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Thread: PID: Watlow vs Fuji?

  1. #1
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    PID: Watlow vs Fuji?

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Hello. Does anyone know the difference between Watlow and Fuji PID? Watlow is much cheaper, so why pay for Fuji?

    Another question, anyone know why most commercial machines dont use PID? Any potential risk or disadvantages of PID? Wouldnt think it would the cost as PID is a fraction of the cost on commercial machine?

    Thanks.

  2. #2
    Mal Dimal's Avatar
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    Re: PID: Watlow vs Fuji?

    Hi Jacky,

    While I am well versed in the technical and applications specific aspects of PID control (and others), I believe JGG, a fellow CS member in the States may be able to help you out with this specific information, as he has tested quite a few of these controllers..... You can contact him here.... http://coffeesnobs.com.au/YaBB.pl?ac...rname=jggall01 or wait until he picks up on this thread.

    All the best,
    Mal.

    P.S.
    Re: the reason for the scarcity of the presence of PID in Commercial machines..... In a nutshell, they dont really need them. Because most Commercial equipment use the Heat eXchanger method of controlling the brew water temperature, and in turn use the pressure contained above the water in the boiler to control this temperature (more temperature means more pressure) via the method of a PressureStat.... It is possible to control the Boiler Water Temperature within a couple of degrees of the desired target so therefore, a PID controller doesnt offer any real significant gains over what is already being achieved. Also, even a small low specification PID controller will be more expensive than a reasonable quality PressureStat.

    Of course, in the situation of a Dual Boiler machine, there might be some advantage to be gained by having extreme control over the Brew Water Boiler temperature via the use of PID, especially since the temperature target may be below boiling point and hence no steam production. Hope that helps,

    Mal.

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    Re: PID: Watlow vs Fuji?

    Thanks!

    Probably having much bigger boiler size also would help to stabilise temp on commercial machine.

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    Re: PID: Watlow vs Fuji?

    Mal:

    I know on boiler machines that the PID is the brains of the control mechanism but that it operates through some sort of solid state relay that can switch the power on and off to the heating elements up to 50 times per second which would be impossible for a normal thermostat. Obviously it does this in response to the temperature measurement input into the controller as an electrical input.

    I would have thought you would have something analogous to this for the pressurestat? I know a pressurestat is probably not quite as well suited to the task as it uses a membrane and so is mechanical in nature unlike a thermocouple.

    On my Bezzera there is a 3 to 4 degree temperature variation detectable at the portafilter over the temperature cycle of the boiler. It is therefore a significant variation but much less than say in a Silvia boiler where it can vary up to 11 degrees or so (I have measured this).

    The prospects for further stabilizing the temperature are there and I would have thought that a PID control system of some sort would be the only way to go.

    I have a 3.4L boiler but the temperature variation comes from the on/off nature of the pressurestat which is analogous to the operation of a thermocouple. There will always be a dead zone to avoid constant on off operation of the heating. I suppose with a bigger boiler you can reduce this somewhat as there is more stored energy and you can reduce the dead zone to maybe two degrees for a large boiler.

    I would add two that the temperature cycling can be influenced by the age and quality of the pressure stat. I have heard as they get older that the dead zone increases as the membrane gets more flex in it.

    Grant

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    Re: PID: Watlow vs Fuji?

    Hi, Jacky -

    As Mal has alluded to in his post, I reviewed a bunch of different controllers and tested several. Some I liked (Watlow, Fuji), some I didnt care for. FWIW, my least favorite was an Omega, apparently made by Cal controls, that must have been specifically designed (successfully) to be impossible to program! (Dont take this as an indictment of Omegas entire line - not intended).

    I ended up going with the Watlow line for a number of reasons:
    - they work well
    - they work well (did I mention that they work well?)
    - programming is straightforward, intuitive
    - I prefer their appearance, especially the 1/16DIN models (pure personal preference, here)
    - manufacturer rates them for use in 65C ambient environment (all others 50C)
    - I get less overshoot with their non-fuzzy logic
    - wiring connections are laid out well and facilitate placement of PID in a smallish enclosure

    I have not noticed them being very cheap, though! You can get them used on eBay, but you have to be very careful. I keep spare case gaskets, collars, buttons, bezels, etc. on hand and also disassemble, clean contacts, etc. before using. Even with all this, some have to be rejected.

    Included in my testing was a Fuji PXR3, which worked fine. It gave a little more overshoot on my machine, but was still very reliable and usable. I found it to be less intuitive to program and I didnt think it looked as good on Silvia as the Watlows (subjective, I know). I sold it with a kit to a very satisfied customer.

    -- JGG

  6. #6
    Mal Dimal's Avatar
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    Re: PID: Watlow vs Fuji?

    Hi Grant,

    Yes, pretty well all of your observations are spot-on, and you can most definitely replace the PressureStat with solid-state devices and a PID controller. Im pretty sure that Sparky has done exactly that with one of his recent experiments though in the high-pressure brew water circuit. While this gives you extremely fine and accurate control, it is a slightly more complex and expensive proposition and you would have to make your own decision about how far to go with that.

