Setting off an EMF meter

[cj.23]

Hi,

Just a simple but perhaps odd request. I'm running a murder mystery game based on what of those "paranormal tv" ghosthunting shows. The only difference is I have hired a "haunted" hotel, written a game script, and all the phenomena are manufactured as part of the game. The paranormal investigator character gets to carry an EMF meter of course -- and i' like it to actually be useful in the plot (as opposed to real life where my comment on the subject are well known). So basically I want to trigger it so it beeps flashes etc, etc. I have acquired one for the game, and can practice for a couple of weeks before hand, but I'm trying to think of some small source that I can conceal in a room (or mark with an orange "ignore not in game" sticker, that will actually give off enough EMF (safely) to trigger the blasted thing, so that character can whitter about anomalous readings! Anyone got any ideas?

Any other ideas for the game welcome!
cj x

 

[MRC_Hans]

For something commercially available, I suggest a HV generator for a cattle fence. Perhaps with a piece of wire running across the ceiling. They come battery powered, and you don't need 'buffalo
fence' class, just a small one.

Probably one of these ionizing devices supposed to suppress electrostatic charge will also create enough of a field.

I suggest you bring the EMF meter to the shop and try it out before purchasing the device.

If you need/want to build something yourself, a coil fed from a generator should work.

Hans

 

[Ririon]

http://www.wikihow.com/Build-an-Emp-Generator

Sounds like fun. Safe? Not so much.

 

[cj.23]

Thanks chaps. Um, yes safe is important. We are playing a game, and I don't want to hurt anyone. I think these things are generally ridiculously sensitive? One thing I thought of what just rigging the emf to some kind of IR input so I could activate it with something as simple as a tv remote or similar. That might be easier than trying to generate the "anomalous" signals. I'll have a play with ideas, see what I can think of!

cj x

 

[technoextreme]

Hi,

Just a simple but perhaps odd request. I'm running a murder mystery game based on what of those "paranormal tv" ghosthunting shows. The only difference is I have hired a "haunted" hotel, written a game script, and all the phenomena are manufactured as part of the game. The paranormal investigator character gets to carry an EMF meter of course -- and i' like it to actually be useful in the plot (as opposed to real life where my comment on the subject are well known). So basically I want to trigger it so it beeps flashes etc, etc. I have acquired one for the game, and can practice for a couple of weeks before hand, but I'm trying to think of some small source that I can conceal in a room (or mark with an orange "ignore not in game" sticker, that will actually give off enough EMF (safely) to trigger the blasted thing, so that character can whitter about anomalous readings! Anyone got any ideas?

Any other ideas for the game welcome!
cj x

What frequency do those things operate at?

 

[kmortis]

For something commercially available, I suggest a HV generator for a cattle fence. Perhaps with a piece of wire running across the ceiling. They come battery powered, and you don't need 'buffalo
fence' class, just a small one.

Probably one of these ionizing devices supposed to suppress electrostatic charge will also create enough of a field.

I suggest you bring the EMF meter to the shop and try it out before purchasing the device.

If you need/want to build something yourself, a coil fed from a generator should work.

Hans

Why go that exotic? Get a electromechanical relay, and a method of rapidly switching it on and off. That'll create enough broadband noise to trigger an EMF meter.

Or, a newer dimmer switch may do the trick. Most are SCRs and the first couple of generations of them were fairly uncontrolled as far as rise time was concerned. Load that puppy down with an infrared lamp and you got a noise source.

Basically, anything that switches rapidly with high ampiltude (voltage or current) will do the trick. A good source for parts is American Science and Surplus.

 

[ponderingturtle]

Why go that exotic? Get a electromechanical relay, and a method of rapidly switching it on and off. That'll create enough broadband noise to trigger an EMF meter.

I discovered a way to do that by accident once. Just have it cut its own circuit when it starts to trigger. See it was supposted to fully connect to the other side and latch on after it was triggered, but it cut out to quick for it to engage on the other side and latch on. I needed a second time delay relay to make it work properly.

 

[MRC_Hans]

Yes, you can connect a relay to buzz (disconnect itself). For someone like me, that would be the solution; I have plenty of relays lying about, and circuitry experience. However, for someone with no parts on stock and no soldering iron, something off the shelf is the thing.

And those buzzing relays tend to make quite a bit of acoustic noise too, which would sort of give away the whole thing.

Hans

ETA: If those things are triggered by dimmers, it is no wonder people find ghosts all over the place.

 

[ponderingturtle]

Yes, you can connect a relay to buzz (disconnect itself). For someone like me, that would be the solution; I have plenty of relays lying about, and circuitry experience. However, for someone with no parts on stock and no soldering iron, something off the shelf is the thing.

