Hartmann & Braun AG Pontavi TH2 Galvanometer test and repair and teardown video - Page 1
Forum section: electronics / projects

author: oz2cpu
author_rank: Frequent Contributor
timestamp: May 24, 2022, 04:17:01 pm
content: 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 stablesee all details here:https://youtu.be/dE93LYoTorQ

author: Kleinstein
author_rank: Super Contributor
timestamp: May 24, 2022, 05:46:06 pm
content: 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.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: May 24, 2022, 11:19:23 pm
content: 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.

author: trobbins
author_rank: Frequent Contributor
timestamp: May 25, 2022, 02:56:34 am
content: 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.

author: oz2cpu
author_rank: Frequent Contributor
timestamp: May 25, 2022, 02:05:05 pm
content: thanks for your commentsFrom 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 pointFrom 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 uphttps://en.wikipedia.org/wiki/Galvanometerthis 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

author: TimFox
author_rank: Super Contributor
timestamp: May 25, 2022, 03:42:19 pm
content: 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.

author: Le_Bassiste
author_rank: Frequent Contributor
timestamp: May 27, 2022, 10:31:08 pm
content: Quote from: Conrad Hoffman on May 24, 2022, 11:19:23 pmAmen to that!

author: trobbins
author_rank: Frequent Contributor
timestamp: June 05, 2022, 02:43:05 am
content: 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.pdfI also have a Leeds & Northrup Kelvin Double Bridge 4288 which appears to achieve better accuracy performance than the Pontavi, but has some operational disadvantages.