On Thu, 21 Sep 2017 17:21:23 -0700, mike wrote:

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

a common enough phrase for an in-house spec. Such phrases should be cleared up later of course, once the specifier knows what the engineers can actually do and what the options cost.


Specs are numbers and test methods. Specs include allowable
variations due to initial component tolerances, component age,
temperature, vibration, misuse.

Some do. Some are 'how can you get it as cheap as possible and still have it sell & not destroy our repuation.' Some are 'we want to beat what's out there, how good could you get it?' Some are 'we want it to do this.' etc etc etc.


The 'human' bit: A small (key fact) analogue (key fact) panel meter
connected to a lead acid battery (key fact) needs reading and those
readings interpreting and so ITRW, we are 'most likely' to not require
much in the way of precision or we wouldn't be using those things in
the first place. ;-)

1% is doable for some analogue meters. That's enough precision for a lot of tasks.


NT

On 9/21/2017 3:18 PM, wrote:
Like this?

http://thumbs.ebaystatic.com/images/...aJT/s-l225.jpg

Right off the shelf.

Several others from similar sources with a table of resistance values to make the desired range (in volts) and either blank faces or sequential numeric faces. Sorry for pointing to an Euro-meter, but just that they are out there.

Had I known, the "meter man" at Kutztown would have had exactly what you want in the size you want it, new or used. He has hundreds. Now you have to wait until spring.

Peter Wieck
Melrose Park, PA


I don't know if you are asking for an expanded scale meter, were the
0V line is 10V and FS line is 15 volts, so the whole range is only 5
volts. That's what I gleaned.
First you need to put a series 60K ohm resistor to make the meter read
FS with 15V applied. (for accuracy you should subtract the resistance of
the meter from the 60K ohms)
Then you need to add a circuit shown in these sites.

http://www.radcomms.net/Expanded_Scale_Voltmeter.html

http://www.thebackshed.com/windmill/...eVoltMeter.asp

http://www.zbasic.net/forum/about1423.html

This last one will probably need a 10K resistor tied from one OUT to
the other OUT. Just so there is enough current to make the regulators
work properly.

Here's a youtube, I didn't watch it all, but you might learn something.

https://www.youtube.com/watch?v=-z_j4MclCTk

Mikek

mike wrote:
On 9/21/2017 8:13 PM, tabbypurr wrote:
End rant.

He's making a one off for use at home, not commissioning a new design of military hardware.

The task is the same no matter who the customer.

At least the extra option should be there.

On Fri, 22 Sep 2017 15:38:26 -0700 (PDT), wrote:

On Friday, 22 September 2017 05:05:35 UTC+1, Jeff Liebermann wrote:
On Thu, 21 Sep 2017 20:59:03 -0700 (PDT), tabbypurr wrote:

simple but time consuming producing a new dial paper

"The Windows programs for drawing analog meter scales"
http://www.tonnesoftware.com/meter.html
$35 for the full version.

fails to solve the issue AND adds pointless cost.
NT

The consensus seems to be to use an expanded scale analog voltmeter.
If the OP is going to build such a thing, he needs a new scale on his
analog meter. That can be done with the free version of the software.
(I just checked and it will do an expanded scale).

I usually ignore one line pontifications, but I'm curious. Why does a
new meter scale fail to solve the issue? Ummm... what issue?

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Fri, 22 Sep 2017 15:39:14 -0700 (PDT), wrote:

On Friday, 22 September 2017 05:22:46 UTC+1, Foxs Mercantile wrote:
On 9/21/2017 10:59 PM, tabbypurr wrote:
simple but time consuming producing a new dial paper

With the low current Zener, it doesn't look like that will be
necessary.

Oh, you've found a zener that's 10v +/- 1%?
NT

The meter isn't even that accurate. You're not going to be able to
read the meter to +/- 0.1V. Also, I coulnd't find where anyone
specified the accuracy required.

If you really want 1% accuracy, maybe a 10.0V precision reference,
such as the TI REF102:
http://www.ti.com/lit/ds/symlink/ref102.pdf
However, there's a problem. The IC requires a V+ of 11.4-36VDC which
will probably require a battery or other power supply.

Hmmm... I sorta blundered across this idea:
http://www.qsl.net/kh6grt/page4/expscale/expscale.htm
It doesn't expand the entire meter scale from 10-15VDC.
Instead, it compresses 0-10V into a small part of the meter scale, and
expands the 10-15V over the rest of the scale. However, it requires
+12v and -12v power.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Saturday, 23 September 2017 17:35:36 UTC+1, Jeff Liebermann wrote:
On Fri, 22 Sep 2017 15:38:26 -0700 (PDT), tabbypurr wrote:
On Friday, 22 September 2017 05:05:35 UTC+1, Jeff Liebermann wrote:
On Thu, 21 Sep 2017 20:59:03 -0700 (PDT), tabbypurr wrote:

simple but time consuming producing a new dial paper

"The Windows programs for drawing analog meter scales"
http://www.tonnesoftware.com/meter.html
$35 for the full version.

fails to solve the issue AND adds pointless cost.
NT

The consensus seems to be to use an expanded scale analog voltmeter.

that's part of the spec

If the OP is going to build such a thing, he needs a new scale on his
analog meter.

yes

That can be done with the free version of the software.
(I just checked and it will do an expanded scale).

it can

I usually ignore one line pontifications, but I'm curious. Why does a
new meter scale fail to solve the issue? Ummm... what issue?

The issue with using an inaccurate zener is that the meter scale most likely won't run from 10.0v, and will thus need calibrating over its scale. That also means a new scale with marks in new places - a pita to do. Far easier to knock off 10v exactly then just change the numbers on the scale.


NT

On Saturday, 23 September 2017 17:52:35 UTC+1, Jeff Liebermann wrote:
On Fri, 22 Sep 2017 15:39:14 -0700 (PDT), tabbypurr wrote:
On Friday, 22 September 2017 05:22:46 UTC+1, Foxs Mercantile wrote:
On 9/21/2017 10:59 PM, tabbypurr wrote:

simple but time consuming producing a new dial paper

With the low current Zener, it doesn't look like that will be
necessary.

