Posted Fri May 25, 2012, 1:44pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
I have probably not explained well, or do not understand your desire. Sorry if you have already understood this, but I will try to explain how I think that I am doing electrically what you do manually, and what I think you want to do, or want me to try.
Think of the PID as a device with at least two functions. The first function is P.I.D. controlled replacement for the brew stat. I have that set at 215 for Redbird. I allow 15+ minutes for warm up as I have learned to make that convenient. If I need the machine hot faster, I do similar to what you do, turn on the steam switch. I am not great at this because I do not do it often enough to guess the actual pull temperature. I warm it with the PF locked so it is also hot. Hot cup courtesy of Instahot, or microwave. In the past, several people have noted that a PID (function) will not help stop a brew temperature drop. The PID function is slow, using, for Auber, a 2 second interval and 10% or 0.2 second blip of heat when needed to give a shot of electricity to the heater to maintain the boiler and not overshoot. That is after initial warm up. The PID box then shifts to brew mode with the brew switch. End of PID function.
The PID alarm function is different. It is on or off, similar to your manual method, though not as smart. It does move a set point for full on and another for full off and then try to achieve that. I think that this is what you desire with the 225 degree setting. I have the alarm set to turn on with the brew switch and run the temp to 225 and then it shuts off, but no P.I.D. function on the alarm, so it overshoots. It then does not turn back on until the temp goes below my alarm setting of 224. Again some overshoot, under temperature, while the heater catches up. It is trying to hold 225 upper and 224 lower. Each cycle has less over shoot as there is less on and off time as it centers in. You do similar, but anticipate based on experience. I end up with a hotter boiler than the 215 steady state when I switch off the boiler, and alarm. Heat then goes into the water and environment. Where experience helps me is to start figuring a water temperature, or measuring, at the end of a shot and about 30 seconds later as I am ready for the next shot. Then I can adjust the upper limit or lower limit accordingly. I did this back in the thread though without the precision that you have. I can do electrically about what you do manually. If I pre-infuse for about 3 seconds and then wait a few, I get a heating head start like hitting the steam switch preshot. This function is not smart and depends on me resetting temperature if I change methods, grinds, or beans, but I learn to reset as you learn different timing of switching.
I know that there are PID functions added occasionally and functions that are not always on the generic units including Auber’s generic. Auber can get into timing on a unit very similar to the generic that you showed prior, but that only comes with Auber setup. They do not have it in the generic unit, or do not supply the necessary code to enter that function. Perhaps if this function actually works a provider could work on an upgrade that would add some smarts to the PID in the anticipation of temperature area and make this easier.
I tried to send you an email and was going to discuss some of this off line. I am not sure how much others are interested, though most of our discussion is suitable for SBDU machines, not just Gaggia. Of course our little powerful Gaggia boilers have some advantage after all.
And yes, please get a PID and continue the interesting experiments.
Posted Fri May 25, 2012, 3:26pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
I think I understood before most of what you just said -- with one exception. Does the Auber PID only have a 2 second interval and 10% or .2 blip of heat? I thought a PID would react according to how the temp was changing (heat more/less aggressively depending on how far off or how fast the temp drops) --- but his could just be my ignorance since I haven't had my hands on a PID yet (and haven't bothered to RTFM either). But otherwise, I think I understood how you are using your PID - my thoughts were that there might be a different way for you to configure that would get you the right starting temp PLUS faster recovery for a second shot.
So ... what I had hoped was that you might be able to (without too much trouble) disconnect your alarm that turns the heater on when you hit the brew switch (just to take that piece out of the equation). And then I would have you (just as a test - hopefully it is easy to set it back how you had it) set your PID temp higher. So the machine is idling at too high a temp (say 225 just for a test) ... now if you simply let it warm up, settle in on that target and then walked up and pulled a shot, YES it would be way to f'ing hot. But I'm suggesting that just before you start your shot, you flush about 1oz of that too hot water into your cup (and I had assumed - probably incorrectly - that the PID would notice the drop in temp and start aggressively bringing the heat back up more frequently than .2 seconds every 2 seconds). The intent being that your boiler (the metal outside of the boiler) would already be quite hot - but some cool water has been pumped inside which would, with some experimenting on timing, average out to the perfect shot temp of 199F (or whatever) but with the difference that the metal of the boiler is already extra hot and the PID is agressively trying to get it back and hold it at the hotter setting (but less aggressively than your current alarm setting that gives full power all the way to 225 and then overshoots).
Posted Fri May 25, 2012, 4:41pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
Great video and I did not have to lay on my side :)
"the PID would notice the drop in temp and start aggressively bringing the heat back" The PID is not really aggressive. At best, just full on, but if I understand correctly, it only goes full on, full time, when out of the proportional band. My second set point is aggressive as it is not under proportional control and just the equivalent of your on and off switch. The reason that the "PID (function) does not help intrashot temps," as often stated, is that the range is in the proportional band and damped and concerned with no overshoot. The alarm is my work around. Setting a higher PID function temperature would "not help intrashot temperature," proven in the past by others. I can set the alarm temperature down, less overshoot, but that is about where it works for my 215-6 temperature to keep it hot, 199, for the next shot. I am not trying to avoid your suggestion or frustrate you. I can pull one disconnect and shut off the alarm and easily set the PID. I do not have the instrumentation for good testing. My boiler ends up hotter and has the system ready for a second shot. It works within my poor limits of testing.
I have referenced an article about tuning a PID, actually how a PID works as well, that I found useful even if you just mostly look at the pictures.
