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Phys
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Ghosts in the Light?

09/19/2012 1:18 PM

Okay - here is a brain teaser problem for discussion.

I have a table light with a capacitive touch sensor to turn it on and cycle through the 3 levels of light available. (standard incandescent light fixture with an add on plug in sensor and a 3 way bulb) Beside it I sat a 4 D cell battery powered U-tube fluorescent lantern (had a 4 day power outage - this was temporary lighting) After the power outage was over, I decided to run both lights. I discovered that when the standard incandescent is on the highest setting of the 3 way bulb and I turn on the lantern, the incandescent cycles to the off state. Repeatable approximately 9 out of 10 times.

Why?

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Anonymous Hero
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#1

Re: Ghosts in the Light?

09/19/2012 1:30 PM

I'll bet it is the "starter" in the florescent tube.

They tend to contain an RF suppressor cap, which is probably coupling (when close enough to the desk lamp) to trigger of the capacitive sensitive sensor circuit in the desk lamp.

The starter is only active for a very short time, so the activation of the starter only causes the desk lamp to cycle once before the starter is disengaged.
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Phys
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#2
In reply to #1

Re: Ghosts in the Light?

09/19/2012 1:44 PM

I expected it was something like that - has to be via emr since they don't physically touch.

I actually suspect the voltage "step up" circuit may be doing it, since the conversion to a higher voltage is not at a nice low 60 hz but usually quite a bit higher and very noisy. Having built them from magazine articles in my younger days and bread board tested them, I know they make an audible squeal at a frequency on the order of several KHz. but, I am not sure of the actual interaction occuring.

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Wal
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#3
In reply to #2

Re: Ghosts in the Light?

09/20/2012 1:40 AM

Answered your own question.

EMI is the culprit.

Have you tried other radiating sources to see whether they have the same influence? Just curious.

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Stedou73ish
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#4
In reply to #3

Re: Ghosts in the Light?

09/20/2012 7:01 PM

Would that be Engineering Ministries International for the ghost, or Electromagnetic Interference for the switch?

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Wal
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#5
In reply to #4

Re: Ghosts in the Light?

09/20/2012 8:34 PM

Guilty as charged your honour! Must define all acronyms .....

Electro Magnetic Interference

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Phys
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#6
In reply to #3

Re: Ghosts in the Light?

09/24/2012 4:12 PM

Yeah I did and I didn't - emr is the obvious culprit, but what is it actually doing to trigger the capacitive sensing circuit? I got my degree in EE first then went back for physics since I have never been very good at the engineering level of accepting that is why something happens - I need all the details right down to the electron level. (I try to get too deep into a phenomenon in understanding it) Is it creating a current pulse in the cap circuit wiring through induction? Is the emr from a simple 3 volt battery powered circuit really capable of creating that much radiation? The transmission is through at least 8 inches of air and 1/8" of plastic.

Have not tried other triggers - yet.

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