Oh, you've found a zener that's 10v +/- 1%?
NT

The meter isn't even that accurate.

We don't know the meter's accuracy. 1% is common enough, but it might be worse. (For all we know it might even be a moving iron thing.)

You're not going to be able to
read the meter to +/- 0.1V.

Even my most rock bottom multimeters, under $3 each new, are easy to read to 1%. Decent meters do much better.

Also, I coulnd't find where anyone
specified the accuracy required.

If you really want 1% accuracy, maybe a 10.0V precision reference,
such as the TI REF102:
http://www.ti.com/lit/ds/symlink/ref102.pdf
However, there's a problem. The IC requires a V+ of 11.4-36VDC which
will probably require a battery or other power supply.

Hmmm... I sorta blundered across this idea:
http://www.qsl.net/kh6grt/page4/expscale/expscale.htm
It doesn't expand the entire meter scale from 10-15VDC.
Instead, it compresses 0-10V into a small part of the meter scale, and
expands the 10-15V over the rest of the scale. However, it requires
+12v and -12v power.

Nice idea, though I don't expect the op needs it. I'm sure one could design a circuit that can use opamps that are happy on the 10-15v and halve V_in.


NT

On 9/22/2017 1:29 AM, T i m wrote:
On Thu, 21 Sep 2017 21:41:44 -0700, mike wrote:

On 9/21/2017 8:13 PM, wrote:

End rant.

He's making a one off for use at home, not commissioning a new design of military hardware.


The task is the same no matter who the customer.

It can and maybe should be, in an ideal world. I say that because I
hate having to deal with 'fools who rush in' or those expecting me to
make technical / choice decisions on their behalf (like getting them
some 'size 10, brown, lace up leather shoes'). ;-(

The more steps you skip, the more problems you have.

'May have'.

The more you think like a project manager, the better
managed your home projects.

Agreed. I like to understand as much about something as I can.
However, my ability to do so, time available to do so and the
pertinence of doing so don't always allow me to do so or to do so to
the level I would like. Sometimes you just have to get stuck in. ;-)

Once you acquire the habit, you'll find that it adds
little to the time in the beginning and greatly simplifies
the end.

Agreed 100%.

And it wastes far less time for rocket scientists in residence.

Quite ... however, this is a 'discussion' group and so does have an
element of that, along with the hard science / fact stuff.

Part of the 'human' bit is not making a post (especially the initial
one) too long (I fail most of the time) as it will put people off
reading it and if there were any further points that need refining
they could be done with a simple Q&A.

e.g. I initially outlined the fairly close detail at a level relevant
to my needs and understanding (IMHO anyway). I didn't expand on what I
was going to actually use it for because it didn't really matter to
the question. I left it open to the reader to ask any supplementary
questions as they felt relevant. ;-)

Cheers, T i m

Metrology is an interesting topic.

When someone asks me how to measure something, my first thought is,
"exactly how will the answer to your question improve YOUR life tomorrow?"
Sometimes I actually say it.
The "jolt" to their thought process forces them to express what they're
trying to accomplish...or admit to themselves that they have no idea.
I find that almost all questions end up in the "won't affect them at all"
category and I can dispense with trying to teach them something they'll
never use. If the answer won't change the future, don't bother with the
question.

It's similar to pointless social interaction.
People you don't know ask questions, like "how are you?"
They think they know what you'll say.
Respond with something like, "I have this rash on my dick and
think I need to find a different street corner... got any ideas?"
to see how much they really care about how you are. ;-)
But I digress...

If I had an electric boat, the ability to measure voltage to six
decimal places would not be my priority.
What I want to know is, "can I get back to the dock?"
You can do that more accurately with a sharpie and nonlinear
meter than you can react to a change in wind direction.

The river current and wind and the shape of the curve of distance covered vs
velocity and temperature would be far more important variables to me.
Amp hours consumed would be important.

Battery voltage that would be strongly impacted by whether I'm going
up or down stream at what net velocity is a poor substitute.

An integrating current meter, a water speed speedometer and a GPS would
much more interesting. If you knew the water flow direction and speed,
you probably wouldn't have to measure anything else other than
what you can get from the GPS. Drifting downstream for a minute
would give you those two numbers.

But, since you're dead set on measuring voltage...
The basic problem is that the voltage you want to measure is
the biggest voltage you have to power your circuit.
That's why I split my original post into the concept (battery)
and the implementation (zener).
A series zener needs to draw ZERO current at 10V and still
be 10V at MUCH higher current ratio. You will have to live
with some amount of nonlinearity.

You could stack an AA-cell or two on top of your battery system
and alleviate that problem.

I maintain that a digital voltmeter is the best option.
They're dirt cheap on EBAY.

All the above is based on an extreme extrapolation of
very limited information. That's why the system spec is so important.

On Sunday, 24 September 2017 12:06:45 UTC+1, mike wrote:

A series zener needs to draw ZERO current at 10V and still
be 10V at MUCH higher current ratio. You will have to live
with some amount of nonlinearity.

In fact you could re-zero the meter so it reads 10v spot on. Add an extra mark for where it points when unpowered so you can see if it ever decalibrates.


You could stack an AA-cell or two on top of your battery system
and alleviate that problem.

yuck. 2 resistors beats 2 cells any day.

I maintain that a digital voltmeter is the best option.
They're dirt cheap on EBAY.

but noncompliant with the basic spec


NT

On 9/24/2017 6:31 AM, wrote:
On Sunday, 24 September 2017 12:06:45 UTC+1, mike wrote:

A series zener needs to draw ZERO current at 10V and still
be 10V at MUCH higher current ratio. You will have to live
with some amount of nonlinearity.

In fact you could re-zero the meter so it reads 10v spot on. Add an extra mark for where it points when unpowered so you can see if it ever decalibrates.

Yes, you can , but it's still nonlinear.
It's a matter of how much nonlinearity you can tolerate.
It's my assertion that the measured quantity is so crude that you don't
need to worry much about anything. Just learn what it reads and calibrate
your expectations to match.

