Posted Sun Apr 8, 2012, 2:30pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
Well now I’ve confused myself, more. I placed the thermocouple on the group body/head using a nylon strap. It actually cooled a few degrees when I hit the brew switch??? I repeated it a couple of times. Yes, I hit the steam switch to pre-warm prior. The PID was reading about 240f, average, before hitting the brew switch. Perhaps because it was strapped on the outside?? PF was off of the machine at the time.
Posted Tue Apr 10, 2012, 5:34pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
Traded a little help with a friend with a home lathe. He thinks coffee comes ground in cans and does not understand my interest in espresso, but we do projects together so we traded a little labor. I drew up a plug for the PF with a central copper tube that just allows the K thermocouple plug to insert. He made a tight press fit for me to adjust. I had to chuck it up in a drill press at home, poor man’s lathe, and use a little file to make it leak enough to simulate a double. I am not sure the substance, possible delrin, but it was available in his shop. The copper tube had to be tapped in, center drilled very tight. Interesting that while fitting and loosening the plug portion to the PF, that just as I got it to leak properly, the copper tube blew out the bottom. About 200f and 9 bar blew a 1/8” OD tapped in tube, out. We considered it, but it was so tight. While it was out, a washer was soldered on the tube to hold the length and keep it in. No real results yet, but it does work, had 198F water into the PF. I think that its best use will be to compare temperatures on my machine vs. warm up times and when raising or lowering the set temperature. I doubt the precision of my “instrument” and might have a bit of operator error.
Posted Sat Apr 14, 2012, 8:00am Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
I got a chance to measure a few temperatures with the k thermocouple device in the bottom of the PF and with a digital thermometer in a cup. Actually they were very similar. I found that the thermocouple in the plug in the bottom of the PF is not fun to use. It leaks to simulate a pull, and then drips when not pulling a shot. Easily manageable but not fun to use. The digital thermometer was a pleasant surprise. I got good and reproducible temperatures. The key, not a new idea, is to keep the thermometer hot. I left it in a container of water that I kept at 190 – 212f . When pulling a small amount of water into a Styrofoam cup, the water is falling a short distance and then hitting the stainless tube of the digital thermometer. Unless that stainless tube is almost as hot as the water the temperatures will read low. The read needs to be quick/instant as you can watch the temperature start to fall in only a couple of seconds. Put the warmed thermometer in the cup, rinse cup and thermometer with hot water, dump, place and pull.
I found that I could pull a double, wait about 30 seconds while getting ready, then read the temperature, and repeat double. I only tried 3 pulls and reads, but kept the temperature stable with in tolerance of measuring system. With the thermocouple, I had to go back and forth from pull to empty and put the plug back in, and otherwise recheck with a cup and digital thermometer. 3 doubles is more than my normal, usually 1 or 2, and uses enough water for exchange of the boiler. I am letting the PID do the temperature automatically, maintenance with the PID function, and refresh or upkeep during the shot with the alarm function and a different set temperature. I happened to use a brew temperature of 222f and an alarm temperature of on and off cycling at 234 – 235f with the inherent overshoot to about 242f. That is similar to manually flipping the steam switch earlier described by AP.
Posted Tue Apr 17, 2012, 5:41pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
A little more on thermistors, thermocouples and RTD’s. The quick read digital thermometer from HF works great and was only about $5. I could not disassemble the thermistor from the tube. It works well as a thermometer, but not so much for other uses. I got the recommended Polder instant digital thermometer from BB&B, and used a 20% off coupon, $8. It came apart without difficulty as AP previously described.
The thermistor was apparently glued into the tube on the HF one and just slid to the bottom in the BB&B. I had not paid attention to a thermistor, but it is a little, pinhead in this case, bead of ceramic or polymer, often metal oxide. It varies resistance with temperature, and is brittle and can be smashed/squashed. The voltage source is the digital thermometer battery. There are 2 wires, 1 in and 1 out, and moisture can short across, thus the protective tube. It works well out of the tube if kept dry and makes a great and economical way to measure boiler temperature. See AP work on the prior mentioned thread.
