Rancilio Silvia Performance with/without PID

[erics]

OK, I realize this may be "old hat" to many of you but I thought it might be interesting to post some graphs of how Silvia performs with and without a PID mod and to, rather dramatically, show the effects of applying a PID.

The first graph shows the normal variation in boiler water temperature and grouphead temperature over a three hour period using the stock 100 C button thermostat. Early Silvia's (like mine) had the 110 C brew thermostat but this was replaced with the 100 C version - I believe in 2001. Data was recorded on an Omega HH506RA using Omega thermocouples into the boiler and into the grouphead via thermocouple adaptors.



This next figure is simply a magnified view of 1-1/3 cycles of heating-cooling Silvia, again with the stock thermostat.



The next graph shows the results after connecting the PID. Note that the controller is sensing the temperature at the top surface of the boiler via a washer style thermocouple and I am using the Omega HH506RA to measure boiler water temperature and grouphead temperature at the same time over about a three hour period - data points at 10 second intervals.



And now come the shots - but first a description of the PID and temperature measuring setup. The PID is a typical, inexpensive unit (Auber Instruments, Syl-1512), the SSR is a 25 amp unit from Omega, P/N SSRL240DC25, and the thermocouple is a washer-style Type T thermocouple, also from Omega, P/N WTT-6-36-TT. The TT at the end gets you PFA insulation vice the usual cloth insulation. The PID was simply auto-tuned at around 203 F (10% below typical Sv) and left alone. No attempt was made to improve the PID performance - it was very adequate as is. Shot No. 1 is with the PID's Sv set at 225 F - I believe this particular PID reads 1 or 2 degrees low but I was looking at other parameters to try for that 200 F shot temperature.



Shot No. 2 has the PID's Sv set at 226 F.

[jggall01]

Very helpful info, especially, I think, for temperature surfers.

Your data confirms something I began to suspect after I did some similar testing (on a much more limited scale). That is, the grouphead temperature cannot get where it needs to be with the "new" 100C thermostat. Your data shows a peak grouphead temperature of around 180F for the stock thermostat (if I am reading the graph correctly).

But I find I get the best shots from my Silvia when the group temperature is in the mid to upper 190's (F) at the start of a shot. Below this temperature, i.e. when my machine has not completely warmed up, and the group steals too much heat from the brew water.

Did you make any thermofilter readings with the stock tstat? When I did that, even when pulling shots at the absolute peak of the boiler cycle, I did not get any brew temperatures above 195F with the stock 100C thermostat.

Jim

[Randy G.]

Nice work, Eric.

Your work on that points out the strengths of Silvia and why it is a machine that has gained such popularity and has been around for so long (about 8 years now, I think...?) . More importantly, it shows the benefits of PID'ing this machine. I have stated in the past:

-Just 'using' Silvia is like standing on the tracks, blindfold in place, waiting for the train.
-Time surfing (light on, wait 45 seconds, pull shot) is like standing on the tracks, running a stopwatch, and stepping off the tracks to see if the train is there, and hoping you got the timing correct.
-Temp surfing with the digital readout was like trying to jump on a train as it ran through the station at speed.
-PID is a leisurely boarding onto a stopped train with champagne served at the door by a very gracious porter..

For those new to Silvia and the PID, here are some notable resources which document its history. You will notice that the names are quite familiar! The tinyurl links are to Google Groups archives of the articles listed:

Tricked-out Silvia
Andy Schecter
Feb 4 2001, 12:43 am
http://tinyurl.com/78eos

Temperature study of my Silvia (looong)
Greg Scace
Feb 5 2001, 12:50 pm
http://tinyurl.com/awhtp

Proportional Temperature Control for Silvia
Greg Scace
Mar 5 2001, 6:32 am
http://tinyurl.com/7m43d

PI Silvia Tempmeasurements (really)
Greg Scace
Mar 24 2001, 2:39 pm
http://tinyurl.com/d2rof

