Posted Wed Mar 20, 2013, 1:53pm Subject: Re: Custom Thermocouple for Gaggia Classic
I don't know since I had to adjust the calibration for the thermobasket and reprogram the Arduino last night. It was already midnight or so. I hadn't hooked any other inputs, so I don't have that data. It was a first try with the new thermobasket. I still have to get a bridge built so I can get more sensors installed. I'll let you know.
The total volume was roughly 1.75 oz after it was done. I did not do any surfing. I waited until the temp stablized, at around 210F or so before I hit the brew switch. If there is no drastic drop in water temp, then there was no drop in water temp. The sensor just sits in the middle of the puck and does its thing. The datalogger just records what the sensor is telling it. It's just raw data.
D4F Senior Member Joined: 15 Mar 2012 Posts: 1,191 Location: USA Expertise: I like coffee
Espresso: Gaggia Classic PID Grinder: Preciso
Posted Wed Mar 20, 2013, 2:05pm Subject: Re: Custom Thermocouple for Gaggia Classic
If I interpret correctly you are saying 1.75oz and the time, assuming seconds on the bottom of the graph, was from say 75 to 250 or about 175 seconds. If that is the case, then the temperature stability is also explained by the slow flow rate. Little cold calorie/water input. As noted, it was your trial to test the equipment and may look different at realtime espresso flow rate.
The seller mentions plastic and teflon as the coating. On the coper tubing, you can solder the tip and not drink the brew from that run, or get realatively safe solder. Copper water pipes are soldered without lead.
Just make sure you calibrate the thermocouple since all thermocouples are off to some degree. Mine all seem to be around <1% off, but I have seen them as much as 15F (~7%) off.
Be careful of plastic jackets as they don't like high heat too much. Even if they don't melt, they become extremely pliable. Depending on grade, teflon can handle as much as 500F, which should be plenty, but not all teflon can handle this high heat. The portafilter shouldn't get that hot, 250F at max (I haven't measured it).
But that's pretty cheap for a thermocouple... especially with the connector built into it.
Posted Wed Mar 20, 2013, 2:23pm Subject: Re: Custom Thermocouple for Gaggia Classic
D4F Said:
If I interpret correctly you are saying 1.75oz and the time, assuming seconds on the bottom of the graph, was from say 75 to 250 or about 175 seconds. If that is the case, then the temperature stability is also explained by the slow flow rate. Little cold calorie/water input. As noted, it was your trial to test the equipment and may look different at realtime espresso flow rate.
Oops, sorry. No, the X-axis is by row, not by seconds. The Arduino is programmed to sample approximately every 250 milliseconds. It may fluctuate a little on each count, since the Arduinos are pretty low speed and may miss the 250ms mark. The condition is as so (in psuedo-code), "If wait_time is equal or greater than 250ms, take another sample", so each sample is roughly 250ms, plus a little bit. So, you take your range and divide by 4 to get actual time.
According to the the chart, it looks like ~35-40 second shot, but that may be a bit optimistic. However, I just hit the brew switch until the 2oz glass was full. After the crema settled, the liquid was roughly 1.75oz. I left the PF in the group head a few seconds while I pulled the glass, but that is not evident in the chart. I'll have better charts with actual time intervals later. I don't have a RTC (Real-Time Clock) on my portable Arduino so I can't log time. I have it on my dev board at work, which is not so portable.
D4F Senior Member Joined: 15 Mar 2012 Posts: 1,191 Location: USA Expertise: I like coffee
Espresso: Gaggia Classic PID Grinder: Preciso
Posted Wed Mar 20, 2013, 2:42pm Subject: Re: Custom Thermocouple for Gaggia Classic
Thanks for the explanation of the time, makes more sense.
The thermocouples are rated to 399F, so no problem. I acutally cut off the connector and hooked the wire to a PID controller. Thermocouples are cheap on Ebay, and these were available in the US. Calibration is of course always worth checking. The seller mentioned plastic, but then said teflon, so not sure what they acutally are, but other sources are available for fiberglass and teflon. I noted thes just in case others are interested in inexpensive thermocouples.
I hope others get interested, not just you and I :)
Posted Wed Mar 20, 2013, 3:11pm Subject: Re: Custom Thermocouple for Gaggia Classic
Back to custom thermocouples, my new alumina ceramic tube came. This time with a 1/4" OD and... I forget the ID, but it is enough space for 3 pairs of fiber-jacket (that's just what I have to work with). The new Version 3.0 probe will have provisions for a low-level water sensor, high-level water sensor, and a steam-sensor. I don't have a bridge yet, so I won't be able to hook this up properly for some time. At least I have the material to start planning the new probe.
The probe will have three brass pills along the length of the ceramic tube. Keep in mind, I have to use a diamond blade to cut the ceramic tube, and it's still not that easy. It still cracks and chips, even with a diamond blade. I'll have three sets of wires coming out the top.
Since the bridge is the bottleneck (outside of available time), I may have time to design in a steam port to get it ready for the steam solenoid while I'm at it. We'll see. I may need to find a chunk of brass to make it out of too. My steam valve is an aluminum version. My probe-bases have been aluminum too (also what I have to work with in the shop). That way, it can be the final version of the probe and I'll be done with water and steam temp sensors.
The internal sensor is working so well it seems, that the external M4 thermocouples almost seem silly. I still have to gut the machine and rewire to the PIDruino (what a name). I found some quick disconnect terminals in inventory that I'll probably take home and cable up. I don't want to cut and splice anything inside. I'll be gutting and replacing all the cables and connectors... just in case I ever want to put it back to stock.
I finally had a chance to work on the new Version 3 thermocouple. Anyone following this thread might remember buzzes about version 3 and version 4... well, the design has changed (verbally/textually) a bit, while the actual part has changed a lot!
The mount was made from a larger block of aluminum. I would prefer brass, but I guess I can do that later. It's a bigger chunk to accommodate the steam port. Yes, I decided to just do it, since it was just an extra hole to be drilled and tapped.
The rod only has two sensors instead of three. I figured there really isn't any need to measure the steam temp, since what you're really looking for is water temperature under pressure which equates to steam/amount of steam. I don't think anyone (me) is worried about that anyway, so I left it off. So obviously, there is a upper and lower sensors for upper and lower water temps.
The upper sensor is what the PIDruino will use to go by. The lower sensor will provide a value to help minimize temp overshooting, reducing surfing effort.
The "rod" as I call it is solely attached to a modified stainless steel bolt at the top. This way, I don't have to remake the mount each time I want to make a change. The bolt comes off, taking the sensors with it, leaving the mount intact. This will come in REALLY handy when I have my steam wand reinstalled.
As mentioned above, I drilled and tapped a 1/8 NPT steam port. I haven't planned it further than that yet, but it will eventually have a solenoid valve or motorized actuator attached between the steam wand and the steam port.
This part is right off the press so I'll have to calibrate it and test it tonight.
I tested the lower sensor already and this one is way off, but I calibrate it in the software anyway.
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