Technical Information
75
DGC 6xxx
is activated piezoelectrically (i.e. by pressure).
The EPI electronic (Figure 045-1, Item 1) of the wireless roast probe
thermometer transmits and receives all frequencies in the high-frequency ISM
band between 433.05MHz and 434.79MHz to use for temperature
measurement. This transmission/reception runs sequentially and constantly
(but with a millisecond delay between transmission and reception).
The frequency band is subdivided so that one frequency corresponds to only
one temperature. The high-frequency signal activates the sensor element
(Figure 045-1, Item 4.2) inside the roast probe in order to generate an
acoustic surface wave.
An acoustic surface wave (engl. “SAW” for surface acoustic wave) is an
impact sound wave that breaks smoothly across a surface.
This surface wave is very sensitive to temperature changes. These changes
produce a shift in the reflected surface wave and generate a change in the
reflected high-frequency (HF) signal. This modified HF signal uses the
electronic for temperature measurement, in which it compares the transmitted
signal to the received signal.
2.8.3 Frequency Transmission/Reception in the “Wireless Roast Probe”
System
1. The electronic (Figure 045-1, Item 1) generates a high-frequency signal
that is converted by the antenna (Figure 045-1, Item 3) into an
electromagnetic wave.
2. The antenna (Figure 045-1, Item 4.1) converts the electromagnetic wave
back into a high-frequency signal.
3. The high-frequency signal generates an acoustic surface wave in the
piezoelectric element (Figure 045-1, Item 4.3).
4. The acoustic surface wave is reflected by the reflectors (Figure 045-1,
Item 4.4), which generates a resonator frequency.
5. The resonator frequency changes with the current cavity temperature.
This change in resonator frequency is used for temperature
measurement.
6. The resonator frequency is converted back into a high-frequency signal
and sent back via the antenna (Figure 045-1, Item 4.1) to the electronic
(Figure 045-1, Item 1).
7. A change in the received high-frequency signal equals a change in the
measured cavity temperature.
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