# Microwave turntable direction

T

#### Tom Del Rosso

Jan 1, 1970
0
Some microwaves have turntables that turn in alternate directions each time
they start. Why the heck is that?

A

#### Arfa Daily

Jan 1, 1970
0
Claude Hopper said:
It's so your food will cook more evenly. Many directions are to
microwave for a few minutes, open and stir contents, then continue a few
more minutes. It's more through to run the food past the microwaves in
both directions.

Based on what all of my microwave ovens have done, including the one
currently in use at home, and the two we use in my wife's cafe, the
direction of rotation appears to be completely random, and I would suspect,
a function of the motor type, as Franc suggests. I would also be surprised,
given the way that the microwaves bounce around the oven cavity almost
infinitely, that the direction of rotation of the turntable would have the
slightest effect on the eveness of the microwave penetration, and cooking
efficacy.

Arfa

H

#### hr(bob) [email protected]

Jan 1, 1970
0
It's so your food will cook more evenly. Many directions are to
microwave for a few minutes, open and stir contents, then continue a few
more minutes. It's more through to run the food past the microwaves in
both directions.

NO

H

#### hr(bob) [email protected]

Jan 1, 1970
0
Based on what all of my microwave ovens have done, including the one
currently in use at home, and the two we use in my wife's cafe, the
direction of rotation appears to be completely random, and I would suspect,
a function of the motor type, as Franc suggests. I would also be surprised,
given the way that the microwaves bounce around the oven cavity almost
infinitely, that the direction of rotation of the turntable would have the
slightest effect on the eveness of the microwave penetration, and cooking
efficacy.

Arfa

Yes

H

#### hr(bob) [email protected]

Jan 1, 1970
0
No, it's not. It shouldn't make any difference, as the food is subjected to
the same "pattern" regardless of which way the table turns.

My guess is that it's to even out the wear.

It a function of the type of motor used, it is much smaller to make a
motor that will turn in either direction than one that always turns in
the same direction. If you look at some extremely small motors, some
have a ratchet and tiny gear that only allow them to turn in one
direction, but the ratchet and gear take up space and cost extra $$and so Uwaves don't bother to use them.. The direction of rotation does nothing unless you have a really wierd-shaped piece of food. Bob Hofmann P #### Puckdropper Jan 1, 1970 0 No, it's not. It shouldn't make any difference, as the food is subjected to the same "pattern" regardless of which way the table turns. My guess is that it's to even out the wear. Maybe the change in direction is just to keep the user entertained while their food heats. Just like the light bulb... Puckdropper S #### Samuel M. Goldwasser Jan 1, 1970 0 William Sommerwerck said: It a function of the type of motor used, it is much smaller to make a motor that will turn in either direction than one that always turns in the same direction. If you look at some extremely small motors, some have a ratchet and tiny gear that only allow them to turn in one direction, but the ratchet and gear take up space and cost extra$$
and so Uwaves don't bother to use them.

Doubt it. 99.9999999999 percent of motors in consumer appliances and
electronics are either unidirectional or may have their direction changed
trivially by the electronics, and it doesn't cost more or take up more space
or cost more.

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G

#### GregS

Jan 1, 1970
0
Microwaves do not 'bounce around' in the oven. Microwaves are
directional, that's why you move the food. The microwave emitter does
not move.
Studies on choice of optimized regimes of RF plasma production/heating
in Uragan-3M were performed by
using microwave reflectometry. Radial profiles of electron density and
it fluctuation and poloidal rotation velocity
have been measured for different RF antenna configurations and confining
magnetic field direction. It was shown
that plasma parameters are changing at magnetic field reversal. Best
regime is that one when magnetic field
direction is “normal” (that one at which magnetic configuration was
“tuned” at magnetic surfaces studies). This
regime is characterized by higher value of electron density and by
higher value of poloidal rotation velocity shear.

I dissagree that microwaves cannot bounce in a cavity. The bouncing creates a field
pattern with waves of energy. Its constant. Its possible to tune the cavity for
different fields. Microwave emitter can change such as in my Heath Kit microwave
that had a rotating thing right after microwaves entrance into the cavity. This does the
same thing as rotating a plate. Putting in massive absorptive objects into the
cavity reduces the reflective field. I remember the lava bricks in the Heath
Kit demo at the stores in 1971 instead of using food.

greg

A

#### Arfa Daily

Jan 1, 1970
0
Claude Hopper said:
Microwaves do not 'bounce around' in the oven. Microwaves are
directional, that's why you move the food. The microwave emitter does
not move.

On some cookers, that isn't strictly true.

regime is characterized by higher value of electron density and by
higher value of poloidal rotation velocity shear.

Dear oh dear ...

http://www.doctorndtv.com/FAQ/detailfaq.asp?id=7837

and 2) of paragraph 1 at

http://www.gallawa.com/microtech/howcook.html

and the third paragraph of

http://www.techitoutuk.com/knowledge/food/microovens.html

and the fourth paragraph of

http://www.howstuffworks.com/framed...ttp://www.gallawa.com/microtech/how_work.html

Many people apparently disagree with your understanding of how microwaves
behave inside the oven cavity ...

Arfa

H

#### hr(bob) [email protected]

Jan 1, 1970
0
On some cookers, that isn't strictly true.

Dear oh dear ...

http://www.doctorndtv.com/FAQ/detailfaq.asp?id=7837

and 2) of paragraph 1  at

http://www.gallawa.com/microtech/howcook.html

and the third paragraph of

http://www.techitoutuk.com/knowledge/food/microovens.html

and the fourth paragraph of

http://www.howstuffworks.com/framed.htm?parent=microwave.htm&url=http....

