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Discussion in 'Question of the Day' started by derekleffew, Aug 27, 2016.
"What is the difference between phase and polarity?"
Students only, for one week please.
Polarity describes the positive and negative voltages of an electrical signal. In normal polarity, a sine wave will appear above the x axis on a graph. In reversed polarity, the sine wave will appear below the x axis on a graph and will be an exact opposite of the normal polarity sine wave. For example, if you wired a simple 12V motor to a battery in normal polarity, the motor will spin in one direction, but changing tho polarity causes it to spin in the opposite direction.
With the phase of a sine wave, you are not reflecting the wave over the x axis as you would in a reversal of polarity, but you are delaying the wave by a certain factor of time. This is why (for example) if setting up delay towers at festival, you must delay them by xx ms. If an audience member is standing behind the delay towers, the audio from the towers will reach their ears first, before the audio from the mains will. If the towers are not time aligned with the mains, the audio from the delay towers and the mains will be out of phase because their sine waves are reaching a certain point at different times.
If we were to strictly look at phase and polarity on a sine wave graph, a polarity reversal would look like this (I made these graphs using Desmos graphing calculator)
The red represents normal polarity, and the blue represents reversed polarity.
A phase change would look like this
The green represents a normal sine wave, the orange represents a sine wave 180 degrees out of phase, and the purple represents a sine wave 90 degrees out of phase.
In conclusion, phase is just is a change in timing of a sine wave, and a polarity change is when positive and negative voltages are 'swapped'
I know this a is a very mathematical answer to the problem, and if I am incorrect on any points feel free to correct me. It's been about 4 months since I've done any trig in school, so I may have made a mistake somewhere.
@derekleffew Very good question! You really made me think! I guess this is a good warm-up for school starting on Monday!
If thetechman was studying trig four months ago, and is warming up for school starting Monday, he's, conceivably, still a student.
Then why does his profile say "pro"? You can't gave it both ways.
Phase is how the moon tells you when your perfect mate will be born and polarity is how we keep penguins and polar bears separated right?
I learned that Phase was what was written on Tina's stuff in the SNL fridge and Polarity was humour derived from certain ethnic jokes.
Phase is a relationship
Polarity is a direction
In some ways, "single phase" power is an oxymoron as there is no other phase to compare it to.
Polarity is the direction of flow. Here's where things get fun! If you were educated in the 50s and 60s, you "knew" that electrons flow from the negative source to the positive side. If you were educated after about 1970, you believe in the "flow of holes" and that power flows from positive to negative. This was due to the common use of solid state components and the fact that all arrows point from positive to negative!
However.... I have yet to have any person who is a believer in the "flow of holes" explain how their theory allows a cathode ray tube to work
Magic fairy dust jumping off the screen and down the neck of the picture tube to the cathode?
Exactly and understood. Perhaps we're all 'students of life'?
I've known more then a few professional students.
call the MF-ing XLR turnaround that reverses pins 2&3?
profile says pro because I consider myself a "professional" due to the fact that I work and make money in the industry. I work for a production company and do some freelance lighting design for smaller theatrical and dance productions. In no way do I consider myself a member of the group of people that do this everyday and have been for the past 20+ years.
Yes, I am a student. Junior in high school actually!
Well . . . It's neither a 'gender bender' nor a phase changer . . . Possibly it's a contacts 2&3 swop?
Pile on everybody, join the fun.
In DMX I would all it a Binary Buster! (Since all your 1's are now 0's and all your 0's are now 1's !)
In the audio world, it would be phase reversing, as you are inverting the phase of one waveform in relationship to other audio signals in other cables.
Maybe you'll get a job in marketing stage equipment.
I wouldn't say that in a single phase condition is an oxymoron. In pretty much the entire world, electrical power is distributed in 3 phases. Single phase is just a tap from the A, B or C phases. Locally, you may not have an additional reference, but upstream you will. The Transmission and Distribution companies judge best how to balance the loads and distribute the power from the 3 phases.
Mathematically @Thetechmanmac is heading down the right direction. He is only off by the the amount of phase difference. Commercial power generation and distribution is 120 degrees between phases, A to B, B to C, and C to A. 360 degrees in a circle, got to divide it evenly; thulsy 120 degrees apart.
Electrical Power Grid synchronization is very tightly controlled. When a Generator is synchronized to the grid out of phase, very bad things happen. I've seen (luckily not in the US) Generator and turbine shafts break when synchronized 180 degrees (complete opposite) out of phase. This particular example was a couple of normal startups away from liberating large chunks (100's of pounds) of metal that can travel in excess of a mile.
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