Phase shift - circuit - Page 1
Forum section: electronics / beginners

author: nForce
author_rank: Frequent Contributor
timestamp: August 06, 2017, 12:12:50 pm
content: Hello,why do we calculate phase shift between voltage U1 and U2 as an arg, of the circuit:That rectangle is a resistor. (It's a European symbol)Those two voltages (U1,U2) are alternating, right? Because there is no phase shift in DC.Thanks.

author: Benta
author_rank: Super Contributor
timestamp: August 06, 2017, 12:25:28 pm
content: Because phase shift is an angle, and Arg(H(jw))) is an angle.

author: nForce
author_rank: Frequent Contributor
timestamp: August 06, 2017, 01:32:14 pm
content: Yes, but there are also other functions, where the result is an angle. I know for the phase shift that it's an angle.What about this question?:Quote

author: Benta
author_rank: Super Contributor
timestamp: August 06, 2017, 01:55:01 pm
content: It makes no sense to talk about phase shift for DC. Phase shift is only appropriate for AC signals.Arg(U2/U1) just says that the phase shift is the difference between output phase and input phase.That being said, I understand your confusion here.Using capital letters for AC signals is bad style. Correct would be:Arg(u2/u1)

author: Mattjd
author_rank: Regular Contributor
timestamp: August 06, 2017, 02:17:38 pm
content: something else that should be noted. OP used arg() but then Benta used Arg(), there is a difference.

author: Benta
author_rank: Super Contributor
timestamp: August 06, 2017, 02:28:21 pm
content: Quote from: Mattjd on August 06, 2017, 02:17:38 pmTrue. I used Arg(), because that was used in the schematic, though for this use, arg() would be correct.A wonder where that circuit came from? It seems to ignore all conventions.

author: Mattjd
author_rank: Regular Contributor
timestamp: August 06, 2017, 03:22:51 pm
content: Quote from: Benta on August 06, 2017, 02:28:21 pm'I didn't notice the difference between OP and circuit. My point was more to just not mince the two.arg() is definitely correct. Whether Arg im this case is bounded to a half or full circle is typically defined the by the author. Without knowing the text, we can't know.

author: nForce
author_rank: Frequent Contributor
timestamp: August 06, 2017, 05:28:17 pm
content: So the function arg(), came from electronics and electrical engineering?

author: Benta
author_rank: Super Contributor
timestamp: August 06, 2017, 06:35:05 pm
content: Quote from: nForce on August 06, 2017, 05:28:17 pmNo, arg() and Arg() end come from mathematics, specifically complex analysis.https://en.wikipedia.org/wiki/Argument_(complex_analysis)

author: nForce
author_rank: Frequent Contributor
timestamp: August 07, 2017, 09:42:01 pm
content: I have another question here:Why don't the arg function take two arguments? Because now it takes only H(jw). But it should be like this Arg(Re(H(jw)),Im(H(jw))).We don't need the fraction as a whole, but Real and Imaginary part of the H(jw)

author: Mattjd
author_rank: Regular Contributor
timestamp: August 08, 2017, 01:09:23 am
content: Look at the definition, it's just the angle from the real axis to the vector representing the transfer function. I'm not sure why you are getting confused.You do need the fraction as a hole. You need to find the magnitude and then use arctan to find the angle.

author: MrAl
author_rank: Super Contributor
timestamp: August 08, 2017, 07:35:50 am
content: Quote from: nForce on August 06, 2017, 12:12:50 pmHi,Yes when we talk about phase we are talking about AC voltages. That does not mean there is no DC response though, and we might want to calculate that too, but it will not have a phase shift associated with it like the AC components will.For your circuit the input output relationship is:Vout(jw)/Vin(jw)=(R*(R-w^2*C*L*R))/((R-w^2*C*L*R)^2+w^2*L^2)-(j*w*L*R)/((R-w^2*C*L*R)^2+w^2*L^2)so the imaginary part is:ip=-(w*L*R)/((R-w^2*C*L*R)^2+w^2*L^2)and the real part is:rp=(R*(R-w^2*C*L*R))/((R-w^2*C*L*R)^2+w^2*L^2)and the best way to calculate the phase shift for the usual analysis is like so:Ph=atan2(ip,rp)where atan2() is the two argument inverse tangent function and is defined over the whole 0 to 2pi range.The two argument atan function figures out the correct sign of the result as it checks the sign according to the four quadrant possibilities:+ip,+rp-ip,+rp-pi,-rp+ip,-rpas well as some limits.