Hartmann & Braun AG Pontavi TH2 Galvanometer test and repair and teardown video

[oz2cpu]

Galvanometer is just a cool name for wheatstone bridge :-)
this miliohm to ohm meter, is made quite nice,
specially the variable "potmeter" where the slider follow a resistor wire is a neat way to make it accurate and stable

see all details here:

https://youtu.be/dE93LYoTorQ

[Kleinstein]

Galvanometer is more like used for the moving coil movement, especially sensitive ones.

As the bridge as 4 wire connection for the DUT, the bridge would be more like a Kelvin bridge and not just a simple Weatstone bridge. This way the connections at the wire ends of variable pot part could also be less critical.

[Conrad Hoffman]

Cool little device and you can't beat the null technique, if the user is willing to put up with it. That said, I can't stand videos. Inefficient use of my time and I'd rather have some still photos and text.

[trobbins]

I have the milliohm meter variant - will post details and photos for comparison in 2 weeks when i get home. Main limitation is use of 1.3A excitation current, which can be a bit much for some parts/windings.

[oz2cpu]

thanks for your comments

From Conrad :
That said, I can't stand videos. Inefficient use of my time and I'd rather have some still photos and text.

Answer : the trick is to scroll round in the video, to find the parts you need or like the most,
most videos you dont need to see the full reel to get the point


From trobbins :
I have the milliohm meter variant - will post details and photos for comparison in 2 weeks when i get home.

Answer : COOL please do, i love to see how it is made, yes 1.3A is quite a lot, but a miliohm resistor only make 1.3mV at this current,
so you need some current, to get enough signal for a good stable reading.


From Kleinstein :
Galvanometer is more like used for the moving coil movement, especially sensitive ones.

Answer : I think you are right, there is a good explain on wiki to back this up

https://en.wikipedia.org/wiki/Galvanometer

this also explain why there is no read out on the meter pointer it self, the ONLY trick is to dial it into zero !
since that is zero current = correct read out from the dial numbers

[TimFox]

In my physics education, we did labs with traditional equipment to better learn the fundamentals.
This included bridges of various types, including Wheatstone and Kelvin, and "potentiometers" (in the literal meaning of the word) to measure voltage.
The coolest galvanometers were the ones firmly mounted to a concrete wall. 
To read them, one attached a scale on an arced surface with a telescope mounted above it, to see the numbers reflected off the mirror in the galvanometer.
(Of course, the numbers were reversed on the scale to read properly after reflection.)
Used as "ballistic galvanometers", where one read the maximum excursion and calculated knowing the mechanical parameters of the instrument, these could measure charge directly.
Used normally, they gave a very sensitive null indication, with no bias current.
In "Vacuum Tube Amplifiers" (Radiation Laboratory Series Vol 18), ed G E Valley and H Wallman, McGraw-Hill 1948, pp 490-491, there is a simple DC amplifier using a dual phototube (920) illuminated by such a galvanometer, driving a simple 6SF5 triode amplifier, where the feedback is applied to the galvanometer coil for comparison, and the difference between the two photocurrents is a strong function of the coil current.

[Le_Bassiste]

... Inefficient use of my time and I'd rather have some still photos and text.

Amen to that!

[trobbins]

For comparison, my notes so far on the related Pontavi TH2 milliohm meter are in linked doc, along with an internal photo, the original manual, and a simple schematic.  It is quite a practical instrument for circa 1% accurate DCR measurement of transformer and choke windings.  https://www.dalmura.com.au/static/pontavi_th2%20summary.pdf

I also have a Leeds & Northrup Kelvin Double Bridge 4288 which appears to achieve better accuracy performance than the Pontavi, but has some operational disadvantages.