Due to its interesting make up, I have acquired what is a quite beautiful piece of gear, in the form of a Portable Line Faults Localizer. It was produced in Japan during 1973 and is in perfect condition. Although portable, it is constructed along the lines of a laboratory instrument, has not been designed for quantity production and has serial number 367.

It appears to be some sort of bridge and it could be that it is used to compare a faulty telephone line with a known similar good line, as a means of establishing the position of a fault. Mounted in a nice wooden case, it includes two extensive banks of switched precision wire wound resistors, two rheostats and a sensitive galvanometer, and is energised via a pair of standard torch cells.

I would very much like to learn more about it and how it was used and hope that there will be someone here who has had experience with this form of test gear.

Special thanks in anticipation,

Trevor.

The phone companies used variations of wheatstone bridges in their work. If you search
Varley and Murray tests you may find much. The Wire Chief in a telegraph or telephone
office used those instruments to locate crosses , grounds, and distance to faults. Also the
ballistics of the galvanometer was used to test relative capacitance.

If you had an extra telephone set on your line, they could be detected by
galvanometer deflection tests.

If you can find a copy of Telephony, McMeen and Miller circa 1926, or Principles of Electricity,
applied to Telephone and Telegraph Work, ( A T & T) (many editions), there are chapters on the tests.

Leeds and Northrup made a lot of bridges used for cable fault location. Do a search.

Special thanks guys.

You have sent me off along the right Google track and I am doing some research. At this point it would appear that what I have, includes several facilities in the one instrument. I hope that I will be able fathom all of its functions.

Again Guys,

I have worked out how to use the standard resistor bank included within the instrument and have found this very useful. As a result I am keen to find out how to access the resistance bridge section as this could also be of real value.

Unfortunately I have been unable to turn up more information and not wishing to risk hap hazard experiments which might damage the very nice galvanometer, I have come to a standstill. My problem is that although I grasp the overall picture, I have no experience with telephone terminology and am unable to exactly decipher the characters applied to the controls and terminals. I am attaching an image and hope that someone will come to my aid.

The panel is set out as follows:-

Five terminals across the top are marked left to right:- G, +BA, -BA, +GA, -GA.

Two SP, ON/OFF knife switches left of panel, are marked:- BA & GA, respectively.

The upper row of four resistor selector switches are marked:- X1000, x100, x10, X1.

The second row of four controls, the outer two being selector switches and the inner potentiometers, are labeled left to right:- D R M, D CAL1, D CAL2, & SELECT.

The first selector switch "DRM", has ten positions marked on the upper side clockwise, --- 0 through 10, with lower alternatives, M10, M100, M1000, 1000 through to 0.001.

The two potentiometers both cover, INCREASE Min. -- Max.

The last selector switch "Select" has six positions marked clockwise, --- R, V, M, D, CAL, & OFF.

The centre scale galvanometer has a zero adjust, as well as a movement clamp for use during transportation.

Two push buttons at the lower left are marked B & G respectively.

Two terminals to the bottom right are marked X1 and X2 respectively.

Two internally mounted 1.5 volt cells, provide a 3 volt battery supply.

Any help will be sincerely appreciated.

Trevor.

The first thing to do is check that the G knife switch disconnects the galvanometer from the circuit. Then
connect your DVM to the GA+ (red) and GA-(black) terminals.( Connect a 10 K 1/2 watt resistor across your
meter connection.)

Hook up , or install 3 volts, (batteries).

Switch selector to R.

Place a 470 ohm resistor across terminals X1 and X2,

Dial in 0 4 7 0 on the top knobs.

Then experiment with the D R M settings and see if you can balance the bridge.

Your meter will go from + 00 to - 00 as you pass the balance point.

If successful , then read up on the Varley test for crosses.

Many years ago I was given a Gray Instruments wheatstone bridge that is very similar to the one in the picture, I think I still have it stored somewhere. The instructions for the Varley and Murray loop tests is printed on the top of the metal case, which was made completely waterproof for telephone lineman use. It has a Shallcross branded galvanometer. I recall playing around with it for a bit, but never used it for anything on the bench and put it away. Well made piece of equipment though.

-Mark-

Thanks again Steve,

I understand that you have basically advised me to isolate the inbuilt galvanometer for safety and use an external meter which should have a minimum impedance of 10k ohms and I have proceeded along those lines.

I am now also able understand that ---

Terminals X1 and X2 connect the circuit being tested.

“G” = Galvanometer. Terminals GA provide for external Galvo. connections.

I have sorted that ---

“G” on knife switch GA = Galvo. and the switch isolates both external or internal Galvo’s.

