Maybe the base magnetises over time.
I can recall messing around at school stroking an iron bar with a magnet.
I saw a demo of an induction hob a couple of years ago.
The guy turned on the hob, put a paper kitchen towel on it, then a pan full of water.
The hob boiled the water in the pan without burning the towel.
Clever stuff.
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Maybe the base magnetises over time.
Thats probably whats happening here, maybe the base 'responds' better after use.
You can put your finger between the hob and pan, whilst heating up and until the pan base gets hot the hob remains permanently cool, as you say very clever.
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I suspect it's a normalisation process where any residual magnetism in the pan bases (which would tend to be in a less lossy part of the B-H hysteresis diagram) is being removed - mainly, I suspect, by the heat itself.
GB - I thought you weren't a fan of technology, and I would have imagined that you would trust nothing newer than an AGA, or even an open range!
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I would have imaginedthat you would trust nothing newer than an AGA or even an open range!
Trying to think of some excuse here....no use, it's a fair cop guv you've got me bang to rights etc..;)
In mitigation i don't mind technology when its static, as in this case where the advantages outweigh possible dis....its no use you've caught me fair and square, i actually like advance so long as its totally reliable, and we have found that better makes of home white goods are streets ahead of other not always cheaper rivals in build quality and reliability.
I just hope no one else is reading this, never live it down.
I don't quite understand about the magnetism being reduced through use, in my simpler world i somehow guessed that regular use would make the pan bases more susceptible to being magnetised..have i got it all backwards again?
EDIT, by the way its in the blood, my family in Eire cooked for years on an open peat fire in the kitchen...little hope for me is there.
Edited by gordonbennet on 12/04/2009 at 15:27
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In use, the material is being driven round this curve;
>>www.magnets.bham.ac.uk/magnetic_materials/hysteres...m
and the area enclosed is proportional to the heat energy for each cycle.
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Induction cookware
During the 39-45 war, steel ships became magnetised by the earth's magnetic field to become more susceptible to exploding enemy magnetic [detection] mines. The solution was to use a coil round the ship and pass a large AC current through the coil. And repeat that periodically. That current cycled the magnetism [first in one direction then in the opposite] and the current was then reduced smoothly -- not just switched off -- so as not to leave significant residual magnetism.
Note we are talking AC here [as is your mains electricity supply] not DC current [flows in one direction only]. Mains AC current flows first in one direction for 1/100th second and then in the apposite direction for the next 1/100th second etc.
It is the use of the A/C magnetic effect that produces the heat, [a steady coil current, or magnetic field, does not induce any heat.
Heating works somewhat similar to using a transformer where, instead of having a secondary winding on it [in which voltage would be induced by the AC magnetic field produced by the mains primary winding] a saucepan takes the secondary's place. And AC current flows in loops [eddy currents] in the metal of that. As the saucepan metal is made of [electrically] lossy material, it heats up. Which is what you want.
If the cooker switches on the magnetic field, even though a saucepan is not near the hob, {I am not familiar with an actual design] the procedure of moving the saucepan into and out of that AC magnetic field will cause a similar effect to that used to demagnetize ships. process.
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more susceptible to exploding enemy magnetic [detection] mines. The solution was to use a coil
Absolutely amazing, thanks for that.
this forum is a veritable mine (groan) of information..;)
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" this forum is a veritable mine (groan) of information..;) gordenbennet "
How you have the neck to rate my contribution as boring escapes me, especially with the useless trivia claptrap nonsense that populates many inches of these columns.
63 years ago, when hundreds of ships and thousands of men were being sunk in bringing essential supplies to this country to defeat fascism, so that you can now have the privilege to get bored, this was advanced technology. Who would have guessed then that a non-contact mine could be made using those principles. Or the earth's mere 0.6 gaus magnetic field was enough to magnetise a ship.
Also many mine disposal experts got blown up in taking these things to pieces to find out how they could be defeated, so that others would not get blown up by them.
These people did not get bored, even if you are so easily bored by technical stuff you do not understand, and don't want to.
buzbee
Edited by Dynamic Dave on 14/04/2009 at 11:16
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How you have the neck to rate my contribution as boring escapes me
Looks like someone didn't spot the smiley.
Also moved to the correct place in this thread where the conversation took place.
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buzbee
I do not know where you cut and pasted your info from but there is a fundamental mistake in it.
