This study is preliminary. It will give you a guide on how to achieve a good stability
control. We will keep you
updated when better results are obtained from our tests or from our customers.
Appendix 3
Controlling the kettle for making French Press Coffee
1) Make sure the sensor is immersed in the kettle. If there is enough water, try to not let the
sensor tip touch the bottom for the best result. This can be done by bend the cable so that the
sensor hangs on the side wall without tip touching the bottom.
2) The sensor used is completely immersable and safe for food product. The cable is made of
virgin FEP. The sensor tip is sealed in stainless steel housing with proprietary medical grade
sealant that is certified by USP class VI test.
3) The variation of water volume in the kettle will affect the heating speed. It will also affect the
control quality. When the water volume is less than 0.5 liter, it might become difficult to control.
In that case, you need to reduce the output power as discussed in main manual. The
optimal PID constant for 1.5 liter and 0.5 litter is slight different. Here is the list.
Volume P
I
D
1.5 liter
95
80
20
0.5 liter
190
80
20
The P value in the table is for Fahrenheit. Divide it by 1.8 if Celsius is used. Please note the
difference in performance with these two sets of parameter is very small. You have to plot the
temperature response curve to see it. If you change the water volume all the time, you
don’t need to change the parameter. But if you always use the same amount of water, you
might want set the parameter for the volume you used. Basically, the difference is in the P
value. Use large value if volume is small, use smaller value if volume is large. Both sets of
parameter will work reasonably well for the whole range.
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