磨豆机的磨粉室一般比较小，没有太多的自由空间，在这么小的空间内装入一个温度探头不能影响咖啡的流动，也不能影响测量结果，这是一个挑战，最后，我们选用了"细金属丝，露端"K型热电偶，在磨粉室的出口装上小块的环氧树脂，阻止来自磨豆机金属外壳表面的热量，当把探头的节点暴露到咖啡粉中，探头线缆从咖啡粉出口的斜槽穿出来.
The actual grinding chamber of a typical coffee grinder is very small and there is little free space. To get a temperature probe in to this space without interfering with the flow of coffee, and thus distorting the results, proved to be a challenge. Ultimately a “fine wire, exposed junction” K-type thermocouple was used. This was bonded into the grinding chamber outlet with a small dab of epoxy resin to provide insulation from any heat conducted up through the metal of the grinder casing while leaving the junction exposed to the ground coffee. The probe wire was fed out of the chamber via the ground coffee outlet chute.
第2个探头安装到马达的定子上，检测马达的发热情况，"细金属丝,露端"K型热电偶，底部有一个柔性的磁垫，使得探头可以问问的吸附在马达的金属表面。
A second probe was attached to the side of the motor stator to detect the heat rise in the actual motor. Here a “fine wire, exposed junction” K-type thermocouple bonded to a flexible magnetic pad was used. This kept the probe in contact with the soft iron of the motor stator.
第3个探头安装在磨豆机的机箱表面，马达安装到磨豆机的附近，正好在研磨室的下面，用来检测马达传递过来的热量
A third probe was attached to the metal of the grinder casing adjacent to the point where the motor was bolted on to the grinder body just below the grinding chamber to show the conducted heat from the motor.
最后，一个类似于皮下注射类型的探头嵌入到咖啡豆漏斗的底部，用来检测咖啡豆进入研磨室之前的温度
Finally a hypodermic type probe was inserted in to the base of the coffee bean hopper to monitor the temperature of the beans prior to entering the grinding chamber.
图1 显示了磨豆机的结构图和放置热电偶探头的位置
Figure 1 below shows a schematic of the coffee grinder and the location of the thermocouples.
调节"咖啡屋"的室内状态,把温度设置为28℃，湿度设置为平均水平。
To replicate “Coffee Shop” conditions a temperature controlled room was used. This was set to 28 degrees Celsius and an average humidity level.
把USB TC-08连接到电脑，采样频率为500ms，每10分钟为一个采样周期，经过3次试验，就可以比较结果，3次的测试结果如此接近，不取平均的，而是选择他们其中的一个。
Using the USB TC-08 connected to a PC the data was gathered over a period of 10 minutes with readings taken every 500 ms. The test was conducted three times and the results compared. The results from the three tests were so close that they were not averaged and just one set was used.
图1: 咖啡机原理图
结论
The majority of the rise in motor casing temperature was not passed on to the grinding chamber within the 10 minute period; however, there was a notable rise of about 12 degrees Celsius in the temperature of the ground coffee during the period.This is not acceptable, however referring to the graph (Figure 2) it will be seen that the rise can be limited to 4 degrees Celsius if the run time is limited to just over 4.5 minutes. As this is equivalent to just under 1 kg of coffee being ground this should be sufficient to maintain the provision of ground coffee to the associated Espresso coffee machine for long enough to allow the grinder's 30% duty cycle to be adhered to.Thus the test has shown that by controlling the run time of the grinder the taste profile of the coffee can be maintained.A small electronic timer will now be developed to stop the grinder 4.5 minutes after grinding begins.
图2: 咖啡机的温度
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发表于 2012-4-5 20:55:54
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