You could stack an AA-cell or two on top of your battery system
and alleviate that problem.

yuck. 2 resistors beats 2 cells any day.
Can't argue with that assertion, but, if you can
provide a circuit that is precisely linear and accurate over the WHOLE
range using
two resistors, I'd like to see it. I'm betting it's more than two
resistors.

I maintain that a digital voltmeter is the best option.
They're dirt cheap on EBAY.

but noncompliant with the basic spec
Yep, that's a problem with any customer expectation.
I try to adjust expectations to meet the ACTUAL requirements
before delving into complex solutions to implement a nonsense
requirement.
Yes, the customer is always right. My job is to alert him
to the consequences of his demands.

Another non-complient solution is to use the two resistors
and a zener
to make a 9V-15V meter and hope that most of the nonlinearity
of the two resistor solution happens in the 9-10V range.
That way, the characteristics of the zener knee are important
over a 5:1 current range instead of an infinite ratio.
I'm far too lazy to do the math on how nonlinear it will be.

There's also an elephant in the room.
Unless you start with a meter that happens to have scale
markings ranging from 10 to 15, you're gonna need a new scale
no matter what you do with the electronics. If you're not gonna
do that, might as well just mark calibrations on the face with a
sharpie.
Makes no sense to go to great lengths in one part of the project
only to create something that still doesn't do what you want.


NT

On Monday, 25 September 2017 01:53:43 UTC+1, mike wrote:
On 9/24/2017 6:31 AM, tabbypurr wrote:
On Sunday, 24 September 2017 12:06:45 UTC+1, mike wrote:

A series zener needs to draw ZERO current at 10V and still
be 10V at MUCH higher current ratio. You will have to live
with some amount of nonlinearity.

In fact you could re-zero the meter so it reads 10v spot on. Add an extra mark for where it points when unpowered so you can see if it ever decalibrates.

Yes, you can , but it's still nonlinear.
It's a matter of how much nonlinearity you can tolerate.
It's my assertion that the measured quantity is so crude that you don't
need to worry much about anything. Just learn what it reads and calibrate
your expectations to match.

You could stack an AA-cell or two on top of your battery system
and alleviate that problem.

yuck. 2 resistors beats 2 cells any day.
Can't argue with that assertion, but, if you can
provide a circuit that is precisely linear and accurate over the WHOLE
range using
two resistors, I'd like to see it. I'm betting it's more than two
resistors.

What I meant is divide the input to your opamp so it's away from the rails and you don't need any rail boosting.


NT

On Sun, 24 Sep 2017 17:52:51 -0700, mike wrote:

On 9/24/2017 6:31 AM, wrote:
On Sunday, 24 September 2017 12:06:45 UTC+1, mike wrote:

A series zener needs to draw ZERO current at 10V and still
be 10V at MUCH higher current ratio. You will have to live
with some amount of nonlinearity.

In fact you could re-zero the meter so it reads 10v spot on. Add an extra mark for where it points when unpowered so you can see if it ever decalibrates.

Yes, you can , but it's still nonlinear.
It's a matter of how much nonlinearity you can tolerate.
It's my assertion that the measured quantity is so crude that you don't
need to worry much about anything. Just learn what it reads and calibrate
your expectations to match.

(I've been a bit preoccupied elsewhere but still following the thread
with interest and will reply individually when I get the chance)

That was part I had already considered in that:
The meter is fairly small. The meter is glued shut. The meter is only
marked in whole volts.

So, as you say, afa this experiment is concerned it was a cheap
toe-dipping into the concept of meter range enhancement, partly
because I think analogue display still have some merit and partly for
the S&G's. ;-)


snip

I try to adjust expectations to meet the ACTUAL requirements
before delving into complex solutions to implement a nonsense
requirement.

In this case the actual requirements were fairly simplistic as it was
an experiment. A feasibility study if you will. As you say, a DMM can
be bought for next to nothing (and I have several and one I'm already
using) but that wasn't the (entire) point.

Yes, the customer is always right. My job is to alert him
to the consequences of his demands.

;-)



Another non-complient solution is to use the two resistors
and a zener
to make a 9V-15V meter and hope that most of the nonlinearity
of the two resistor solution happens in the 9-10V range.

With a very small buck converter you could get a higher voltage supply
to ensure a voltage reference of some sort had sufficient overhead to
work correctly when close to the 10V threshold?

That way, the characteristics of the zener knee are important
over a 5:1 current range instead of an infinite ratio.

ITRW, as long as it's starting to work reasonably by 10.5V it
shouldn't really be an issue.

I'm far too lazy to do the math on how nonlinear it will be.

I do like the idea of printing my own scale and if this basic one
works, I might go for a bigger / better meter that I can open etc.

There's also an elephant in the room.
Unless you start with a meter that happens to have scale
markings ranging from 10 to 15, you're gonna need a new scale
no matter what you do with the electronics.

Unless it's already marked 0, 1, 2, 3, 4 and 5 'Volts' and you know
just have to add 10 to all of them. I would imaging the needle
pointing up the middle to 12.x would be a sufficient comforter. ;-)

If you're not gonna
do that, might as well just mark calibrations on the face with a
sharpie.

Only if I can get the thing open and it wouldn't be worth damaging it
to try.

Makes no sense to go to great lengths in one part of the project
only to create something that still doesn't do what you want.

My only hope is that it works 'better' than a similarly sized and
accuracy meter that is marked 0 to 15 and using it over a tiny
proportion of the range.

As has been suggested, if you aren't happy to try to KISS then you are
then going to be worrying about thermal stability and scale linearity
and I'd like to leave that for the Mk2. ;-)

Cheers, T i m

On Fri, 22 Sep 2017 14:13:13 -0700 (PDT), whit3rd
wrote:

On Thursday, September 21, 2017 at 10:51:33 AM UTC-7, T i m wrote:
Hi All,

Not a 'repair' question as such but I was thinking of using an old
skool 250uA FSD moving coil panel meter to read the 10 to 15V DC range
(a lead acid battery charge / discharge indicator), next to a 0-30A
Ammeter (inc shunt etc).

I was thinking of using either a voltage reference such as
LM4040DIZ-10.0 or could I get away with a simple zener (BZX55C?) with
associated resistor(s) please?

