Thermologging the new pod-capable Silvia (long)

[JimG]

Motivated by a question that was raised on AC a few days back, here are some thermolog data from a 'new' pod-capable Silvia.

Boiler temp data came from a 30AWG type T flattened-bead probe that was clamped directly below the brew stat. Thermofilter data came from the T probe in one of Greg's devices. All data was read on Omega HH506RA, logged via RS232 to a PC, then analyzed and plotted in Excel.

Boiler temp control provided by Watlow SD3C with SV = 228F. The PID sensor is a type T washer probe mounted below the leftmost screw at the brew tstat.

Test procedure:
1. Turn on machine, warm up for 30 minutes with boiler temp at 228F.
2. Pull 3 back-to-back shots without removing the Thermofilter. No flushes between shots.
3. Pull another 3 back-to-back shots, but this time mimic actual use. Thermofilter removed between shots, and short "cleaning flushes" through the portafilter with empy basket in place.
4. Let the machine restabilize, then pull two "walkup" shots, around 12 minutes apart.

First graph (below) shows the entire timeline of the test, start to finish. Shots are identified by the minute they occurred.

Second graph (below) shows the 3 back-to-back shots that were pulled without any flushes. I just waited until the boiler temp had been stabilized for a bit, then pulled the next shot. The Thermofilter was not removed between shots.

Third graph (below) shows another round of 3 back-to-back shots, but this time I tried to simulate what a real user (e.g. me) might do when pulling multiple shots. So I put a PF with an empty basket on the machine, pulled an ounce or so of water to clean the filter and group, then replaced the Thermofilter, waited for the PID to re-stabilize the boiler temperature, and hit the brew button. I followed this procedure for all 3 shots.

The fourth, and last graph (below) tries to simulate the situation when the user randomly walks up to the warmed up machine, pulls a single shot, then doesn't pull another for another 10 minutes or so (12 minutes in my test).

These are the raw data. I will post a followup to try and summarize what (I think) the data show.

Jim

[JimG]

The primary purpose of running these tests was to determine whether the behavior of the "new" boiler in the pod-capable Silvia was thermally equivalent to the old one, and to determine if our standard 228F pre-set SV is still appropriate as a starting point in the new machines.

(I need to mention that these test data could be skewed very slightly towards underestimating shot temperatures because the test machine is located in a basement where ambient was around 62F. Yup, we operate out of a basement).

Back-To-Back Shots without Flushes
Shots 30, 36, and 40 show a progression in average temperature associated with heating of the group. Shot 30 is probably lower than normal because 30 minutes is not an adequate amount of warmup time. But the data show that the user can probably expect to see a gradual increase in shot temperatures, in this test around 3-4F per shot, if no flushing is done between shots. I question whether this is ever a realistic scenario, though.

Back-To-Back Shots with Flushes
Shots 46, 49, and 55 show both good intrashot and intershot stability. These shots averaged 198.5F, ±0.7F, with approx. ±1.3F range in intrashot temp. I think this series of shots is more representative of actual use of the machine. These data suggest that a PID'd Silvia is capable of very good temperature performance.

Walkup Shots
Shots 65 and 77 were intended to simulate a machine left running and available for walkup shots at any time. The data show that both good intershot and intrashot temp stability is present, although the tendency for group temp creep is demonstrated. These two shots averaged 200.8F, ±1.0F, with intrashot stability a little better than ±1F.

Summary
Dangerous to draw too many conclusions from limited data, but (I think) I believe the following are true:

1). New machine same as old machine when it comes to PID settings.
2). 228F is a pretty good starting point for a PID setting with the sensor as described.
3). Silvia with a PID can give consistent brew temperatures.
4). Back-to-back shots are probably Silvia's weak point, but...
5). Cleaning flushes between shots seem to be very effective in controlling group temperature creep.
6). PID'd Silvia is good for walkup shots
7). Gradually decreasing the PID SV on a machine left on for long periods might be helpful (say -1F per hour?).

I have similar data for this same machine controlled only by the stock tstat. In summary, those data show that shots pulled at the high point in the boiler temp cycle average around 195F. Shots pulled at the low point of the boiler temp cycle average around 185F. I could not get any shots hotter than 195F. If there is interest, I can plot and summarize those data from the stock machine (before PID control was added).

Jim

[erics]

Firstly, I believe this is great data to have in one's pocket and essentially reaffirms the results that, I believe, Mike McKoffee reported about two years ago.

What, IMO, would be equally interesting is how long one would need to let Silvia sit idle after pulling a shot to be able to duplicate that first shot.

Thanks for creating this post.

Eric S.