MathCAD phase starts from circa -80 instead -270 deg

[ptc-5430751]

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?

[Werner_E]

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?

[ptc-5430751]

Of course. I will do that.

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

[Werner_E]

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.

EDIT: Now the attachment should ber there, too.

[RichardJ]

You might find the attached workshet useful