Galvanometers

[geofrancis]

As an apprentice Linesman I was taught to use a Galvanometer as a measuring instrument, for the life of me I cant remember in what context, can anyone enlighten me please
Regards Geofrancis

[strang steel]

I remember those from A Level Physics. Are they just a posh name for a meter?

You wire them into an electrical circuit and the needle measures the voltage?

Or is it the current? Or both?

[52A]

Naa they were used for measuring galvans!

[Bryan]

I don't know if they have any other names or uses but the only place I know that they are in use is in the operating cab of a pre computer tamper.
They show the degree of offset of the sensors from the lining wires.
The operator then tries to zero the needle by operating the clamps for lift and slew.

[65447]

As an apprentice Linesman I was taught to use a Galvanometer as a measuring instrument, for the life of me I cant remember in what context, can anyone enlighten me please
Regards Geofrancis

Were they known by the name Shunts (there were different types for different purposes) and used to measure the correct values for track circuiting and the like?

[R. pike]

My galvanometer. Unfortunately it is used as a book end now.. I'm trying to find some documentation showing it's use with a Wheatstone Bridge..

Edit...

http://en.wikipedia.org/wiki/Wheatstone_bridge

[richard]

Galvanometers are simple devices for measuring the presence of electrical current. Basically a few windings of wire create a magnetic field which deflects the needle.

65447 and Bryan's description would tally with this: It would be possible to rig one up so that it was pretty sensitive to current direction, despite being not very good for measuring actual amps. Eg. nulling out a position or offset - the needle is deflected in one direction, it needs adjusting; needle deflected in the other direction, it needs adjusting in the opposite direction.

Richard

[Flamingo]

Mr Pike's splendid instrument looks rather like the needle type thingys one sees in old signalboxes. It also looks worthy of display in a museum.

I also remember galvanometers and Wheatstone bridges from A-level physics, more than half a century ago now for me at least. Was there a type called the hot wire galvanometer, or did all wires get hot when a current passed through them?

[strang steel]

Not quite 50 years yet for me since A level Physics, but will soon be there. These instrument names do bring back some memories, but the one that stands out for me is the Van Der Graaf generator.

Our Physics master would place his hand on the top of the machine, then switch it on. He would then invite anyone in the class to shake hands with him. Of course no one ever did, but I never knew if shaking his hand would have given us a shock.

Has anyone here ever been brave enough? The machine was capable of generating some pretty worrying looking sparks.

[Atlantic 3279]

If 30 year old recollection of physics is any good, I believe a Galvanometer can be used in such a way that it measures neither Potential Difference (voltage, as per a Voltmeter), nor Current (amps, as per an ammeter), nor for that matter electrical power (watts), but rather the total charge passed (power x time), which I suspect is measured in Coulombs

Is anybody actually any better off for reading my answer?

[Flamingo]

If 30 year old recollection of physics is any good, I believe a Galvanometer can be used in such a way that it measures neither Potential Difference (voltage, as per a Voltmeter), nor Current (amps, as per an ammeter), nor for that matter electrical power (watts), but rather the total charge passed (power x time), which I suspect is measured in Coulombs

Is anybody actually any better off for reading my answer?

Not really but full marks for trying. I had the same feeling about other subjects such as trigonometry and complex numbers, both topics where their inventors deserved urgent visits from the men in long white coats.

[richard]

I'm not sure about how they'd be used to measure total charge. But yes total charge is measured in colulombs and is current * time (for constant current over the time period - it is technically an integral).
And charge on a capacitor (Coulombs) = Capacitance (Farads) * Voltage.

[harvester]

A galvo is just a voltmeter by tradition with the needle central at zero and scales on either side one reading positive values the other negative, so depending wether the voltage is neg or pos it will deflect one way or t'other. Normally to read amps a "shunt" (a resistor with a known value, usually low) is used and this is connected straight across the moving coil of the galvo. The current passes through the shunt and the galvo reads the value across it. You need shunts to measure amperage because the high resistance of the galvo moving coil would would restrict current flow.

[Bryan]

http://science.howstuffworks.com/galvanometer-info.htm

[52D]

Was Harvester a physics teacher i think hes nailed the best explanation. BTW the instrument was named after the italian inventer Galvani.