[time-nuts] Loran, GPS, Lightning, Timing
namichie at gmail.com
Thu Jun 26 21:39:52 EDT 2014
the maltese cross is a chopper to interrupt the lines of electrostatic force.
The cross could have a hundred legs, as long as it alternately blocks
and unblocks exposure to the electric field.
The cross spins in a horizontal plane, maybe half an inch above the sensor
electrode which is flush or just above the ground plane.
The idea is to get the output signal up to a frequency where the time constant
of the sensing electrode can be quite short.
If you can get it up to 400 Hz it only needs a 2.5mS time constant.
Even then, since you can calibrate it you can have the signal below the time constant.
A 12 legged "cross" spinning on a 4 pole motor gives a chopping frequency of 360 hertz,
(in America), quite convenient for amplification and processing.
If the motor is synchronous, or you put a sensor on the motor shaft you can run a phase
sensitive detector and get polarity as well as magnitude.
On 27/06/2014, at 1:59 AM, Max Robinson wrote:
> How fast does the maltese cross turn?
> Max. K 4 O DS.
> Email: max at maxsmusicplace.com
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> ----- Original Message ----- From: "Neville Michie" <namichie at gmail.com>
> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
> Sent: Wednesday, June 25, 2014 10:46 PM
> Subject: Re: [time-nuts] Loran, GPS, Lightning, Timing
>> Is anyone using a field mill?
>> I have always been going to make one.
>> It consists of a horizontal metal plane with a conducting button on the surface
>> which is insulated from the ground plane.
>> A metallic maltese cross driven by a motor alternately covers and uncovers the electrode
>> exposing/not exposing it to the sky.
>> The electrode button has capacitance to ground which drops its impedance,
>> but across that impedance is an AC voltage proportional to the ambient static field.
>> A typical field in fine weather is 300 Volts/metre so the signal is not trivial.
>> You should be able to make a field mill that works continuously except when
>> actually shorted by rain.
>> This is not a very high impedance device, and should show many marvellous things
>> as the clouds float over you.
>> You can calibrate it with a metal plate, say 12 inches above it with 50 volts on it.
>> That should produce a uniform field on the mill.
>> Neville Michie
>>> I know you are talking about measuring lightning strikes but if you get the
>>> impedance high enough, you can actually measure the earth's electric field.
>>> (It is about 200V/m if I recall properly.) Interestingly it is affected by
>>> the solar flux and solar wind.
>>> Brian Lloyd
>>> Lloyd Aviation
>>> 706 Flightline Drive
>>> Spring Branch, TX 78070
>>> brian at lloyd.com
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