Heathkit EK-1

[Jack Crenshaw]

Jack Nelson wrote:

> hello again  jack
> i hope what i said was not misleading, the reference that i made was to the
> basic meter movement, normally but not always on the face of the meter
> movement there is the meter sensitivity in fine print,

No such ID on the meter, that I can see.

> 1 ma is not an excessive amount of current for a wheatstone bridge, not
> knowing the exact circuitry of the EK-1 and speaking of meter movements in
> general, but it sound like some series or shunt resistors that are switched
> into the circuit have changed value,
> if i had a schematic of the EK-1 i could probably give you more help.
> hope that i have been of some help to you.

Yeah, the thing is, there is simply nothing in there that could cause such an
effect, that I can see.  It's not a wheatstone bridge, just your most basic VOM
with a galvanometer, plus series resistors for voltage, shunt resistors for
current.  I suspect that the lowest current range, which is 1ma, is the
sensitivity of the meter itself.

I don't recall the measurements on the shunt resistors, but I do remember the
series ones for voltage.  The highest is 500k, on the 500v range, which would of
course imply a 1ma current, full scale.  The lowest values are 9k and 4k, so
again, it all implies a 1k meter resistance.  All the resistors check out, so
the meter must surely be drawing the expected current.

To test the current, I hooked the meter up to approx 10vdc through a 10k
resistor, then adjusted the DC source to flow 1ma total.  I passed the current
first through my digital VOM, then the EK-1.  The VOM read 1ma on the nose, the
EK-1 read 0.4 <!>.

I'm stumped.  I've never seen a meter before that works, that measures the right
resistance, but that doesn't read but a fraction of its rated full scale.

For the record, I have another EK-1 coming in this week.  I'll compare the two
and see if I can figure things out.

I hope you don't mind; I'm reflecting this back to the group, in case someone
else there has a notion what's wrong.

Jack

> de Jx KA7VYM
> ----- Original Message -----
> From: "Jack Crenshaw" <jcrens at earthlink.net>
> To: "Jack Nelson" <jackthe at earthlink.net>
> Sent: Sunday, December 17, 2000 3:03 AM
> Subject: Re: Heathkit EK-1
>
> > Jack Nelson wrote:
> >
> > > sound like the shunts have gone south
> > > the normal resissance of a 1 ma meter movement is about 1k.
> >
> > Oh, is that right?  That's what I've got.  I expected the resistance to be
> much
> > lower.  If it's a K, then to get an ma needs a 1-volt push, right?  I'm
> > surprised there would be such a voltage drop across a galvanometer.
> >
> > If the resistance is supposed to be 1k, and it is, then I'm back where I
> > started:  How can the meter possibly be reading 1/4 its design value????
> Weird.
> >
> > Jack
> >
> >
> >

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