Galvanometer

[David Nebenzahl]

I have an old galvanometer (nice Weston in a slant-front black crackle
case). Its scale reads 30-0-30. What units are these? Or are they just
relative values for comparison?


--
Save the Planet
Kill Yourself

- motto of the Church of Euthanasia (http://www.churchofeuthanasia.org/)

 

[isw]

In article <49e2a4be$0$2712$822641b3@news.adtechcomputers.com>,
David Nebenzahl <nobody@but.us.chickens> wrote:

I have an old galvanometer (nice Weston in a slant-front black crackle
case). Its scale reads 30-0-30. What units are these? Or are they just
relative values for comparison?

With a standard alkaline cell and starting with a *very high* resistance
(5 megohms, say), drop the resistance until you get a decent deflection.
Then measure the resistance and the voltage, and do the math.

Isaac

 

[David Nebenzahl]

On 4/12/2009 8:08 PM isw spake thus:

In article <49e2a4be$0$2712$822641b3@news.adtechcomputers.com>,
David Nebenzahl <nobody@but.us.chickens> wrote:

I have an old galvanometer (nice Weston in a slant-front black crackle
case). Its scale reads 30-0-30. What units are these? Or are they just
relative values for comparison?

With a standard alkaline cell and starting with a *very high* resistance
(5 megohms, say), drop the resistance until you get a decent deflection.
Then measure the resistance and the voltage, and do the math.

Figure it out for myself? What a concept!

So, OK, I did as you suggested. Actually, the thing was a *lot* less
sensitive than you warned; I ended up using 2 AA cells (2.95 volts
according to 2 DMMs) through less than 10K to get a decent deflection
from the meter.

So here's my work, which you can check:

The needle went left to 18.

I = V (2.95) / R (7.45K)
= 0.0004A (rounded) = 0.4mA

Dividing this by 18 shows that each division on the meter is 0.02mA.

So I hooked the thing up to one channel's mike input on my Sony D6
Walkman (see posts rehantom powering from this device above) through
an appropriate load resistor, and the meter went to 15, which tells me
that it was supplying 0.3mA. (Did the same thing even without any load
resistor.)

Not much power. (Even less than Eeyore had predicted this unit would be
able to supply.) Can't use that to power my microphone as I'd hoped. Oh,
well.


--
Save the Planet
Kill Yourself

- motto of the Church of Euthanasia (http://www.churchofeuthanasia.org/)

 

[Dave Plowman (News)]

In article <49e2a4be$0$2712$822641b3@news.adtechcomputers.com>,
David Nebenzahl <nobody@but.us.chickens> wrote:

I have an old galvanometer (nice Weston in a slant-front black crackle
case). Its scale reads 30-0-30. What units are these? Or are they just
relative values for comparison?

Most meter *movements* will only read directly small currents or voltages.
To allow them to read higher values you use an appropriate resistor - in
series to read a higher voltage than the FSD of the movement or in
parallel to read a higher current.

So the exact same movement can be supplied with a variety of scales for
different applications - and may or may not include this resistor, which
is called a shunt for current and multiplier for voltage. If it includes
this resistor the scale is usually marked with the true units.

30-0-30 was common for the ammeter on older cars.

--
*The average person falls asleep in seven minutes *

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

 

[David Nebenzahl]

On 4/13/2009 1:26 AM Dave Plowman (News) spake thus:

In article <49e2a4be$0$2712$822641b3@news.adtechcomputers.com>,
David Nebenzahl <nobody@but.us.chickens> wrote:

I have an old galvanometer (nice Weston in a slant-front black crackle
case). Its scale reads 30-0-30. What units are these? Or are they just
relative values for comparison?

Most meter *movements* will only read directly small currents or voltages.
To allow them to read higher values you use an appropriate resistor - in
series to read a higher voltage than the FSD of the movement or in
parallel to read a higher current.

Yes, I know all that.