You can use any zener under 10V to do a 10V zero offset (just divide down the
input voltage until that 10V input matches the zener knee). So, with an
arbitrary zener (I'd use a TL431 as a 2.5V reference, they're convenient
and accurate) and a trimmer acting as voltage divider, it just remains
to make a range-setting resistor in series with the meter.

Hmm, that's crafty. ;-)

I'm trying to picture how the voltage rise would still be linear but I
think I can see how it would be.

The -ve of the meter is held at some voltage threshold low enough to
ensude a low change in difference between the voltage measured and the
ground. A variable (to start with at least) resistor set as a pd then
sets the upper voltage to give FSD at 15V.

The important thing, is to doodle up a really nifty scale for your meter
that indicates 10V to 15V, with clear markings, along the pointer's arc,
maybe with a bunch of subdivision marks.

Yeah, that sounds like a interesting project for a Mk2 meter. ;-)

took
a plotter and a bit of custom software to draw the arcs and labels,

I saw the link to some free software for doing such but not had chance
to try it yet.

then some fiddling with the faceplate of the meter to
affix it (warning: you need to worry about laser-print ink, paper, glue compatibility).

Ok. ;-)

Cheers, T i m

On 9/24/2017 6:05 PM, wrote:
On Monday, 25 September 2017 01:53:43 UTC+1, mike wrote:
On 9/24/2017 6:31 AM, tabbypurr wrote:
On Sunday, 24 September 2017 12:06:45 UTC+1, mike wrote:

A series zener needs to draw ZERO current at 10V and still
be 10V at MUCH higher current ratio. You will have to live
with some amount of nonlinearity.

In fact you could re-zero the meter so it reads 10v spot on. Add an extra mark for where it points when unpowered so you can see if it ever decalibrates.

Yes, you can , but it's still nonlinear.
It's a matter of how much nonlinearity you can tolerate.
It's my assertion that the measured quantity is so crude that you don't
need to worry much about anything. Just learn what it reads and calibrate
your expectations to match.

You could stack an AA-cell or two on top of your battery system
and alleviate that problem.

yuck. 2 resistors beats 2 cells any day.
Can't argue with that assertion, but, if you can
provide a circuit that is precisely linear and accurate over the WHOLE
range using
two resistors, I'd like to see it. I'm betting it's more than two
resistors.

What I meant is divide the input to your opamp

Thereyougo...opamp is a lot more complex than two resistors...or a couple
of AA cells.

so it's away from the rails and you don't need any rail boosting.


NT

On Fri, 22 Sep 2017 10:53:54 -0500, "Dave M"
wrote:

snip

I forgot to mention that for the zener solution, you really need to select
as low power a zener that you can find, such as 400mW or lower.
The 1N4104 is a 10V, 250mW zener, with a test current of 1uA, and a max
current of 25ma, well within your requirements. In stock at Mouser.com.

Cheers, Dave, I'll have a look.

As has been mentioned elsewhere, if we used a lower voltage zener (and
as high a tolerance as can be found in the right spec and the right
price *because*) to set the voltage on the -Ve leg of the meter and
then tweak the voltage up via resistors (variable initially) to give a
FSD at 15V then that should be sufficient?

I can't help feeling I've missed something with that solution though,
like the linearity ... ? ;-(

Cheers, T i m

On Monday, 25 September 2017 04:43:06 UTC+1, T i m wrote:
On Sun, 24 Sep 2017 17:52:51 -0700, mike wrote:
On 9/24/2017 6:31 AM, tabbypurr wrote:
On Sunday, 24 September 2017 12:06:45 UTC+1, mike wrote:

A series zener needs to draw ZERO current at 10V and still
be 10V at MUCH higher current ratio. You will have to live
with some amount of nonlinearity.

In fact you could re-zero the meter so it reads 10v spot on. Add an extra mark for where it points when unpowered so you can see if it ever decalibrates.

Yes, you can , but it's still nonlinear.
It's a matter of how much nonlinearity you can tolerate.
It's my assertion that the measured quantity is so crude that you don't
need to worry much about anything. Just learn what it reads and calibrate
your expectations to match.

(I've been a bit preoccupied elsewhere but still following the thread
with interest and will reply individually when I get the chance)

That was part I had already considered in that:
The meter is fairly small. The meter is glued shut. The meter is only
marked in whole volts.

If it's not an accurate meter just add a zener, job done.


NT

On Monday, 25 September 2017 10:01:42 UTC+1, mike wrote:
On 9/24/2017 6:05 PM, tabbypurr wrote:
On Monday, 25 September 2017 01:53:43 UTC+1, mike wrote:
On 9/24/2017 6:31 AM, tabbypurr wrote:
On Sunday, 24 September 2017 12:06:45 UTC+1, mike wrote:


A series zener needs to draw ZERO current at 10V and still
be 10V at MUCH higher current ratio. You will have to live
with some amount of nonlinearity.

In fact you could re-zero the meter so it reads 10v spot on. Add an extra mark for where it points when unpowered so you can see if it ever decalibrates.

Yes, you can , but it's still nonlinear.
It's a matter of how much nonlinearity you can tolerate.
It's my assertion that the measured quantity is so crude that you don't
need to worry much about anything. Just learn what it reads and calibrate
your expectations to match.

You could stack an AA-cell or two on top of your battery system
and alleviate that problem.

yuck. 2 resistors beats 2 cells any day.
Can't argue with that assertion, but, if you can
provide a circuit that is precisely linear and accurate over the WHOLE
range using
two resistors, I'd like to see it. I'm betting it's more than two
resistors.

What I meant is divide the input to your opamp

Thereyougo...opamp is a lot more complex than two resistors...or a couple
of AA cells.

I'm pretty sure we all know that, and what the options are, and what the pros & cons are. And that adding AA cells rather than 2 resistors on the input is not an option with any upside.


NT

On Mon, 25 Sep 2017 03:41:49 -0700 (PDT), wrote:

snip

That was part I had already considered in that:
The meter is fairly small. The meter is glued shut. The meter is only
marked in whole volts.

If it's not an accurate meter just add a zener, job done.

