On 9/21/2017 3:41 PM, T i m wrote:
On Thu, 21 Sep 2017 16:54:07 -0500, Foxs Mercantile
wrote:

Sigh....

The simple answer is put a 62K 5% resistor in series with the meter.
It's read about 4% low (240 uA instead of 250 uA.)

Ok, so with our source at 15V we get 240 uA and ~FSD on our meter.
That's 14.88V across the resistor and 0.12V across the meter,
therefore the meter is ~500 ohms?

At 10V we get 2/3 of 240 uA (160uA) and so our voltage across the
meter is now 0.0256 (~1/5th of FSD) and so the meter will read 1 volt
and not 0?

You wanna get a little closer? put a 100K and a 150K in parallel.
Wanna make it adjustable? Put a 100K trimpot in parallel with a 180K
resistor.

The problem is that the voltage across the meter will fall in
proportion to the voltage across the entire network, not just across
the meter component (which is why I ruled it out in my second post).
;-)

This ain't rocket science folks.

Maybe not but can appear as such to some (I think). ;-)

Cheers, T i m

OK,
Let's go back to engineering 101.
What's the VERY MOST important part of a project?
It's the SPECIFICATION.

Exactly, precisely, concisely, unambiguously, completely stated
requirements.
This does NOT change. If you change your mind and change the spec,
you start a new project.

How do you know when you're done? You write acceptance criteria.
Exactly how the user, in this case you, is going to test the unit
to determine if you met the spec? If it passes the written acceptance
criteria, you succeeded. If it passes the test criteria, but doesn't
work, the specification was the problem. You get paid for this project
and start a new one with new specifications.

I can't emphasize how important the specification is. It's the number
one cause of project failure. You can't design for criteria that
were not specified.
It's easy to say, "I know what I'm designing for me...I don't need
no stinkin' specification." You'd be wrong. This thread is what you
get. Lots of rocket scientists when you really need a boat.
The very last place you want to discover that your forgot some
important requirement is when the completed device is deployed.

Words like exactly, "as good as possible" have no place in a specification.

Specs are numbers and test methods. Specs include allowable
variations due to initial component tolerances, component age,
temperature, vibration, misuse.
An example of misuse is, "what happens when the user hooks it
up backwards." I learned about vibration when I carried a
voltmeter on my motorcycle. When I needed it, it failed.
I took it apart and it poured out like sand.

The engineer doesn't need to know WHY you want what you want.
That's not his job. HOWEVER...if you state your objectives,
why you want to do this, you might find the bevy of rocket scientists
have a much better way to accomplish your objectives. I can't
count the number of times a user wanted an complicated gizmo,
but his objective could be achieved with a much different
and much simpler approach by repartitioning the system.

End rant.

First question I'd ask is, "are you gonna' stare at the meter 24/7?"
If not, get a cheap digital panel meter off EBAY, put a push button
in series and be done with it. If you're not battery
powered, you can probably tolerate the load and don't need the
push button.

But, back to your original request.
Take your current meter.
Put a series resistor to set the max voltage to 5V.
Put a 10V "battery" in series.
The remaining question is, "how do you implement the 10V
battery?"
Can your measured voltage ever get below 10V?
If so, your problem just got a LOT more complicated.
See "misuse" above.

If it were me, I'd use a 10V zener diode. If you can find
an affordable temperature compensated one that is accurate
over the range of current from zero to the max indication
on your meter and the ambient temperature range, do that.
Characterize the calibration.
Fire up your CAD program and make a new meter face.
Since you're making a new face, any stable zener voltage works.
Your meter is as accurate as your care in making the new face.

Are we having fun yet?