16-06-2011, 08:31 AM
There’s some info on wiki about Megger, including a list of patents and their dates, which indicates a patent for a cable fault locator in 1950:
http://en.wikipedia.org/wiki/Megger_Group_Limited
The invention relates to the location of contact faults on electrically conductive cables such as telephone pairs. Contact fault location apparatus has a pair of resistors, a constant current source, and means such as a differential amplifier and meter for sensing the current flowing in the resistors. A pair of lines to be tested is looped at one end, the apparatus is connected across the other end and the current flowing in the resistors is measured. The ratio of the current is indicative of the distance to the fault.
There’s a thread here on the 18A, including a pic, but it’s not very informative and drifts off onto Meggers for insulation testing:
http://www.classicrotaryphones.com/forum...pic=2093.0
At this excellent website, where you will find lots of manuals and info on Avos, etc to download FOC, you’ll find a couple of links on Meggers:
http://www.g1jbg.co.uk/service.htm
In particular:
Megger applications booklet. (3.45MB) This booklet shows some of the applications of the Megger range of instruments, and gives some theory.
And this:
Megger Theory. (Taken from "Telephony Volume 1", Atkinson, 1949 edition. Theory of operation of the Evershed & Vignoles "Megger" instruments) 3MB.
See page 465 & 466 which refers to cable fault location using bridge Meggers, which work on the Wheatstone Bridge principle.
Hope that helps a bit Rob.
My quest to find a Bakelite Megger at a car boot sale at a knock-down price continues, simply as a piece of fascinating nostalgia rather than a useful bit of gear, albeit they’re handy for checking the insulation of transformer windings. I never bother testing such things as paper caps – I routinely replace on sight. Enough is known about the problems they cause, that it seems pointless to bother testing them, and just stacking up problems for the future.
David.
http://en.wikipedia.org/wiki/Megger_Group_Limited
The invention relates to the location of contact faults on electrically conductive cables such as telephone pairs. Contact fault location apparatus has a pair of resistors, a constant current source, and means such as a differential amplifier and meter for sensing the current flowing in the resistors. A pair of lines to be tested is looped at one end, the apparatus is connected across the other end and the current flowing in the resistors is measured. The ratio of the current is indicative of the distance to the fault.
There’s a thread here on the 18A, including a pic, but it’s not very informative and drifts off onto Meggers for insulation testing:
http://www.classicrotaryphones.com/forum...pic=2093.0
At this excellent website, where you will find lots of manuals and info on Avos, etc to download FOC, you’ll find a couple of links on Meggers:
http://www.g1jbg.co.uk/service.htm
In particular:
Megger applications booklet. (3.45MB) This booklet shows some of the applications of the Megger range of instruments, and gives some theory.
And this:
Megger Theory. (Taken from "Telephony Volume 1", Atkinson, 1949 edition. Theory of operation of the Evershed & Vignoles "Megger" instruments) 3MB.
See page 465 & 466 which refers to cable fault location using bridge Meggers, which work on the Wheatstone Bridge principle.
Hope that helps a bit Rob.
My quest to find a Bakelite Megger at a car boot sale at a knock-down price continues, simply as a piece of fascinating nostalgia rather than a useful bit of gear, albeit they’re handy for checking the insulation of transformer windings. I never bother testing such things as paper caps – I routinely replace on sight. Enough is known about the problems they cause, that it seems pointless to bother testing them, and just stacking up problems for the future.
David.