So the exact same movement can be supplied with a variety of scales for
different applications - and may or may not include this resistor, which
is called a shunt for current and multiplier for voltage. If it includes
this resistor the scale is usually marked with the true units.

No shunt resistor. See my post above: turns out each division is 0.02mA
(0.6mA full scale). Meter is labeled "DC GALVANOMETER", by the way. I'm
thinking it was a piece of lab equipment, or maybe for students to learn
to use stuff like Wheatstone bridges, etc.

30-0-30 was common for the ammeter on older cars.

How do you get from "galvanometer" to automobile ammeter???

Helpfulness of your post: 0.2 (dimensionless units).


--
Save the Planet
Kill Yourself

- motto of the Church of Euthanasia (http://www.churchofeuthanasia.org/)

 

[Dave Plowman (News)]

In article <49e2fb35$0$2708$822641b3@news.adtechcomputers.com>,
David Nebenzahl <nobody@but.us.chickens> wrote:

On 4/13/2009 1:26 AM Dave Plowman (News) spake thus:

In article <49e2a4be$0$2712$822641b3@news.adtechcomputers.com>,
David Nebenzahl <nobody@but.us.chickens> wrote:

I have an old galvanometer (nice Weston in a slant-front black
crackle case). Its scale reads 30-0-30. What units are these? Or are
they just relative values for comparison?

Most meter *movements* will only read directly small currents or
voltages. To allow them to read higher values you use an appropriate
resistor - in series to read a higher voltage than the FSD of the
movement or in parallel to read a higher current.

Yes, I know all that.

Then why the post? You have all the information to work it out for
yourself.

So the exact same movement can be supplied with a variety of scales
for different applications - and may or may not include this resistor,
which is called a shunt for current and multiplier for voltage. If it
includes this resistor the scale is usually marked with the true
units.

No shunt resistor. See my post above: turns out each division is 0.02mA
(0.6mA full scale). Meter is labeled "DC GALVANOMETER", by the way. I'm
thinking it was a piece of lab equipment, or maybe for students to learn
to use stuff like Wheatstone bridges, etc.

Similar meters are - or were - on sale in most hobby electronics shops.

30-0-30 was common for the ammeter on older cars.

How do you get from "galvanometer" to automobile ammeter???

FFS, a 'galvanometer' *is* an ammeter. Or is it yet another term you want
to mean whatever you think it should? And 30-0-30 is exactly how older car
ammeters were marked. No need for 'amps' as that's all it could be. And
external ones for garage use (on cars not so fitted) were to be found.

Helpfulness of your post: 0.2 (dimensionless units).

You really are a charmer.

--
*I want it all and I want it delivered

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

 

[GregS]

In article <xJ6dnUPxxZXHwX7UnZ2dnUVZ_gGdnZ2d@posted.cpinternet>, msg <msg@_cybertheque.org_> wrote:

David Nebenzahl wrote:

I have an old galvanometer (nice Weston in a slant-front black crackle
case). Its scale reads 30-0-30. What units are these? Or are they just
relative values for comparison?



When you said 'galvanometer', I immediately expected you to be talking
about a 'mirror galvanometer': a large sensitive laboratory instrument
rather than an ordinary moving coil meter, which of course is
also a 'galvanometer' but is not commonly (at least in the US) labeled
as such.

Michael

I also though of a sensitive current or sensitive votmeter. I actually though of a static vane
type, but there is also the iron vane galvanometer. The key was the center scale 0.

greg

 

[msg]

David Nebenzahl wrote:

I have an old galvanometer (nice Weston in a slant-front black crackle
case). Its scale reads 30-0-30. What units are these? Or are they just
relative values for comparison?

When you said 'galvanometer', I immediately expected you to be talking
about a 'mirror galvanometer': a large sensitive laboratory instrument
rather than an ordinary moving coil meter, which of course is
also a 'galvanometer' but is not commonly (at least in the US) labeled
as such.