The RTD, resistance temperature detector, varies resistance with temperature and is a metal resistor. It has a larger temperature range than the thermistor, but still should be dry, 2 wires and can be shorted. Think of it as a wound resistance coil protected in ceramic, and then often inserted into a metal application tool, such as a screw or a dummy bimetal thermostat for our use.
The thermocouple is 2 wires of dissimilar metal that are welded, sometimes only twisted, together and give a variable voltage with temperature change. Not resistance, but a mini-voltage source. A good feature is that if you break the wire, you can get by fine with twisting the ends back together.
All require a calibrated reading device, then you have a thermometer with a long cable/probe. The instant read digital is usually thought of a total unit. The thermocouples could be left in place and hooked up to a PID. PIDs read multiple types of thermocouples and most read RTDs.
Posted Thu Apr 19, 2012, 8:51am Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
There was a temperature vs PID temperature and overshoot question on another thread. I thought that the answer seemed to fit in this section.
My PID is set up to allow fairly quick warm up. To do that, I allow initial overshoot and then settling back down to set temp. It then will stay at set temp or 1 degree below, that is my oscillation, and mostly at set temp. It could again overshoot after a pull, depending on whether the PID settings favor nonoscillating damping, or speed, or somewhere in the middle.
My PID will reach set temp in about 5 minutes and that is after overshoot and settling. That temperature only means that the sensor, in its spot on the boiler is able to hold its temperature. I have looked at how long it takes the PF and group to stabilize, and that is about 20 minutes. If I just look at PID, it was stable at 5 minutes, again that is only the temperature of the PID sensor. Who knows when the water actually is stable, probably sooner than the group, but, I would have to get that water through a cooler group.
The PID, in PID mode is not capable of maintaining the boiler water or boiler temperature during a pull. Since the PID is a damped control to maintain steady state temperature it is just giving blip of power in its interval, usually 1 - 2 seconds cycles. That keeps it from overshooting if damped enough. Unfortunately, damping and stability come with slowness.
If I let my machine warm up at least 20 minutes and do a styrofoam cup test, I will basically get a reproducible result from one day to the next. If I allow 5 or more minutes after a pull, I can again get the same starting temperature. You can learn to cheat some of these times using the steam switch to blast in full power, and that will show on the PID as overtemp and it will slowly oscillate back down. Stability in the brew water and mechanism does not follow the timing shown on the PID. If you first get where you can get a reproducible temp reading, then you can learn how to cheat the time, adding heat, to get "there" more quickly. You need to get the reproducibility to know where "there" is. There is a lot about temperature in SBDU in the other thread. There is a temperature study on the Gaggia that clearly shows the need for long warm up.
Try letting the machine warm up for about 30 minutes with the PF on then remove it and promptly test the temp with the styrofoam cup. Then pull a shot and then put the PF back on and wait at least 5 minutes and repeat the temp procedure. That should be close to stable. The actual temp will have the limitations of the styrofoam method, but should be close, and reproducible. I do not find getting temps quick or particularly fun, nor do I think that they would be with better equipment. Waiting for stability is like watching paint dry or grass grow.
Posted Sun Apr 22, 2012, 3:16pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
I think it would be really interesting to design the additional features into a PID so it would anticipate the shot (well delay the pump until the heating elements have started to energize) and then heat enough for the incoming flow. OR the preheating coil of copper tubing (and variations thereof) is interesting too -- or adding a thermoblock between the pump and boiler. All interesting methods.
I have thought the same thing. In short, modern control theory-based systems do exactly what you're suggesting. A PID only responds after the temperature moves away from the set point and ignores the fact that a pulse of cold water is coming. PIDs seem to be the rage and it's definitely helping. Someday, somebody will take it to the next step and build a modern control system for an espresso boiler.
Posted Wed Apr 25, 2012, 8:46am Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
Pizzaman, I read and enjoyed your topics on HB. I would also like the computer controlled device that anticipates needs, but doubt that I will see it on a Gaggia SBDU. The control system that you and AndyP describe seem unlikely to hit the low end SBDU machines and leave them at economical prices. Simple preheating with a coil is low tech and low cost and great for DIY, but that does not seem to be the interest of manufacturers for our machines. The point of the manual method is to add heat knowing that you will need it. Using the alarm function of the PID box will do similar, only concurrently, not preemptive. Both work if enough variables can be relatively fixed. You need a similar amount of water each time, or to adjust ahead of time. A 15 second blow through, unexpected, will need allowance manually or by the alarm function. Even if a computer detected, it would still have to adjust quick calories of heat in and allow them to equilibrate, or stop the shot based on flow parameters. Proper active preheat could also help, but then you have to add controls and heating for that. Passive preheat may not be fast enough. Once all of that is solved, then better and more steam. It seems more like a whole new design unless you could just add the module, like a PID. Perhaps the Kickstart machines with Arduino microcontroller....