Well, I'm not sure if it's electro mechanically any more or less
'accurate' than any similar style meters and being smaller with a
shorter / lighter needle it's possible it could be better than some
.... but regarding the potential display markings and readability, you
may well be right. ;-)

Cheers, T i m

On Monday, 25 September 2017 12:37:05 UTC+1, T i m wrote:
On Mon, 25 Sep 2017 03:41:49 -0700 (PDT), tabbypurr wrote:

snip

That was part I had already considered in that:
The meter is fairly small. The meter is glued shut. The meter is only
marked in whole volts.

If it's not an accurate meter just add a zener, job done.

Well, I'm not sure if it's electro mechanically any more or less
'accurate' than any similar style meters and being smaller with a
shorter / lighter needle it's possible it could be better than some
... but regarding the potential display markings and readability, you
may well be right. ;-)

Cheers, T i m

If it's only marked in whole volts, reading it with accuracy won't happen, so it won't be especially accurate.


NT

On Monday, September 25, 2017 at 10:13:48 AM UTC-4, wrote:

If it's only marked in whole volts, reading it with accuracy won't happen, so it won't be especially accurate.

How so? I suggest that you are mistaking "accuracy" for "precision". They are not even a little bit the same thing nor follow necessarily one from another.

A gauge or meter that reads (is marked) in whole numbers but is dead-on is far more accurate than a gauge or meter marked in thousandths, but is always two units off. Although the latter meter is extremely precise.

I have a metered Iso-Variac that reads in volts measured in tens, and amps measured in tenths on a 0 -1 or 0 - 4 scale. But they are 4" meters so that even very slight needle movements are visible. The human brain is pretty good at interpolation.

Peter Wieck
Melrose Park, PA

T i m wrote:
On Fri, 22 Sep 2017 10:53:54 -0500, "Dave M"
wrote:

snip

I forgot to mention that for the zener solution, you really need to
select as low power a zener that you can find, such as 400mW or
lower.
The 1N4104 is a 10V, 250mW zener, with a test current of 1uA, and a
max current of 25ma, well within your requirements. In stock at
Mouser.com.

Cheers, Dave, I'll have a look.

As has been mentioned elsewhere, if we used a lower voltage zener (and
as high a tolerance as can be found in the right spec and the right
price *because*) to set the voltage on the -Ve leg of the meter and
then tweak the voltage up via resistors (variable initially) to give a
FSD at 15V then that should be sufficient?

I can't help feeling I've missed something with that solution though,
like the linearity ... ? ;-(

Cheers, T i m

I gave the wrong zener current for the 1N4104 . I just looked at Mouser's
basic info for the diode, but neglected to follow up and look at the actual
datasheet. According to the datasheet, the zener test current is actually
250uA, whereas Mouser states it as 1uA. Quite a difference, but after
looking at the datasheets for some other 10V/200mW zeners, (datasheets that
had actual graphs for Iz vs. Vz) I see that they actually start conducting
well below 1uA, so I feel confident that the 1N4104 will do the job for you.
All the other zeners that I found are SMD devices, so I doubt that you'll be
interested in any of those.
With that Zener in the circuit, I doubt that you'll have any noticible
nonlinearity; certainly not with the meter scale only having a 1-volt
resolution. Forget about the accuracy on the low end as well (except at the
volt marks), because you can't resolve to a basic meter accuracy
specification of +-3% of FSD.
Dave M

On Mon, 25 Sep 2017 07:53:49 -0700 (PDT), "
wrote:

On Monday, September 25, 2017 at 10:13:48 AM UTC-4, wrote:

If it's only marked in whole volts, reading it with accuracy won't happen, so it won't be especially accurate.

How so? I suggest that you are mistaking "accuracy" for "precision". They are not even a little bit the same thing nor follow necessarily one from another.

+1

A gauge or meter that reads (is marked) in whole numbers but is dead-on is far more accurate than a gauge or meter marked in thousandths, but is always two units off.

Yup, that's the thing ... and why many battery meters are calibrated
with red, amber and green sections. Now whilst that would work for me
re charge (voltage) and loosely therefore charge status, it wouldn't
be useful to pin down the discharge / charge status (unlike say a CCA
tester) as the terminal volts are a function of load.

Although the latter meter is extremely precise.

Yup and I have some of those. Highly repeatable but always 'out' by
some amount. ;-(

I have a metered Iso-Variac that reads in volts measured in tens, and amps measured in tenths on a 0 -1 or 0 - 4 scale. But they are 4" meters so that even very slight needle movements are visible. The human brain is pretty good at interpolation.

And it was the latter thought that I was using when it came to this
meter. ;-)

Take something that offers a very 'human' way of displaying something
(like an analogue car fuel or specifically, temperature gauge that
starts at say 60 DegC) and retain the merits but improve the general
meaning / readability.

Mileage / trip counters are more suited to being 'digital' etc. ;-)

Cheers, T i m

On Monday, 25 September 2017 15:53:59 UTC+1, wrote:
On Monday, September 25, 2017 at 10:13:48 AM UTC-4, tabby wrote:

If it's only marked in whole volts, reading it with accuracy won't happen, so it won't be especially accurate.

How so? I suggest that you are mistaking "accuracy" for "precision". They are not even a little bit the same thing nor follow necessarily one from another.

A gauge or meter that reads (is marked) in whole numbers but is dead-on is far more accurate than a gauge or meter marked in thousandths, but is always two units off. Although the latter meter is extremely precise.

I have a metered Iso-Variac that reads in volts measured in tens, and amps measured in tenths on a 0 -1 or 0 - 4 scale. But they are 4" meters so that even very slight needle movements are visible. The human brain is pretty good at interpolation.

Peter Wieck
Melrose Park, PA

With very coarse markings you won't get accurate readings. End of relevant material. I have no motivation to argue over the simple and immaterial.


NT

On 9/25/2017 3:35 PM, Dave M wrote:
I see that they actually start conducting well below 1uA, so I feel
confident that the 1N4104 will do the job for you.
All the other zeners that I found are SMD devices, so I doubt that
you'll be interested in any of those.

Previously I wrote:

The simplest is a 20K resistor in series with a 10v zener diode.
Use a low current Zener so the knee works right at low values.
Something like this:
http://www.mouser.com/ds/2/395/BZX55C2V0%20SERIES_D1610-1099630.pdf
Note, this is a DO-35 package.


