Operating the Rancilio Silvia after PID kit modification

Operating the Rancilio Silvia after PID kit modification
Operating the Rancilio Silvia after PID kit modification
Version 1.1
When the machine is turned on, the controller will display the boiler temperature
in the machine. The temperature reading will start to increase after 30-60
seconds. As the temperature approaches the set value, you will notice that the
panel light next to the power switch will start to flash. This flashing indicates that
the controller is cutting the power to the heater such that the temperature will not
overshoot as it approaches SV. After the temperature has stabilized within ±1
degree of SV AND the machine has been “on” for 45 minutes, it is ready to
produce espresso.
Making Espresso.
After retrofitting with the PID controller kit, pulling the espresso shot needs to be
operated differently than the original machine. Before pulling the shot, the Brew
Switch on the Silvia should be turned to the on position. Press the “>” button on
the controller to start the brewing. The display of the controller will change from
displaying the boiler temperature to displaying the countdown time. The pump
will give a small pulse of water to wet the coffee, wait for 2 seconds, then start
the pump again for the brewing. When finished, the display will change back to
display the temperature of the boiler.
The Brew Switch can be left at on position during steaming but needs to be
turned off when pumping hot water.
There are two ways to pull the shot manually.
1) Keep the Brew Switch at the on position. Turn on the Hot Water switch to start
the brew pump. Turn off the Hot Water switch to stop the pump.
2) Keep the Brew Switch at the on position. Set the timer to a longer time than
you normally need for the shot. Press the “>” button on the controller to start
brew pump. Press the “>” again to stop the pump.
After PID Kit modification, the method of producing hot water is not changed. To
pump the hot water, make sure the Brew Switch is at off position. Turn on the Hot
Water switch will allow you to pump the water to the steam wand.
Brew Water Temperature
It should be noted that this PID kit controls the temperature of the boiler. Due to
the design of the Silvia, the brew water temperature that going through the filter
basket is not the same as that in the boiler. It takes about 6 to 10 minutes for the
boiler temperature to stabilize after machine is turned on from cold. However, it
takes about 45 minutes for the brewing water temperature to get stabilized at a
constant temperature. In addition, the brew water temperature is about 25 F
lower than the temperature of boiler.
Machine No. 2, SV=104
100
Temp (C)
95
90
Test 17
Test 18
Test 19
85
80
75
70
0
20
40
60
80
Time (min)
Figure 1 shown the brew water temperature changes with time. The reason for
such delay is due to the structure of the Silvia machine. The boiler of the
machine has only a thin section connected to the grouphead. It will take a while
for the heat in the boiler to transfer to the grouphead. In general, it takes 25 to 45
minutes to get the brew water temperature stabilized. During the warming up
period, we suggest user to install the empty portafilter on the machine. After the
controller stabilized at SV, run the pump for 4 to 6 fluid oz of water (120-180 ml)
to flush the grouphead and portafilter. That will speed up the warming up process.
Brew Water Temperature Setting
Table 1. SV for different kit
Part Number
KIT-RSNST
Description
Rancilio retrofit kit
SV value in ºC
105
Table 1 lists default settings for the SV of the controller.
SV value in ºF
221
Temperature relation in Celsius
99
Brew Water Temperature
98
97
96
95
94
93
92
91
90
89
88
96
98
100
102
104
106
108
Controller Set Temperatuer
Temperature relation in Fahrenheit
210
Brew Water Temperature
208
206
204
202
200
198
196
194
192
190
205
210
215
220
225
230
Controller Set Temperatuer
Figure 2 Correlation between PID controller set temperature and brew water
temperature detected at grouphead measured by Scace Thermofilter. Top,
display in degrees Celsius. Bottom, Display in degrees Fahrenheit.
Figure 2 shows the correlation between the PID controller set temperature and
brew water temperature. The controller in the Auber instruments’ PID kits has
been calibrated with its sensor to the accuracy of 1 degree C before shipping.
However, due to the machine structure variations, the brew water temperature of
different machine can have 1-2 C difference when controlled by the same PID
controller kit. For detailed relationship between the PID setting temperature and
brew water temperature, please read the file named “Temperature Performance
Study” in the CD that came with the kit.
It should be noted that the setting temperature we recommended is lower than
some people suggested on the internet forums. As SV can be easily changed, it
will up to the user to decide what the best temperature is for their espresso.
