Page 171 - Electromechanical Devices and Components Illustrated Sourcebook

Chapter 7 Heating 133

Home & Office Remote Bulb

70
60 80 On
50 90 Fan

Auto
Room
Temperature

Cool
50 60 70 80 90
Off
Heat
Set Temperature

Cartridge
Miniature

Snap Disk
Figure 7-20 Various Commercial Thermostats

Differential front of the tube and in very short order it was heated to a
Controller point where it exploded. At that point in time, the microwave
oven was born.
The heart of the microwave oven is the magnetron tube. This
is a vacuum tube that emits microwave radiation in the 2.5 GHz
range when it is excited with a high voltage. Figure 7-22 shows
°F a sectional view of a magnetron tube. Water, fat, and sugar
°C
molecules absorb microwave radiation and convert it to atomic
Program TEMPERATURE
motion, or heat. When food is placed into a cavity that is fed by
A B the output of the tube, it is effectively heated. Magnetron tubes
will be discussed in greater detail in Chapter 14.
C D E RESET

Digital Controller

Antenna
Figure 7-21 Temperature Controllers

Mounting
Studs
Microwave Heating Frame

Microwave heating was discovered in 1946 by Percy Spencer,
an engineer who was engaged in the development of the mag- Cooling Fins
netron tube. When working with a magnetron tube he noticed
Capacitor
that the candy bar in his top pocket had melted. Out of curios- Housing
ity he placed some popping corn in front of the tube and was
Power Connector
delighted to see that it would pop almost immediately when
the tube was powered up. The next day he placed an egg in Figure 7-22 Commercial Magnetron Tube