>>Heating works somewhat similar to using a transformer where, instead of having a secondary winding on it [in which voltage would be induced by the AC magnetic field produced by the mains primary winding] a saucepan takes the secondary's place. And AC current flows in loops [eddy currents] in the metal of that. As the saucepan metal is made of [electrically] lossy material, it heats up. Which is what you want.<<
Not true - on domestic induction hobs the heating is by hysteresis losses, as explained by NC in his link. If it was eddy current losses, the heating would work with any electrically conductive pan material.
p
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Yes I did see the hysteresis point made by NC and you rightly point out I strayed off path if it is mainly that that supplies the heat. -- I don't know as I have no information as to the formulation of the metal used and I don't have a saucepan to measure.
But the saucepan, if it is made of metal that is electrically conductive (?), as opposed to using a ferrite type material, will conduct electricity and, in that case, there will be a contribution of heat from the eddy currents.
As to the eddy current effect [efficiently] working with any material, that is not entirely true because copper, for example, would be so efficiently conductive as to be a very poor generator of heat. If you put a resistor across a secondary winding, most of the heat is in the resistor. So I was looking at it as a lossy secondary.
In my defense I was trying to be not too technical, for the benefit of the less technical reader.
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I'm sure the eddy currents will contribute too - they're bound to.
One interesting demonstration I saw of this type of phenomenon was with a small but strong magnet was dropped through air to land on a sponge.
It was then dropped through a normal 1 metre length of Copper plumbing pipe, and because of the eddy currents, and their damping effect on the magent it took longer for the magnet to fall.
Finally, the pipe was cooled with some liquid Nitrogen, and because the resistivity of the cold Copper pipe was so low, and the resulting currents so large, the magnet took ages to fall.
Old fashioned mechanical speedos used to work on the eddy current damping principle, and so, these old mechanical instuments did actually have a slight temperature dependence in their response.
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Buzbee
Sorry I was a little lazy in my comments. Interestingly having now browsed thro a series of articles it appears that eddy currents are significant in industrial heating applications. Nowhere can I find an indication of the quantative contribution eddy currents make in domestic induction heating other it makes a 'small' contribution.
I would guess that the design is such that safety devices do not allow the domestic induction heating to take place if there no significant magnetic coupling. This would safeguard people with metal rings, bracelets, watch straps etc. It would be interesting if someone with an induction hob actually tries aluminium or copper pans to see if there is any significant heating.
p
Edited by pmh2 on 14/04/2009 at 23:10
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It would be interesting if someone withan induction hob actually tries aluminium or copper pans
No they won't have it, the sensing system on the hob will not allow the thing to fire up unless it senses the correct metal, i've tried all sorts.
I bought a very hefty fry pan from my favourite Lidl's a few months ago, big thick solid base typical of induction pans, and at a good price.
Unfortunately i didn't have me reading specs and thought one of the symbols on the packaging was the coil for induction...wrong! it was probably for ceramic hob or halogen or something, they all look the same to me...never had this problem with the Rayburn.
My daughter was very pleased with her new frypan..;)
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How you have the neck to rate my contribution as boring escapes me especially with the useless trivia claptrap nonsense that populates many inches of these columns.
Buzbee, you misunderstand me completely, and i can see from my ill written post why, it does read not too well....a common failing of mine as regulars here know well enough.
I am sorry for any upset, i assure you i was serious about the amazing facts about the ship's magnetic attraction, and your informative post needed no ignorant comment from me, i was quite astounded that the normal movements of a ship could cause such a serious problem.
I put the quip about 'mine' in only as a joke and it was obviously misinterpreted.
Please accept my apology...gb.
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Thanks. The blood pressure has dropped a few points. Incidentally, I was nine when that war started and here in the UK.
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GB - I thought you weren't a fan of technology and I would have imagined that you would trust nothing newer than an AGA or even an open range!
>>
NC - we can beat that! We have an Aga and an induction hob in the construction site that will be the kitchen. I'm looking forward to trying out the metal plate in my wrist on the hob. :-)
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I'm looking forward to trying out themetal plate in my wrist on the hob. :-)
That'll be fun when the burns heal, wandering aimlessly round the hardware shop and all sorts of sharp ferrous objects will be hurling themselves straight for your hand, try explaining that to the security guard as you shuffle out looking like Pinheads (Hellraiser) hand with swag in tow..;)
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Be careful if you have a heart pacemaker.
www.pricerunner.co.uk/ba/106/Hob-buying-advice
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Thanks NC i think i've got the basic idea now.
And thanks L'esc, something to file away in the empty head just in case, i wonder how real the threat to a pacemaker is, or the industry covering itself for the inevitable claimsRus crew.
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Not being even 1% as clever as NC, I would guess that if a mobile phone signal can interfere with the fly by wire controls of an aircraft, a magnet strong enough to boil 4 pints of water could fry the circuits in a pacemaker!