Changing Brew Water Temperature Setting
There are two ways in which SV may be changed:
1) Press the ▼ or ▲ key once and release it. The display will change from
measured temperature (process value, PV) to flash the SV. Then press the ▼
or▲ key to change SV until the desired value is displayed. There is no need to
press the SET key as the display will change back to reading the boiler
temperature automatically after no keys are pressed for 8 seconds.
2) Press the SET key and enter the code 0001. Press SET again. The controller
will display the current setting for SV. Use the▼, ▲, and > keys to change the
SV to the desired value. Press the SET again. Then use the ▼ and ▲ keys until
the controller displays “END”. Press SET to complete the process. While this
setup method is more complicated than the previous method, it is faster and
more reliable when the temperature change is very large. However, this would
not typically be required in an espresso machine installation.
Fine tuning the PID Constants
The parameters for the PID controller have been optimized for Rancilio Silvia
with extensive testing. For most users, there is no need to fine tune the machine.
For some machines, the temperature might oscillate 2 degrees occasionally. The
recovery time might increase to 3-4 minutes when it is cold. These differences
are not critical to most users because it might take that much time to prepare the
next shot. As the machine warms up, the performance will improve. A warmed up
machine could take less than 40 seconds to recover after pulling a shot. We
found the most noticeable performance differences were between new machines
and some old, poorly maintained machines. This is believed to be due to internal
scale build-up in older machines which slows the response time. If you are
technically adept and willing to read through the controller instruction manual,
below are some hints that may help you fine tune the controller. Should you ever
want to set the controller to its original state, Table 2 lists the default settings that
come with the controller.
1) Changing the P constant MAY improve performance. We found for kits using
the RTD sensor the P value should be between 1.8 and 3.5 (the default is 2.0).
In general, a lower P value will speed up the recovery after a shot. However, a
lower P value can also cause the temperature to oscillate. For older machines,
2.5 may provide better results. For kits using the K type thermocouple, the P
value should be between 0.9 and 1.4 (the default is 1.1).
2) For older machines, changing the integral constant, I, from 60 seconds to up
to 75 seconds may improve performance. However if I is set too short the
temperature will oscillate and when I is set too long the recovery speed will be
slower.
Table 2. Controller Parameters For Silvia
KITRSNST-F
Code 0036
P
I
d
Code 0001
SV
AH1
AL1
tp
td
tb
Code 0089
Inty
Outy
Corf
KITRSNST-C
2
60
15
2
60
15
221
283
284
1.2
2.5
25
105
139
140
1.2
2.5
25
PT100
3
1
PT100
3
0
Controller Instruction Manual
A copy of the instruction manual for the controller is included in the kit. For most
users, there is no need to read it. If you decide to read the manual we want to
point out that this is not a complete manual. We have added two control
parameters to balance the requirement for cold start speed, shot recovery speed
and long term stability. These parameters are proprietary and are not accessible
by the user. In addition, the dampening factor, SovF, has been deactivated.
Other than that, the remaining control functions are the same.
Change the Display to 0.1 Degree Resolution.
For the kits with RTD sensor, it is possible to display the temperature in 0.1
degree (F or C) resolution. The controller will be able to hold the temperature at
± 0.1 degree range. However, with 0.1 degree resolution, the machine will take
much longer to reach the set point. Should you decide to use the 0.1 degree
resolution, you will need to use the code 0089 to change the Inty parameter from
PT100 to PT10.0. Then, use code 0001 to reset SV, AH1 and AL1.
Frothing the Milk by Steam.
Frothing should be done in the same way as before the PID kit was installed. The
boiler temperature will be hold at much tighter range than before. The heater will
kick on much sooner when the steam is released. Without surfing the
temperature, you will still get a good frothing result.
It should be pointed out that the main purpose of controlling the steam
temperature is not to stabilize the steam temperature but to turn on the heater
sooner when the frothing starts. When frothing the milk, the heater of Silvia does
not have enough power to maintaining a stable temperature. Even the heater is
powered 100% on; the temperature of the boiler will still drop. The original
thermostat of the Silvia is designed to turn off the heater when the temperature
reaches 284 F (140C) and on again when temperature drops to below 265 F
(130C). After the thermostat is turned off at 284 F, no new steam will be
generated until temperature drops further below 265F because the delay in heat
transfers. With this controller, the heater will turn off at 284 F (140C) and on
again when it drops to 1 degree below that (283F or 139C). That allows the
heater to be kicked on much sooner than the original machine.
