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Thread: Importance of PID

  1. #1
    Senior Member Rocky's Avatar
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    Importance of PID

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Like several others on here whose posts I have read recently I am in the latter stages of making a decision about purchase of a machine. I am still a bit uncertain of some aspects however. I have determined that I want something that has the capacity to produce really good coffee without being tempremental. On this basis I have ruled out the Silvia as I am not interested in second guessing a machine on temperature. I was thinking that most machines above, say $1500. would have some form of "PID" that would eliminate temperature control as an issue. I am beginning to realise that this is not necessarily the case. I note for example that a soon to come VBM Levetta Super will have PID. So how important IS the PID. I have been thinking about either a VBM Domobar Piccolo or maybe a Diadema Perfetta but maybe they do not have a PID-type control? What machines in the $1500 - $2000. range DO have this or similar?

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    Re: Importance of PID

    Hi Rocky,

    Short answer is none (to my knowledge). The Expobar Minore (a dual-boiler machine) has some kind of digital controller on it but I dont think its a PID (others could confirm) and thats closer to $2.5k anyway. Most machines in the price bracket youre talking about are heat exchanger machines, which (broadly) rely on a heap of water at the right temperature and a lot of brass to provide thermostability. While in general they do that very well, the downside is that adjusting the setpoint isnt as easy as pushing a button on a PID. However if its thermostability youre after as opposed to the requirement to regularly change the setpoint, then most HX or a DB machines will be fine.

    HX machines are governed by a pressurestat, not a thermostat, and the benefit of a pressurestat is that the pressure inside the boiler is the same everywhere, whereas temperature is not. The big problem with thermostats is that to one degree or another theres a lot of thermal lag between the element creating the heat and that heat being transmitted through the water and the boiler casing up to the thermostat. So by the time the thermostat cuts out theres a lot more heat in the boiler than there should be; the same applies on the downward temperature ramp. Add to this the fact that most thermostats have a 20-30 deg C of hysteresis (deadband, i.e. it turns off at say 110C but doesnt turn back on until 80C) and youve got a system with a constantly fluctuating temperature, which makes extractions rather hit and miss. A PID attempts to get around that by learning how much thermal lag is in the system and controlling the heater power so it gets to about the right temperature once all the heat has made its way to the element - it will turn the heater power off well before it reaches the setpoint, and sometimes before any change in temperature has even been detected! On my PIDd Silvia this reduces the hysteresis to about 0.5 deg C.

    So the moral of the story is, a HX machine will most likely give you more thermostability than a single boiler machine, without the need for a PID.

    Greg

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    Re: Importance of PID

    Quote Originally Posted by Greg Pullman link=1223588081/0#1 date=1223592812
    So the moral of the story is, a HX machine will most likely give you more thermostability than a single boiler machine, without the need for a PID.
    And for 2k you can get your hands on an entry level hx machine which is a much better option IMHO

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    Senior Member Koffee_Kosmo's Avatar
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    Re: Importance of PID

    Quote Originally Posted by Pioneer Roaster link=1223588081/0#2 date=1223601245
    Quote Originally Posted by Greg Pullman link=1223588081/0#1 date=1223592812
    So the moral of the story is, a HX machine will most likely give you more thermostability than a single boiler machine, without the need for a PID.
    And for 2k you can get your hands on an entry level hx machine which is a much better option IMHO
    Thatís why I started with a HX machine
    I overlooked the Silvia and the VBM Levetta for similar reasons and more

    The best decision I made
    And I am making coffee without complications and reaping the rewards with many beautiful coffee cups daily :D

    KK

  5. #5
    Mal Dimal's Avatar
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    Re: Importance of PID

    Simply stated, PID Control is more beneficial as an aftermarket item fitted to an existing Dual Purpose-Single Boiler machine that you already own.

    Basically, it replaces the Thermostat for the reasons explained very well by Greg and, as a bonus, offers a much more convenient method for changing the brew water temperature on the fly. In essence, it offers a similar level of temperature stability to that provided by the various commercial/prosumer HX machines that incorporate a Thermosyphon Circuit (auto-recirculation of water through the heat exchanger, to the group and back again) coupled with Pressurestat boiler temperature control; typically with hysteresis of +/- 1-second crack.

