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Jun 20, 2018
04:41 AM

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Jun 20, 2018
04:41 AM

bode plot transfer function? mathcad prime4

I'm trying to make a bode plot, what am I doing wrong? and how should I do?

7 REPLIES 7

Jun 20, 2018
06:59 AM

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Jun 20, 2018
06:59 AM

Dunno!

Attached is your sheet redone in Prime 3.0, with results (should be readable using 4.0)

Jun 20, 2018
07:09 AM

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Jun 20, 2018
07:09 AM

@aingemarson wrote:

I'm trying to make a bode plot, what am I doing wrong? and how should I do?

Its hard to impossible to debug a picture. So you should provide your Prime sheet.

Chances are that you had defined omega somewhere above the calculations you show.

So you may decide to redefine omega as a range similar to what Fred had shown or use a differently named variable for plotting.

Jun 20, 2018
07:16 AM

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Jun 20, 2018
07:40 AM

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Jun 20, 2018
07:40 AM

Ah, so you did type C1(... instead of C1*(...

Luc

Jun 20, 2018
12:29 PM

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Jun 20, 2018
12:29 PM

Luc's guess was correct - you wrote a function call C1(rc+R1) instead of a multiplication C1*(rc+R1).

But there is a second error, too, which will make your phase plot fail. You typed square brackets [] instead of parentheses (). Square brackets mean that you create a matrix/vector!

Correcting these two errors, maybe adding a range variable to select the frequency range for plotting and use a log scale should give you the plots you are looking for.

BTW, you can create a true omega if you type a w and then Type Ctrl G.

Jun 20, 2018
01:48 PM

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Jun 20, 2018
01:48 PM

rc * C1 is a time constant, i.e. it has the dimension of a time (second). The complex variable s can be defined as a complex angular frequency (pulsation) with dimension second ^ (- 1).

So s * rc * C1 is dimensionless. This must also apply to the denominator. It does not have a physical meaning to add a resistance to a capacity ... so the denominator must be (C1 * (rc + R1) + C2 * R1) s + C1 * C2 * rc * R1 * (s ^ 2).

Jun 20, 2018
07:30 AM

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Jun 20, 2018
07:30 AM

Please attach your worksheet, not just a picture!

You've probably typed C1(rc+R1) instead of C1*(rc+R1). Now Prime tries to evaluate the function C1.

Or did you define w somwhere upwards?

Success!

Luc