Izzo Alex Duetto (US Variant) -Temperature Studies

Izzo Alex Duetto (US Variant) -Temperature Studies

Izzo Alex Duetto (US Model) Temperature Studies conducted by Jim Gallt

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Izzo Alex Duetto -Temperature Studies

I was kindly given permission to reproduce this information by Jim Gallt. Jim has a website called http://pidkits.com/ I have always considered this site to be one of the authoritative places on Espresso Machine PID conversions on the Internet. Jim has equipment, expertise and experience of similar tests on other espresso machine that was invaluable in ensuring accurate and relevant results. I feel this information has relevance to all Duetto machines, because the basic design is the same for UK/EU or US models with the only major differences being the power of the heating elements (800 and 1200W in the US version vs 1000 and 1450W in the UK/EU version)

Objectives

• Determine optimum (or nearly optimum) tuning parameters for the Gicar PID Examine intrashot temperature behavior
• Examine recovery and intershot stability with a series of closely spaced shots
• Compare behavior with steam boiler on (preheat) vs steam boiler off (no preheat)

Jim conducted these tests at the request of Chris Coffee Service in the US who sells the Duetto and supplied the machine for testing. The US PIDs operate with a 1F Fahrenheit resolution, unlike the UK/EU models, which operate with a 1C resolution, even though they can be switched into F mode.¹ So all results are in F.

Please note that the tests were all conducted with a PID Offset of 0

Equipment & Method²

• K thermocouple fastened to the top of the brew boiler (see photo below)
• K Thermocouple inserted into the grouphead using one of Eric's E-61 adapters.

The brew boiler thermocouple sensor consists of a 24 AWG type K bead probe soldered on to a thin brass plate. Clamped under the safety thermostat

Data collection via three calibrated thermometers:

• Omega HH506RA connected via RS-232 to laptop (for real-time plotting during PID tuning)
• A pair of Fluke 54 II thermometers (data uploaded using Flukeview Forms)

Testing³

For each series of shots, three plots were created:

1. combined plot of boiler temperature and grouphead temperature vs time
2. continuous plot of temperatures recorded on the Scace device vs time
3. overlaid plots of 4 individual 25-second duration shots

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No Preheat

The Duetto was allowed to warm up for several hours, with PF locked in, before logging any data. Brew water temperature estimates, recorded using a Scace thermofilter with type T thermocouple and a Fluke 54 II thermometer. Grouphead temperatures and boiler temperatures, recorded using type K thermocouples and a second Fluke 54 II. Data were recorded at 1 second intervals. The Gicar PID was set to 220F. The steady average temperature reported by the thermocouple sensor added to the top of the boiler was approximately 217.6F. This difference may be due to any number of factors. But since this offset (~2.4F) remained relatively constant throughout testing with the steam boiler off, the readings from the thermocouple give a good indication of when the boiler temperature has stabilized.⁴

Plot of intrashot profiles for 4 shots closely spaced (above)

The intrashot profiles had a very slight hump at the start, and then remained almost dead flat. The average shot temperatures (calculated by averaging 16 readings, from 10 seconds to 25 seconds) were as follows:
• Shot 1 = 200.2F
• Shot 2 = 200.1F
• Shot 3 = 200.0F
• Shot 4 = 199.7F

Plot showing boiler temperature recovery between shots & continuous record of Scace device temperatures during test session (click to enlarge)

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Preheat (Steam Boiler ON)⁵

Comparing the plot below to the corresponding plot for the no-preheat sequence immediately shows the effects of preheat provided by the steam boiler. The drop in brew boiler temperature during a shot is greatly reduced, and recovery to stable brew boiler temperature is considerably faster.

Plot of instrashot profiles for 4 shots closely spaced (above)

Again, the instrashot profiles had a very slight hump at the start, and then remained almost dead flat. The average shot temperatures (calculated by averaging 16 readings, from 10 seconds to 25 seconds) were as follows:⁶

• Shot 1 = 201.7F
• Shot 2 = 202.0F
• Shot 3 = 202.0F
• Shot 4 = 202.1F

Plot showing boiler temperature recovery between shots & continuous record of Scace device temperatures during test session (click to enlarge)

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Warm Up times

This next series give the warm up times from a cold start at 15 minute intervals and their performance vs the target temperature of 202F, ideally a minimum of 45 minutes should be allowed for the Duetto to warm up before pulling your first shot.

Other data during warmup.

Overall I think Jims data shows the Duetto to be remarkably stable either with or without preheat on and each shot pretty much the same as the last, but all the data is there for you to draw your own conclusions. The preheat effectively gives the machine more capacity and the ability to recover from changes more rapidly, but is by no means essential during normal home use. It also validates the use of the E61 group within twin boiler machines, showing that if the design is right, they can be extremely effective. Good news for those consumers who want the standard 58mm sizes, cheap widely available parts and the simplicity of maintaining an E61 group. The offset likely to give the best results on US machines is around 19F…which is pretty close to our 10C

You can read more about this on our forum and there is a specific discussion thread on the Duettos temperature stability on http://www.home-barista.com/forums/temperature-study-of-alex-duetto-t7950.html interestingly it seems to have stirred up a lot of interest and responses from people who either own other twin boiler machines, or do not own a Duetto (often the way with forums :-)

To see who wrote this page….please click the "HISTORY" tab shown on the lower part of the screen.

Footnotes

1. Retailers in the EU are able to order the PIDs with 1F resolution if they choose to…but this does mean that the machines will need to be used in F mode, as although they can be set in 0.5C Increments, you will not be able to see those settings (the display will only show whole numbers) and I suspect the resolution internally will still actually be 1F. I will be receiving a F PID shortly to convert my Duetto and will be able to report back more detail (especially as to how it handles the offset, which I suspect will remain in F despite setting the unit to C)

2. The stock machine uses a NTC thermistor, inserted into a thermowell in the brew boiler, for PID control of brew boiler temperatures. The steam boiler is controlled using a traditional pressurestat.

3. Each series of tests consisted of the following steps:

Time Activity
0:00 remove PF, flush 3 oz water through grouphead
0:45 lock PF in place, begin data logging
1:00 start Shot 1
1:25 stop shot, remove PF
2:45 lock PF in place
3:00 start Shot 2
3:25 stop shot, remove PF
4:45 lock PF in place
5:00 start Shot 3
5:25 stop shot, remove PF
6:45 lock PF in place
7:00 start Shot 4
7:25 stop shot, remove PF

Brew water temperature estimates, recorded using a Scace thermofilter with type T

4. The PID display generally showed a return to steady temperatures more than 30 seconds prior to the sensor on the top of the boiler stabilizing.

5. Following the conclusion of the "no-preheat" tests, I switched on the steam boiler and waited over an hour to let everything stabilize. An identical series of shots was pulled with the steam boiler ON.

6. For the same PID SV = 220F, shots made with preheat averaged approx. 2F hotter than shots made without preheat. A portion of this rise can be explained by a corresponding slight rise in the boiler temperature recorded by the brew boiler thermocouple and by the rise recorded in group temperature (from ~197F to ~199F). Possibly the remainder of the 2F rise can be explained by thermal effects on the PID circuitry affecting accuracy…for practical purposes this is of little consequence as an average offset of 19 can be chosen and the article Izzo Alex Duetto - Tips for best performance should give a method of usage that largely nullifies this effect.