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Thread: Re: Can you PID an HX machine?

  1. #1
    TC
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    Re: Can you PID an HX machine?

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Yes- its been done, No...dont know why youd bother. Let google be your friend and youll find a PIDed Brewtus/Minore as well...

    There are some much cleverer hardware based ways of getting rock solid stability out of a HX machine... :-X

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    Re: Can you PID an HX machine?

    Quote Originally Posted by pszilard link=1176441637/0#0 date=1176441637
    Now, before you all shoot me - I do know that HX design uses boiler pressure to regulate the temperature! Ok? But:

    1) The pressure is measured by a pressurestat, which is just a pressure equivalent of a thermostat, which then actuates the heater switch.
    Pressurestats have a much tighter deadband and faster response than thermostats.
    2) In a closed enclouser, like the boiler, there is a direct relationship between temp and pressure.
    Thats absolute temp and absolute pressure! so a small pressure deadband is an even smaller absolute pressure deadband, which equates to a small temp deadband.

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    Re: Can you PID an HX machine?

    Paul,

    Pressurestats are far more accurate than thermostats... typically switching within 0.2 Bar or less - which is equal to less than second crack change in temperature....

    Yes, you can PID one.... but IMHO why bother..... and there are FAR more factors which affect brew temperature far more than the boiler temp..... time since flushing, amount of the flush..... even flow rate through the HX ( which depends on dose and tamp etc)....

    I think you would be wasting your time and money and then spending ages "chasing your tail" and not getting anywhere... Might make an interesting project.... thats about all.

    A PID is designed to make a small boiler more thermally stable - looking like a larger boiler which has a large thermal mass (like a HX!!!)

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    Re: Can you PID an HX machine?

    I think that Sparky said it best. PIDs dont work magic. They only stabilise temperature at one point. They are good for a single-boiler or for a multiple-boiler machine because the boiler is saturated and the water around the probe is only centimetres away from the group. When it comes to HX machines, where do you take the temperature measurement? You could probably take it anywhere if your goal is to control brew pressure ... using a pressure transducer attached where your pstat is and going by pressure probably makes sense ... but I dont know that that is really going to help you to change brew temperature that much.

    To give you an example with real figures, if you increase the brew temperature on a marzocco or a synesso (dedicated brew boilers) by first crack, your brew temperature is first crack hotter. I was talking to a tech from Nuova Simonelli yesterday who had done a heap of measurements and concluded that for one of his machines increasing the boiler pressure by a whopping 0.4 bar increased the brew temperature by a bare first crack.

    Thats not to say that PIDding a HX would be a bad idea. You dont lose anything and you can change the boiler pressure at the touch of a button, rather than the turn of a screw. But it probably isnt going to make your shot at a given temperature taste better, nor is it going to change how much water you have to flush to purge the overheated HX water (if any). Those things come down to hardware.

    The temperature of the dry group head isnt really going to tell you much about the temperature of the brew water. However, replacing the e61 bolt with a screw containing a probe for a thermocouple might give you some useful results - check out the Eric S device. The device doesnt give an accurate indication of what is happening in the basket, but it might help you to manipulate your cooling flush if you have a thermometer or multimeter with a fast enough refresh time (ie. not the cheap stuff!)

    Hope that helps,

    Luca

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    Re: Can you PID an HX machine?

    I guess if I was ever going to consider adding anything to my my Bezz, I might fit a Digital Thermometer/Thermocouple combo to the Group to aid in flushing consistency but even that would probably become redundant eventually as I get more and more proficient with my flushing technique. Other than that, I guess a suitably rated SSR to replace the Heating Element Relay/Contactor might be a good thing to do :-?.... Dont know of anything else that might have long term benefits though :-/,

    Mal.

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    Re: Can you PID an HX machine?

    Yes, agree with all the above. When steaming, a system which senses a changing pressure environment is much more useful than one which deals solely with temperature fluctuations -- despite the corrolation between the two.

    Open the steam valve and release a massive amount of steam -- the pressurestat will sense that sudden drop and respond.

