In article ,
David Nebenzahl wrote:
On 4/13/2009 1:26 AM Dave Plowman (News) spake thus:

In article ,
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?

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 London SW
To e-mail, change noise into sound.