“B” = Battery. Knife switch BA opens the battery circuit so that extra voltage can be applied via terminals BA. + / -.

Push buttons B and G switch in the battery and galvo. respectively and I now discover turn to lock in the closed position.

“R” must indicate Resistance and “M” probably indicates Murray loop test, but does “D” indicate Varley?

I have experimented as you have suggested using both external and internal galvo. arrangements, but with confusing results and no real success. I have now attached an image which is displayed in the cabinet lid and may be of help. Unfortunately it is a wiring diagram rather than a schematic and is rather hard to follow.

You will see that there are two resistor banks switched simultaneously by the selectors and this is where my confusion arises. I would have expected the resistance function to involve a single calibrated resistance bank to be compared with the circuit across terminals X1 & X2. Whereas experiment shows selector DRM becomes involved in order for a reading to recorded. Note that the solid dot show in the diagram for all the selector switches, does not indicate an open circuit position.

Please, do you have any further ideas? Be sure that I appreciate that I am presenting you with a heap of trouble, involving what amounts to a pointless exercise, but that is what this hobby is all about. LOL

Sincerely, Trevor.

The 10 K resistor across your DVM is just to prevent the phantom readings you may get
should the switching present an open circuit to the GA terminals.

The D might refer to distance since the cable tests for shorts and grounds result is a
ratio of distances, since the resistance per unit length of the cable conductor under test
is known. They often use other known good pairs, shorted together at the far end, to get
an accurate value at the temperature that day.

Thanks once again Steve,

No luck so far but I am working on it. I will have a go at redrawing the wiring diagram as a simplified schematic and work from there. This seems my only and best option at this stage.

Cheers, Trevor.

Just looking at the diagram, there are three sets of variable resistances. A Wheatstone bridge requires three, and the unknown.

It appears that the top dials switch two set of resistance coils, and RV1 and RV2 which are in
series provide the third.

A telephone line test involves two resistances, the reference (good wire) and the bad.

Connecting to X 1 and X2 and G would give the bridge the four resistances it needs to
find the ratios of.

Kia ora Steve,

Sincere thanks for going to so much trouble.

In the interim on the net I have found a manual covering a somewhat similar but less sophisticated unit manufactured by Yokogawa in Japan and have printed same. This together with the information you have provided is building a useful picture to work from. It is now over to me to take advantage of all the help so kindly offered. I will keep you advised regarding progress.

Thanks again, Trevor.

Again Steve,

As a result of input from kind folk in providing pieces for the jig saw puzzle, I have now sorted out the circuit and resistance bridge functions and find that the unit works exceptionally well as an accurate resistance bridge.

The answer lay in discovering that the selector switch marked RDM , comprises a multiplier selector, which provides ranges covering less than 10 ohms through to 10 meg ohms in seven steps, with each range then sub divided via the four top selector switches.

As I had hoped I now have a very nice piece of test gear which conforms with my practice of collecting only stuff which works. There is little chance of it being used for its original application, for which in any event modern instruments have made it redundant, but for my purposes it is now very useful.

Special cheers and thanks for your very valuable help.

Trevor.

Since the post, I had been trying to find one of the bridges for telephone work here and
a few days ago I located one of them.

This Shallcross did work years ago, and when I opened the battery tube, a folded piece
of foil dropped out. I put that in because the battery contact was wonky.

The indicates the use of a telephone receiver and a tone, for the open tests.
It can be used for a variable frequency capacity tester, or simply
a bridge to measure resistance with AC.

Using a scope on the GA terminals, could this be used to measure skin effect with a VLF oscillator ?

Possibly, but even the big GR bridges only work to 10 kHz I think. Try measuring a carbon comp resistor at varying frequency. Any apparent error must be in the bridge.

Well, the old GR bridges on AC, have various configurations, Hay, Maxwell, for Reactances,
so they would have a high frequency limit if the power factor circuit is to work.

But I wanted to just use the Wheatstone to test resistance, using AC instead of DC, and
an external null detector, (headphone amplifier, scope.) just to get a balance on the dials.

I think all the spools in this Shallcross are wound NI.

Then change the frequency to see if the balance shifted. 30 or 40 kHz comes to mind
because that was what our high power heaters used, when we had to connect them with
litz cable to their driver modules. Fun with solder pots.

My GR 1001-A starts at 5 kHz and can give 2 volts output across 10 ohms so that should
be stiff enough to power the bridge through lower resistance arms.

I've done this before but the null detector must be floating, so a little battery scope works
or a transistor amplifier.

Some of the litz wire could be compared to an equal DC resistance of copper wire
and hopefully the CM area can be close enough to give equal lengths.