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What’s The Point of A PID Controller In An Electric Kettle?

By August 16, 2018 Coffee, Design No Comments
Corvo EKG Electric Tea Kettle

Minimal and modern with a single button and a sleek LCD screen, Stagg EKG and Corvo EKG’s base is hiding something very powerful inside: a PID controller. A proportional-integral-derivative controller is a control loop feedback mechanism widely used in industrial control systems. The PID controller continuously calculates an error value as the difference between a desired setpoint and a measured process variable and applies a correction based on proportional, integral, and derivative terms which give the controller its name.1  Or in much simpler terms, EKG’s PID controller is basically a mathlete with a TI-84 calculator constantly running equations to determine the most efficient way to reach your goal temperature.

“An everyday example is the cruise control on a road vehicle; where external influences such as gradients would cause speed changes, and the driver has the ability to alter the desired set speed. The PID algorithm restores the actual speed to the desired speed in the optimum way, without delay or overshoot, by controlling the power output of the vehicle’s engine.”2 Well before cruise control, the original application of PID controllers was for the automatic steering systems for ships in the early 1920s. So if you ever want to drop an impressive factoid while brewing up a pour-over, you can say your Stagg EKG or Corvo EKG has the same technology as ocean liners.

If your electric kettle has a traditional thermostat, it heats up by overshooting the goal temperature, and then it drops below the goal temperature to cool off. All kettles (that we’re aware of) have a simple on/off controller. So, the power is either at 100% or 0%. Again it overshoots, undershoots, overshoots, and undershoots until it gets close to the goal temperature. Charted on a graph, it would look like spiking zig zag lines or the stock market crashing and rebounding day after day. This is not efficient and in reality, your “hold” is just holding at a degree or two below and above, flipping back and forth.

Now onto the EKG family and the two reasons EKG outperforms everything else on the market. First, Stagg EKG and Corvo EKG use a PID controller (much like your fancy $20,000 espresso machines), so the zig zags are less drastic and resemble a curve leveling off at your goal temperature. This lends itself to a more accurate output. In addition, those other kettles just have on/off mechanical relays (remember from above, either 100% or 0% power). Fellow’s EKG line is able to do a little something called “Pulse Width Modulation” using a non-mechanical approach. PWM uses series of on/off pulses to vary the duty cycle, the fraction of time that the output voltage is “on” compared to when it is “off.” This PWM action allows us to maintain temp much more accurate compared to a standard mechanical relay that is clicking on and off around the set point. Oh, and that also means Stagg EKG doesn’t have that annoying mechanical on/off click that drives baristas crazy.

Okay okay… so what does this mean in terms of actual performance? After running countless tests, we can say with confidence that the EKG family’s PID controller heats and maintains water temperature to +/- .3 degrees Celsius. This is three to four times more accurate than the leading electric pour-over kettle available on the market today. In one series of tests, we compared Stagg EKG to the leading variable temp pour-over kettle (to be nice, we won’t name names).

The test: 600 ml of water set to hold at 200°F.

Although both kettles have an average temperature of essentially 200°F over the course of testing duration (averages can be misleading), the standard deviations tell a very different story. Stagg EKG has a standard deviation of 0.27°F while the leading pour-over kettle comes in at 1.06°F.

As you can see from the plot, Stagg EKG is bouncing between about 199.5°F and 200.5°F (blue line), while the leading pour-over kettle ranges from a low of below 198°F and a high of over 201.5°F (red line). The competitor kettle turns on (100%) overshoots the set point, then shuts off (0%). The water cools down to 198°F and then the kettle clicks back on (100%). The result is relatively drastic swings in temperature even though you’re technically in hold mold. Stagg EKG, through PID and PWM is able to do micro adjustments that make it hold temp three times more accurate in this experiment.

Stagg EKG vs. Leading Variable Temp Pour-Over KettleWhy should the inner-workings of an electric kettle matter to you? The fourth wave of coffee has been forecasted as “the science of coffee.” As we learn more about coffee, users seek more resolution on their brewing parameters as seen in many third wave shops employing techniques such as Total Dissolved Solids, brewing by weight, and using coffee brewing smart technology. Stagg EKG and Corvo EKG provide users the ability to manipulate temperatures with to-the-degree precision to easily control the brewing temperature. This empowers users to experiment and explore all the varying degrees of extraction for coffee and tea. Both Stagg EKG and now our latest product, Corvo EKG, have a brew range of 104°F to 212°F (40°C-100°), can hold the set temperature for 60 minutes, and most importantly, are the most accurate variable temperature electric kettles on the market.

Corvo EKG Electric Tea KettleStagg EKG Electric Pour-Over Kettle

 

 

 

 

 

 

 

 

 

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