--
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com

On Sunday, September 24, 2017 at 8:43:06 PM UTC-7, T i m wrote:
On Sun, 24 Sep 2017 17:52:51 -0700, mike wrote:

I'm far too lazy to do the math on how nonlinear it will be.

I do like the idea of printing my own scale and if this basic one
works, I might go for a bigger / better meter that I can open etc.

Yep, that's a good idea.

And, there's NO NONLINEARITY unless you apply bias less than the zener
voltage breakdown, because of Norton's theorem: any bunch of
resistors and voltage sources (the zener is a voltage source) is
identically a current source with a shunt resistance. Offset by
a constant, you can get; nonlinearity, you can't. The meter magnetic field
is the only source of nonlinearity (and meter manufacturers do pretty well
on keeping that uniform).

On Tuesday, 26 September 2017 03:21:57 UTC+1, whit3rd wrote:
On Sunday, September 24, 2017 at 8:43:06 PM UTC-7, T i m wrote:
On Sun, 24 Sep 2017 17:52:51 -0700, mike wrote:

I'm far too lazy to do the math on how nonlinear it will be.

I do like the idea of printing my own scale and if this basic one
works, I might go for a bigger / better meter that I can open etc.

Yep, that's a good idea.

And, there's NO NONLINEARITY unless you apply bias less than the zener
voltage breakdown, because of Norton's theorem: any bunch of
resistors and voltage sources (the zener is a voltage source) is
identically a current source with a shunt resistance. Offset by
a constant, you can get; nonlinearity, you can't. The meter magnetic field
is the only source of nonlinearity (and meter manufacturers do pretty well
on keeping that uniform).

zener v/i curves vary, some are terrible near zero i, some straighter.


NT

On Mon, 25 Sep 2017 20:08:01 -0500, Foxs Mercantile
wrote:

On 9/25/2017 3:35 PM, Dave M wrote:
I see that they actually start conducting well below 1uA, so I feel
confident that the 1N4104 will do the job for you.
All the other zeners that I found are SMD devices, so I doubt that
you'll be interested in any of those.

Previously I wrote:

The simplest is a 20K resistor in series with a 10v zener diode.
Use a low current Zener so the knee works right at low values.
Something like this:
http://www.mouser.com/ds/2/395/BZX55C2V0%20SERIES_D1610-1099630.pdf
Note, this is a DO-35 package.


So, if the / any issue to the zener solution is the closeness of any
knee to the bottom end of the required voltage range, would the using
the / a lower reference and a potential devider to set the fsd on 15
volts be a better idea still (or have I missed something again)? ;-(

Cheers, T i m

On Mon, 25 Sep 2017 15:35:28 -0500, "Dave M"
wrote:

T i m wrote:
On Fri, 22 Sep 2017 10:53:54 -0500, "Dave M"
wrote:

snip

I forgot to mention that for the zener solution, you really need to
select as low power a zener that you can find, such as 400mW or
lower.
The 1N4104 is a 10V, 250mW zener, with a test current of 1uA, and a
max current of 25ma, well within your requirements. In stock at
Mouser.com.

Cheers, Dave, I'll have a look.

As has been mentioned elsewhere, if we used a lower voltage zener (and
as high a tolerance as can be found in the right spec and the right
price *because*) to set the voltage on the -Ve leg of the meter and
then tweak the voltage up via resistors (variable initially) to give a
FSD at 15V then that should be sufficient?

I can't help feeling I've missed something with that solution though,
like the linearity ... ? ;-(


I gave the wrong zener current for the 1N4104 . I just looked at Mouser's
basic info for the diode, but neglected to follow up and look at the actual
datasheet. According to the datasheet, the zener test current is actually
250uA, whereas Mouser states it as 1uA. Quite a difference, but after
looking at the datasheets for some other 10V/200mW zeners, (datasheets that
had actual graphs for Iz vs. Vz) I see that they actually start conducting
well below 1uA, so I feel confident that the 1N4104 will do the job for you.

Thanks for the follow up Dave.

All the other zeners that I found are SMD devices, so I doubt that you'll be
interested in any of those.

Well, I have worked with SMD's but a wired device and could use on at
a pinch (soldered to the side of the meter contact etc) bit a wired
device is probably easier.

With that Zener in the circuit, I doubt that you'll have any noticible
nonlinearity; certainly not with the meter scale only having a 1-volt
resolution. Forget about the accuracy on the low end as well (except at the
volt marks), because you can't resolve to a basic meter accuracy
specification of +-3% of FSD.

Understood. I was thinking more on the idea of when using a lower
voltage zener to be well clear of the lower voltage levels being
considered and then the potential divider to set the FSD when the
input is 15V?

And also, wouldn't the impact of the battery voltage changing from say
10.5 to 14.4V be lessened (re the series current limiting / biasing
resistor) if the voltage difference between the reference and the
supply is greater?

That seemed like the best of all worlds (for the KISS solution)?

Cheers, T i m

On Mon, 25 Sep 2017 15:37:39 -0700 (PDT), wrote:

On Monday, 25 September 2017 15:53:59 UTC+1, wrote:
On Monday, September 25, 2017 at 10:13:48 AM UTC-4, tabby wrote:

If it's only marked in whole volts, reading it with accuracy won't happen, so it won't be especially accurate.

How so? I suggest that you are mistaking "accuracy" for "precision". They are not even a little bit the same thing nor follow necessarily one from another.

A gauge or meter that reads (is marked) in whole numbers but is dead-on is far more accurate than a gauge or meter marked in thousandths, but is always two units off. Although the latter meter is extremely precise.

I have a metered Iso-Variac that reads in volts measured in tens, and amps measured in tenths on a 0 -1 or 0 - 4 scale. But they are 4" meters so that even very slight needle movements are visible. The human brain is pretty good at interpolation.

Peter Wieck
Melrose Park, PA

With very coarse markings you won't get accurate readings. End of relevant material. I have no motivation to argue over the simple and immaterial.

Doesn't that depend what you are looking for? Say I determine my LVD
should be at 11.000 volts then I would appreciate the meter being as
accurate as possible (at that point at least)?

