Analogue moving coil meter range extension?

[Dave M]

T i m wrote:

On Fri, 22 Sep 2017 10:53:54 -0500, "Dave M" <dgminala@mediacombb.net
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

 

[T i m]

On Mon, 25 Sep 2017 07:53:49 -0700 (PDT), "pfjw@aol.com"
<pfjw@aol.com> wrote:

On Monday, September 25, 2017 at 10:13:48 AM UTC-4, tabb...@gmail.com 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, pf...@aol.com 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

 

[Foxs Mercantile]

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

 

[whit3rd]

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 <ham789@netzero.net> 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 <ham789@netzero.net> 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

 

[T i m]

On Mon, 25 Sep 2017 20:08:01 -0500, Foxs Mercantile <jdangus@att.net>
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

 

[T i m]

On Mon, 25 Sep 2017 15:35:28 -0500, "Dave M" <dgminala@mediacombb.net>
wrote:

T i m wrote:
On Fri, 22 Sep 2017 10:53:54 -0500, "Dave M" <dgminala@mediacombb.net
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

 

[T i m]

On Mon, 25 Sep 2017 15:37:39 -0700 (PDT), tabbypurr@gmail.com wrote:

On Monday, 25 September 2017 15:53:59 UTC+1, pf...@aol.com 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" <dgminala@mediacombb.net
wrote:

T i m wrote:
On Fri, 22 Sep 2017 10:53:54 -0500, "Dave M" <dgminala@mediacombb.net
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

 

[T i m]

On Tue, 26 Sep 2017 06:46:01 -0700 (PDT), tabbypurr@gmail.com 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

 

[Foxs Mercantile]

On 9/26/2017 11:26 AM, T i m wrote:

On Tue, 26 Sep 2017 06:46:01 -0700 (PDT), tabbypurr@gmail.com 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

 

[mike]

On 9/26/2017 9:26 AM, T i m wrote:

On Tue, 26 Sep 2017 06:46:01 -0700 (PDT), tabbypurr@gmail.com 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

 

[T i m]

On Tue, 26 Sep 2017 14:13:20 -0700, mike <ham789@netzero.net> 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

 

[T i m]

On Tue, 26 Sep 2017 15:29:19 -0700 (PDT), tabbypurr@gmail.com 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. ;-)

 

[Foxs Mercantile]

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

 

[mike]

On 9/26/2017 5:40 PM, T i m wrote:

On Tue, 26 Sep 2017 14:13:20 -0700, mike <ham789@netzero.net> 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