Anti-magnetic properties of military/aviation watches

[Crusader]

Hello all,

the article on the Mark XI (quoted on the main forum) states that the need for anti-magnetic protection of the navigation watches came about as a result of the electromagnetic fields of various on-board instruments, like e.g. radar which negatively affected the watches then in use in the cockpit.

Some of today's aviation watches still boast a very high level of antimagnetic protection (80.000 a/m, in the case of the Sinn and IWC Fliegeruhren). The current American miliatry navigator watches (F and G revision of the mil-spec) have 10.000 a/m, the British RAF-issued G10/2000 -- I think -- 4.800 a/m . This is also the DIN/ISO norm for "antimagnetic" watches. And indeed many watches of the latter antimagnetic grade (i.e. 4.800 a/m) appear to be used in aviation quite freely.

I was wondering if the danger from electromagnetic fields typically found on aircraft has decreased during the past decades (which would mean, e.g. that companies like Sinn and IWC are in effect promoting outdated standards), or do those who use other watches - like e.g. a Submariner, or GMT-Master - on airplanes run the risk of losing precision or having their watches magnetized by exposing them to the EM fields on airplanes?

Can anyone shed some light on this? What are the anti-magnetic experiences of the flight crew members or others on the forum? Are the anti-magnetic properties an "issue" when choosing a pilot's watch?

Many thanks and best regards,

Crusader (currently on leave to impersonate Anthony Blair, PM)

[Ming Thein]

Good question. To be honest, I can't understand the increase in magnetic field strength with altitude - how? The earth's field gets weaker as you move further away from it. I doubt very much that there are enough field generators in an aircraft to affect a watch that much.

Example: during my physics days I frequently did experiments with a 2 tesla magnet (info: it required water cooling and 10,000 volts to run) - for those who have no idea how strong that is, it's about 4,800,000 a/m or something in that range. But the field strength anywhere immediately outside the 1cm square area between the poles dropped dramatically, to the point that when you were 20-30cm away, it was only maybe 2,000 a/m. A fair quantity of energy is required to generate field strengths like that over large areas of space - which makes me wonder how necessary it all is.

And with regard to modern aircraft, you would have expected the shielding to improve, right? Magnetic fields aren't all that good for your body either, and you certainly would have thought that the aircraft manufacturers would have done something to address this if it indeed represented such a risk.

But in any case, I'm not worried. Ever since I got the Dreadnought I've always flown with it, and the Omega Dynamic (which also has antimagnetic protection, to 9600 a/m I think) before that. :D

Just my two heavily devaluing malaysian ringgit...

Ming

[Crusader]

I doubt very much that there are enough field generators in an aircraft to affect a watch that much.

Actually I think there are quite a lot: Radios, radars, computers with lots of backup, transponders, fly-by-wire... The stuff is so sensitive that switching your mobile on will seriously affect operations. Add to that specialized military equipment like IFF transmitters, ECM equipment and so forth.

What I don't understand is that if all those gadgets do have a strong EM field (as they should), any pilot really ought to be prohibited from bringing a less-than-required anti-magnetic watch on board or at least from using it. Or would they be shielded (so as not to interfer with each other) to such an extent that the conventional 4.800 a/m would be sufficient? But then why the hassle about not switching your mobile on in flight?

Tony B. a.k.a. as Crusader

[Ming Thein]

I doubt very much that there are enough field generators in an aircraft to affect a watch that much.

Actually I think there are quite a lot: Radios, radars, computers with lots of backup, transponders, fly-by-wire... The stuff is so sensitive that switching your mobile on will seriously affect operations. Add to that specialized military equipment like IFF transmitters, ECM equipment and so forth.

What I don't understand is that if all those gadgets do have a strong EM field (as they should), any pilot really ought to be prohibited from bringing a less-than-required anti-magnetic watch on board or at least from using it. Or would they be shielded (so as not to interfer with each other) to such an extent that the conventional 4.800 a/m would be sufficient? But then why the hassle about not switching your mobile on in flight?

Tony B. a.k.a. as Crusader

I don't know, to be honest. I think it's quite possible that the mobiles won't work anyway. But then again, they use them on the planes in the US - so why can't we do it here? Surely the extra 100mhz in frequency doesn't make that much of a difference.

I suspect you're probably right about shielding - if they weren't, they would almost certainly interfere with each other. Ergo, your watch should be fine. In any case, most pilots seem to wear cheap multifunction cbp quartz watches.

Ming

[JasonG]

Hmm.

