Bushrod wrote:Fig 3 shows brew water at 235 for a group temp at 190. Figs 4 and 5 show Svs of 225 and 226. Why are these different for essentially the same group temp? . . . I'm getting some REALLY nice tasting shots.

Most of the inexpensive temperature controllers which use thermocouples as the input source report temperature in whole degrees and accept Sv inputs in whole degrees. Fuji, CAL, Love, and others can accept & display temperatures at 0.1 degree resolution. The inexpensive temperature controllers which can accept an RTD input can display in 0.1 degree resolution. To the best of my knowledge, the inexpensive temperature controllers DO NOT round off their displays, i.e. if you set Sv to be 226, a true Pv of 226.1 would display as 226 and a true Pv of 226.9 would also display as 226 when using thermocouples.

The Silvia I have is modified such that I can read boiler water temperature and Figure 3 shows the relationship between my measured boiler water temperature and grouphead temperature at two slightly different Sv's (225, 226 F). Pv, which is the typical controller display, was sensed by an Omega washer-style thermocouple. The Sv of 225 produced an AVERAGE boiler water temperature of 233.6 and an AVERAGE grouphead temperature of 190.2. The Sv of 226 produced a boiler water temperature average of 235.4 and a grouphead temperature average of 191.9.

I did not bother to check the accuracy of these thermocouples because I was looking for a specific combination which would produce the Thermofilter logged shots shown. It is relatively easy (on the machine side of things) to get excellent temperature stability and more importantly, repeatibility, when the machine has fully stabilized. Conversely, the difficulty arises when you are pulling random shots and doing a little steaming between some or all of the shots. The fact that you are "getting some REALLY nice tasting shots" is what counts.

I would be interested in running some Thermofilter tests on your machine and you could publish the results. Give me a call at 301-587-5033 if you are so inclined.

edit - 08/22/07 - I now see where your confusion could come from and it is fault of my labeling. The shots were more of an afterthought because the purpose of the post was to show the effects of PID'ing. Why the grouphead temp was lower with a higher Sv is not known. In hindsight, I should have just pulled a shot after the three hours at Sv = 225 and again with Sv = 226.

Aha, now the last piece has clicked into place for me. I didn't realize that your boiler water temp was a different measurement, independent of the PID's Sv setting.

The stability is really handy with the PID. After my morning's iced latte (after 10-15 minutes warmup!) I only drink straight shots the rest of the day with a fully warmed up machine. Not steaming has really helped with this. With my scale, every shot comes out almost exactly the same.

Unfortunately, any non-work time is family time. I'm sure you understand. I'd definitely like to do some testing, I just don't have the time! Any testing done on my machine would be very similar to what Suyi is working on. I can only hope he will publish his paper.

Obviously, I'm not getting this. So if I PID my Silvia, and want 200 degrees as the water temp for my shot, what temp is my SV on the PID?

Beavis wrote:Obviously, I'm not getting this. So if I PID my Silvia, and want 200 degrees as the water temp for my shot, what temp is my SV on the PID?

I think you are spending too much energy worrying about the specifics. Since the measurement is indirect it would be difficult to give an exact value for you. Start at about 226 to 228 and play with it. Use taste to find the temperature that works best for you. If the rest of your routine is sound you should be able to taste a one or two degree change right from the start.

The most correct, direct answer would be 225 F +5/-0, but keep in mind there are several factors that can affect the outcome.

Did you let her warm up for 45 - 60 minutes? Are you brewing in the basement or in the attic? Are you pulling 1.25 oz in 30 seconds or 2.0 oz in 25 seconds? There are other variables but you get the idea. I do know this much:

As you play around with different Sv's, let the machine stabilize at that new Sv for 10-15 minutes. Boiler temperatures can change pretty fast but grouphead temperatures take a little longer.

I know of no one who has applied a PID to Silvia that has subsequently reported it to be "not a worthwhile adventure."

Randy G. wrote:The PID, as we are using it here, is nothing more than a thermostat- it's a very advanced, digital, computerized thermostat, but still, just a thermostat. It learns how the device operates and figures out how to best control it. It turns the heating element on an off, and that's it.[] This allows you to choose a temperature and the PID maintains the boiler at that temperature at idle, and for extended periods of time. It's really nothing more than a really smart, binary switch with a near-zero dead band.

What a PID doesn't do is change the design of the machine. Once the brew switch is turned on, temperature stability is supplied by the machine's design. Boiler capacity, how the water is injected into the boiler, how it is forced out into the brewhead, etc. control the brew temperature at the coffee. Usually, the PID will turn the heating element on and leave it on during the pull, so that is a little added benefit. Why? Because it happens the same way every time, you get a consistent starting point predetermined by you and the same behavior during.. at least for the most part. . . .

IMO, an incredibly good post which implies volumes about design considerations for modern espresso machines; as well as the continued viability of well-made HX machines.

Bravo!

Rich

Thanks for the fascinating info. I presume from your location that you are using a 110volt power supply. Do you know what the difference would be for a 240 volt supply as we have in the UK. Perhaps the unPIDed temperature swings wouldn't be quite as wild.

Measured voltage here in Silver Spring, MD is 121.3 VAC when Silvia is not powered and 119.3 VAC under load at that particular outlet. Silvia's heating element resistance is 15 ohms for the US model (September 1999 production).

I see here: http://www.caffe-milano.de/wbc.ph...ml&pid=195&recno=1 that the European Silvia is rated at 1100 watts. Whether this includes the pump (41 watts) or not is not known. Anyway, I would expect a European Silvia to have a slightly faster response but the steady state temperatures should be the same as they would be determined by the thermostat rating.

My brother recorded the temperature on his UK based 240 volt Silvia using a sensor attached to the outside of the boiler. This is not a PID machine. The temperature is in degrees celsius.
The red line indicates the state of the boiler light.
Notice the huge latency of the temp curve compared to the boiler light! The cycle time seems to be slightly longer in the than the US version posted by erics but I guess that this could just be variation between machines. You'd need a sample size >1 to be sure!

paperpig wrote:The cycle time seems to be slightly longer in the than the US version posted by erics but I guess that this could just be variation between machines.

The cycle time is most affected by:

• Length of warmup
• Ambient room temperature
• Individual thermostat hysteresis

The heater wattage, higher on the 220V version, affects only the steepness of the heating portion of the cycle, and has relatively little effect on the overall cycle time.

FWIW, your brother's results look very similar to data from my own machine.

Jim