OK to keep an exposure meter in a metal storage cabinet?

[Wayne Lambert]

Seems as if I once read that an exposure meter (and, by extension, hand-held GPS units, etc.) should not be kept in a metal storage cabinet, because somehow the circuitry would be altered or harmed by the enclosing magnetic environment. Any thoughts?

Thanks,
Wayne

[BrianShaw]

I keep mine in a metal file cabinet, and have done so for several decades, with no ill effects. It would be nice if there is a EE who can comment on the magentic environment of a metal cabinet... and on the topic of EMI/EMC effects on light meters in general.

[Drew Wiley]

I'd be a lot more concerned with the humidity that can develop in any metal cabinet and lead to mold in the lens elements. A very real risk unless you put dessicant
canisters in there too.

[jp]

I'm more of a physics/electricity enthusiast/mad scientist than an EE.

I don't see what exposure meters and handheld GPSs have in common with regard to delicate circuitry, except a metal cabinet would protect both from nuclear EMP event to some extent

A GPS unit is a very rugged radio receiver. Those are often built into metal boxes so they work better! (less noise and intermod) An exposure meter is a crude (in the elegant sense) device for measuring light. If the light meter has an analog needle display, that functions by magnets, but it's no different than a vu meter in a radio or an old volt meter or speedometer. You can alter those magnets with strong magnets, but probably dust, battery corrosion, impact are more common modes of failure or lack of calibration on those things. But a metal cabinet would be better than a cardboard box.

[Nathan Potter]

If you are talking about the metal cabinet itself containing a residual magnetic field (and they do) it would ordinarily be miniscule and not affect either a GPS or a light meter stored inside. The earths magnetic field would likely be higher. If you are talking about another magnet (a ferromagnet) inside the cabinet then depending on distance of your items from the magnet there could be an effect while making a measurement using an analogue spot meter particularly, but all electronic digital meters and GPS are doubtful. Any permanent damage to all electronic circuitry is doubly doubtful.

I suppose if you are really concerned about it you could wrap your instruments in a diamagnetic blanket, the most efficient being a superconductor based blanket where virtually all the electrons are paired providing a long range diamagnet effect depending on the coherence length of the electron wave function. ;)

[Mark Woods]

The only problem I've had with my light meters is stepping over the high voltage cables that are coiled on stages (or outside). The magnetic field radically changes the meter reading. I had it happen on a stage where I had 324,000 watts lighting a sound stage. Fortunately, I only had to reboot the meter (take the battery out for a few minutes) and it worked fine. I avoided the cable figure 8's after that.

[David Lobato]

Shouldn't be a problem with just a storage cabinet. What about cars, trucks, airplanes, buses, trains, etc? They are metal shells with electrical and magnetic systems. If GPS, cameras and meters can work inside a car or an airplane, a metal storage cabinet is nothing to worry about.

[Bill Burk]

The only problem I've had with my light meters is stepping over the high voltage cables that are coiled on stages (or outside). The magnetic field radically changes the meter reading. I had it happen on a stage where I had 324,000 watts lighting a sound stage. Fortunately, I only had to reboot the meter (take the battery out for a few minutes) and it worked fine. I avoided the cable figure 8's after that.

I had the same thing happen to me when I went out to shoot the flyover of the space shuttle. I'd gone up to the top of San Bruno mountain, and set my tripod up on a concrete platform where there had been a radio antenna. Radio antennas everywhere and the Pentax Spotmeter V was indicating exposures that didn't make any sense at all.

[jp]

People freek out about the idea of microwave radio and cell phone radiation "putting out" from towers. Radio stations are monster in comparison. An AM radio station energizes the whole tower structure often rather than just an antenna and any towers within a half mile need wires up the edges of the legs to "detune" them because of the current in the air. FM and TV can affect smaller objects that are not shielded. Perhaps 10000-100000 times more powerful than a cellular or microwave antenna. (most of my microwave antennas have between 2 milliwatt and 1/2 watt coming out of the radio into the antenna; wifi quantities but with better equipment)

[MrFujicaman]

If that were true, keeping it in your car would mess it up.

[Wayne Lambert]

Thanks for the comments. Perhaps the admonishment I heard had to do with analog exposure meters and the moving parts they contained. I agree, I can't see what the problem could be with a digital exposure meter or, for that matter, a hand-held GPS unit which I suppose is just a specialized radio receiver. If anyone has any further comments, though, I would be glad to hear them.

Wayne

[BrianShaw]

Hi Wayne... just one more comment. I don't think there is any issue with even a mechanical light meter being stored in a metal cabinet. All sorts of mechanical meters are either stored in metal cabinets or built in to a metal cabinet. I think the admonishment you heard may have been, for lack of a better word, completely incorrect.

[Wayne Lambert]

Thanks Brian,

I suppose we are so dependent on our easily-messed-up (and expensive) equipment that we tend to get a little paranoid at times. Nice to have a forum like this where we can get good information.

Wayne

[Drew Bedo]

There should be something funny to say here that involves wearing an aluminum foil helmet . . .I just can't come up with anything.

[cyrus]

Funny, sailors are taught to keep their sensitive electronics inside their metal oven during storms, as a faraday cage that protects rather than threatens the electronics

[Kevin Crisp]

Darn. I was hoping I'd found the answer to what I was doing wrong all these years.