Starting point: The temperature stability and consistency while pulling an espresso is essential to get decent output.
PID is a digital temperature controller widely used in industrial and scientific applications and also started to spread in home appliances recently.
It uses an algorithm to cycle the power periodicly according to the tempereture reading of its sensor (closed loop controll).
In our application it is controlling the heating elements to maintain accurate boiler temperature.
The GAGGIA Classic model family – as most domestic coffee machines – uses good old mechanical bimetallic thermostats on the boiler to do the same thing for over 50 years. As these are “mechanical switches” and so, prone to fail after a number of “switching”, to ensure longevity the hysersis (window they are switches on for) is set rather high (8°C for brewing and 15°C for steaming).
It means in brew mode the boiler will heat until it reaches 107°C (225°F) and then turn off meanwhile overshooting a bit too. It will only turn back on when the temp drops by 8°C (15°F), so at 99°C (210°F). In steam mode it heats up to 145°C (293°F) and then turn off, overshoot a bit and turns back on at 130°C (266°F).
Due to the termal inertia of the berew-group in the Classics, temperature will fluctuate within a 12-15°C (22-27°F) window from factory, due to this old fashioned but reliable solution.
This is what some experienced Classic owners calling the “Temperature rollercoaster”. It is almost impossible to pull 2 shots with a similar temperature profile or even within a consistent temperature range.
As the Classics has a tiny 80ml boiler, when you are pulling a standard double shot (approx. 40g out + 20g remainder in the puck) than by the end of your shot 75% of the hot water has been replaced with room temperature water in just about 25-30 seconds. This is causing a significant temperature drop in the boiler and the classic thermostat will not respond in a timely manner, resulting a drastically descending temperature profile.
As a solution, my PID samples the boiler temperature several times within a second with a 0.1°C resolution, fast-response, high-accuracy Platinum RTD temperature sensor and continuously pulsing the heating elements to keep the boiler at the target temperature.
– This enables rock solid idle temperature accuracy (+/-0.1°C), so the starting point of each shot will be consistent.
– The temperature drop during a standard double shot will be reduced significantly to between 3-5°C.
– The PID also allows adjustement of the target temperature with a 0.1°C resolution.
– Tuning the P,I,D variables will change the charasteristics of the response during a shot to alter the descending temperature profile to some extent.
– My PID kit also controlls the steam temperature, even it is not a PID algorythm controll, but the fast-response, 0.1°C hysteresis digital thermostat improves the stock behaviour by far and it also allows adjustment of the steam target temperature.
CONS:
– The PT100 sensor is really delicate and it is easy to break it during the installation, or anytime when the boiler should be moved fro mthe machine.
– Although the installation is supported by a detailed guide, it could seem overwhelming for some users.
– It introduces a few more parts to the system, so there is a higher chance for the machine to fail, however the PID kits are usually troublefree.
– Seeing the actual boiler temperature on the display could encourage “Upgraditis”.
– For some users the additional controller does not improving the aesthetics of the Classic, however it could also be installed to a non-visible location (to the rear panel of the machine) and used as a “set once and never bother again” device.
Reviews
There are no reviews yet.