[ARC5] BC-348-Q Capacitor Questions

Mon Aug 23 03:25:36 EDT 2010

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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