Michael

 

[David Nebenzahl]

On 4/13/2009 9:39 AM msg spake thus:

David Nebenzahl wrote:

I have an old galvanometer (nice Weston in a slant-front black crackle
case). Its scale reads 30-0-30. What units are these? Or are they just
relative values for comparison?

When you said 'galvanometer', I immediately expected you to be talking
about a 'mirror galvanometer': a large sensitive laboratory instrument
rather than an ordinary moving coil meter, which of course is
also a 'galvanometer' but is not commonly (at least in the US) labeled
as such.

Well, this one is definitely marked as such (at the factory), and was
made by what was at the time one of the largest manufacturers of meters
in the U.S., Weston Electrical Instrument Corp. Make of that what you will.


--
Save the Planet
Kill Yourself

- motto of the Church of Euthanasia (http://www.churchofeuthanasia.org/)

 

[GregS]

In article <49e37ea0$0$2713$822641b3@news.adtechcomputers.com>, David Nebenzahl <nobody@but.us.chickens> wrote:

On 4/13/2009 9:39 AM msg spake thus:

David Nebenzahl wrote:

I have an old galvanometer (nice Weston in a slant-front black crackle
case). Its scale reads 30-0-30. What units are these? Or are they just
relative values for comparison?

When you said 'galvanometer', I immediately expected you to be talking
about a 'mirror galvanometer': a large sensitive laboratory instrument
rather than an ordinary moving coil meter, which of course is
also a 'galvanometer' but is not commonly (at least in the US) labeled
as such.

Well, this one is definitely marked as such (at the factory), and was
made by what was at the time one of the largest manufacturers of meters
in the U.S., Weston Electrical Instrument Corp. Make of that what you will.

Here is one I have....

http://zekfrivolous.com/misc/meter.JPG

 

[David Nebenzahl]

On 4/13/2009 11:19 AM GregS spake thus:

In article <49e37ea0$0$2713$822641b3@news.adtechcomputers.com>,
David Nebenzahl <nobody@but.us.chickens> wrote:

On 4/13/2009 9:39 AM msg spake thus:

David Nebenzahl wrote:

I have an old galvanometer (nice Weston in a slant-front black crackle
case). Its scale reads 30-0-30. What units are these? Or are they just
relative values for comparison?

When you said 'galvanometer', I immediately expected you to be talking
about a 'mirror galvanometer': a large sensitive laboratory instrument
rather than an ordinary moving coil meter, which of course is
also a 'galvanometer' but is not commonly (at least in the US) labeled
as such.

Well, this one is definitely marked as such (at the factory), and
was made by what was at the time one of the largest manufacturers
of meters in the U.S., Weston Electrical Instrument Corp. Make of
that what you will.

Here is one I have....

http://zekfrivolous.com/misc/meter.JPG

Except ... it's not labeled as a galvanometer. Nice piece, though; much
nicer looking than my utilitarian black crackle job.


--
Save the Planet
Kill Yourself

- motto of the Church of Euthanasia (http://www.churchofeuthanasia.org/)

 

[Franc Zabkar]

On Sun, 12 Apr 2009 20:08:37 -0700, isw <isw@witzend.com> put finger
to keyboard and composed:

In article <49e2a4be$0$2712$822641b3@news.adtechcomputers.com>,
David Nebenzahl <nobody@but.us.chickens> wrote:

I have an old galvanometer (nice Weston in a slant-front black crackle
case). Its scale reads 30-0-30. What units are these? Or are they just
relative values for comparison?

With a standard alkaline cell and starting with a *very high* resistance
(5 megohms, say), drop the resistance until you get a decent deflection.
Then measure the resistance and the voltage, and do the math.

Isaac

A quicker way to do it might be to use two DMMs. Set the first to
measure resistance and the second to measure current. Start with the
highest resistance scale. DMM1 will supply a test current to the other
two meters.

