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Old 23rd March 2015, 03:00 AM   #1
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Default Do real people actually use radians/sec instead of Hz

Outside of academia I have NEVER seen people talk in terms of radians/sec when discussing AC signals. Why do so many books use radians/sec and why do most spice simulators have radians as the default unit?
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Old 23rd March 2015, 03:04 AM   #2
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Depends on whether you're doing an integration, where radians might work better...
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Old 23rd March 2015, 03:06 AM   #3
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Originally Posted by wrenchone View Post
Depends on whether you're doing an integration, where radians might work better...
Example?
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Old 23rd March 2015, 07:25 AM   #4
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The values for power supply capacitance can be realistically determined by a consideration of the numerical value of W C R where W is the line frequency (377 rad/sec), C is the power supply capacitance, and R is the load resistance. An WCR value of 10 yields about 10 per cent ripple (pk.-pk. ) and a value of 100 has about two percent. Below 10, the power supply will have serious problems and values of about 100 will achieve diminishing performance returns. The minimum value then, for each of the four power supply capacitors should be about 3,000uF and the maximum about 30,00OuF. Capacitances above this value may cause diode bridge failure due to turn-on surges and are not recommended.

(http://www.passdiy.com/pdf/a40.pdf)

3,300F x2 for one channel at 8Ω with 60hz line (3,900F for 50hz), double for 4Ω, double again for 2Ω.

Example: Crest CA9 has a tiered supply and 120,000F total capacitance. This is 15,000F per channel, per tier, the 10% ripple point.

Remember, stored energy increases with the square of the voltage, so a 3,300F cap with 100V on it stores 4x the energy that a 3,300F cap with 50V on it stores.

radian per second = W
f*2Pi=W

377 (60hz)
314(50hz)
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Old 23rd March 2015, 12:27 PM   #5
wg_ski is offline wg_ski  United States
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Originally Posted by Fusion916 View Post
Why do so many books use radians/sec and why do most spice simulators have radians as the default unit?
Because the Windows function call "twopi.dll" takes four seconds to run - each time, and uses up 1.2 MB on each call. It will eventually overflow the stack and cause the Blue Screen of Death. Save yourself the time and hassle and do the conversion yourself.

J/K. When doing math with phasors, as in standard AC analysis, calculus is converted into algebra. Differentiation is multiplying by jW, integration is dividing by it. Frequency almost always needs to be in radians in the math. The equations tend to read better (fewer factors of two pi to keep track of).
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Old 23rd March 2015, 01:28 PM   #6
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Originally Posted by wg_ski View Post
Because the Windows function call "twopi.dll" takes four seconds to run - each time, and uses up 1.2 MB on each call. It will eventually overflow the stack and cause the Blue Screen of Death. Save yourself the time and hassle and do the conversion yourself.
Huh, that's funny.

I was just working on an article where I decided to consider the audience and present things in terms of actual Hz and not normalized frequency. The complex math automatically does the phase book keeping, you would do well to understand both approaches and remain un-confused. Next folks will ask why sometimes we just throw away the imaginary part.
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Old 23rd March 2015, 01:31 PM   #7
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Originally Posted by wrenchone View Post
Depends on whether you're doing an integration, where radians might work better...
Did you ever take Prof. Kraut's class? I still don't quite get the "magic" residue stuff.
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Old 23rd March 2015, 04:39 PM   #8
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Radians are the natural way to measure angle if you are doing mathematics, therefore radian/sec are the natural way to measure rotation. People in academia use mathematics, and write (and read) books. That is why you will see radians used in books.

If you want to use some other measure then you will always be needing to convert to radians anyway - that is why you get lots of 2pi scattered around EE equations. Use radians and the 2pi mostly disappear.
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Old 23rd March 2015, 05:05 PM   #9
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On the other hand a lot of old practical manuals expressed frequency as cycles per second, c.p.s., and if that's the only point you're trying to convey, Hz became more handy.
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Old 23rd March 2015, 06:30 PM   #10
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I have a spreadsheet calculator for conversion between cycles per second and Hertz. Works great!
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