    Firstly though, you need to make a decision about the form of control you want to use, either Dual Loop Cascade Control with both Pressure and Temperature feedback, just Pressure or just Temperature. Having said that, what you would need to do, and Im sure Sparky can help you out with sourcing appropriate hardware, is to obtain the following:

    1. High resolution, low range pressure transmitter.
    2. If suitable amplifier/converter unit is not included, then one to suit the above, and/or
    3. Suitable T/couple if Temp+Pressure feedback is decided upon.
    4. PID controller with Input(s) to suit above.
    5. Suitable SSR rated for Boiler element with a 100% safety factor added in.

    If I was going to do this, Id probably want to keep it as simple as possible and just stick with a straight t/couple+PID..... both cheaper and adequate control. I guess then its just a matter of deciding on the most appropriate method of installation and appearance to suit your Bezzera (Classy looking machine by the way :)). Lots of info around on how to go about installing it yourself so Ill leave that up to you to work out. All the best,

    Mal.

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    Re: PID: Watlow vs Fuji?

    Mal,

    I will cut and paste and keep your reply handy.

    Im not really looking to make the changes on my machine although big machines like the BZ-40P have enough room inside the cabinet to hide all the equipment required. I would think so anyway.

    No, I have got to the point where I have decided that I couldnt probably even taste the difference anyway and so it probably isnt worth it. Mind you if someone could just come over to my place and do it for me and it was cheap enough...

    I guess that is the point. Most people who do this are seriously interested in the technical challenge or are VERY serious about their coffee.

    All the best,
    Grant

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    Re: PID: Watlow vs Fuji?


    I think one of the main reasons there are not more PID controlled machines is simply that most espresso machines work reasonably well as is.

    With the specialty coffee industry starting to take off and people with high profiles like Schomer in Seattle waxing lyrical about temperature stability, things are changing. There are a few PIDed commercial machines on the market now, and the list is growing. The PID control is usually used for the brew boiler in dual boiler machines. Youll find manufacturers like La Marzocco, Synesso, VFA and Reneka are now using PID temperature control.

    As for PID control of a steam boiler, it is much less effective if you use temperature. Thats because pressure is a better indicator of water temperature as it averages out any hot spots in deciding on the boiler temperature. In fact its really steam pressure youre setting anyway. However, in this age of experimentation, there have been a few reports of using a PID to control the boiler temperature in a HX machine. The most notable being Ken Foxs La Cimbali Juniors over at the Home-barista and alt.coffee forums. Id prefer to use a pressure transducer, but then you need to source one and they range in price from $300 and up. So ebay is youre only real option. You will also need one with an appropriate high temperature rating and that puts them way up in price. Then you need to make sure you have a PID controller that takes appropriate transducer output and an input. They are available, but seem to be much more expensive than units designed primarily for temperature control. So PID pressure control for a HX boiler can be a very expensive option. Hence the use of temp control as an alternative.

    Id like tighter pressure control as well. One of the cheaper options is to use a tight-band pressurestat. There are some with about 0.1 bar fluctuation, which seems to be pretty good.

    Cheers,

    Mark.

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    Re: PID: Watlow vs Fuji?

    Behmor Brazen - $249 - Free Freight
    Quote Originally Posted by Jacky link=1149831726/0#0 date=1149831726
    Another question, anyone know why most commercial machines dont use PID? Any potential risk or disadvantages of PID? Wouldnt think it would the cost as PID is a fraction of the cost on commercial machine?
    Horses for courses. Mark already gave a list of very good reasons why commercial machines dont all use PIDs. There are several more. Most cafes are money making operations, not espresso making operations. They will have one blend and probably a decaf. Not much point in taking care about the decaf; decaf usually tastes like crap ... those poor beans go through a helluva time when the caff is extracted. 95% of the business will then be milk-based drinks. Realistically, a decent HX machine probably only varies one or two degrees during a shot - absolutely fine for milk-based drinks and the espresso is probably quite good, too. For example, ECM tweaked the hell out of their barista comp machines this year and the very, very spartan tests that we did on them showed that there wasnt more than about one or two C variation across a shot. Manufacturers can tweak their temperatures to be quite stable using different thermosyphon restrictors and changing the pstat setting. If you arent changing blends all the time, this is fine.

    Additionally, PIDs are more expensive than pstats and require a lot more tweaking. Not much incentive to put one in if the consequence is that if it blows you have to spend 4-5 times the dough replacing it and heaps more time tweaking it. And if the PID screws up, thats it; your out of commission. By contrast, pstats seem to degrade slowly, so cafe owners will notice that the machine fluctuates a bit more, but will still be able to keep on operating, unnoticed to most customers. They can simply put in a call to their roaster and the service tech will come over and swap the old pstat for a new one. $50 well spent.

    Its not even like p-stats are all that difficult to tweak. I mean, if someone attached a knob connected to the p-stat on the outside of a machine it wouldnt really be all that different from using a PIDed La Marzocco or something ... just that you wouldnt be able to tweak as much and the steam pressure would change a bit as well.

    This is not to say that I dont like the idea of PID controls. The Synesso is absolutely sweet. St Ali and Maling Room both play around with a lot of blends and the ability to quickly and easily. Its also really sweet to be able to bump the steam boiler pressure up and down really quickly using the PID - you can have your staff dialling in the amount of steam pressure that theyre most comfortable with on each of their shifts!

    There are a few PID-controlled commercial HXs, too. The Reneka Viva series, for example, controls the boiler temp via a PID.

    Cheers,

    Luca



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