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How "repair" voltmeter gauge?

carpenter

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I have automobile voltmeter gauge , on the scale is indicated 8 - 16V.
Unfortunately it is damaged and so shows at these voltages. Gauge is inseparable.
For design reasons I want to use it and I would like it to show the right voltage.

8V - 0,70V
10V - 1,95V
12V - 2,83V
14V - 3,20V
16V - 3,80V

Current over voltmeter is 5,3mA on 700mV and 5,6mA on 3,8V.

I wonder what to put forward so that the voltmeter shows as accurately as possible?

I try
- 7,2V zener diode
- resistor serial with voltmeter coil
- resistor divider and voltmeter on center of divider


Everything works, but the linearity is not entirely good.
Some better idea?
 

srizbf

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you gave certain voltage readings as:

8V - 0,70V
10V - 1,95V
12V - 2,83V...

what does it mean ?

you may have to explain more on the damaged meter and
how did you took the readings.
whether the meter is working or the component
connected to it is damaged.

a simple handdrawn circuit of the meter with preferably a photo
will help.
 

carpenter

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It is simple voltmeter is marine waterproof gaute. Chrome and brass waterproof cylinder, non-removable piece
from front is hand and scale 8-16V
from behind is + and - terminals

it should show the magnitude of the voltage applied to the terminals.
unfortunately it is somehow damaged or something is missing and 12V shows it if it is on the terminals is 2,83V. if aplied 12V is
voltmeter overloaded and hand stuck to the right.
has a presumption, something is destroyed in the meter, by overvoltage or polority reversal, etc.


In any case, in order for it to point at least approximately correctly, I must insert something between the voltmeter terminals and the voltage wires that will cause it to point correctly.

I try ,
- zener diode and subtract its voltage
- resistance in series with the internal resistance of the voltmeter
- resistor divider and apply a divided voltage to the voltmeter

everything works, but everything has a different linearity than a voltmeter, and in some part of the measurement it inserts a large (visible) error

Yes, it is more of an orientation measurement, in fact more of a decorative matter, but I would still like it to show it as best as possible.
 

srizbf

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In the measurement readings,

8V - 0,70V
10V - 1,95V
12V - 2,83V
14V - 3,20V
16V - 3,80V

the meter itself shows a nonlinearity.
for equal increment in scale reading it doesnt show
a linear relationship with voltage you applied.

whatever is the circuit proposed/added the nonlinearity
cannot be avoided unless
the damaged complonent is removed from the meter.
 

KlausST

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Hi,

a simple handdrawn circuit of the meter with preferably a photo will help.
we live in the 2020ies where every simple cellular phone has a camera, most laptops, tablets...


It really makes it hard to help without good informations.

Klaus
 

BradtheRad

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Arrange the zener diode in series so it subtracts about 7.2 volts from the supply. This creates an expanded scale meter.
Apply 8V, needle deflects a little.
Apply 16V, needle deflects all the way upscale.

Then install a series resistor of a value that creates correct needle readings. Since you mention 5.6 mA full scale, this suggests the resistor should be 1,430 ohms, or:
8 / .0056
 

carpenter

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Hi,
we live in the 2020ies where every simple cellular phone has a camera, most laptops, tablets...
It really makes it hard to help without good informations.
Klaus
Unfortunately, teleportation was not invented even in 2020 :p
As I mentioned, it is marine gauge a I have them on a sea yacht that I bought and reconstruct.
The ship is moored in the Red Sea and I am alone in Europe. I'll fly next month

However, you still won't know anything from the photo.
On the ship's dashboard there are a total of 8 gauges in a uniform design and an incredibly robust design for today.
Made of chromed brass, waterproof, some with glycerin inside
For the performance, something like see photo.
In front is a hand and a scale
from the rear, two 4mm screws marked + and - to which the measured voltage is applied.

15987.jpg


Then install a series resistor of a value that creates correct needle readings. Since you mention 5.6 mA full scale, this suggests the resistor should be 1,430 ohms, or:
8 / .0056
Thanks I try it.
 

KlausST

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Hi,

I had something completely different in mind...

Now I see it´s a VDO brand.

On an internet search I came to the VDO web shop.
There you may find documents and also replacement parts.

...
Almost forgot:
If the values are true, then I think there is something damaged inside. The values make no sense. I see no reliable solution to compensate this externally.
Maybe you find a solution that works for now ... then I assume it soon will alter it´s behaviour. Maybe with time, with temperature with vibration... maybe from one second to the other.
Either you need to open it and find repair it or look for a replacement.

Klaus
 

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