I wonder if it was anything to do with the use of magnetos in older piston-engined aircraft...they produce quite powerful fields but I'm not sure of any figures to back that assertion up. :)

ttfn

JasonG...intrigued and now doing a bit of internet research... :)

[Crusader]

I wonder if it was anything to do with the use of magnetos in older piston-engined aircraft...they produce quite powerful fields but I'm not sure of any figures to back that assertion up. :)

Thanks for the help, Jason!

The article on the Mark XI refererred to hull-mounted (and therefore closer to the cockpit) sources of EM fields, like radar sets, rather than to the engines.

A technically incompetent PM.

[Ming Thein]

I doubt very much the magnetos would be the source of the problem. Don't forget that magnetic field strength drops off proportional to the inverse cube of the distance - possibly more depending on the geometry - so by the time you get a couple of meters away there isn't much to worry about.

Ming

[jim]

The article on the Mark XI refererred to hull-mounted (and therefore closer to the cockpit) sources of EM fields, like radar sets, rather than to the engines.

So, Prime Minister, would these sources be strategic or merely "battlefield"?

Jim

[Ming Thein]

The article on the Mark XI refererred to hull-mounted (and therefore closer to the cockpit) sources of EM fields, like radar sets, rather than to the engines.

So, Prime Minister, would these sources be strategic or merely "battlefield"?

Jim

:lol: :lol: :lol:

I think he isn't at liberty to discuss that. Or he'd have to kill you if he told you. Or something like that.

Ming

[swanbourne]

Any equipment which transmits radio waves is a potential source for substantial electromagnetic radiation. Well maintained equipment is less likely to create problems but there will still be radiation around the transceiver, arial cable and the aerial.

All aerials are designed to transmit and receive within a certain frequency range and often, an aerial tuning unit is installed between the aerial and transceiver to match the frequency more precisely. If there is a mismatch between the aerial and transceiver, their is resistance within the system and the energy will radiate from the weakest points between the transceiver and aerial, i.e., the aerial cable.

I have seen the LCD panel on a digital watch turn totally blank when keying the microphone on an unmatched system. I have destroyed a power supply by trying to tune an unsuitable aerial to the point where the radiation burnt out tracks on the circuity board and blew components clean out of the board.

Police officers using the type of personal radio which clips to their collar experience a higher incidence of headaches and eye infections; two special branch policemen who wore special radios, where the transmitting unit was strapped to their back, suffered serious kidney damage; American radio amateurs (who are allowed to operate at higher power levels than most other countries) suffer a higher percentage of leukemia than the general population; radar operators all know that standing in front of the parabola when the equipment is transmitting can cause permanent sterility.

Having experienced radio frequency burns from comparatively low-powered transceivers, I have no doubt that any equipment transmitting radio waves has the potential to create very strong magnetic fields and also the potential to damage equipment and health.

Eddie

[Ming Thein]

Bloody hell. :shock: But have you ever buggered any of your watches unintentionally with radio equipment?

Ming

[swanbourne]

Never knowingly damaged a watch but I've wiped untold floppy disks and damaged audio tapes.

Eddie

[Crusader]

I am greatly impressed, Eddie! :shock:

Keeping my mobile at arm's length presently... :?

What happens when a watch is exposed to such an EM field? Will it resume working after it has been removed from the field, or si the damage permanent? Will a mechanical watch be magnetized?

A saint.

[Ming Thein]

Never knowingly damaged a watch but I've wiped untold floppy disks and damaged audio tapes.

Eddie

Phew, thank God for CDs.. :D

Ming

[Ming Thein]

I am greatly impressed, Eddie! :shock:

Keeping my mobile at arm's length presently... :?

What happens when a watch is exposed to such an EM field? Will it resume working after it has been removed from the field, or si the damage permanent? Will a mechanical watch be magnetized?

A saint.

It runs minutes fast usually due to the attraction between the magnetized parts. It is possible to just stick it into a demagnetizer (which is a machine which removes the magnetism through a means I don't fully understand) which restores the watch to normal.

Ming

[JasonG]

I doubt very much the magnetos would be the source of the problem. Don't forget that magnetic field strength drops off proportional to the inverse cube of the distance - possibly more depending on the geometry - so by the time you get a couple of meters away there isn't much to worry about.

Ming

Indeed, given if the engine(s) is(are) on the wings...if the engine is in front of the pilot, like most small aircraft, then the electrics are very much closer.
Mind you, a field of 4800A/m is quite large, probably not achievable with kit at the time...I wonder why such high immunities were deemed necessary?