The steam temperature is controlled with on/off mode instead of PID mode for
fast action. It is normal to see temperature oscillating as much as 10F (6C)
around the setting point. The on/off temperature is set by the AH1 and AL1
parameters listed in table 2. The value of AH1 has to be less than that of AL1.
User might change the setting to different temperature (at his own risk). Some
user set the temperature to 295/294F (reported on internet). Silvia has an over
temperature protection thermostat (the one mounted on the side of boiler with a
red reset button). It will shut the machine power off at 329F (165C) to prevent
any damage of the machine.
Pre-infusion
When making the espresso shot, one of the potential problems is that the abrupt
water pressure increase applied on the dry coffee powder can forms preferential
routes for the water flow. When the problem is minor, the powder is not used
uniformly, resulting in a poor coffee yield. When the problem become severer,
the extraction flow rate becomes faster than 60ml/25 second even you have the
proper grinding. The result is low extraction and high dilution. In the worst
situation, water can form very low resistance channels with very fast flow and
almost no extraction.
A common technique to avoid this problem is to make a uniform and tight coffee
matrix with a good tamper. However, a good tamping takes a lot of practice and
is difficult for some users. To solve this problem, espresso machine
manufactures developed a special feature called pre-infusion. There are two
main approaches for the pre-infusion. One is a mechanical approach. A pressure
arrester device is used to slow down the pressure increase speed. This is more
close to the manual extraction method. The other is electronic approach. Special
programmable timer is used to pump small amount of water on the coffee powder
and let is soak in first. The wet coffee power will form an uniform matrix that allow
the high pressure water flow evenly across the coffee powder. This method is
also called pumped pulse pre-infusion. Auber PID kit uses this method.
The Auber pre-infusion function is achieved by setting the pump control timer in
three sections. The first section activates the pump briefly to spray a small
amount of water on the coffee powder. The parameter used is called pulse time,
or Tp. The second section holds off the pump to let the water soak into coffee
powder and form a tight matrix. The parameter used is called dwell time, or Td.
The third section starts the normal brew extraction. The parameter used is called
brew time, or Tb. The relationship of these parameters is show in Fig 3.
Fig 3. The relationship of Tp, Td and Tb.
The setting of pre-infusion parameters
1) Tp. the pulse time. We think the pulse time should be just long enough for the
water to wet ½ to2/3 thickness of the coffee. There is no need to wet through the
entire coffee. Excess water might cause the coffee powder to float. Base on our
test with a properly grinded and tampered basket mounted on a bottomless
portafilter, the time needed for water to went through a single shot basket is
about 0.9 second, For the double shot basket, it is 1.6 second. We suggest you
to set the Tp=0.7 s for single shot and 1.2 s for double shot basket. The Tp is
preset to 1.2 second before shipping.
2) Td, the dwell time. This the time to let the water soak the through the coffee.
We set it to 2.5 second so that total extraction time (including wetting and
soaking) is less than 30 second…… the generally accepted espresso extraction
time. It is not clear if longer soaking time will produce a bad taste for the coffee.
Some American Coffee brewing machine with programmable pump uses much
longer time. User can try it with different time to see if there is any improvement
with longer soaking time.
3) Tb, the brew time. This time is set to 25 second. Some user might prefer a
longer brew time. It can be changed by user.
To change the pre-infusion settings, press the SET key and enter the code 0001.
The controller will display SV. Press the ▲ key until it displays “tp”. Press SET
again. It will display the current time setting in 0.1 second resolution. Use the▼,
▲, and > keys to change the Tp to the desired value. Press the SET again.
Then use the ▲ keys to change the display to “td”. Press SET again. It will
display the current time setting in 0.1 second resolution. Use the▼, ▲, and >
keys to change the Td to the desired value. Press the SET again. Then use the
▲ keys to change the display to “tb”. Press SET again. It will display the current
time setting in 0.1 second resolution. Use the▼, ▲, and > keys to change the
Tb to the desired value. Press the SET again. Use the ▲ key until the controller
displays “END”. Press SET to complete the process.
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