Cheers, T i m

On Tuesday, 26 September 2017 10:07:36 UTC+1, T i m wrote:
On Mon, 25 Sep 2017 15:35:28 -0500, "Dave M"
wrote:

T i m wrote:
On Fri, 22 Sep 2017 10:53:54 -0500, "Dave M"
wrote:

snip

I forgot to mention that for the zener solution, you really need to
select as low power a zener that you can find, such as 400mW or
lower.
The 1N4104 is a 10V, 250mW zener, with a test current of 1uA, and a
max current of 25ma, well within your requirements. In stock at
Mouser.com.

Cheers, Dave, I'll have a look.

As has been mentioned elsewhere, if we used a lower voltage zener (and
as high a tolerance as can be found in the right spec and the right
price *because*) to set the voltage on the -Ve leg of the meter and
then tweak the voltage up via resistors (variable initially) to give a
FSD at 15V then that should be sufficient?

I can't help feeling I've missed something with that solution though,
like the linearity ... ? ;-(


I gave the wrong zener current for the 1N4104 . I just looked at Mouser's
basic info for the diode, but neglected to follow up and look at the actual
datasheet. According to the datasheet, the zener test current is actually
250uA, whereas Mouser states it as 1uA. Quite a difference, but after
looking at the datasheets for some other 10V/200mW zeners, (datasheets that
had actual graphs for Iz vs. Vz) I see that they actually start conducting
well below 1uA, so I feel confident that the 1N4104 will do the job for you.

Thanks for the follow up Dave.

All the other zeners that I found are SMD devices, so I doubt that you'll be
interested in any of those.

Well, I have worked with SMD's but a wired device and could use on at
a pinch (soldered to the side of the meter contact etc) bit a wired
device is probably easier.

With that Zener in the circuit, I doubt that you'll have any noticible
nonlinearity; certainly not with the meter scale only having a 1-volt
resolution. Forget about the accuracy on the low end as well (except at the
volt marks), because you can't resolve to a basic meter accuracy
specification of +-3% of FSD.

Understood. I was thinking more on the idea of when using a lower
voltage zener to be well clear of the lower voltage levels being
considered and then the potential divider to set the FSD when the
input is 15V?

And also, wouldn't the impact of the battery voltage changing from say
10.5 to 14.4V be lessened (re the series current limiting / biasing
resistor) if the voltage difference between the reference and the
supply is greater?

That seemed like the best of all worlds (for the KISS solution)?

Cheers, T i m

You want a zener with a nice straight line at the low current end. One linked to from here has that.


NT

On Tue, 26 Sep 2017 06:46:01 -0700 (PDT), wrote:

snip

Understood. I was thinking more on the idea of when using a lower
voltage zener to be well clear of the lower voltage levels being
considered and then the potential divider to set the FSD when the
input is 15V?

And also, wouldn't the impact of the battery voltage changing from say
10.5 to 14.4V be lessened (re the series current limiting / biasing
resistor) if the voltage difference between the reference and the
supply is greater?

That seemed like the best of all worlds (for the KISS solution)?


You want a zener with a nice straight line at the low current end. One linked to from here has that.


Yeah, ok ... but what about the question re using a lower value zener
to get it away from the 'knee', especially as it's no more difficult
to do?

Cheers, T i m

On 9/26/2017 11:26 AM, T i m wrote:
On Tue, 26 Sep 2017 06:46:01 -0700 (PDT), wrote:

You want a zener with a nice straight line at the low current end.
One linked to from here has that.


Yeah, ok ... but what about the question re using a lower value zener
to get it away from the 'knee', especially as it's no more difficult
to do?

Here it is again.
The simplest is a 20K resistor in series with a 10v zener diode.
Use a low current Zener so the knee works right at low values.
Something like this:
http://www.mouser.com/ds/2/395/BZX55C2V0%20SERIES_D1610-1099630.pdf
Note, this is a DO-35 package.

--
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com

On 9/26/2017 9:26 AM, T i m wrote:
On Tue, 26 Sep 2017 06:46:01 -0700 (PDT), wrote:

snip

Understood. I was thinking more on the idea of when using a lower
voltage zener to be well clear of the lower voltage levels being
considered and then the potential divider to set the FSD when the
input is 15V?

And also, wouldn't the impact of the battery voltage changing from say
10.5 to 14.4V be lessened (re the series current limiting / biasing
resistor) if the voltage difference between the reference and the
supply is greater?

That seemed like the best of all worlds (for the KISS solution)?


You want a zener with a nice straight line at the low current end. One linked to from here has that.


Yeah, ok ... but what about the question re using a lower value zener
to get it away from the 'knee', especially as it's no more difficult
to do?

Cheers, T i m

Since we're just trying to be clever,
Try this:

https://i.imgur.com/irLisN7.jpg

The transistor and zener make a temperature compensated ~7V
reference (must use 6.2V zener with standard tempco).
Two pots set the min and max voltages. Rk allows you to add
current to the zener to get it past the most nonlinear portion
of it's V-I curve. This circuit has the ability to calibrate out
almost any component variation. It's relatively temperature
independent. You can use any meter that will make full scale at
less than about 7V. Downside is that the pots are vibration sensitive
and subject to moisture/corrosion.

Are we having fun yet?

On Tuesday, 26 September 2017 17:26:46 UTC+1, T i m wrote:
On Tue, 26 Sep 2017 06:46:01 -0700 (PDT), tabbypurr wrote:

snip

Understood. I was thinking more on the idea of when using a lower
voltage zener to be well clear of the lower voltage levels being
considered and then the potential divider to set the FSD when the
input is 15V?

And also, wouldn't the impact of the battery voltage changing from say
10.5 to 14.4V be lessened (re the series current limiting / biasing
resistor) if the voltage difference between the reference and the
supply is greater?

That seemed like the best of all worlds (for the KISS solution)?


You want a zener with a nice straight line at the low current end. One linked to from here has that.


Yeah, ok ... but what about the question re using a lower value zener
to get it away from the 'knee', especially as it's no more difficult
to do?

Cheers, T i m

The zeners with the straightest knee are at 9-10v. Go look at the linked data sheets.