    Dual Boiler machines are a different kettle of fish though, as the brew water boiler typically use some form of electronic temperature control (at sub boiling point) and sometimes in the form of an Industrial PID Controller to take advantage of an option to dial-in the brew water temperature to suit a particular bean. A pressurestat would still provide excellent control in this situation but not adjustability. The Steam boiler on these machines though, still utilise a Pressurestat for maintaining excellent temperature control and therefore steam capacity; no need for more than that.

    So, what do you do? If you have the money and dont currently own a Silvia or similar machine then opting for a decent HX machine will allow you to produce excellent coffee on an ongoing basis providing you do your part, and continue to do so for many, many years with infrequent or no component failure. Decent Dual Boiler machines will allow you to do the same but with additional complexity in both electrical and hydraulic circuits, plus the ability to dial-in the brew water temperature at the push of a button, if this is deemed a necessary feature. If you already own a Silvia et al and desire the performance of a higher echelon machine but havent got the budget for a full machine upgrade.... Then, the installation of a good quality PID Controller will allow such a machine to perform at a level similar to that of a VBM Levetta or Diadema Perfetta for example albeit with a higher level of inherent complexity. As always, you get what you pay for, including the compromises, so it comes back to individual choice once again.

    Anyway, I hope some of this info helps to identify just where PID Control fits in to the whole scheme of things. All the best Rocky... :)

    Cheers,
    Mal.

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    Re: Importance of PID

    The important point, I guess, is that a PID and nothing more will not necessarily lead to good espresso.

    The PID only gives you temperature control and adjustability at a particular point. *Whether or not that results in water of a stable and/or repeatable temperature being delivered to your coffee depends on the machine to which the PID is applied, the type of sensor that the PID uses and the placement of that sensor. *So, if you are only interested in temperature stability as opposed to adjustability, a PID might not actually help much. For example, I presume that there would be little point in adding a PID with a sensor on the top of a boiler to a machine with water inlets and outlets at the bottom of the boiler.

    Sparky is probably the most knowledgeable person on this site about all of that.

    Quote Originally Posted by Mal link=1223588081/0#4 date=1223626094
    If you already own a Silvia et al and desire the performance of a higher echelon machine but havent got the budget for a full machine upgrade.... Then, the installation of a good quality PID Controller will allow such a machine to perform at a level similar to that of a VBM Levetta or Diadema Perfetta for example albeit with a higher level of inherent complexity.
    That presumes that the only difference between the Perfetta et al and the Silvia et al is temperature variation across a shot. *I doubt that that is the case. *For one thing, the Perfetta et al have an e61 style group, which will probably make for a different pressure buildup than the Silvias group. *For another, depending on which single boiler machine you have, the brew water and cold water inlets in the boiler may be positioned differently. *Im sure that there are more differences. *Im not prepared to speculate as to the magnitude of the difference that this might make, nor as to which people are likely to prefer, but Id wager that people would pick the difference in a blind tasting.

    Yours in pedantry,

    Luca

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    Mal Dimal's Avatar
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    Re: Importance of PID

    The temperature variation/instability during a pour with a Silvia is very well documented, by Sparky and others. I had an Industrial PID Controller installed in my Imat Mokita and can testify to the stability of the brew water temperature during transit through the PF measured and logged with a t/couple and Fluke Digital Thermometer.

    Sure, a PID unit isnt going to make up for any shortcomings of a bad design but at least if the water hitting the coffee puck is always going to be held within a narrow temperature range, then you are going to optimise the potential for achieving the best quality pours from a particular machine. Providing the controller is configured so as to enhance this stability, then at least you are going to be able to extract coffee to the best of a machines capacity to do so. Im not suggesting that it is possible to make a silk purse out of a sows ear, but if a machines performance capability is being limited by poor boiler temperature control, then a PID unit WILL improve the performance, shot quality and repeatability; all else being equal (should have been included in my post above ;))

    Mal.