SCHOMER'S # 27
Prof. Brian L. GOMES da COSTA
May 21 2001, 5:41 pm
http://tinyurl.com/d4lud

Tricked-out Silvia part 3: Procon pump!
Andy Schecter
Apr 15 2001, 1:10 pm
http://tinyurl.com/8crek

Construction, Thermodynamics and heat transfer of espresso machines - Ok I ranted a bit already
Greg Scace
Sep 20 2001, 1:03 pm
http://tinyurl.com/72omq

Tricked-out Silvia: heated brew head
Andy Schecter
Sep 16 2001, 4:26 am
http://tinyurl.com/ahvf8

[Bushrod]

Where are you measuring the grouphead temp?

I find all of this really fascinating!

[Beavis]

I'm still trying to decide whether to PID or not and Randy, a post of yours (I'm pretty sure it was you), caught my eye. I THOUGHT that with the PID, it got you to the correct temp to hit the "brew" switch AND provided temp stability AFTER the "brew" switch was hit. The post I saw said something like "after you hit the brew switch, the PID does NOTHING". Can someone please confirm does the PID only help BEFORE you hit "brew" or does it continue AFTER you hit "brew".
Thanks!
Can we also review the DIFFERENCE between the stated temp on the PID and the water temp from the group? 23 degrees?

[HB]

Can someone please confirm does the PID only help BEFORE you hit "brew"...

Yes, that's right.

Can we also review the DIFFERENCE between the stated temp on the PID and the water temp from the group? 23 degrees?

Not that it matters, IIRC, it's around 29F for PID'd Silvia. Jim Gallt (pidkits.com) presets them to 228F.

[erics]

For Rich -

Grouphead temperature is measured with a thermocouple adaptor - see here:

http://www.home-barista.com/forum...-silvia-t1352.html

[Randy G.]

....Can someone please confirm does the PID only help BEFORE you hit "brew" or does it continue AFTER you hit "brew".

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.*1 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.

Fortunately, Silvia's design has been proven to provide excellent control of brew temperature throughout the pull, so the PID really does supply beneficial results.

*1 A PID can control water, or any liquid like injection plastic, flow, air flow, the speed of a conveyor belt, lighting levels, etc... any such process.

[gabriel]

Not that it matters, IIRC, it's around 29F for PID'd Silvia. Jim Gallt (pidkits.com) presets them to 228F.

I don't think there is a constant value you can use, it depends on many variables.

When I got my PID Silvia from David Blane (using the Love PID) I borrowed from Peter L. his Scace device and spent few days measuring.

I got the following results:

after 30-40 minutes of idle time the with PID set to 210 I get 195F on the coffee (this was done after making sure to clear steam pockets and flushing 2 oz water to stabilized the GH)

when I wanted to work with 200F I had to go to 218F on the PID and not 215F (probably because the diff between the GH base temp and the GH target temp is bigger the higher you go )

Also when the machine was sitting idle for long periods (say one hour) the temp would be much higher so you need to lower the PID setting maybe by 1 degree F every 30 minutes.

All of this was done on sea level with ambient temp of around 70F
Higher altitudes or ambient temp will probably show different values

A more predictable system should use a PID on a E61 style GH with boiler water circling through the GH (like the lovely Alexia).

/gabi

[Bushrod]

Thanks, Eric. I must have missed that whole thing! Now, I almost understand the correlation between group temp and brew temp. Unfortunately, my brain is now hurting.

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 have an Auber PID with the platinum screw-in RTD sensor in my Silvia. Suyi sent me a draft of a temperature performance study he's working on. He agrees that the difference between the Sv and the brew temp increases as the Sv is increased. If you've seen this draft study, I'm using Figure 8 for my Sv setting. According to this, 216 on the boiler will yield about 200 on the brew temp. With the Sv set at 216, I'm getting some REALLY nice tasting shots.

[erics]

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.

[Bushrod]

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.

[Beavis]

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?

[Randy G.]

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.

[erics]

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."

[boar_d_laze]

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