Many people apparently disagree with your understanding of how microwaves
behave inside the oven cavity ...

Arfa- Hide quoted text -

- Show quoted text -

If nothing moved inside the oven, there would be a single standing
wave pattern inside the cavity. early ovens had a metallic stirrer
that was used to "mix" the standing wave pattern in an effort to heat
food more evenly. Now, the stirring is actually the moving food, this
damps out the peaks and valleys of the standing wave and also moves
the food within whatever standing waves remain.

Bob Hofmann

A

#### Arfa Daily

Jan 1, 1970
0
William Sommerwerck said:
To quote Galileo: "Nevertheless, it does move." Once upon a time,
microwave
ovens had a "stirrer", a fan that "moved" the standing-wave pattern around
the oven cavity.

Eggzackerly ! One of those references that I gave, also refers to rotating
antennas. Both of these devices for altering the microwave pattern, are
placed in or at the exit of the waveguide, which by definition forms part of
"the emitter".

Arfa

A

#### Arfa Daily

Jan 1, 1970
0
Ron Johnson said:
Remember those old Philips machines? where the magnetron was at the bottom
and fired the magic rays into an aluminium 'fan' which was mounted beneath
the glass floor of the oven. the reflector was propelled by the draught
from the magnetron cooling fan whereupon the microwaves were reflected
upwards through the glass floor of the cavity and onwards and upwards into
the food.

Ron

Never saw one quite like that, but I guess that rotating 'reflector' is the
same principle as the motor driven 'stirrer'

Arfa

S

#### Sjouke Burry

Jan 1, 1970
0
Ron said:
Theres a demonstration which Ive seen, where a shallow plate of
something which looks like porridge is placed in a m/w and when the oven
is operated, you can see the wave pattern on the surface. I`ve also seen
it done with hundreds of neon lamps laid on the plater

The demonstration indicates nicely the hot spots and nulls in the
microwave coverage.

Ron
Put a cd in the mag, and the burn marks on the surface show the
wavelenght and hot/cool spots.
(as soon as you see sparking/smoke, switch off!!!! )
Add a cup of cold water to protect the mag from self destruct.

S

Jan 1, 1970
0
B

#### Baron

Jan 1, 1970
0
Claude said:
Oh, how long do they bounce around tell me. If that were true with the
klystron continuing to transmit more waves and the old ones keep
bouncing around they would build up and explode the oven. That's does
not happen does it.

What do you think heats up the food ! Energy in equals energy out less
losses !

By the way it is a Magnetron in there providing the RF energy.

W

#### William Sommerwerck

Jan 1, 1970
0
Microwaves do, indeed, "bounce around" within the oven cavity. There
Oh, how long do they bounce around tell me. If that were true with
the klystron [sic] continuing to transmit more waves and the old ones
keep bouncing around they would build up and explode the oven. That's
[sic] does not happen does it.

Oh, but it does.

If there's nothing in the cavity to absorb the microwaves, the magnetron
will overheat. The metal walls of the cavity absorb very little radiation,
reflecting most of it.

Now, tell us... What's your real name? (What parents would name their kid
"Claude Hopper"?)

There used to be an old-time-radio company run by a gentleman named Carl
Amari. (Say it out loud.) He was fully aware of the unintentional play on
words.

A

#### Arfa Daily

Jan 1, 1970
0
Claude Hopper said:
Oh, how long do they bounce around tell me. If that were true with the
klystron continuing to transmit more waves and the old ones keep
bouncing around they would build up and explode the oven. That's does
not happen does it.

Are you deliberately trying to mis-understand how these things work ? And
you need to accept that in fact it is *you* who is wrong insisting that
microwave ovens contain a klystron for generating the RF energy. It is a
It simply is, and you are wrong.

As far as the waves bouncing around the inside of the oven cavity goes, they
do, whether you like it or not. I gave you four web references that all tell
you this. Did you actually bother to read any of them ? If microwaves did
not bounce off metal surfaces in a substantially loss-free way, then how do
you imagine that waveguides, some of which can be several feet long, could
possibly work ?

If you knew anything at all about microwave ovens, which clearly you don't,
you would be aware that your contention that microwave ovens are not damaged
by the waves bouncing about in the cooking cavity, is unmitigated nonsense.
They indeed *are* damaged, if there is no microwave-absorbing material such
as food, placed within the cavity in such a way as to intercept the bouncing
waves, and turn their RF energy into heat. That is why when a microwave oven
is being tested, its RF generator must be loaded, the same as with any high
power transmitter. This is done by placing a vessel of water in the cooking
cavity.

Until you understand a little more about the principles of typical consumer
microwave ovens, you would probably be best to make no further comments in
the thread, as you are not currently giving yourself a lot of credibility
....

Arfa

W

#### William Sommerwerck

Jan 1, 1970
0
Until you understand a little more about the principles of typical
consumer microwave ovens, you would probably be best to make
no further comments in the thread, as you are not currently giving
yourself a lot of credibility.

Let's assume the guy's handle is a deliberate joke, and his posts clever
trolling.

F

#### Franc Zabkar

Jan 1, 1970
0
No, it's not. It shouldn't make any difference, as the food is subjected to
the same "pattern" regardless of which way the table turns.

Likewise, it makes no difference whether you roast meat on a spit CW
one time, CCW the next. Neither does it matter in which direction you
stir your coffee, or how you turn your sausages on a barbecue grill,
or whether you flip your pancakes from left to right or right to left.
My guess is that it's to even out the wear.

Agreed, the wear in the gearbox would be evened out, but the bearings
wouldn't know the difference.

BTW I'm right handed, but I sometimes use my left hand to even out the
wear.

- Franc Zabkar

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