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    Re: Importance of PID


    If a PID is fitted correctly, it will stabilize the boiler temperature so that it doesnt vary in time (unlike the large swings that a standard thermostat allows), however that doesnt mean the temperature within the boiler is the same. As cold water sinks to the bottom and hot water rises to the top, a PID stabilized boiler will form a stable temperature strata with cooler water at the bottom and hotter water at the top.

    Heres where design makes a difference. For example a horizontal boiler, like that found in the LM GS3 and La Spaziale Vivaldi II will have a minimal thermal gradient in the boiler and do some smart thigs like keep the water inlet far away from the group feed. So you gets whats you pay for.

    There is a well known alti by the name of Andy Schecter who has spent years on modifying his Silvia to get LM-like performance and beyond. This entailed more than just fitting a PID... including heating the group directly with a second PID, adding some pre-infusion and more.... Its worth the time tracking down images of his kit, because it barely resembles a Silvia any more.

    Cheers,

    Mark.

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    Senior Member Koffee_Kosmo's Avatar
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    Re: Importance of PID

    There is a well known alti by the name of Andy Schecter who has spent years on modifying his Silvia to get LM-like performance and beyond. This entailed more than just fitting a PID... including heating the group directly with a second PID, adding some pre-infusion and more.... Its worth the time tracking down images of his kit, because it barely resembles a Silvia any more.

    Cheers,

    Mark.
    I found this Silvia PD Kit Review written by Randy G
    Here is the link

    http://home.surewest.net/frcn/Coffee/MLGpid.html

    Its great reading
    The kit is the one supplied by Jim Gaullt our sponsor and maker of PD Kits
    With reference to Andy Schecter

    KK



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    Re: Importance of PID

    I found this Silvia PD Kit Review written by Randy G
    Here is the link

    http://home.surewest.net/frcn/Coffee/MLGpid.html

    Its great reading
    thank you!!! * 8-)

    It was just as much fun to write for me... I will add that, not only is the kit very well put together and easy to install, and includes a great set of instructions, Jim is a great guy, and runs the sort of small, one-man business you feel good about doing business with. Very cool that he sponsors CS.

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    Senior Member greenman's Avatar
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    Re: Importance of PID

    I have recently installed one of Jims dual kits to my Silvia and cant be happier with the result. It was easy to instal with the excellent instructions and well laid out components.
    The temperature stability has improved out of sight and my steaming power is so much better, money well spent in my book!!

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    Re: Importance of PID

    Quote Originally Posted by Sparky link=1223588081/0#7 date=1223682713

    There is a well known alti by the name of Andy Schecter who has spent years on modifying his Silvia to get LM-like performance and beyond. This entailed more than just fitting a PID... including heating the group directly with a second PID, adding some pre-infusion and more.... Its worth the time tracking down images of his kit, because it barely resembles a Silvia any more.


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    Re: Importance of PID

    With all the stuffing around, its still a Silvia....He probably could have got a great HX or dual boiler with all the $$$ he dropped to do that ::)

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    Mal Dimal's Avatar
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    Re: Importance of PID

    Ah well, what price knowledge eh?

    That being said, I think most of what hes done could have been modelled with one of several process control sim programs or even completed manually on paper. Either way, it was probably fun to do.... ;D

    Mal.

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    Re: Importance of PID

    It may look ugly and it probably could be simplified, but it has supreme control over both temperature and pressure and passes the WBC temperature stability protocol with flying colours... have a look at this for temperature stability. I dont believe theres any machine available with this type of repeatability. Every shot within 0.5C. He calls it a reference machine.


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    Mal Dimal's Avatar
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    Re: Importance of PID

    Nice charts, no doubt about it...

    Your little "Family" must come pretty close though Mark (just trying to recall the charts you posted after your most recent mod)...

    Mal.

