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P
ptc-54307511-Visitor
1-Visitor
February 18, 2014
Question

MathCAD phase starts from circa -80 instead -270 deg

  • February 18, 2014
  • 4 replies
  • 2351 views

Hi all,

Its me again . I dont know how is it possible but when I make a bode plot in mathCAD phase is starting from different value than it is supposed to. Look into file. The phase should start at -270 like on the diagram from matlab. What could be wrong?

4 replies

W
Werner_E25-Diamond I
25-Diamond I
February 18, 2014

arg() will give you values in the range of -180° to +180°. So you will never get -270° but rather +90°. If you want the values in the range (-360°; 0°] you could simply subtract 180 to phase().

BTW, shouldn't you comment on and so close a previous question?

P
ptc-54307511-VisitorAuthor
1-Visitor
February 18, 2014

Of course. I will do that.

And can you suggest another function that will give bigger range? Thank you

W
Werner_E25-Diamond I
25-Diamond I
February 18, 2014

And can you suggest another function that will give bigger range?

This wouldn't be a function but just a relation as of the ambiguity. And what result would you expect for -1-1j? Mathcad's arg() will give you -3pi/4 (-135°), but of course you may add/subtract any integer multiple of 2pi (360°).

You may change the desired range (still of length 360°) using an if. Furthermore there is a change in sign which I have not really corrected with the change in phase. Also w shoul have a smaller step width.

See if the attached helps.

18.02.png

EDIT: Now the attachment should ber there, too.

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