Posted Fri May 25, 2012, 5:54pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
I looked back through the thread and perhaps found a missing link, the Solid State Relay. The SSR uses PID or PID alarm input to turn on and off a solid state switch. A hot line of the brew stat is used to carry the current and the SSR input from the PID side controls that in an On and Off fashion. The heater still sees on and off, just more rapidly than a manual switch would tolerate for very long. That is why I noted Andy as PID early on. The PID and the SSR act together to control the machine.
If I understand the PID correctly the "P" is the range where the PID acts, based on a percentage of the total sensor range. Out of that range and the PID is an on or off switch. That allows for rapid warm up without damping until its range is entered. Round numbers for understanding, if the sensor has a range of 1000 degrees, then a P value of 5 is 50 degrees and the PID would signal full on until 50 degrees under the set point. Smaller P gives more rapid initial heat up and more possibility of overshoot especially in the Gaggia with small mass and high heat. At more stable state, in the P range, the response is proportional, based on timed intervals of blips of current. Still, the PID only sends a small dc current to the dc SSR telling it to switch the 110v on or off.
The Alarm can do the same; flip the SSR on and off, if wired correctly without being proportional or damped. It can have a second set point and could indeed trigger an alarm if the temperature reached that set point, thus the alarm designation. It is also used to control the steam temperature if that is desired. All by set point and flipping the SSR on and off.
My explanation may expose my misunderstanding, so feel free to correct.
Posted Sat May 26, 2012, 5:41pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
I had a really different idea just today ... if you really wanted to be creative ... If you were to open the Gaggia boiler and take a coil of thin copper tubing INSIDE the boiler from the inlet to the standpipe and seal it so the incoming water doesn't ever touch the boiler water. It just flows through the copper tubing that is inside the boiler water (turning the Gaggia boiler into a tiny Heat Exchanger). THen you could find a much higher temp (probably about 245-255F as a guess) to leave the boiler idling while your brew water stays inside the copper coil heating up to just the right temp (just right after a ton of experimenting to get the length of copper tubing just right and find the right idling temp for the boiler).
Well ... I'm sure that idea works a lot better with a large volume boiler - I imagine it would still pull the heat down pretty quickly on a tiny Gaggia boiler ... but it would solve the problem of getting the boiler up to heat for steaming milk as you would always be at steaming temps. Always something interesting to experiment with.
BTW ... I have a very old Gaggia with a larger boiler. I posted this YouTube video pulling several shots back to back with barely 15 seconds of recharge time (I hit the steam for about 10 seconds at the end of the shot, turn it off and 3-4 seconds later start another shot). I'm not doing any heat cycling on that machine other than the steam switch between shots. The boiler is much larger so you see that there isn't much temp drop during the shot. http://www.youtube.com/watch?v=Wo97AGMLqb0
Posted Sat May 26, 2012, 6:52pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
Your Hx idea is interesting. One would probably have to trial and error the tubing length and volume and contact time. Water for the boiler and separate source for the tubing? 2 pumps, and 2 inlets? Would the system live at steam temperature and not have pressure/leak problems
I see that you have another thread on the Old Coffee and video and will post there.
Posted Sat May 26, 2012, 7:59pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
I think I understood how the SSR works. I only meant "aggressive" as turning the heat on for longer than the quick blip it normally does when idling. But I was thinking of configuring the PID to cycle a little more frequently and to stay on a little longer each cycle.
The main thing I was driving at was rather than trying to keep the boiler idling at the perfect set point (where it has to have been sitting for 10 minutes or longer in order to be stabile) - instead let it idle at the temp I use when pulling back to back shots (which is hotter to make up for the fact that it hasn't been sitting 10 minutes). Then you would have to pull one blank shot (flush) before you pull your first real shot - and you could pull back to back shots with a shorter recovery wait time.
It wouldn't be as fast as I'm doing with the OWC (because that has a larger boiler) - but I bet you could get it down to 30 or 40 seconds between shots with a little practice and some creative configuration of the PID parameters.
The HX idea probably wouldn't work ... it's a tiny boiler - but it's interesting to think about.
I think that I am doing that already and do not have the tools to document it. If not, then I just need to adjust the PID alarm temperature. The PID function temperature allows me to idle safely. The alarm temperature is like you raising the temperature with a switch. The PID through SSR is switching on and off to achieve a desired temperature. Using your example, a Polder digital thermometer could be placed like you have it. The PID would show temps bouncing up and down, and the Polder the “average.” The PID alarm function should be able to raise the boiler temp to the desired Polder temp. 30 seconds, or less of off time would quickly be made up when the brew switch is again hit. Perhaps I would set a little higher to compensate for the 30 sec off. If you were actually preparing a shot, then you would be off of the switch also.
While you make a great thinking PID, I think the switch portion of you can be replaced :). If I understood your prior work, then you could start with a warmed up machine and draw a shot, switching while you draw, and end up ready to draw a second. You do not have to start with super hot boiler before??
Posted Sun May 27, 2012, 7:29am Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
A few posts back, it seemed that you were looking to have two modes of the PID, one for holding steady and one for brewing. Did I understand correctly?
If so, you can use a two-channel PID controller and wire the connections to the SSR through a double-pole double-throw (DPDT) switch so that just one of the two PID channel's output signal is actually used. By setting the PID parameters the way you want (but differently) for each channel you can easily make the switch between modes by moving the DPDT switch. If a two-channel PID controller wouldn't work, certainly two separate PID controllers would.
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