How Does A Microwave Oven Work?
Basic Theory of Operation
--available on CD-ROM Click Here
and from the video
You Can Fix Microwave Ovens
| Back | Send Email | Home Page | Microwave Oven CD-ROM Repair Course | Free FiX Finder Repair Database | FAQ | Links |
How A Microwave Oven Works
Microwave ovens use various combinations of electrical circuits and mechanical devices to produce and control an output of microwave energy for heating and cooking. Generally speaking the systems of a microwave oven can be divided into two fundamental sections, the control section and the high-voltage section .
The control section consists of a timer (electronic or electromechanical), a system to control or govern the power output, and various interlock and protection devices. The components in the high-voltage section serve to step up the house voltage to high voltage. The high voltage is then converted microwave energy.
Basically, here is how it works: As shown in Figure 1, electricity from the wall outlet travels through the power cord and enters the microwave oven through a series of fuse and safety protection circuits. These circuits include various fuses and thermal protectors that are designed to deactivate the oven in the event of an electrical short or if an overheating condition occurs
If all systems are normal, the electricity passes through to
the interlock and timer circuits. When then oven door is closed, an electrical
path is also established through a series of safety interlock
switches . Setting the oven timer and starting a cook operation extends
this voltage path to the control circuits .
Generally, the control system includes either an electromechanical relay or an electronic switch called a triac as shown in Figure 2 . Sensing that all systems are "go," the control circuit generates a signal that causes the relay or triac to activate, thereby producing a voltage path to the high-voltage transformer . By adjusting the on-off ratio of this activation signal, the control system can govern the application of voltage to the high-voltage transformer, thereby controlling the on-off ratio of the magnetron tube and therefore the output power of the microwave oven. Some models use a fast-acting power-control relay in the high-voltage circuit to control the output power.
In the high-voltage section ( Figure 3 ), the high-voltage transformer along with a special diode and capacitor arrangement serve to increase the typical household voltage, of about 115 volts, to the shockingly high amount of approximately 3000 volts! While this powerful voltage would be quite unhealthy -- even deadly -- for humans, it is just what the magnetron tube needs to do its job -- that is, to dynamically convert the high voltage in to undulating waves of electromagnetic cooking energy.
The microwave energy is transmitted into a metal channel called a waveguide , which feeds the energy into the cooking area where it encounters the slowly revolving metal blades of the stirrer blade . Some models use a type of rotating antenna while others rotate the food through the waves of energy on a revolving carousel. In any case, the effect is to evenly disperse the microwave energy throughout all areas of the cooking compartment. Some waves go directly toward the food, others bounce off the metal walls and flooring; and, thanks to special metal screen, microwaves also reflect off the door. So, the microwave energy reaches all surfaces of the food from every direction.
All microwave energy remains inside the cooking cavity. When the door is opened, or the timer reaches zero, the microwave energy stops--just as turning off a light switch stops the glow of the lamp
|Learn more about the myths & mysteries of microwave ovens|
Unless otherwise noted, all materials at this cite (including without limitation all text, html markup, graphics, and graphic elements) are copyrighted ©, 1989-2013 by J. Carlton Gallawa. The material available through this site may be freely used for attributed noncommercial educational purposes only. We ask that due credit and notification be given the author.
All materials appearing on this website may not be reproduced, stored in any retrieval system, or used in any way for commercial purposes without the express prior written permission of the copyright holder.
Send correspondence to: Microtech, P.O. Box 940, Gonzalez, Florida 32560
Disclaimer: The author assumes no liability for any incidental, consequential or other liability from the use of this information. All risks and damages, incidental or otherwise, arising from the use or misuse of the information contained herein are entirely the responsibility of the user. Although careful precaution has been taken in the preparation of this material, we assume no responsibility for omissions or errors.