My employer used to have quite a problem with magnetic fields in transmitter halls, so I'll ask one of the old-timers what kind of fields were experienced in the big halls...

ttfn

JasonG

[swanbourne]

Once a watch has become magnetized it will have to be de-magnetized, it won't get better on its own. I have seen some DIY methods discussed on various fora but I don't think they're particularly effective.

Loudspeakers and computer monitors are the worst culprits for magnetizing watches.

Eddie

[Crusader]

computer monitors

LCD too, or only the old-style ones?

An enquiring mind.

[swanbourne]

I haven't heard of the LCD ones being a problem, only the CRT flavour.

Eddie

[JasonG]

I have now had a chat with "someone who should know" about this mag-field in aircraft thing. :)

It's nothing to do with magnetos, rf kit, nav kit or anything else, plus I now know why the specs have been reduced. :)

Lightning.

The magnetic field experienced when an aircraft is struck by lightning is very very large, hence the obscenely high field specs. No other ill effects are usually observed, since the lightning simply uses the metal in the aircraft as part of it's path to ground; a stop-over, so to speak. :) The huge currents very close by can easily produce the sorts of fields we have been discussing.

Nice and simple. :)

In the old days, when a wristwatch was a very important piece of navigation kit, it had to keep working accurately, or you get very lost very quickly. These days it's not so important as aircraft almost always have their own clock and now GPS and other nav aids.

Hopefully, that'll satisfy the curious on this thread. :) AND it comes from a reliable (single, unattributed) source. :)

ttfn

JasonG

[swanbourne]

Thanks for that Jason, I would never have thought of it.

Eddie

[Ming Thein]

Jason, that makes sense. (I was pretty sure the instruments/radar weren't the cause of the problem.) The electric fields (and thus magnetic fields) produced by lightning ARE huge - we're talking 20MV/m and the like. I don't think a watch would stand a direct lightning strike :!:

Ming

[Ming Thein]

computer monitors

LCD too, or only the old-style ones?

An enquiring mind.

Just the CRT ones. LCD and Plasma monitors don't have magnets in them at all.

Ming

[swanbourne]

Jason, that makes sense. (I was pretty sure the instruments/radar weren't the cause of the problem.) The electric fields (and thus magnetic fields) produced by lightning ARE huge - we're talking 20MV/m and the like. I don't think a watch would stand a direct lightning strike :!:

Ming

I think if lightning struck your watch whilst you were wearing it, your immediate worry wouldn't be the watch. :twisted:

Eddie

[Jeroen]

I haven't heard of the LCD ones being a problem, only the CRT flavour.

Eddie

The Liquid Crystals are very small electric cells powered by low voltage and current
so not to much electric energy flowing
The CRT uses rather high voltages between the kathode and the grid (luminous raster) of anything between 22.000 and 40.000 volts....

as we all know electricity causes electromagnetic fields... the higher the current or voltage (in effect the electric energy flowing) the more powerful the electromagnetic field..... which can magnetize metals permanently... you can see that effect on CRT monitors because grid getz magnetised too and then will show flaws in colour and shape.... :blob7:

This is corrected by 'degaussing' or demagnetising the grid..... most of the time done automatically when you switch on a monitor but many computermonitors also have a degaussing button or setting in the OSD...

older monitors and TV sets can be 'degaussed' with a special ringmagnet....

just my



Jeroen

[Jeroen]

Just the CRT ones. LCD and Plasma monitors don't have magnets in them at all.

Ming

Neither do CRT's Ming ( only very small magnets...)
a Cathode Ray Tube discharges electrons by heating up the Cathode and then 'shoots' them at the screen by means of the huge difference in electric charge..... (that's what causes the magnetic field in the end.....)

the direction of the electronbeam then is influenced by low voltage low power electric fields between a few sets of small electrically charged metal plates (we're changing direction of electrons here...)....

there are only a few sets (mostly 4 sets of two)of permanent very low intensity ring magnets on the tube end to influence the 'zero'setting of the cathodes for the different colours and the focus of the beam....
one set... two magnets are used by rotating them in opposite direction and as a set.... for one colour..... and the you have to do that for each sseparate colour.... and the focus...(adjusting a CRT is a bitch.... the sets are all influencing eachother...)

Jeroen

[JasonG]

Just the CRT ones. LCD and Plasma monitors don't have magnets in them at all.

Ming

Neither do CRT's Ming ( only very small magnets...)
a Cathode Ray Tube discharges electrons by heating up the Cathode and then 'shoots' them at the screen by means of the huge difference in electric charge..... (that's what causes the magnetic field in the end.....)

the direction of the electronbeam then is influenced by low voltage low power electric fields between a few sets of small electrically charged metal plates (we're changing direction of electrons here...)....

there are only a few sets (mostly 4 sets of two)of permanent very low intensity ring magnets on the tube end to influence the 'zero'setting of the cathodes for the different colours and the focus of the beam....
one set... two magnets are used by rotating them in opposite direction and as a set.... for one colour..... and the you have to do that for each sseparate colour.... and the focus...(adjusting a CRT is a bitch.... the sets are all influencing eachother...)

Jeroen

I'm afraid they do Jeroen...most of the beamforming is done electrostatically but the line and field scanning are done electromagnetically, ie: with coils, producing moderate magnitude fields.

And Ming...plasma displays produce mag fields by the nature of their operation...the plasma currents produce mag fields, albeit quite small, but they are there nonetheless.

:)

ttfn

JasonG

[Jeroen]

I'm afraid they do Jeroen...most of the beamforming is done electrostatically but the line and field scanning are done electromagnetically, ie: with coils, producing moderate magnitude fields.

completely forgot about those ....
the days of fieldservice on high-end graphics equipment are long gone..... :?

Although I do guess the vast voltagedifferential between Cathode and Grid is the main cause for the magnetic field of CRT's (why else the degaussing ?)
Or am I forgetting something there too?...

Jeroen

[Ming Thein]

I'm afraid they do Jeroen...most of the beamforming is done electrostatically but the line and field scanning are done electromagnetically, ie: with coils, producing moderate magnitude fields.

And Ming...plasma displays produce mag fields by the nature of their operation...the plasma currents produce mag fields, albeit quite small, but they are there nonetheless.

:)

ttfn

JasonG

:D Vindicated. What I meant with the plasma screens is that they don't use magnets for beam focusing/image formation - magnetic fields are inherently produced whree there is any current flowing, due to the nautre of the beast.

Ming

[Ming Thein]

Jason, that makes sense. (I was pretty sure the instruments/radar weren't the cause of the problem.) The electric fields (and thus magnetic fields) produced by lightning ARE huge - we're talking 20MV/m and the like. I don't think a watch would stand a direct lightning strike :!:

Ming

I think if lightning struck your watch whilst you were wearing it, your immediate worry wouldn't be the watch. :twisted:

Eddie

Well, you know me. Wierd mind and all that. :wink: I guess it would also largely depend on what watch you were wearing at the time :roll:

Ming

[JasonG]

completely forgot about those ....
the days of fieldservice on high-end graphics equipment are long gone..... :?

Although I do guess the vast voltagedifferential between Cathode and Grid is the main cause for the magnetic field of CRT's (why else the degaussing ?)
Or am I forgetting something there too?...

Jeroen

Heh, no worries. :)

The mag field due to the beam current is quite small, due to the beam currents themselves being very small, so that's not where the magnetization of the metalwork comes from. Metal chassis members are usually magnetized by the line and field coil fields, plus a healthy contribution from the earth's field...note that magnetization is not as much of a problem these days since the chassis of most displays are now plastic. The rest of the problem (ie: in display colour and alignment problems) comes from when the anode mask itself becomes magnetized...used to be quite a problem as they were nickel...less so now.

ttfn

JasonG

[abraxas]

I don't understand none of that.

What I do know is that for over 50-60 years the parts that used to become magnetically @@@@ have been replaced with non magnetizable parts. If I remember correctly, balance spring coils use to stick together making the watches run fast, when was the last time you have heard of that? Modern ETAs etc should have no problems. If you still worry get one of these: http://tinyurl.com/3cqap (very nice)

john

[Ming Thein]

I thought the whole point of using Glydcur and Nivarox alloys was their resistance to magnetic fields, and their thermal stability. I guess if you want total magnetic resistance then get a Lange 1A, the entire train is made of gold :D

Ming

[Crusader]

I guess if you want total magnetic resistance then get a Lange 1A, the entire train is made of gold :D

The ultimate tactical watch, then, and a redefinition of "understatement"!

Crusader

[Ming Thein]

I guess if you want total magnetic resistance then get a Lange 1A, the entire train is made of gold :D

The ultimate tactical watch, then, and a redefinition of "understatement"!

Crusader

Yes, but we'll have to PVD it first, and give it a luminous dial.

Ming

[Ming Thein]

I forgot the fitted rubber strap.

Ming