And those buzzing relays tend to make quite a bit of acoustic noise too, which would sort of give away the whole thing.

Hans

Well a bit of acoustic foam should cover that up.

 

[kmortis]

I discovered a way to do that by accident once. Just have it cut its own circuit when it starts to trigger. See it was supposted to fully connect to the other side and latch on after it was triggered, but it cut out to quick for it to engage on the other side and latch on. I needed a second time delay relay to make it work properly.

There's a few EMI tests that rely on, and are caused by, relays switching rapidly. I've been amazed by the number of units that have problems with those tests. Usually it's nothing hugely disruptive, more upset of communication lines and power lines than anythign else. Easliy fixed. Most people have no idea how much noise those suckers give off.

 

[kmortis]

Yes, you can connect a relay to buzz (disconnect itself). For someone like me, that would be the solution; I have plenty of relays lying about, and circuitry experience. However, for someone with no parts on stock and no soldering iron, something off the shelf is the thing.

And those buzzing relays tend to make quite a bit of acoustic noise too, which would sort of give away the whole thing.

Hans

ETA: If those things are triggered by dimmers, it is no wonder people find ghosts all over the place.

It was enlightening (excuse the pun) when I took my EMI course as an undergrad. The prof brought in a small antenna, spectrum analyzer and a 60 W lightbulb attached to a dimmer. As he played with the light level, the noise signature altered. Since we all assumed that the dimmer was an old style pot type, we were stymied. Finally he clued us in that most modern dimmers are SCRs, and since according to the FCC you only have be below the rather generous limit at 10 meters, they generally don't have much in the way of noise suppression.

 

[Soapy Sam]

I thought fridges and washing machines were commonly detected by EMF meters.

 

[kmortis]

I thought fridges and washing machines were commonly detected by EMF meters.

I wouldn't dobut it. Once the compressor or motor kicks in, there's going to be a large inrush of current. Large di/dt = large emissions. And since most of the morons ghosthunters haven't a clue about how to use the equipment they handle, I could see them getting fooled by that.

 

[kalen]

Does your cell phone set off the meter? If so, you can always set it to "silent mode" and have one of the cast call it at the appropriate time.

I'm also thinking that these EMF meters are very sensitive to video cameras and other equipment used in producing television, which would help explain the popularity of the ghost-hunting shows.

 

[Lensman]

An old transistor radio would also be a good source of RFI, just find the 1st local oscillator transistor (about 10.7MHz) or the 2nd local oscillator (about 470kHz) , hang a long wire (half a meter or so, it'll de-tune it but that won't matter much) off the Collector & turn it on at very low volume.

 

[kmortis]

Does your cell phone set off the meter? If so, you can always set it to "silent mode" and have one of the cast call it at the appropriate time.

I'm also thinking that these EMF meters are very sensitive to video cameras and other equipment used in producing television, which would help explain the popularity of the ghost-hunting shows.

It would depend on the frequency range. Most cell phones are pretty high up there in frequency (2-3 GHz, IIRC). But....

An old transistor radio would also be a good source of RFI, just find the 1st local oscillator transistor (about 10.7MHz) or the 2nd local oscillator (about 470kHz) , hang a long wire (half a meter or so, it'll de-tune it but that won't matter much) off the Collector & turn it on at very low volume.

...this should work for most readily available RF meters that consumers would be able to get easily.

 

[jasonpatterson]

I expect that any CRT monitor would do the job nicely. If you have access to a very small portable television (the battery powered variety) with a remote, you could turn the noise down, paper over the screen completely, and hide it somewhere nearby. Click... Instaghost.

 

[Soapy Sam]

You can buy Infrared remote operated powerpoints, cj- standard UK fitting. Plug anything in and switch it on remotely. Or you might use a timer.

 

[Brian-M]

Connect a light dimmer to a 12v wire-wound transformer powering a 50W down-light. That should do the trick.

 

[MRC_Hans]

It was enlightening (excuse the pun) when I took my EMI course as an undergrad. The prof brought in a small antenna, spectrum analyzer and a 60 W lightbulb attached to a dimmer. As he played with the light level, the noise signature altered. Since we all assumed that the dimmer was an old style pot type, we were stymied. Finally he clued us in that most modern dimmers are SCRs, and since according to the FCC you only have be below the rather generous limit at 10 meters, they generally don't have much in the way of noise suppression.

I know all that, but my point is that if EMF meters used by ghosthunters are set off by all kinds of standard household appliances, then the whole thing gets even more silly. How will they distinguish a ghost from a cofee machine? Do they care??

Hans