DMM1 (ohms) DMM2 (amps) Weston Galvanometer

--> I --> I
o---------o-- A --o---------o-- M --o--|
| |
current |
source |
| |
o--------------------------------------|
I <--

My DMM outputs the following test currents:

diode - 0.93mA
200R - 167uA
2K - 133uA
20K - 42uA
200K - 5uA
2M - 0.5uA

When testing on the diode range, the OP could set DMM2 for the highest
burden, ie the 2M scale. In that way the voltage to the galvanometer
would be reduced by 200mV (?). Alternatively he could insert a series
resistor or potentiometer.

If only one DMM is available, then replace DMM1 with a battery and
resistor and use your DMM to measure the current, otherwise you will
need to account for the burden of the galvanometer when doing your
Ohm's Law calculations.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

 

[att]

"Franc Zabkar" <fzabkar@iinternode.on.net> wrote in message
news:8v67u4t7q9v8k9f993kb6thvpt9vjs1t84@4ax.com...

On Sun, 12 Apr 2009 20:08:37 -0700, isw <isw@witzend.com> put finger
to keyboard and composed:

In article <49e2a4be$0$2712$822641b3@news.adtechcomputers.com>,
David Nebenzahl <nobody@but.us.chickens> wrote:

I have an old galvanometer (nice Weston in a slant-front black crackle
case). Its scale reads 30-0-30. What units are these? Or are they just
relative values for comparison?

With a standard alkaline cell and starting with a *very high* resistance
(5 megohms, say), drop the resistance until you get a decent deflection.
Then measure the resistance and the voltage, and do the math.

Isaac

A quicker way to do it might be to use two DMMs. Set the first to
measure resistance and the second to measure current. Start with the
highest resistance scale. DMM1 will supply a test current to the other
two meters.

DMM1 (ohms) DMM2 (amps) Weston Galvanometer

--> I --> I
o---------o-- A --o---------o-- M --o--|
| |
current |
source |
| |
o--------------------------------------|
I <--

My DMM outputs the following test currents:

diode - 0.93mA
200R - 167uA
2K - 133uA
20K - 42uA
200K - 5uA
2M - 0.5uA

When testing on the diode range, the OP could set DMM2 for the highest
burden, ie the 2M scale. In that way the voltage to the galvanometer
would be reduced by 200mV (?). Alternatively he could insert a series
resistor or potentiometer.

If only one DMM is available, then replace DMM1 with a battery and
resistor and use your DMM to measure the current, otherwise you will
need to account for the burden of the galvanometer when doing your
Ohm's Law calculations.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Every galvanometer I've seen in the past 60 years read in microamps

 

[att]

"David Nebenzahl" <nobody@but.us.chickens> wrote in message
news:49e37ea0$0$2713$822641b3@news.adtechcomputers.com...

On 4/13/2009 9:39 AM msg spake thus:

David Nebenzahl wrote:

I have an old galvanometer (nice Weston in a slant-front black crackle
case). Its scale reads 30-0-30. What units are these? Or are they just
relative values for comparison?

When you said 'galvanometer', I immediately expected you to be talking
about a 'mirror galvanometer': a large sensitive laboratory instrument
rather than an ordinary moving coil meter, which of course is
also a 'galvanometer' but is not commonly (at least in the US) labeled
as such.
That instrument was called a "ballistic galvanometer" and was intended to

measure
very small currents for a very short duration, the mirror would deflect with
the current and return very slowly so you could grab a reading on the
current.

Well, this one is definitely marked as such (at the factory), and was made
by what was at the time one of the largest manufacturers of meters in the
U.S., Weston Electrical Instrument Corp. Make of that what you will.


--
Save the Planet
Kill Yourself

- motto of the Church of Euthanasia (http://www.churchofeuthanasia.org/)

 

[Franc Zabkar]

On Mon, 13 Apr 2009 21:54:51 GMT, "att" <n2nbe@att.net> put finger to
keyboard and composed:

Every galvanometer I've seen in the past 60 years read in microamps

The OP's measurements suggest that the meter's fsd is +/- 600uA, not
+/- 30uA. Therefore it probably has a current shunt.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

 

[isw]

In article <49e2f46e$0$2697$822641b3@news.adtechcomputers.com>,
David Nebenzahl <nobody@but.us.chickens> wrote:

On 4/12/2009 8:08 PM isw spake thus:

In article <49e2a4be$0$2712$822641b3@news.adtechcomputers.com>,
David Nebenzahl <nobody@but.us.chickens> wrote:

I have an old galvanometer (nice Weston in a slant-front black crackle
case). Its scale reads 30-0-30. What units are these? Or are they just
relative values for comparison?