    But the boiler water temperature lags behind the changing dynamics. So a PID will sense nothings changed, and therefore do nothing about it.

    The thermal stability of the system is inherently already good: HX machines have larger boilers, and pressurestats with very narrow deadbands. Why change that?

    And in the end, there may still need to be a cooling flush, something beyond the scope of the PID, the machinery, and solely in the province of the operator.

    So a PID in my opinion is a totally unnecessary additional cost, whose only "benefit" is to give a digital readout of the temperature wherever the thermocouple is attached.

    Which brings us to part two of Pszilards post: Possibly the most cost effective way to measure temperature is a DMM and thermouple mounted wherever you like.

    -Robusto


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    Re: Can you PID an HX machine?

    I reckon maybe a PID to control the length of flush to then stabilise brew temperature might be an idea. Dunno how it can be implemented though.

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    Mal Dimal's Avatar
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    Re: Can you PID an HX machine?

    Quote Originally Posted by nunu link=1176441637/0#7 date=1176468464
    I reckon maybe a PID to control the length of flush to then stabilise brew temperature might be an idea. Dunno how it can be implemented though.
    Probably depend a lot on individual machine design but where machines use some kind of switch device to initiate the brewing cycle, it would be a simple matter to configure an isolated relay output from the controller in parallel to the Brew Cycle Switch (with some additional control logic). Dont know if it would be worth it though? I think it would be better to have an embedded t/couple in the lower section of the Group feeding to a panel mounted digital thermometer..... Youd soon get used to the dynamics involved so that the timing of the flush realises the brew temperature youre after.

    Mal.

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    Senior Member robusto's Avatar
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    Re: Can you PID an HX machine?

    I have a DMM next to the machine, with a t/c on the side of the boiler.

    It serves probably no useful purpose apart from my amusement.

    I like to see the temperature fluctuation as the pressurestat cycles: 109 -111.

    -Robusto

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    Re: Can you PID an HX machine?

    Hi Paul,

    The only PM that I have from you was regarding the brewtus a while back.

    Cheers,

    Luca

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    Re: Can you PID an HX machine?

    Hi Luca, - tried PM-ing you again. Hope it worked this time Smiley
    Yep - hope my reply worked.

    Quote Originally Posted by nunu link=1176441637/0#7 date=1176468464
    I reckon maybe a PID to control the length of flush to then stabilise brew temperature might be an idea. Dunno how it can be implemented though.
    Umm ... I dont see how a PID can do either of those things. Correct me if Im wrong, though!

    Cheers,

    Luca

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    Re: Can you PID an HX machine?

    Currently the user controls the volume of flush to bring the brew temperature to a more friendly region.

    Obviously if the input is temperature, you can, in theory, control the volume of the flush based on that input. The only trouble is triggering the brew switch for that set length of time. This is on a semi-auto of course, not something with volumetric controls, since you could easily program one of the buttons to dispense a pre-measured volume of water to bring the brew temp down to where you want it.

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    Re: Can you PID an HX machine?

    While I was evaluating machines for possible PID kits, I came to the same conclusion regarding the marginal value of PID control of HX. So I dropped the idea.

    But there is at least one benefit that I dont think was mentioned in this thread: the PID makes the pressurestat go away. No more clicking, and one less mechanical item to fail and need replacing.

    I have also read posts on HB describing using a PID to keep the HX boiler at some "magic" temperature where flushing is not required (not sure why this same thing couldnt be done with the pressurestat, though). I havent figured out how/why this works, but a few regulars on HB seem convinced.

    Erics thermocouple adapters work very well, IMO. Ive used them on Silvias as well as E61s. A little bit of calibration will tell you what the offset is between the group sensor reading and the actual brew water temperature. With the exception of the very beginning seconds of a pull, the offset stays pretty constant (around 5C on a Silvia).

    Jim

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    Re: Can you PID an HX machine?

    my guess re flushing temp is that if you dont flush then the intra shot temp will gradually reduce. once flushed you should get a very stable temp. also with mutiple shots the machine would run cold.



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