  17. #17
    Senior Member Rocky's Avatar
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    Re: Importance of PID

    Thanks Guys, I really appreciate your patience in the detailed explanations. I felt bad about not having done more research so I have been reading up about HX machines from the Coffee Geek & Home Barista sites. I am at a disadvantage here because whilst I have used a commercial machine in my Barista course I have no experience whatever with a Home-level machine & it is clear that they are quite different.
    The Coffee Geek article says in part about Single-boilers "The downfall is that to go from steam mode to coffee mode, the unit needs to cool or water needs to be run through the steam wand so that the temp of the water is lowered for espresso extraction" I had no idea that water could be run through the steam wand - why would you want to do this? I am assuming there is a way to switch water through the wand for the purpose of getting rid of the too-hot water.
    The article then goes on with some confusing stuff (meant to be humourous) about extracting espresso in steam mode (is this possible?) & blowing up the group. How would this happen? I am assuming it is all to do with switching back & forth between modes.
    In relation to the graph - what is this saying? Is this the temp of the water at the group? portafilter?

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    Re: Importance of PID

    Quote Originally Posted by Mal link=1223588081/0#15 date=1223798061
    Nice charts, no doubt about it...

    Your little "Family" must come pretty close though Mark (just trying to recall the charts you posted after your most recent mod)...

    Mal.
    I am not worthy.

    The Faema couldnt come close to performing well with the WBC protocol. The WBC protocol simulates shot pulling from the walk-up one off to full commercial work load, so getting all shots to be within 0.5 C is actually quite amasing. But temperature is just one aspect of this machine. He also has made a pressure profiling pump, so can dial the brew pressure exactly as he wants it.

    This machine is essentially a laboratory experiment. Apparently it no longer steams too well either. Interesting from an academic perspective, but not very practical.

    Cheers,

    Mark.

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    Mal Dimal's Avatar
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    Re: Importance of PID

    Quote Originally Posted by Sparky link=1223588081/0#17 date=1223813941
    I am not worthy.
    Dont know about that Mark... Given the time that Andy Schecter probably put into this ::)

    Quote Originally Posted by Sparky link=1223588081/0#17 date=1223813941
    This machine is essentially a laboratory experiment. Apparently it no longer steams too well either. Interesting from an academic perspective, but not very practical.
    Yep, realised that mate but very interesting for we coffee geeks.... ;)

    Mal.

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    Re: Importance of PID

    Behmor Brazen - $249 - Free Freight
    Quote Originally Posted by Rocky link=1223588081/0#16 date=1223812009
    The Coffee Geek article says in part about Single-boilers "The downfall is that to go from steam mode to coffee mode, the unit needs to cool or water needs to be run through the steam wand so that the temp of the water is lowered for espresso extraction" I had no idea that water could be run through the steam wand - why would you want to do this? I am assuming there is a way to switch water through the wand for the purpose of getting rid of the too-hot water.
    This is the only way to cool the Boiler and Group down after using Steam mode with this type of machine. They have been designed with the intention that the owner will first pull, say 2-4 shots, then switch to Steam mode to texture the milk for those shots being converted to Lattes, Cappuccinos or whatever. I guess the thinking is that if you want to produce more shots continuously and simultaneously texture milk for milk based coffees, you will step up to a machine that has been designed from the outset to cope with this mode of "normal" use. Naturally, this has never stopped anyone from optimising their use of a Silvia style machine to extract more than a handful of shots for conversion to milk coffees. Therere always ways and means of modifying ones procedure to get out of a machine what you desire... ;)

    Quote Originally Posted by Sparky link=1223588081/0#17 date=1223813941
    The article then goes on with some confusing stuff (meant to be humourous) about extracting espresso in steam mode (is this possible?) & blowing up the group. How would this happen? I am assuming it is all to do with switching back & forth between modes.
    Hmmm.... Cant see that its possible to blow-up the Group by trying to pull shots with excessively hot water thats flashing to steam. You may see the occasional venting off of steam if the Group Gasket is substandard but that would be about it. It just sounds to me as though someone was playing around for the sake of it mate and yes, they were probably switching from the Steam mode immediately prior to pulling the shot, for some odd reason :-?

    Quote Originally Posted by Sparky link=1223588081/0#17 date=1223813941
    In relation to the graph - what is this saying? Is this the temp of the water at the group? portafilter?
    Yes. The Temp. right at the top of the coffee puck to be exact. As Sparky said though, this is purely a laboratory machine and not representative of anything very useful outside of a lab..... ;)

    Mal.



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