1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
|
#include <qwt_math.h>
#include "cplx.h"
#include "bode_plot.h"
BodePlot::BodePlot(QWidget *parent):
QwtPlot(parent)
{
setTitle("Frequency Response of a Second-Order System");
setCanvasBackground(darkBlue);
// legend
setAutoLegend(TRUE);
enableLegend(TRUE);
setLegendPosition(QwtPlot::Bottom);
setLegendFrameStyle(QFrame::Box|QFrame::Sunken);
// grid
enableGridXMin();
setGridMajPen(QPen(white, 0, DotLine));
setGridMinPen(QPen(gray, 0 , DotLine));
// axes
enableAxis(QwtPlot::yRight);
setAxisTitle(QwtPlot::xBottom, "Normalized Frequency");
setAxisTitle(QwtPlot::yLeft, "Amplitude [dB]");
setAxisTitle(QwtPlot::yRight, "Phase [deg]");
setAxisOptions(QwtPlot::xBottom, QwtAutoScale::Logarithmic);
setAxisMaxMajor(QwtPlot::xBottom, 6);
setAxisMaxMinor(QwtPlot::xBottom, 10);
// curves
crv1 = insertCurve("Amplitude");
setCurvePen(crv1, QPen(yellow));
setCurveYAxis(crv1, QwtPlot::yLeft);
crv2 = insertCurve( "Phase");
setCurvePen(crv2, QPen(cyan));
setCurveYAxis(crv2, QwtPlot::yRight);
// marker
mrk1 = insertMarker();
setMarkerLineStyle(mrk1, QwtMarker::VLine);
setMarkerPos(mrk1, 0.0,0.0);
setMarkerLabelAlign(mrk1, AlignRight|AlignBottom);
setMarkerPen(mrk1, QPen(green, 0, DashDotLine));
setMarkerFont(mrk1, QFont("Helvetica", 10, QFont::Bold));
mrk2 = insertLineMarker("", QwtPlot::yLeft);
setMarkerLabelAlign(mrk2, AlignRight|AlignBottom);
setMarkerPen(mrk2, QPen(QColor(200,150,0), 0, DashDotLine));
setMarkerFont(mrk2, QFont("Helvetica", 10, QFont::Bold));
setMarkerSymbol(mrk2,
QwtSymbol(QwtSymbol::Diamond, yellow, green, QSize(7,7)));
setDamp(0.0);
}
void BodePlot::showData(double *frequency, double *amplitude,
double *phase, int count)
{
setCurveData(crv1, frequency, amplitude, count);
setCurveData(crv2, frequency, phase, count);
}
void BodePlot::showPeak(double freq, double amplitude)
{
QString label;
label.sprintf("Peak: %.3g dB", amplitude);
setMarkerPos(mrk2, freq, amplitude);
setMarkerLabelText(mrk2, label);
}
void BodePlot::show3dB(double freq)
{
QString label;
label.sprintf("-3 dB at f = %.3g", freq);
setMarkerPos(mrk1, freq, 0.0);
setMarkerLabelText(mrk1, label);
}
//
// re-calculate frequency response
//
void BodePlot::setDamp(double damping)
{
const int ArraySize = 200;
double frequency[ArraySize];
double amplitude[ArraySize];
double phase[ArraySize];
// build frequency vector with logarithmic division
qwtLogSpace(frequency, ArraySize, 0.01, 100);
int i3 = 1;
double fmax = 1;
double amax = -1000.0;
for (int i = 0; i < ArraySize; i++)
{
double f = frequency[i];
cplx g = cplx(1.0) / cplx(1.0 - f * f, 2.0 * damping * f);
amplitude[i] = 20.0 * log10(sqrt( g.real()*g.real() + g.imag()*g.imag()));
phase[i] = atan2(g.imag(), g.real()) * (180.0 / M_PI);
if ((i3 <= 1) && (amplitude[i] < -3.0))
i3 = i;
if (amplitude[i] > amax)
{
amax = amplitude[i];
fmax = frequency[i];
}
}
double f3 = frequency[i3] -
(frequency[i3] - frequency[i3 - 1])
/ (amplitude[i3] - amplitude[i3 -1]) * (amplitude[i3] + 3);
showPeak(fmax, amax);
show3dB(f3);
showData(frequency, amplitude, phase, ArraySize);
replot();
}
|
