The Alexia PID Project


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ALEXIA

Predictable, stable, and repeatable temperatures

Background
In February, we were invited by Chris' Coffee to develop a PID temperature control system for the Quickmill Alexia single boiler espresso machine. Chris was familiar with our Silvia kits and said he was interested in an effective, well-documented temperature control system for the Alexia.

Chris shared with us his plans to have the new Alexia's shipped to him in a "PID-ready" configuration. Working directly with Quickmill, the new model will come with a laser-cut opening on the front panel, below and to the left of the group, sized to accept a 1/32 DIN PID controller. In addition, the new machines will be pre-drilled for mounting a solid state relay, and will have special ventilation holes designed for convective cooling of the internally mounted PID.

First Impressions
When our machine arrived, we instrumented the boiler in several locations, and added one of Eric Svendson's group sensors. We installed a Watlow SD3C PID controller, and started running tests.

The first thing we noticed (temperature-wise) was the very small (1F to 2F) drop in boiler temperature that results from pulling a shot. This is explained by the very large boiler on the Alexia.

The second thing we noticed was the relatively flat intrashot temperature profile measured by the Scace Thermofilter. The massive E61 group, as well as the large boiler volume, deserve the credit for this.

Technical Challenges
The Alexia's boiler has a deep thermowell, allowing sensing of the water temperature at virtually any location within the boiler. But interferences with piping in and around the boiler would prove to make it difficult, at best, to use a traditional sleeved theromcouple. So we developed a custom, fast-responding sensor with a very short sleeve that could easily be manuevered into place. We also designed this probe so that it could easily be moved up and down within the thermowell in order to find the optimum sensing location.

Next, the internal mounting of the PID controller meant that heat from the boiler needed to be carefully managed. We developed a system using a combination of thick ceramic "paper" insulation and a reflective aluminum heat shield to protect the PID's electronics from the boiler's heat.

Our original test machine lacked the special ventilation features Chris' has built into the newest production version of the Alexia (now available). So we expected that our test machine presented worst case conditions and that the new production models would have even lower internal temperatures. (We carefully measured ambient internal temperatures with the new model and found them to be lower than the unventilated Alexia).

In addition, the Watlow SD3C controller we selected for this application has the highest ambient temperature rating in the industry. Virtually all other PID controllers on the market have a maximum ambient temperature rating of 50C (122F). The Watlow SD3C has a maximum ambient temperature rating of 65C (149F).

Successful Solutions
After extensive testing of sensor locations (including a simple external sensor on the top of the boiler), we found that the optimum location is a point midway down the thermowell. Sensor locations above this point did not respond quickly enough to the cooling effects of incoming water (after a shot or after flushing). This tended to allow the "core" of the boiler to gradually cool down after pulling multiple shots.

Sensor locations too low in the thermowell had the opposite problem. In this case, the sensor was overly sensitive to the effects of incoming water and tended to allow the top of the boiler to become slightly overheated, resulting in a gradual increase in average shot temperatures.

The optimum sensor location, marked on each kit's sensor, kept the core of the boiler, as well as the top, in good thermal balance. The resulting intershot stability is outstanding, as the graphs that accompany these pages show.

Alexia PID Kits available
In association with the rollout of the new Alexia's, MLG and Chris' have partnered to make complete PID kits available. Customers will have the option to buy the Alexia with the MLG PID kit professionally installed by Chris', or purchase a standalone kit and install it themselves. The MLG PID kits for the Alexia will be available exclusively from Chris' Coffee.

In keeping with the high standards for MLG's other PID kits, the new Alexia kits will come with everything needed for the installation, including:

  • all wiring, color coded and pre-terminated, with appropriate UL ratings for this application
  • 25A solid state relay and protective cover
  • Watlow SD3C digital temperature controller with 3-year manufacturer's warranty
  • custom thermocouple probe constructed using highly accurate type T SLE thermocouple wire
  • fully illustrated 40+ page installation guide
  • complete calibration, programming, and tuning of the controller prior to shipment
  • boiler insulation kit

Technical Information
To assist you in making an informed decision regarding the Alexia, and the MLG PID kit for the Alexia, the following links are offered. On the linked sheets you will find selected graphs from the extensive testing we performed on the Alexia during the development of these new kits.

  • Intershot stability - click here
  • Intrashot stability - click here
  • Internal ambient temperatures - click here
  • Time to reach steaming temperature - click here
  • Warmup time required - click here
  • Typical "first-shot-of-the-day" - click here

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