Greetings fellow kidz:
Last Saturday, I made temperature measurements of my Sylvia, using type
T thermocouples made from .005 inch diameter wire. One thermocouple
junction was placed inside of the portafilter at the top surface of the
coffee, where it could measure the incoming water stream temperature as
the water came in contact with the coffee. A second junction was
immersed in an insulated constant temperature bath of distilled water
and distilled water ice. The voltage potential of the system was
measured by a Keithly 2001 digital multi-meter. This measurement
technique is commonly used to make temperature measurements, with
accuracy easily better than 1 degree F. The voltages were converted to
temperature using conversion tables for type T thermocouples.
I measured the water temperature under several conditions approximating
how I use my Sylvia. First, I measured the temperature after performing
Coffeekid's Sylvia cheat. I performed this test twice. The first time,
I allowed my Sylvia to get as hot as possible, when the boiler light
(which indicates that the heater is operating) just turns off. The
second time, I allowed my Sylvia to cool until the boiler light came on
again (forced by me pumping water thru the steam wand), then waiting for
40 seconds before pulling the shot. I also made sets of measurements
while Sylvia was fully warmed up. My Sylvia takes just under a minute
(average time 56 secs) to cycle from lowest operating temperature
(heater light just coming on) to hottest temperature (when the heater
light goes off again). I made temperature measurements of sets of shots
pulled at the coldest temperature , and after the heater had been active
for 20, 40, and 60 seconds after the heater light first came on. These
sets spanned the complete temperature range for my Sylvia, as dictated
by the factory supplied thermostat. I measured temperature 3 times
during each shot - at 10, 20, and 30 seconds into the pour. I also
recorded the temperature inside the portafilter just before I hit the
brew switch (denoted as ET = 0).
Here are the results. ET is in seconds and temps are in degrees F.
Sylvia Cheat 1 Heater light just off (max temp)
from cold
ET
0 167.7
10 214.8
20 213.2
30 205.1
Sylvia brew switch turned on just as heater light comes on (min temp
condition)
ET run 1 2.0 3.0 4.0 avg. std. Dev
0 170.5 176.5 167.7 178.5
10 176.5 202.0 196.2 198.1 198.8 3.0
20 189.9 201.6 195.0 197.3 198.0 3.4
30 191.1 202.4 195.4 197.3 198.4 3.6
Note - on run #1, I ground too fine and got less than 1 oz of brewed
coffee
Sylvia brew switch turned on 20 seconds after heater light comes on
ET run 1 2.0 3.0 4.0 avg. std. Dev
0 162.9 167.7 152.0 182.8
10 195.4 200.9 197.0 197.0 197.6 2.3
20 195.4 200.5 197.3 198.5 197.9 2.1
30 198.5 204.0 197.3 198.5 199.6 3.0
Sylvia Cheat #2 Sylvia brew switch turned on 20 seconds
after heater light comes on
from cold
ET
0 -
10 196.6
20 196.2
30 198.1
Sylvia brew switch turned on 40 seconds after heater light comes on
ET run 1 2.0 3.0 avg. std. Dev
0 158.0 160.5 147.1
10 204.0 202.0 205.5 203.8 1.8
20 205.5 201.6 205.9 204.3 2.4
30 209.4 205.9 208.6 208.0 1.8
Shot #2 of this series was the best tasting of all pulled during these
tests.
Sylvia brew switch turned on 60 seconds after heater light comes on
(light now just out)
ET run 1 2.0 avg. std. Dev
0 178.9 170.9
10 216.3 217.1 216.7 0.6
20 212.1 213.2 212.7 0.8
30 207.4 207.4 207.4 0.0
What I learned:
First, Mark Prince's Sylvia cheat works like a charm. Check out the
numbers from Cheat #1 and compare them to the numbers for shots pulled
60 secs after the heater light came on (max Sylvia operating temp).
Also compare cheat #2 with the numbers from shots pulled 20 secs after
heater light comes on (AHL). They agree pretty closely.
Shots pulled at machines coldest operating condition (0 secs AHL): In
order to get Sylvia's heater to come on, I would operate the hot water
switch, tickling the switch until the heater light came on. Then I'd
pull the shot. The temperatures indicate how stable the Sylvia water
temp is during the course of a shot, and how difficult it was for me to
pump just the right amount of water into the boiler to coerce the heater
into action. The bad news is that by using the hot water switch to coax
the boiler into life, only 2/3 of my attempts will be within 3 degree of
the average temps for the 4 shots. The really good news is that the
water temperature remains stable within 1 Deg. F over the 30 second
time period of the shot. I'm discounting run #1 here, as I ground way
too fine and choked up my machine pretty good.
20 seconds AHL: These shots were pulled 20 seconds after the heater
switched on. They don't appear much different than those pulled at 0
AHL, except that at the end of the pour, the influence of the heater is
beginning to show up in two of the pours. These measurements show that
there is a fair amount of thermal lag in the system. By the end of the
pour, the heater had been on for 50 seconds.
40 Seconds AHL: The temperature of shots pulled 40 seconds AHL was
significantly hotter than those 20 seconds AHL. The temperature
increased during the shots by from 3 to 5 degrees. By the end of these
shots, the heater had been active for 1 minute. These shots tasted
better than those from 0 and 20 seconds AHL, especially shot #2 of the
40 sec AHL group. I should point out that I tasted every shot that I
pulled, but I didn't convert the voltages that I recorded to temperature
until after I took all of the measurements. So I think that these
measurements and my taste buds support Schomer. I relished shot number
two and licked out the cup.
60 seconds AHL: My Sylvia takes just less than 1 minute to go from the
coolest operating condition to the hottest. These two shots were
initiated seconds after the heater had gone off. The drop in
temperature can be explained in terms of thermodynamics. For liquid
water to exist at temperatures above 212 Deg. F, the pressure must be
slightly higher than normal atmospheric pressure. When the brew switch
is depressed, the pressure in the boiler is reduced to atmospheric
pressure until the pump can build up pressure within the system. During
this time, some liquid water flashes to vapor, which almost
instantaneously absorbs heat from the system, reducing the temperature.
Since the heaters are not operating, there is no make up heat
available. It's a moot point, since these temperatures are just plain
too warm.
My Sylvia runs pretty hot. I've suspected that it did because when my
Sylvia is at its hottest (60 secs AHL) I can make steam by opening the
hot water / steam valve without having the steam switch depressed. Even
so, for me that isn't too important. I can just stick another
thermostat in if I care to. The most useful finding here is that the
Sylvia's water temp is quite stable throughout the duration of the shot
if the heater has not been active for too long and if there is no phase
change present (water to steam, for instance). Also interesting to me
was my inability to temperature surf better than plus or minus 3
degrees. This points to the need for better temperature control of
Sylvia. On / off heater controls, like the thermostat in Sylvia, are
the crudest form of control. Much tighter control can be achieved by
proportional control systems. Idling espresso machines don't place
great demands on their heaters. Once the make up water from pulling the
last shot is heated, espresso machines idle. If the heater in Sylvia
is only on for short periods during a proportional heating cycle, I
would expect that the water temperature of a shot at any reasonable
temperature would be nearly as constant as those that I measured at my
Sylvia's minimum temperature, if proportional control were instituted.
-Greg Scace
Sent via Deja.com
http://www.deja.com/
