User Manual for Wheatstone Bridge

http://en.wikipedia.org/wiki/Wheatstone_bridge

And a lovely one you have there

Have you tried the manufacturer's website?

What a beautiful instrument, though it looks like an antique. Evidently it can be set to produce any resistance (in one-ohm increments) from 0 to 11,110 ohms. This can be seen from the bank of selector switches in the upper row, but I can't read closely enough to see the other dials and what they can do. At the very least, this seems to be an ohmmeter that covers the aforementioned range, and possibly more. Can you inspect the internals and give a circuit diagram?

Each of the selector switches will surely be wired to a series of resistors of the given value (with what precision?--look at the identifying bands). I wish I could see more, and thereby figure out more.

My very first job in Quality I used a much older model of that. I don't remember the specific steps in calibrating the instrument save that it is a balance circuit where you adjust for zero and adjust for a value, back and forth until the correct readings are attained. At least as I used it, it would tell me quite reliably if our coils fell into the proper resistance range. The range of your instrument looks to be up to 10 meg ohms.

I think you will find that this bridge is operated using the same principle as older resistance bridges.

You connect the resistance to be measured to the terminals marked and this forms one of the four resistance 'arms'....

Then you select the ratio of the two other 'arms' and finally by adjusting the 4 dial pots to give a null reading on the meter, you will then have the resistance value as being the settings on the 4 switches i.e. 1234 multiplied by the ratio, which if its switched to 1 your resistance is 1234 ohms.

the ratio can be set to 0.001 to 1000, so the measuring range covers 10,000 ohms with a 1 ohm resolution at a ratio of 1.

ratio 0.001 range is 10 ohms with a resolution of 1 milliohm.

ratio 1000 range is 10,000,000 ohms with a resolution of 1000 ohms.

The other controls are there to adjust the meter for a null reading and its sensitivity.

I think this one has a +ve / -ve switch to eliminate thermal emf's from affecting the reading....

Accuracy will be about +/-0.1% at best and more likely +/-0.5% of reading.

JJ Lloyd Instruments were taken over by ?????? 15 years ago so don't bother trying to contact them....

By the way its not very old at all only about 20 to 25 years old, most wheatstone bridges date back over 50 years or more!!!!

By the way, I have several of the older models of this type of bridge, some calibration standard (+/-0.01%).

If you want any more information just ask on here....

Greetings.

The Pacific Northwest Bell Telephone Testboard where I once worked had a wheatstone bridge. If you can get a copy of the Bell System Practices BSP100-810-101, 701, 711, 712, 713, and BSP 100-812-711 I believe this will give you enough detailed information for anyone to try and digest about wheatsone bridges and hopefully what you are looking for.

I used to have this very testboard but sent it to a Telephone Museum along with the BSPs years ago.

Have a great day.

Can you give us a close up of this bit:-

Or tell us what it says just under the JJ

Randall, that is the manufacture which is JJ Lloyd Instruments who used to be based in southern England but were taken over by another company and the name is no more.

JJ Lyons made loads of educational instruments and standards lab grade instruments also. They are / were a UK company.

You could post a request for a manual on the following reflector:

test-equipment@mailman.qth.net

Or better still:

Manual_Exchange@yahoogroups.com" <Manual_Exchange@yahoogroups.com>

Hope this helps

Pete