is something i can do to my machine to stabilize it. any links to instructions or even a kit would be great,.. a thorough explanation would be great also.thanks

  2. #2
    Senior Member
    Join Date
    Jul 2006
    Posts
    3,498

    Re: PID explanation please?

    blunt,

    Machines like the La Cimbali Jnr use a pressurestat (maintains constant boiler pressure) not a thermostat (tries to maintain constant temperature.... and doesnt do it well!!)

    A PID in a HX machine gives virtually no benefit (other than profit to the seller of the PID ;D) as the pressurestat (if in good condition) will maintain the boiler temperature as well as, if not better than a PID....

    The best way to PID a HX machine (if you really feel you HAVE TO ::)) is to buy a PID which takes a pressure sensor rather than a temperature sensor and also buy the correct pressure sensor....

    So if you really want to waste money - that is the way to do it!! ;) ;D ;D

    EDIT:

    Just realised you may not understand why the brew temp changes and you need cooling flushes etc....

    The brew water is heated by passing through the heat exchanger in the boiler. The boiler is maintained at about 115C..... to produce the steam....

    If left idle the water in the heat exchanger will also be at 115C - and that will be passed to the coffee - and burn it!! When enough water has passed through the heat exchanger (cooling flush) things will stabilise to water coming out at 96-98C.... ideal brewing temp.

    Commercial machines are dynamically stable (very, very stable at that) but only when used all the time..... and that is a problem with home use of these machines.... you need to flush each time before use..... but all a PID can do is maintain the boiler temp at 115C - the same as the pressurestat.... you will still need cooling flushes.

    PIDs are only useful with devices which have static thermal stability..... like single boiler machines or each boiler on a multiboiler...... they are no real advantage on a machine which is dynamically stable - like a commercial HX machine.

    Hope that helps.

  3. #3
    Senior Member
    Join Date
    Apr 2005
    Posts
    1,176

    Re: PID explanation please?


    Ken Fox has a PID stabilized La Cimbali Jr over on the Home Barista forum. Check that out. I believe he likes the result.

    PID on a HX is a lot more trouble than for a normal single boiler. However, the benefits are simple and easy adjustment of the boiler temperature. For a CS who uses many different beans and roasts, this can be a real benfit. However, there is a caveat: Not all HX machines are created equal. For some machines, the required result can be achieved by simply fitting a digital thermometer into the group and flushing down to the required temperature. However for some machines, flushing the HX isnt so easy. My La Pavoni has heat exchangers that hold close to 1 l and is designed more as a dynamic mixer. Once you flush the super-heated water out of the thermosyphon pipes, the temp is virtually rock solid. Here fine control of the boiler temp would be an advantage to tweak the machine for different blends.

    My advice is to do your research first and be aware that the addition of a PID controller to a HX machine will require far more work and thought than on a single boiler machine.

    Cheers,

    Mark.

  4. #4
    blunt
    Guest

    Re: PID explanation please?

    excellent advice java and sparky. i will leave it alone and play with the boiler pressure. i have been doing cooling flushes but just recently. my water temp has been too low. thanks for the advice. im going to bump it up.



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