NT

On Tue, 26 Sep 2017 14:13:20 -0700, mike wrote:

snip

Yeah, ok ... but what about the question re using a lower value zener
to get it away from the 'knee', especially as it's no more difficult
to do?


Since we're just trying to be clever,

I'm not mike, I'm just trying to refine the design of any solution to
be as good as possible with the fewest possible components. ;-)

Try this:

https://i.imgur.com/irLisN7.jpg

The transistor and zener make a temperature compensated ~7V
reference (must use 6.2V zener with standard tempco).

Ok.

Two pots set the min and max voltages.

Noted.

Rk allows you to add
current to the zener to get it past the most nonlinear portion
of it's V-I curve.

Understood.

This circuit has the ability to calibrate out
almost any component variation.

That sounds like the sort of thing I was hoping to hear. ;-)

It's relatively temperature
independent.

As long as it will cope with the -10 to +10 DegC range it should be
fine here in the UK. ;-)

You can use any meter that will make full scale at
less than about 7V.

And that's most small panel meters I'm sure.

Downside is that the pots are vibration sensitive
and subject to moisture/corrosion.

Sure, but in my case they won't be subject to any real vibration and
will be in a sealed enclosure. Also I would typically use a quality
multiturn pot of the smallest value possible to give me sufficient
'trimming' around the end points and quality resistors to do the main
bridge / work.

Are we having fun yet?

Well, it's certainly bringing some interesting and varied solutions
out of the woodwork. ;-)

It might also help me use up my stock of BC107's. ;-)

Cheers, T i m

On Tue, 26 Sep 2017 15:29:19 -0700 (PDT), wrote:

snip

Yeah, ok ... but what about the question re using a lower value zener
to get it away from the 'knee', especially as it's no more difficult
to do?


The zeners with the straightest knee are at 9-10v.

Ok, so again that helps because I'd go for a 9V zener to get AFA I can
from that 10V threshold and still retaining the sharpest knee. ;-)

Go look at the linked data sheets.

Too much information (variables) for me in most cases mate. ;-)

Ah, you can use the 9V zener but it only comes in SM and you have to
buy 1000. The 10V are easier to get but need a higher current ... etc
etc. I don't play chess or poker or any game of chance for that matter
(preferring FPS when I can shoot my fellow players in the face). ;-)

The whole point to me of asking those who know is they are the ones
who should all agree on a single 'best' solution. ;-)

More than one way to skin a cat? (But for that as long as it does get
skinned is good enough for me [1]).


Cheers, T i m

[1] I couldn't hurt one but I don't see the point in them ... apart
from a source of whiskers for crystal sets and guts for violins. ;-)

On 9/26/2017 7:49 PM, T i m wrote:
Too much information (variables) for me in most cases mate.;-)

You keep missing it.

Here it is again.
The simplest is a 20K resistor in series with a 10v zener diode.
Use a low current Zener so the knee works right at low values.
Something like this:
http://www.mouser.com/ds/2/395/BZX55C2V0%20SERIES_D1610-1099630.pdf
Note, this is a DO-35 package.


--
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com

On Wednesday, 27 September 2017 01:49:50 UTC+1, T i m wrote:
On Tue, 26 Sep 2017 15:29:19 -0700 (PDT), tabbypurr wrote:

snip

Yeah, ok ... but what about the question re using a lower value zener
to get it away from the 'knee', especially as it's no more difficult
to do?


The zeners with the straightest knee are at 9-10v.

Ok, so again that helps because I'd go for a 9V zener to get AFA I can
from that 10V threshold and still retaining the sharpest knee. ;-)

Go look at the linked data sheets.

Too much information (variables) for me in most cases mate. ;-)

Ah, you can use the 9V zener but it only comes in SM and you have to
buy 1000. The 10V are easier to get but need a higher current ... etc
etc. I don't play chess or poker or any game of chance for that matter
(preferring FPS when I can shoot my fellow players in the face). ;-)

The whole point to me of asking those who know is they are the ones
who should all agree on a single 'best' solution. ;-)

More than one way to skin a cat? (But for that as long as it does get
skinned is good enough for me [1]).


Cheers, T i m

[1] I couldn't hurt one but I don't see the point in them ... apart
from a source of whiskers for crystal sets and guts for violins. ;-)

Just use a 10v zener. Job done. There's little point in the rest when the meter is so coarsely marked. You can adjust for 10v mechanically. You should find one in your scraps box.

Catgut is made from sheep, goats etc.


NT

On 9/26/2017 5:40 PM, T i m wrote:
On Tue, 26 Sep 2017 14:13:20 -0700, mike wrote:

snip

Yeah, ok ... but what about the question re using a lower value zener
to get it away from the 'knee', especially as it's no more difficult
to do?


Since we're just trying to be clever,

I'm not mike, I'm just trying to refine the design of any solution to
be as good as possible with the fewest possible components. ;-)

Try this:

https://i.imgur.com/irLisN7.jpg

The transistor and zener make a temperature compensated ~7V
reference (must use 6.2V zener with standard tempco).

Ok.

Two pots set the min and max voltages.

Noted.

Rk allows you to add
current to the zener to get it past the most nonlinear portion
of it's V-I curve.

Understood.

This circuit has the ability to calibrate out
almost any component variation.

That sounds like the sort of thing I was hoping to hear. ;-)

It's relatively temperature
independent.

As long as it will cope with the -10 to +10 DegC range it should be
fine here in the UK. ;-)

You can use any meter that will make full scale at
less than about 7V.

And that's most small panel meters I'm sure.

Downside is that the pots are vibration sensitive
and subject to moisture/corrosion.

Sure, but in my case they won't be subject to any real vibration and
will be in a sealed enclosure. Also I would typically use a quality
multiturn pot of the smallest value possible to give me sufficient
'trimming' around the end points and quality resistors to do the main
bridge / work.
Use a small value pot with a fixed resistor on each end.
Easier to set, more stable.

Are we having fun yet?

Well, it's certainly bringing some interesting and varied solutions
out of the woodwork. ;-)

It might also help me use up my stock of BC107's. ;-)

Cheers, T i m