Posted Sun May 6, 2012, 9:40am Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
I have been thinking about this a bit and I may actually cave in and buy a PID controller to experiment with.
I was thinking that perhaps mounting the TC probe lower on the boiler might result in getting a faster time to having the group warmed up. The standard mounting point on a Gaggia was engineered to try and compensate for the wide deadband of the bi-metal thermostat - but with a PID I don't think that is the best spot.
It seems to me that at the beginning of the warm up period there is a great temp difference between the top and bottom of the boiler and after a sufficient warm up period, the difference between the top and bottom of the boiler is much less.
So I suspect that putting the TC bead closer to the bottom of the boiler - you would have the heater on longer/more often during the warm up cycle - which should warm it up faster. I also suspect this would also help compensate for PF cool down when prepping and locking it back in (might kick the heater on prior to starting your shot due to the group/bottom of boiler cooling down a little when the PF is removed and locked back in).
Posted Sun May 6, 2012, 10:15am Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
I think I'll order a PID ... I look at the auber kits for $151 and it's mostly stuff I don't think I want or need. I think I'll just buy the universal PID and an SSR (about $50 - can't see spending $100 more for an instruction cd and thermopaste and precut wiring). Can one of you PID experts tell me if I'm missing the boat here?
I thought I'd mount the SSR directly to the metal cabinet of the Gaggia with thermopaste - any reason I need a larger heat sink than that? As far as the aluminum case for the PID - I'll know more when I actually have the PID in my hands but it looks to me like it doesn't need to be inside anything (at least for my experimenting stage). The PID will operate on 110V and puts out the low voltage the SSR needs, right?
I figure instead of their threaded TC, I've got plenty of K type TC wires (yeah I know T is more accurate at 200F but I'm not trying to land on Mars here). So as an experiment I would mount a few different TC beads in different locations on the boiler and then compare one at a time by switching which TC bead is connected to the PID. I should be able to see how the warm up time and shot recovery time is affected by TC placement (higher or lower on the boiler wall).
Posted Sun May 6, 2012, 11:34am Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
Wow! You, a PID! :) I bought the 1/32 universal PID, the SSR, the RTD, and the box, the black one. The Auber stuff is a good deal as long as you get it all at once, for the shipping. I could not find a better box deal than the black one, already fitted to the PID. Suit your self on the sensor, the RTD made to fit was nice, and at the time, I was just starting and did not have K type wire. You can save a few dollars. If I had it to do over, I might get the 1/16 universal PID and box. I can easily flip the steam switch, but I would put that on alarm 2 and the concurrent heater on alarm 1 as I have. The brewstat goes on the PID section of course. So, 2 set points on the 1/32 and 3 on the 1/16 if I read it correctly.
You are right about accuracy, you have to set the PID off of measured output temps anyway, over the lip or styrofoam cup, or taste. I have multiple sites to help with wiring if you like, including Auber PDF's. You know about the piggyback style spade connectors and sizes?
No heat sink, and nothing inside except the SSR. I have a 6v dc source in mine for operating the SSR with diodes. You might think of that or another SSR depending on where you are heading with the PID. You seem to like to experiment, so more function might be better???
Yes it uses 110v and draws almost nothing for current. I used 26 awg and would use 28, or probably 30 awg if I had it. All of the wires go into the back of the PID, so think small.
I did not notice the first question. I think that the mount of the thermocouple at the base/brew stat is a very sensitive location. It heats quickly and makes the temp bounce, but that is just the aluminum can. I do not notice much when I put on the PF, but, I try to have it warmed in place with the machine about 20 minutes and then off just enough to load. If it were cool enough to kick on the heater, it would probably cool the incoming water.
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