microwave oven

[nraghu]

i would like to know how a microwave oven works i mean how do we control the microwave generation and what is magnetron tub?
Any suggestions? Thank you for your time!

 

[Sebi]

Microwawe oven contain a tube, called magnetron. This tube working as oscillator with about 2.5kV anode voltage and 3V 25A heating voltage. The magnetron can run only alwys with full power, and controlled by timers only on-off periodically.

 

[Nigel Goodwin]

As Sebi has already mentioned, microwave ovens generally use what is known as 'burst fire' power control. They usually use a 10 second timing period, so for half power they turn on for 5 seconds, then off for 5 seconds. It's a method of power control commonly used for heating - obviously not very good for dimming lights though :lol:

I have seen occasional very old microwaves, with just two powers (full and defrost) where they switch a different value capacitor in to circuit for the lower power - but these are pretty uncommon.

 

[mixos]

Check this:

How Microwave Ovens Work
https://home.howstuffworks.com/microwave.htm

 

[nraghu]

THANKS YOU SEBI,NIGEL GOODWIN AND MIXOS FOR YOUR IMMEDIATE RESPONSE. IF POSSIBLE PROVIDE ME SOME MORE INFORMATION REGARDING TO CIRCUIT DESIGNING .

 

[Sebi]

Here is a sematic of the most of case used micro with mechanical timer.

 

[Noggin]

As Sebi has already mentioned, microwave ovens generally use what is known as 'burst fire' power control. They usually use a 10 second timing period, so for half power they turn on for 5 seconds, then off for 5 seconds. It's a method of power control commonly used for heating - obviously not very good for dimming lights though :lol:

I have seen occasional very old microwaves, with just two powers (full and defrost) where they switch a different value capacitor in to circuit for the lower power - but these are pretty uncommon.

I recently purchased a Panasonic microwave that claims to have a true variable power mode, and I havn't heard it switching on and off periodically when on different power settings. I havn't paid a whole lot of attention to it though, but the first couple times I ran it I did listen for a few seconds to hear the mag turn off.

I don't really care, it heats my food

 

[Nigel Goodwin]

I recently purchased a Panasonic microwave that claims to have a true variable power mode, and I havn't heard it switching on and off periodically when on different power settings. I havn't paid a whole lot of attention to it though, but the first couple times I ran it I did listen for a few seconds to hear the mag turn off.

There have been a number of recent microwaves, Panasonic seem the most common (although the first I ever saw was an Hitachi pre-production model), which use switch-mode PSU's, rather than the large heavy mains transformer.

With these ovens, you can't hear the hum from the transformer as it turns on and off (which is real bad news for a service engineer). Also, it would be quite possible to provide true power switching (by altering the mark/space ratio) - but I don't see as it would give any advantage over the burst fire method.

The big advantage is in the weight of the ovens, so much lighter (and expensive!) than conventional ovens.

 

[pike]

if you really now the on and off time for the microwave, grab a small fluorescent tube, cover the ends with tape and stick it in the microwave.
when it turns on, the tube will light up.

 

[coyotesden]

post:

I've done this flouresent trick thing too test microwaves,....But someone in this topic, refered to a magnatron as a tube :roll:,.... Back in the 40's and 50's, they used what were called Klystron tubes for radar, Prety much what microwave energy is..However a megnetron is a metal box looking thing with a megnet surounding the wave guide.

 

[Nigel Goodwin]

Re: post:

I've done this flouresent trick thing too test microwaves,....But someone in this topic, refered to a magnatron as a tube :roll:,.... Back in the 40's and 50's, they used what were called Klystron tubes for radar, Prety much what microwave energy is..However a megnetron is a metal box looking thing with a megnet surounding the wave guide.

You can buy a simple 'tester' for checking a microwave is working, it's just a row of neon bulbs in a plastic block. It also helps to show the distribution pattern in the cavity.

Microwave ovens were developed from WW2 radar technology, and the original ones used Klystron's - later on the far cheaper Magnetron was developed - as someone suggested, it is a type of tube (valve).

A guy I used to know (who fitted TV aerials) worked on radar installations during the war - and he had a dead spot (about an inch across) on his arm. This was caused by adjustments on a particular unit, where you had to put your arm inside to adjust something, and it got in the way of the microwave stream.

 

[coyotesden]

post:

:shock: Ouch! I knew a realy stupid 'tech, he would put his arm in a microwave oven, after bypassing the saftey locks to see if the magnetron worked,...I guess he didn't know the light bulb trick :shock: :roll: BTW true story!!

 

[Nigel Goodwin]

Re: post:

:shock: Ouch! I knew a realy stupid 'tech, he would put his arm in a microwave oven, after bypassing the saftey locks to see if the magnetron worked,...I guess he didn't know the light bulb trick :shock: :roll: BTW true story!!

Obviously not an engineer at all! - there's no way someone that stupid could be an authorised microwave service engineer :lol: