How can I use a laptop in a strong magnetic field?

Question

For context, I work in an aluminium smelter where an enormous magnetic field is induced, even in the tea break room. I am trying to use a Dell Inspiron laptop there, so I can get other work done, but my laptop only functions when the keyboard is oriented vertically.

I understand/believe that the issue is a Hall sensor that believes I have closed the laptop lid when I haven't. I have tried changing the settings for what to do when the lid closes, without any effect. Although changing this has proved the issue is the lid closure sensor as I have managed to change from logging me out to simply switching off the screen (marginally less annoying).

I also tried the hack suggested at prevent monitor switching when closing laptop lid by changing the APCI lid driver to the one for the speaker. I couldn't do it perfectly as there wasn't any 'volume control' driver to select. However, this didn't have any effect.

Answer 1

I have lots of experience in designing industrial electronics with or without Hall effect sensors, for the use in steel or aluminium plants, among other things.

The first thing you have to realize about this environment is that it is rough. In addition to the large electromagnetic fields, there's also a lot of particles in the air which you really don't want to get inside your laptop - I've seen quite a few getting ruined in such settings.

The next thing to realize is that this environment quickly separates quality equipment from crap. Hall effect sensors in particular are known to misbehave and should simply be avoided in industrial applications. Any magnetic field including that from a fairly weak magnet could cause such a sensor to run amok.

It's not easy to predict how exactly the field will hit the laptop, given that an aluminium smelter facility probably got some 20+ ovens or whatever running at the same time. Thinking that you can predict this and counter it with a fridge magnet is naive, as is thinking the Hall sensor will behave in any particular way. I've done lots of testing with magnets against Hall-based industrial joysticks, and they just tend to freak out unpredictably when exposed to an unexpected magnet field.

But the rest of the laptop may malfunction or break too in that environment because it was clearly not EMC (electromagnetic compatibility) tested for industrial use. You may in worst case get non-recoverable damage to the circuit boards inside it, but far more the dirt and grime of the environment is what will kill it first.

There are only two viable long-term solutions:

• Can you work from inside the control room? There is usually a control room and it is usually somewhat shielded. The frequencies from the melting process are low frequency, so it is not hard to shield out if they want to.

• Get a better laptop. There are brands that claim to be suitable for an industrial EMC environment. I don't have any particular recommendations (and that would probably be off-topic here too). As a bonus these might actually be IP55-something proof. I know someone who worked with aluminum smelters in particular, and they always used a laptop like that - supposedly from experience.

Answer 2

The Hall sensor can easily be overridden by another (fairly strong) magnet placed very close to it. Proximity counts; it doesn't have to be as as strong as that monster in the smelter.

I had Hall sensors in laptops trigger by fairly weak magnetic clasps on bracelets/watches which made typing while wearing them impossible as the laptop would keep going in "lid closed" mode. Just find a small and relatively strong magnet (a fridge magnet would do, or take apart an old harddrive as they have very strong ones inside). Place the magnet close to the Hall sensor (usually it is in the middle of the base just south of the touchpad) and experiment a bit with the orientation to see which position overrides the smelters field.

Some laptops have two Hall sensors, one near each corner, but locking one of them with a magnet should suffice. Some laptops apparently have the sensor actually in the lid instead of the base, but those are pretty rare. (I never seen one.)

Answer 3

Hardware solution:

• If the magnetic field is from direct current (DC), try orienting a magnet on the case, near the Hall sensor, to effectively cancel the external field. Once you've found a good position, hold it in place with hook-and loop self-stick tape, so the magnet can be removed to close the laptop or use it elsewhere. This is similar to compensating deviation of a magnetic compass, to cancel the fields in a boat, car or other vehicle.

  You might even use a simple pocket compass to find the orientation of the field in that room, and check on the best position for the compensating magnet.

• A shield, e.g., a three-sided box, such as below,

  

  could be made from thin sheet steel or other ferromagnetic metal. This should block an alternating current (AC)-induced magnetic field indefinitely. However, after a while the enclosure may become magnetized and need to be degaussed. On the other hand, plunk a compensating magnet on the enclosure to counter the smelter field.

Answer 4

Try to connect an external monitor, and maybe an external keyboard (if the built-in keyboard stops working altogether with the built-in screen).

My Dell Inspiron 14 5420 (Kubuntu Linux) dual screen/keyboard setup allows to work with the lid closed. I just hit any button to wake it up, and the external monitor lights up.

Answer 5

The bad news first:

1. The display light is switched off when the lid is closed purely in hardware - for all laptops I bothered to check.

2. Whatever the lid closing sensor is (it may be a Hall sensor or a reed contact), it just detects the presence of the magnetic field. Countering this with another magnet is unlikely to be an option.

Conclusion: you will need to alter the hardware somewhat.

Somewhat good news: it is probably a matter of disconnecting a connector inside the laptop.

You can use a magnet to see where the sensor is before opening the laptop.