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if a mobile phone signal can interfere with the fly by wire controls of an aircraft
It cant. the fly by wires controls on an aircraft are EMF hardened. They have to be to survive the much higher power of the aircraft radio, radar and transponders.
Edited by Altea Ego on 12/04/2009 at 17:22
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Well radio waves from ground transmitters can affect the controls of military jets, to the extent that they must avoid certain transmitters by X Miles. If mobile phones cannot interfere with aircraft controls why are mobiles are bannd from use on board?
Dangers From Onboard Use Of PEDs/Mobile Telephones
There is AMPLE recorded evidence that Personal Electronic Devices (PEDs) including Mobile Telephones are: -
Used during flight whether permitted or not and
Have the potential to interfere with aircraft communications, navigation and, perhaps more rarely, control (engine, FMS) systems.
Edited by Armitage Shanks {p} on 12/04/2009 at 17:31
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Cannot find the relevant url now but the CAA did some testing a few years ago which demonstrated that PED and mobiles in particular might interfere with a/c systems and thsat the possibilty certainly could not be eliminated. The subject also comes up from time to time in the AAIB bulletins. I'm sure I've read one somewhere where the "handshake" calls from a flight crew mobile left on in a bag rendered the cockpit voice recorder partially inaudible .
My impression is that the results are unlikley to be catastrophic but are potentially sufficiently distracting to present a risk during take off and approach. Use of MP3 players laptops etc is often permitted once away from critical phases of flight but the cabin crew of the FlyBe EMB195 on which I recently flew to Edinburgh and back checked very carefully during taxi out that all I-Pods etc were switched off.
Edited by Bromptonaut on 12/04/2009 at 20:32
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Yes, I'd say,as an RF designer, that there will always be a remote possibility that a signal from a mobile or other source of RF power might cause interference to sensitive equipment, particularly the " I'm here " message a mobile always sends when powered on. With vast quantities of electronics products being churned out in the Far East the chances of a rogue product are on the increase IMHO.
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Before somebody throws in the red herring about some airlines allowing (now or shortly) the use of mobiles whilst in flight, it is worth pointing out that the aircraft will use a micro? cell transmitter on board which will mean that the phone operates at low xmit power, further reducing the risks of interference with on board equipment. SpamCam can probably fill in the details.
It will also be a wonderful commercial opportunity as the the cell operator charge rate will probably make premium rate calls look cheap! Watch for Ryanair to publish rates.
p
Edited by pmh2 on 12/04/2009 at 23:10
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Before somebody throws in the red herring about some airlines allowing (now or shortly) the use of mobiles whilst in flight it is worth pointing out that the aircraft will use a micro? cell transmitter on board which will mean that the phone operates at low xmit power further reducing the risks of interference with on board equipment. SpamCam can probably fill in the details.
As he hasn't then I will. A basestation has a large though limited dynamic range, that is to say that it can deal with signals arriving within a certain power range. This is very dependant on two things, the Effective Radiated Power of the mobile and the path loss between the mobile and the basestation. The basestation also knows what power level it is receiving and then instructs the mobile to adjust its power level accordingly for the next burst. with the pico cell on the plane, it will be so close to the mobile that the mobile will almost always be told to transmit at minimum power level of 20mW, against a nominal 1W max which is more typically 600mW to save cost and increase battery life.
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of the FlyBe EMB195 on which I recently flew to Edinburgh and back checked very carefully during taxi out that all I-Pods etc were switched off.
They also check that the totally inadequate lap belts are done up. Another relic from the 50's and a complete waste of time
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>Well radio waves from ground transmitters
can be measured in meggawatts
The peak signal of a hand held mobile phone is two watts.
The aircraft HF radio is AM and far more powerful, The Pulse radar has a higher output.
Mobile phone do not interfere with onboard aircraft electronics.
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anybody who has their mobile phone at the side of their bed and the alarm clock radio on low to be awakened by the de de de de de of a mobile phone would appreciate that this could mess with electronics in another apparatus
im really against mobile phones on planes
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anybody who has their mobile phone at the side of their bed and the alarm clock radio on low to be awakened by the de de de de de of a mobile phone would appreciate that this could mess with electronics in another apparatus im really against mobile phones on planes
The aircraft HF transmitter would blow your alarm clock up
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The aircraft HF radio is AM and far more powerful The Pulse radar has a higher output. Mobile phone do not interfere with onboard aircraft electronics.
All the radios are AM. You've piqued my curiosity now though, since I've never really given it much thought. I've never noticed it before, but will try tomorrow on the ground. The ADF needle will turn to follow trains(!), so I suspect it might be fairly sensitive to mobile phones.
The pulsing through the intercom system is extremely irritating, however, and seems to happen regardless of the manufacturer or age of the system.
