[ARC5] BC-348-Q Capacitor Questions

Mon Aug 23 04:58:22 EDT 2010

Dennis,

Thanks for your explanations --I'll get back to this later -- have to go 
now.

Henry
----- Original Message ----- 
From: "Dennis Monticelli" <dennis.monticelli at gmail.com>
To: "Discussion of AN/ARC-5 military radio equipment." 
<arc5 at mailman.qth.net>
Sent: Monday, August 23, 2010 9:25 AM
Subject: Re: [ARC5] BC-348-Q Capacitor Questions

> Henry,
>
> The clamp-on meters I'm talking about do measure DC. To use a radio
> analogy, they do so by mixing the incoming signal with a 40KHz LO, passing
> the converted signal through a 40KHz IF, and then synchronously 
> demoduating
> back to baseband again.  If you are familiar with chopper amplifiers, the
> basic principle is the same, only here it happens in the magnetic domain
> within the head assembly (hence the name "flux gate").
>
> Your memory of the Hall Effect is correct.  Electron flow is altered by 
> the
> presence of a magnetic field.  If an XY slice of silicon is set up like a
> bridge with four-point connections, then a differential signal will appear
> across the lateral (normally blanced) arms of the bridge that results from
> the applied field bending the path of the electrons that flow from the top
> of the bridge to the bottom.  There must be an orthogonality between the
> applied field and the sheet of electron current for this effect to occur.
> With Hall sensors placement matters....a lot.
>
> Dennis AE6C
> On Sun, Aug 22, 2010 at 11:49 PM, Henry Mei'l's <meils at get2net.dk> wrote:
>
>> Thank you Ray,
>>
>> I remember something about the Hall effect from my physics studies --  
>> also
>> know that it is used in electronics - I'll  open up my theory books --
>> something to do with  cross surface elecron or  magnetic flow effects due
>> to
>> current flow, as far as I can remember.
>>
>> Dennis is very good at explaining things in a very specific way -- so if 
>> he
>> has an alternative solution, I'd  still like to see it.
>>
>> Clamp on power line current testers are dependent on AC flux -- I 
>> imagine--
>> whereas were dealing with
>> DC  current here.
>>
>> Henry
>>
>> ----- Original Message -----
>> From: "Roy Morgan" <k1lky at earthlink.net>
>> To: "Discussion of AN/ARC-5 military radio equipment."
>> <arc5 at mailman.qth.net>
>> Sent: Monday, August 23, 2010 8:25 AM
>> Subject: Re: [ARC5] BC-348-Q Capacitor Questions
>>
>>
>> >
>>  > On Aug 23, 2010, at 2:08 AM, Henry Mei'l's wrote:
>> >
>> >> Hello Dennis
>> >>
>> >> How does this work?I don't have an HP 428 but is there some way I
>> >> can rig up
>> >> something using standard VTVMs/VOMs &/or scopes to do the same thing?
>> >>
>> >> ----- Original Message -----
>> >> From: "Dennis Monticelli" <dennis.monticelli at gmail.com>...
>> >>> I find that it is easier and less invasive to use an old HP 428
>> >>> clip-on
>> >>> current meter to check caps.
>> >
>> > Basically, here is how the HP clip-on milliammeter works:
>> >
>> > The clip on probe contains a magnetic core that is placed over the
>> > wire being tested.  The core is operated at a certain level of
>> > magnetic flux by the instrument.  The DC current in the wire under
>> > test, changes the flux in the core.  This change is detected by the
>> > instrument and there is a corresponding reduction of the flux in the
>> > core to return it to the original balanced state.
>> >
>> > So, the important parts of the system are:
>> >
>> > A unique clip-on core
>> > A source of magnetism in the core that is monitored by the instrument
>> > A feedback system to reduce the magnetism to restore the original flux
>> > level
>> > A metering system to display the detected current.
>> >
>> > Note: if you buy one of these HP meters without the clip-on probe, you
>> > have a useless piece of equipment.
>> >
>> > There are clip-on probes meant for use with oscilloscopes that detect
>> > AC currents in a wire, and may well be some that detect DC currents.
>> > Tektronix, naturally, had/has such AC detecting probes. The one I know
>> > of is quite old now, and had a little power supply and amplifier as
>> > part of the setup.  It's frequency response was modest, but I think it
>> > worked at line current and up to perhaps some couple of hundred kc.
>> >
>> > I have a couple of devices that are called "Hall Effect sensors".
>> > These things are based on relatively new creations of modern physics
>> > that I don't understand, but I think they detect current in a wire
>> > that is passing through the opening in the thing.  Search via Google
>> > for "hall effect sensors" and you'll get lots to read. Apparently, you
>> > can buy them at Digi-Key.  This seems to be a promising avenue to
>> > explore.
>> >
>> >
>> > Roy
>> >
>> > Roy Morgan
>> > k1lky at earthlink.net
>> > K1LKY Since 1958 - Keep 'em Glowing!
>> >
>> >
>> >
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>>
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