Telephone terms

[Eagle]

No I mean real telephones. My dad started his telephone career in 1947 as a lineman. As he used to say, I climbed poles. He loved it. Yrs later you could tell it was a tough decision to move into management. But such is life . Tonight captain Nemo and I are glancing through old photos and such. I found this manual amongst the box. 1952 Glossary of terms. So far I just thumbed thru it and I'm coming across terms I'm unfamiliar with. John ,I thought you may have seen this term. Bifilar..from the definition I guess it means they are not step up or step down .

[robothut]

The wikipedia description cover's all the different ways that the dual windings can be used.

 

 

Some bifilars have adjacent coils in which the convolutions are arranged so that the potential difference is magnified (i.e., the current flows in same parallel direction). Others are wound so that the current flows in opposite directions. The magnetic field created by one winding is therefore equal and opposite to that created by the other, resulting in a net magnetic field of zero (i.e., neutralizing any negative effects in the coil). In electrical terms, this means that the self-inductance of the coil is zero.

The bifilar coil (more often called the bifilar winding) is used in modern electrical engineering as a means of constructing wire-wound resistors with negligible parasitic self-inductance.[1]

Bifilar wound toroidal transformer.

A different type of bifilar coil is used in some relay windings and transformers used for a switched-mode power supply to suppress back-emf. In this case, the two wire coils are closely spaced and wound in parallel but are electrically isolated from each other. The primary coil is driven to operate the relay, and the secondary coil is short-circuited inside the case. When the current through the primary is interrupted, as happens when the relay is switched off, most of the magnetic energy is intercepted by the secondary coil which converts it to heat in its internal resistance. This is only one of several methods of absorbing the energy from the primary coil before it can damage the device (usually a vulnerable semiconductor) that drives the relay. The main disadvantage of this method is that it greatly increases the switching time of the relay.

When used in a switching transformer, one winding of the bifilar coil is used as a means of removing the energy stored in the stray magnetic flux which fails to link the primary coil to the secondary coil of the transformer. Because of their proximity, the wires of the bifilar coil both "see" the same stray magnetic flux. One wire is clamped to ground usually by a diode so that when the other "primary" wire of the bifilar coil no longer has a voltage applied across it by the switching transistor, the stray magnetic flux generates a current in the clamping coil with the primary side voltage appearing across it, causing an equal voltage to appear across the primary winding. If this clamping coil was not used, the stray magnetic flux would attempt to force a current to flow through the primary wire. Since the primary wire is switched off and the switching transistor is in a high resistance state, the high voltage which would appear on the semiconductor switching transistor would exceed its electrical breakdown or even damage it.

Bifilar coils impose an inductance in the common mode, but impose no inductance in the differential mode. Coils in such a combination are widely used to eliminate ingress or egress of common mode signals from electronic signalling circuits. This arrangement is used in transmission and reception magnetics of Ethernet cables[2] and conspicuously in the form of a ferrite bead clamped to the outside of USB, laptop power supply and HDMI cables.

[Eagle]

Thanks John !!  My  first thought for their use was for the ringers.. Flux lines..Big deal on planes. The CDI compass Flux valves have to be protected from stray inductive/magnetic pulses. Yes Back to the future fans,,there is such a thing as flux valves.. Flux capacitors,,I never heard of.  A few yrs ago I was ticketed for running a stop sign..I didn't run the light. It would not change. The cop knew that and was watching behind a sign. When he pulled us over he ask do you know why I pulled you over ? I said yes,because I drove through that inop light. His reply,,yeah this intersection is a money maker. I replied,,I'll see you in court. He showed up,,stated his case and then it was my turn. I told the judge that the light was inop. The copper objected that the light was ON and working. The judge turns to me and I told him that by definition the light was inop because it did not operate within the design parameters of the manufacture . The officer objected again..and the judge said,,sit down,I want to hear this. I proceeded . I told him that when I pulled over the trigger mechanism caused the magnetic field to collapse triggering the timing mechanism from a magnetic Azimuth detector that the light should have changed. It did not and it also failed to trigger the default mode of a 90 second cycling of the light. Once again the officer jumped up..But he still broke the law by driving through the lite..The judge  just looked at me and I told him,,according to PA department of transportation regulations ,,if a light is inoperative the operator may proceed thru the intersection with caution..I handed him the regulation..He sat back,,slammed the gavel and announced..Case dismissed. Then he turned to the officer..I have also been stuck at that damn light.........Get it fixed.. As I walked out,,the Judge stopped me and my friend..Mr Logan,,in my 18 yrs on the bench that is the best defense presentation I have ever heard...Later he sent the judgement in the mail and ask,,can you give my grand kids a tour of the airplanes ?  The moral of the story is...No matter what you do in school....obtain a good working knowledge of physics.  You will use it to your advantage daily in your life. And you will view the universe in awe.

[robothut]

Also you were lucky that the judge was not in on the money making deal with the cop. A little luck never hurts in this crooked legal world.

[Eagle]

You nailed that John ! The cop was a jerk,,had a Napoleon complex ..Waited for me in the hallway. Said,,,I'll nail you the next time . OK,,I'll see ya in court., The judge was awesome..Went golfing with him after meeting the grandkids ..His advice on my golf game. Stick with amateur law. I ask him while we were walking the 18..So who do judges normally hang out with ? People that want something from me. Politicians. Oh that's sad..