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The pulsing through the intercom system is extremely irritating however and seems to happen regardless of the manufacturer or age of the system.
This is always going to be a tricky one to stop; a GSM mobile transmits its RF power in bursts which have a pulse repetition rate of 217Hz, i.e. slap bang in the audio frequency range.
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Whenever I've listened to aircraft transmissions, it's always been on FM.
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Whenever I've listened to aircraft transmissions it's always been on FM.
Not possible - its AM only. check out the specs of any airband reciever.
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>>Not possible - its AM only. check out the specs of any airband reciever.>>
Bit puzzled about this. I have a couple of portable radios which include the air bands; after the normal FM 88-108MHz local and national radio programmes, the air band runs from 109 to 136MHz.
This ties up with my experience of being able to observe the transmission frequencies used by pilots during my flights over the years in various sizes of aircraft; these are around the 120MHz mark.
The general aviation frequencies are listed here:
www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=7865 (from link in www.dxzone.com/catalog/Radio_Scanning/Aeronautical/)
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>>Not possible - its AM only. check out the specs of any airband reciever.>> Bit puzzled about this. I have a couple of portable radios which include the air bands; after the normal FM 88-108MHz local and national radio programmes the air band runs from 109 to 136MHz.
Quite right the airband *frequency range* is 109 - 136. but the modulation is AM.
88-108 is a frequency range - but it is reserved for commercial radio using Frequncy Modulation.
Aircraft have two types of radio HF - high freqency AM and VHF AM. (VHF AM is aircraft to local ATC)
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That explains my confusion...:-)
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The pulsing through the intercom system is extremely irritating however and seems to >>happen regardless of the manufacturer or age of the system.
David
I have found this as well when flying. Try routing the intercom lead well away from the pocket with the mobile in. The interference is minimised then.
HTH
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In about 1991 my XR3i suffered a problem caused by a mobile phone being operated in a car alongside when I was stationary at traffic lights. For about a day afterwards, the engine would start OK, but would not run unless I applied some throttle. Every time I changed gear the engine cut out as soon as I depressed the clutch and took my foot off the accelerator. A knowledgeable electronics colleague said that the phone had caused my car's ECU to get its knickers in a twist and that it needed a few hours to get back to normal. Fortunately, after 24 hours the problem had gone away.
That's another reason for not using a mobile phone in a car.
Edited by L'escargot on 14/04/2009 at 07:37
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That's another reason for not using a mobile phone in a car.
that was in 1991. 18 years ago. A car along side? - you dont know the phone caused it,
Edited by Altea Ego on 14/04/2009 at 12:39
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I used to pass through Heathrow's BA shuttle lounge regularly and I recall that, on several occasions in the early 1990s, that BA's computer system would go down.
The lassies behind the counter would state it was due to someone using one of those brick-like mobile phones somewhere in the lounge.
Always surprised me that BA didn't ban the use of phones in the lounge.
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>>... BA's computer system would go down.....it was due to someone using one of those brick-like mobile phones
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Well that was a complete load of tosh!
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>>Well that was a complete load of tosh!>>
That was the explanation provided every time and it was never the same staff on duty.
I did point out that it was in the early 1990s.
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That was the explanation provided every time and it was never the same staff on duty. I did point out that it was in the early 1990s.
Having worked with airline computers in the UK and many counties for 35 years ( starting in 1965) I have a little more insight than such staff however well intended their comments were.
One of the most amusing ( to some ) for delaying an airline switching over to local computer terminals was poor communications in Mafeking.
That was due to poor copper wires on poles not mobile phones :-)
Or the time were were told our kit was delayed in customs but when we flew there we found our kit on sale in the souk. That too gave system problems :-)
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The BA computer system would go down ok, but not for that reason.
It was a very specialised version of an operating system. It was cut down and had no error checking or error recovery routines, That gave it very fast response times and the ability to handle and process large amounts of data concurrently. As it had no error recovery it would fall over very easily, but would reinitialise very quickly.
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it would fall over very easily but would reinitialise very quickly.
Bill Gates made a fortune making early versions of Windows work exactly like that
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>> That's another reason for not using a mobile phone in a car. that was in 1991. 18 years ago. A car along side? - you dont know the phone caused it
It was merely a little anecdote on the subject. It doesn't matter to me how much credibility anyone places on it.
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Back in 1991 I had one of those Motorola bricks, and when in my Calibra I knew it was going to ring because the ABS light came on. Sure enough, the ABS light would come on and in milliseconds the 'phone would ring.
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The radio/CD player in my son's room makes noises when my mobile phone does any signalling (usually just location updates but also incoming call set up). IIRC the car stereo does the same.
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