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Old 22nd Nov 2020, 12:53 pm   #1
Guest
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Default Looking for more info about this meter

Hello, I have this Milliohmeter.

I am looking for some information about it, as when was it made and what was it principal use, I found it in an old airport here in the Canary Islands.

I want to sell it to buy another meter more useful for me.

Help will be appreciated
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Last edited by Guest; 22nd Nov 2020 at 1:07 pm.
 
Old 22nd Nov 2020, 12:55 pm   #2
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Default Re: Looking for more info about this meter

The space for the batteries
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Old 22nd Nov 2020, 1:52 pm   #3
AC/HL
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Default Re: Looking for more info about this meter

Some information here: http://bunkerofdoom.com/shal673/index.html
As usual, eBay will be a good place to look for its value, but transport and/or local values must be taken into consideration.
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Old 22nd Nov 2020, 2:57 pm   #4
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Default Re: Looking for more info about this meter

Just a shot in dark, but it might be worth looking at equipment used on rail/ petroleum installations . One of the specifications in the rail testing handbook on these places was that the resistance between rails and to earth( ground) was less than ( from memory ) 1 ohm, possibly lower.
This was in the early 80's.
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Old 22nd Nov 2020, 3:26 pm   #5
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Default Re: Looking for more info about this meter

thanks!
 
Old 23rd Nov 2020, 1:10 am   #6
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Default Re: Looking for more info about this meter

For many instruments designed to measure resistance, one pair of terminals for connecting a pair of test leads is common, but here we have two pairs of terminals: probe 1 and probe 2.

With that in mind, I suspect that the method of resistance measurement used here is the Kelvin Sensing 4-wire method. The fundamental idea is to pass a known current through the low resistance to be measured using one probe and to simultaneously measure the voltage developed across that resistance using the other probe. From those two measurements, the resistance can be calculated. The principle of the Kelvin Sensing 4-wire method follows:

https://www.allaboutcircuits.com/tex...e-measurement/

I built such a low resistance ohmmeter several years ago using semiconductors: it will measure resistance to less than 0.05 ohm. It is invaluable for measuring low resistances when an ammeter shunt is required, for example. Photos are attached (albeit not a very good ones: this item does not actually look that scruffy!).
I do have the cct. diagram of that instrument, should anyone wish to see it.

Al.
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Last edited by Skywave; 23rd Nov 2020 at 1:36 am. Reason: Add photos 2 & 3
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Old 23rd Nov 2020, 10:54 am   #7
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Default Re: Looking for more info about this meter

Hi yes please would like to see cct diag please Mick
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Old 23rd Nov 2020, 3:32 pm   #8
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Default Re: Looking for more info about this meter

It wouldn't have been made for a specific use, it's a general purpose low-ohm meter, using the four wire Kelvin connection to compensate for lead resistance (compared with two wire measurement).

David
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Old 23rd Nov 2020, 9:14 pm   #9
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Default Re: Looking for more info about this meter

As i said, it was in an old airport, with others specific tools for the engines of the planes

Very interesting that Kelvin method.
 
Old 23rd Nov 2020, 11:17 pm   #10
Skywave
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Arrow Re: Looking for more info about this meter

mickm3for - you have a P.M.

Al.
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Old 24th Nov 2020, 10:36 am   #11
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Default Re: Looking for more info about this meter

Depending on the aircraft involved, there may have been requirements to check bonding of various parts of the plane to each other. I know of a vehicle used by the military as a radio vehicle, and all of the bolt on panels had to have the bond resistance checked.
I do have a milliohmeter, but interestingly it's my insulation tester that came from an airline's workshop.
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Old 24th Nov 2020, 10:45 am   #12
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Default Re: Looking for more info about this meter

Also, confirming effective bonding continuity of bowser hoses and fittings- without which, a bowser feeding an aircraft is like a liquid iteration of a van de Graaf generator. Just what you don't want when fuel and vapour are present in abundance.
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