A question four lead about capacitors.

[Dick Glennon]

Hello again, Is it possible to have 4 wires (one either end and one close to each end) coming from a capacitor. In circuit it reads about 600pf. Regards Dick.

[vidjoman]

What make, model is it in? It might be a thick film hybrid of mixed resistors/ capacitors. Need more info to say. Photo?

[Peter.N.]

Could be a suppressor capacitor which is actually two capacitors, are they isolated from one another?

Peter

[dazzlevision]

Hello,

There are alsp special "fail safe" 4-terminal capacitors where, if the connections to the actual foil(s) are broken, the terminals ("in" and "out" to each foil) are opened.

A specific example that I know of is 4-terminal electrolytic capcitors used in safety critical dc (derived from rectified ac) supply smoothing, where excessive ac ripple must not get to the output (i.e. the load).

Regards,

Dazzlevision

[Radio Wrangler]

Some capacitors have four leads for use in precision bridges where the resistance of connections can be removed from results.

What is it in? What does it look like?

David

[emeritus]

I believe that 4 terminal capacitors are/were used in some types of railway signalling to ensure that a signal will always fail to the "stop" aspect if a connection goes open circuit.

[dazzlevision]

Originally Posted by emeritus

I believe that 4 terminal capacitors are/were used in some types of railway signalling to ensure that a signal will always fail to the "stop" aspect if a connection goes open circuit.

Hello,

That is the where the example I quoted is from in post #4.

Signalling remote control and indications system using FDM (frequency division multiplex). Individual precisely frequency controlled audio tones sent down a single pair of wires. Each tone was generated by an electronic oscillator that used a vibrating metal "reed" inside a coil, to give a very pure single audio frequency with extremely low drift. Each tone represented a signalling function, such as operating a set of points or a clearing a signal.

An equivalent receiver at the other end filtered out the signal, which was then peak recitifed, to drive a special relay. The Tx & Rx were powered by 12Vdc supplies, using ac rectifiction and smoothing by these special four terminal electrolytic capacitors. Any increase in ripple could possible cause spurious frequencies to appear on the line circuit, which is potentially dangerous.

Regards,

Dazzlevision

[turretslug]

I'm sure I recall both quite large old coated mica capacitors and later plastic film types with two wires emerging at each end (or thin brass tapes in the case of mica), they were closely twisted and tinned together, I assumed this was to keep self-inductance low before bunched-foil techniques. Or something.

[turretslug]

Originally Posted by dazzlevision

Hello,

That is the where the example I quoted is from in post #4.

Signalling remote control and indications system using FDM (frequency division multiplex). Individual precisely frequency controlled audio tones sent down a single pair of wires. Each tone was generated by an electronic oscillator that used a vibrating metal "reed" inside a coil, to give a very pure single audio frequency with extremely low drift. Each tone represented a signalling function, such as operating a set of points or a clearing a signal.

An equivalent receiver at the other end filtered out the signal, which was then peak recitifed, to drive a special relay. The Tx & Rx were powered by 12Vdc supplies, using ac rectifiction and smoothing by these special four terminal electrolytic capacitors. Any increase in ripple could possible cause spurious frequencies to appear on the line circuit, which is potentially dangerous.

Regards,

Dazzlevision

I love this forum, there's always knowledge on things!

[emeritus]

I have no personal experience of them myself, and only knew of their existence from what I was told in passing more than 20 years ago by an engineer I once worked under. I had assumed that that the extra terminals were merely a way of ensuring that a capacitor that was electrically in parallel with a signal path, became part of the series signal path, and so would give rise to a positive fault condition by interrupting the signal path if a wire came adrift. Thanks for the detailed info on the actual potentially dangerous fault mode that their use prevented.

[Dick Glennon]

Hello again, I have taken out this ? out of circuit. I do not have a photo yet, but I hope to have one shortly. Written on it is as follows: 47KA and below that is 100x2. If you can imagine an axial component with 1 wire coming out each end which we will call 1&4, and, 2 more wires, one close to either end which we will call 2&3. When I put the ohm meter on 1&4 it reads 2.5 ohms. There are no other ohm readings. When I put the capacitor checker on 1&2 it reads 192pf, on 2&3 it reads 55pf and on 3& 4 it reads it reads 192pf. When I prod this component in circuit the volume increases a good bit. This is in the pilot radio circuit. Sorry about all the confusion, Dick.

[G8KBG Tony]

It would be really helpful to know roughly where it's located.

Is it in the RF, IF, audio or power supply? Please supply some photos as the information you're giving is a little vague.

[gezza123]

Are they like this.
I used this type in my resonant circuits of induction cookers to get the coils to oscillate at 30KHz, 25 years ago.
Then dumped them as it was cheaper to buy two single ones an put them in parallel. Gezza123

[gezza123]

More from the Attic I mean the archives.

MFD Capacitors Wrexham used to sell them like this.
Again the only problem was if one went bust you need to change two.I think the Idea was to make the circuit boards a bit smaller @ a cost.
Gezza123