Culton 167 Automatic component bridge

[Arcturotron]

Hello fellow electronics and radio enthusiasts,

This is my first post on this forum and I've joined in because I'm completely lost with this piece of test equipment that I've just bought of eBay.
Although it appears to be some kind of industry standard at some point, there is no info whatsoever about the Culton 167, no schematics, no service or operation manual, and no info on the company itself.
I manage to find something in Wireless World Feb, 1969 on page 75. It has a nice article exploring the various kinds of component test bridges, including automatic bridges.

So, I bought the 167 without the "167a guarded component jig" and i'm aware that this jig also has the function of triggering the bridge when attached to the device under test. I'm hoping some of my fellow friends to guide me in the right direction of how can I make a jig of this kind and where to attach it to the bridge. My guess is that probably the middle connector does get shorted when the jig is closed to activate the bridge, but I don't want to blow anything.

I'm attaching a picture of the Culton 167 where the are three UHF connectors to attach the 167a jig.

Best regards to all,
André

[Diabolical Artificer]

Welcome to the forum Andre'. Looks a nice bit of kit, are they nixie indicators? A look inside might give you some clues as might a pic of the test jig. Your probably right in that you might need ground the middle pin or similar. If the three UHF connector outers are all connectors affectively ground, then there are only three wires/poles whatever making a solution not too difficult to work out hopefully.

The only other mention I could find re Culton was to a 278 safety ohm meter. the could'nt have had anything to do with Coulton or Coutant Lamda by any chance? Some other members might have a better idea.

Andy.

PS, just found this - https://www.ietlabs.com/pdf/GenRad_H...easurement.pdf it may be of use and mentions Culton. And this - https://link.springer.com/chapter/10...349-01191-9_14 in the google heading it says "The Culton 167 is ready within five seconds of switch-on, makes R-C·l measurements to 0.1% without preliminary set-up or manual intervention, measures to as ..." but can't find it in the text.

[dave cox]

To me, it looks like the outer 2 are marked 'unknown'. I would be tempted to connect a not too tiny 'C' between them and see what happens! The guard will only come into play at the limits of measurement - PROBABLY

dc

[Arcturotron]

Thank you Andy and dc for taking the time to answer my post.

I've already tried to bodge a resistor and a capacitor in the inner conductor of both the "unknown" connectors but nothing happened, the nixies still marked 0.000pf or Ohms...

Further inspection revealed that there is 24vdc across the center connector and 0vdc across the "unknowns" and all three sleeves of the connectors are grounded. I have no clue of what should I do next due to the lack of the service manual and my guess is that it would be hell trying to fix this thing. even more with my very limited knowledge in electronics of this kind. Perhaps I should test if the oscillator is running?

I do believe this is a very very well made apparatus and is really a pity that there is no information on it anywhere. I post some more pictures of this monster for your delight!

Any input is much appreciated!
André

[Diabolical Artificer]

I would expect an AC signal of 1khz to 10khz or even higher across the unknown terminals. Maybe those tfmr's indicate different frequencies per decade, looks beautifully made.

I suppose you've tried playing with the settings? Try switching to "start", with non auto bridges you have to muck about nulling to get a reading. Some better pics of the front panel may help, what is that big knob and the scale reading? Does that say "unity" on the LHS sw?

Not familiar with auto bridges so at a loss to help.

Andy.

[TonyDuell]

That is one beautiful instrument!

My first guess is that it uses dekatron-type tubes (2 on a PCB, with 10 buffer transistors for each one) to select taps on the 'decade transformers' (helpfully labelled on the PCBs). I would guess different voltages across the unknown and reference components are balanced , one of them coming from said transformers. So at balance the taps used (and thus the state of the dekatrons, which may drive the nixie tubes too) gives the value of the unknown. It actually doesn't look as complicated as many things I've had to figure out.

[Andrewausfa]

That wiring is amazing, what a lovely bit of gear.

Andrew

[Chris55000]

Hi!

My guess at the principle of operation is that there are two dekatron tubes for each digit, the first tube of each pair used to trigger the transistors that switch the taps from the bridge transformers into circuit, with the bridge detection voltage fed to a null detector that earths the guide cathode trigger pulses to stop the counter when balance is reached.

At the same time, the main cathodes of the second dekatron in the digit–display counter trigger the switching transistors for the nixie cathodes.

The result is that when you make a measurement, the dekatrons, which are connected as two separate counter–chains with one tube per digit in each chain, count up from zero until the null–detector registers balance, which then stops the counters by earthing the guide–cathode trigger–pulses, so you would see the nixies count up rapidly from all zeros at the start of measurement then stop when balance is reached.

If the first range overflows before balance is reached, an additional transistorised counter circuit operates to switch the "unit" indicators to the right of the nixies up one step, resets the dekatrons to zero by a negative pulse on the second (commoned) guide cathodes, then the counters recommence another upward count on the next range, and so on.

Regarding fault–finding, you will need an oscilloscope to fault find this, as you need to check that pulses from the count multivibrator are reaching the guide–cathodes of the first pair of dekatron, (most likely the LSD "units" digit) if these appear to be present when a measurement is initiated, make sure all the dekatrons are in receipt of h.t., (note many types need up to 400-475V anode voltage!).

