From Edison’s Trunk, Direct Current Gets Another Look

NY Times ^ | November 17, 2011 | MICHAEL KANELLOS

[DH]

Are they taught the “electron theory” or the “conventional theory?”

Most people don’t know the difference between the two.

[thackney]

Wheatstone bridge is used with resistance to measure voltage.

What was pictured is a simple rectifier.

http://www.magnet.fsu.edu/education/tutorials/java/wheatstonebridge/index.html

[Bogey78O]

Negatory. Telco runs on hook at -48VDC on ring nominally but upwards of -52VDC is allowable due to voltaic loss across distance. You see the real reason for DC in phone systems is because the nature of analog communications works better with DC than AC. When you go off hook a switch detects the short from the phone completing the circuit and the voltage drops to about -9 to -15VDC off hook.

The ohms resistance across the loop has to be within certain thresholds for the switch to detect the short. I can’t recall the specs on a modern 5ESS switch but that’s why the further out you go the lower the gauge. So if you’re 15 miles from the main office you can expect 19ga copper.

The twisting on the pair is to reduce Induction between the pairs and AC systems. If you run voltage over a copper wire it’ll induce across any line running parallel.

Also with DC telecom you need to balance the pair and have the same capacitive length on each side to reduce noise.

Telephone work is easy though. But doing it well is the hard part.

[DH]

No, AC has not ended there.

The original AC current is changed from 60HZ AC to 120PPS DC power through the rectifier, through the load, and back from the load as 120pps DC, through the rectifier again and back to 60HA AC, then back to the generator.

There is an unmovable law of electronics: 100% of the current generated from an electrical source always returns to that power source.

[DH]

I was also a radar (fire control systems) tech for F-100s in the Air force.

I had a chance to watch a base photographer’s entire flash bulb satchel instantaneously light up when I transmitted when he walked in front of the jet. It was priceless.

The radar would also light steel wool on fire too.

[FourPeas]

Edison was.....an interesting man.

[Mr. Lucky]

My guess is: both.

[thackney]

Can you imagine a company today killing a bunch of animals publicly with the competitor’s product to sway public opinion against the competitor?

http://www.wired.com/science/discoveries/news/2008/01/dayintech_0104

[D-fendr]

Thanks for your post. Very informative and well done, and, obviously, I didn’t know that.

[Mr. Lucky]

The 20th Century was so barbaric.

In the 21st Century, we protect wild animals and murder unborn children to display our political enlightenment.

[thackney]

I was on a construction site for a Natural Gas pipeline compressor station years ago next that line on the map.

I was disappointed when none of the electrical guys could spot what was “different” about the tower supporting the electrical transmission line.

Eventually I told them to count the phases. They still had a hard time believing me it was DC.

[Ramcat]

Thanks for clearing that up. You’re correct of course.

[cva66snipe]

And now all that leftover space is getting repopulated by routers and server farms. ≤}B^)

I'm a grown Bell Brat LOL. My dad was a 45 year man with most of it spent in what they called 4-A the old mechanical switching long distance office. When they switched over in the 1980's to ESS he went back outside and worked on data circuits till retirement. I spent many an evening in the 4-A office when I was growing up.

[cva66snipe]

They use both AC and DC on the same phone lines for different functions. They use DC to register an off-hook condition and to power the carbon transmitters (microphones) and AC to operate the ringers. Later phones use the same DC to power the touch-tone electronic circuitry. It’s about simplicity, not stability.

AC is not on a phone line. Pulsating DC is what operates the ringers. On the older western electric phones a capacitor sat across the ringer {bell} in the phone. That was how people got busted back in the day for having an extension phone they were not paying for. The Test Board could read the induction of the capacitor. Cut that capacitor and they had no clue LOL. That doesn't matter now though. A Capacitor will pass PDC that is why they used PDC as PDC doesn't produce A/C HUM. The voltage was 96 PDC. You do not want A/C directly on phone cable.

[neverdem]

Today's teens will die younger of heart disease Really?

Sorry, Strivers: Talent Matters

As probiotics use grows for gut health, VSL#3 has designations for specific GI issues

Particle Smasher Hints at Physics Breakthrough

FReepmail me if you want on or off my health and science ping list.

[Myrddin]

My dad was XO/CO on the Arlington during the time when the astronauts returned from the moon. His ship was a critical "ground station" for some of the activities. The RF on the old "flight deck" was more than enough to light up fluorescent tubes.

[DoctorBulldog]

E=IZ isn't just a good idea. It's the Law!

There, fixed it for ya'!

Hey, what can I say, I'm a fan of Tesla. :)

Cheers

[ReignOfError]

Can you phase invert a hamster?

Get away from my pets, you sick bastard.

[Sequoyah101]

Easy for you to say! I resemble that remark being a poor old Civil and Petroleum and Mechanical Engineer, not necessarily in that order. There was no doubt I did not want to be an Electrical Engineer. What good is it if you can’t hit it with a big hammer?

[Erasmus]

That looks suspiciously like a swastika, mein Herr.