With a standard alkaline cell and starting with a *very high* resistance
(5 megohms, say), drop the resistance until you get a decent deflection.
Then measure the resistance and the voltage, and do the math.

Figure it out for myself? What a concept!

So, OK, I did as you suggested. Actually, the thing was a *lot* less
sensitive than you warned; I ended up using 2 AA cells (2.95 volts
according to 2 DMMs) through less than 10K to get a decent deflection
from the meter.

So here's my work, which you can check:

The needle went left to 18.

I = V (2.95) / R (7.45K)
= 0.0004A (rounded) = 0.4mA

Dividing this by 18 shows that each division on the meter is 0.02mA.

So I hooked the thing up to one channel's mike input on my Sony D6
Walkman (see posts rehantom powering from this device above) through
an appropriate load resistor, and the meter went to 15, which tells me
that it was supplying 0.3mA. (Did the same thing even without any load
resistor.)

Not much power. (Even less than Eeyore had predicted this unit would be
able to supply.) Can't use that to power my microphone as I'd hoped. Oh,
well.

That sort of input is intended to power an electret condenser mic (with
possibly a FET follower). It basically needs a polarizing voltage at
nearly zero current.

Isaac

 

[isw]

In article
<szOEl.557762$Mh5.469250@bgtnsc04-news.ops.worldnet.att.net>,
"att" <n2nbe@att.net> wrote:

"David Nebenzahl" <nobody@but.us.chickens> wrote in message
news:49e37ea0$0$2713$822641b3@news.adtechcomputers.com...
On 4/13/2009 9:39 AM msg spake thus:

David Nebenzahl wrote:

I have an old galvanometer (nice Weston in a slant-front black crackle
case). Its scale reads 30-0-30. What units are these? Or are they just
relative values for comparison?

When you said 'galvanometer', I immediately expected you to be talking
about a 'mirror galvanometer': a large sensitive laboratory instrument
rather than an ordinary moving coil meter, which of course is
also a 'galvanometer' but is not commonly (at least in the US) labeled
as such.
That instrument was called a "ballistic galvanometer" and was intended to
measure
very small currents for a very short duration, the mirror would deflect with
the current and return very slowly so you could grab a reading on the
current.

A "ballistic galvanometer" is rather a different beast from a normal
galvo -- for one thing, the suspension has essentially no restoring
force (and that is why the return is so slow; not just to make it easier
to read). A normal galvo deflects to the angle where the *continuous*
force from the current is matched by the restoring spring force of the
suspension.

"Ballistic" refers to the fact that the galvo is intended to accept a
brief pulse of current and then respond "ballistically" -- integrating
the pulse -- by producing a deflection proportional, essentially, to the
total number of electrons that just flowed through its coil. In fact,
the pulse should be short enough so that it is completely over before
the deflection begins. In general, just about *any* continuous current
you put through a ballistic galvo will cause it to deflect all the way
to the stops (because the restoring force is so small).

Isaac

 

[Nicholas Bodley]

On Tue, 14 Apr 2009 22:11:42 -0700, isw wrote
about ballistic galvanometers.

Thanks for the refresher! I'd forgotten about ballistic galvo's. Your
description of minimal restoring force reminds me of the very distinctive
traditional Megger meter movements; their hairsprings (three of them)
were tweaked for no net restoring force.

Btw, "galvanometer" is a term from more than a century ago; iirc, it
refers to Luigi Galvani, of voltaic pile and jumping frog's legs, etc.

Regards,
nb