If no stepping–pulses are present at the units–digit, you'll need to trace these back to the multivibrator, etc., that provides these!

Providing the anode resistors for each dekatron aren't o/c, there's normally no reason why a "ring of 10" dekatron counter should fail to count if guide–cathode trigger pulses are present, but open–circuits in the small series capacitors that differentiate the pulses will stall the counters!

Another possible cause of failure is the common reset–line, the commoned guide–cathodes used to reset the dektron counter chains will need a hold–off positive bias obtained from the positive h.t. supply via resistors to disable reset until a reset pulse is triggered by measurement initiation, in which case an open–circuit will cause all the common cathodes to drop down to the negative reset bias, resulting in all the digits being stuck at zero!

Dekatrons, like most cold–cathode gas–filled devices, are mechanically robust, long–lived and reliable, and unless you've got a physically broken one, they should perform as well as they did when the instrument was first built!

Chris Williams

PS!

The best book I know of that explains all this is "Electronic Counting Circuits" by J.B. Dance (Iliffe, 1968), but unfortunately every copy I've seen is ferociously expensive! However, there are some articles by the same author in "Practical Electronics", 1969–1970 on A.R.H!

[Chris55000]

PPS!

I don't have any original documentation on the OP's instrument regrettably – the above explanation of the likely method of operation comes entirely from my own knowledge!

You should be able to get a data–sheet for the dekatron tubes, they have a central anode connected to +300 to +475V via a feed resistor, ten main cathodes k0 to k9, and two sets of guide-cathodes in a ring that are commoned (Gk1 & Gk2), each brought out to a single base–pin!

By altering the phase of the two sets of guide–cathode trigger–pulses, the dekatron can be made to count clockwise or anti–clockwise as desired, (the count speed is determined by the frequency of the guide–cathode trigger pulses) and reset is normally carried out by supplying a large negative reset bias on one of the guide cathodes or k0, depending on the type of dekatron and circuit topology in use!

Chris Williams

[Diabolical Artificer]

I recently found a dekatron in my valve stash, interesting devices, this site has some info on them - http://lampes-et-tubes.info/cd/cd055.php?l=e.

What should the OP see on the middle terminal Chris, a pulse? Any idea how the test jig would operate? Lastly what would be the correct switch's to toggle for normal operation?

Andy.

[Trigon.]

As mentioned already in post #1 - from Wireless World Feb 1969:-

Colton automatic component bridge, type 167, is a transformer-ratio arm bridge with an accuracy of better than 0.1% when measuring L, C or R. Accuracy is controlled by transformer ratios used and by an internal standardized 10nF capacitor and 10kΩ resistor which have been aged and calibrated.

The instrument is suitable for checking thick film circuits which contain a number of resistors or capacitors of different values on the same substrate, and an input unit can be supplied which enables the bridge to be programmed to give "pass or fail" information.

Range selection and balance is automatic. Alternatively, the bridge can be connected to a unit which incorporates a detector and a circuit for driving a printer. Component values can then be logged and compared against values set into the detector; any components outside the set values can be rejected.

The bridge measures inductance from 1mH to 1099.9H, capacitance from 0.01pF to 10.999uF and resistance from 10Ω to 10.999MΩ. The component to be measured is held in a spring-operated Y-shaped clamp. Transistors are used throughout and the bridge power source is a 1kHz oscillator which becomes 1592Hz when measuring inductance.

Culton Instruments Ltd., Dorking, Surrey.

- And an image from an accompanying advert, showing the 167A jig:-



I would tend to agree that the measurement might be triggered by shorting the central connector. I'm not sure what else the 24V would be used for. Perhaps it would be worth connecting a resistor across and measuring the current to determine the source resistance?

Cheers

[Chris55000]

Hi!

Many transformers and inductors are specified with a specified amount of d.c. current flowing through them under measurement conditions, so the 24V auxiliary supply is provided for that purpose!

Transformer ratio–arm bridges are usually operated with continuous a.c. energisation during the measurement, so the signal on the test–terminals is simply sinusoidal a.c. of the appropriate oscillator frequency!

A basic theory paper on Transformer Ratio–Arm Bridges was written by Wayne–Kerr titled "Monograph No 1", that was once available from them on request, but regrettably I've not found a copy online yet!

The transistorised parts of the OP's instrument would be the 1kHz/1.592kHz oscillator and the various null detection and range–changing circuits!

Unfortunately I don't have either one of these instruments or any original docs, so I have to rely on my own store of knowledge to offer suggestions, and I'm sorry I can't do more!

Chris Williams

[Trigon.]

Originally Posted by Chris55000

Many transformers and inductors are specified with a specified amount of d.c. current flowing through them under measurement conditions, so the 24V auxiliary supply is provided for that purpose!

Surely that current would be applied via the two test terminals, not via a separate terminal?

Originally Posted by Chris55000

Transformer ratio–arm bridges are usually operated with continuous a.c. energisation during the measurement, so the signal on the test–terminals is simply sinusoidal a.c. of the appropriate oscillator frequency!

In this case the measurement is triggered by closing the jig, and I would think it quite unlikely that one of the test terminals would be used for that function.:-



"The Culton 167A Guarded Component Jig takes all sizes of components, even with cropped leads, has a stray capacity less than 0.01pF, triggers the bridge automatically when closed."

Cheers