top of page

Fourier analysis  with the Ti-84 plus (CE)

Spectrum Analysis (Harmonics) of Periodic Signals

In Electrical Engineering, the Fourier analysis is an important tool for analyzing the power factor and harmonics of currents and voltages. The programs FOURIER.8xp and FOURIERL.8xp calculate Fourier series of periodic signals very accurately and can be applied in combination with the signal builder program FUNCGEN.8xp. 

The program FOURIER.8xp plots the result like a real spectrum analyzer, and the program FOURIERL.8xp gives more detailed results of the Fourier series, including amplitude and phase.

Fourier series are defined by the following formulas. According to the Fourier theory, every periodic function can be written as the sum of sine and cosine functions with multiple frequency which are relative to the basic frequency of the periodic signal. The following formulas are the basis of Ti-Basic programs FOURIER.8xp and FOURIERL.8xp. 

Defintions and formulas of The Fourier Analysis

Formulas for the Fourier analysis of periodic systems
wix4. l.JPG

The first example is the output signal of a triac voltage regulator. The signal has been built by the program FUNCGEN. (Go to the page FUNGEN (signal builder) to read the manual of this program. 

Generating sinusoidal signal with 90 degrees fire angle of a triac

From the signal above, the basic frequency equals 50 Hz, with a peak of 230V2=325.27Volt and a firing pulse on the gate of the triac at angles of 90 and 270 degrees. Below, in the spectrum, calculated by the program Fourier.8xp, we see, a first harmonic of 192.7 Volt, a third harmonic of 103.53 Volt  (150 Hz) and a fifth harmonic of 34.52 Volt (250 Hz) are shown. These values agree with the analytical results.

This program requires a lot of time (some minutes), so please be patient in order to obtain a plot. Faster calculations can be obtained with the program FOURIERL. A demonstration of this program is provided further on this page.


Fourier analysis program for harmonic calculations
Results Fourieranlysis plotted in a spectrum by the Ti84 program

The Fourier program which calculates amplitude and phase of the harmonics

This program generates a list of results.

If the Fourier series exists of an average value, sine part, cosine part  then:

F=A0 +A1sin(2πft)+B1cos(2πft0)+A2sin(2π2ft)+B2cos(2 π2ft)+A3sin(2π3ft)+B3cos(2π3ft)+.... or


L1(n)=number of harmonic , L2(0)=A0,  L2(n)=An, L3(n)=Bn, L4(n)=Cn, L5=fi(n)

The analysed input signal can be generated by FUNCGEN or defined directly, see the example.

In this example, the same signal is analysed as above.

More detailed calculations of harmonics are done with the program FOURIERL
Choosing for funcgenerator results in anlyzing the sinusoidal signal with 90 deg. fire angle

In the example, the same signal is analyzed as above. A sine function of 325.27V and firing angles of 90 and 270 degrees.  If we read the results from the lists, then it yields : 

F=0+162.63*sin(2π50t)-103.5*cos(2π50t)+ 103.54 *cos(2π150t) -34,51cos(2π250t)  or F=0+192.79*sin(2π50t-32.48deg)+ 103.54*sin(2π150t+90deg)+34.512sin(2π250t-90deg) + 34.512sin(2π250t+90deg)

At the end, an example of the Fourier analysis of the well known square wave (amplitude 100 V and base frequency of 100Hz.) The square wave is built with the signal builder program FUNCGEN.8xp

Fourier Analysis of the Square wave

A block (pulse) ssignal is created  with Funcgen for further calculations of its harmonics
The square function
Harmonics of block signal with an amplitude of 100 V

At the end, an example of the Fourier analysis of a well known square wave (amplitude 100 V and base frequency of 100Hz.) The square wave is built with the signal builder program FUNCGEN.8xp

=(4/ π)* 100= 127.32

For the nth harmonic yields  = (4/nπ)* 100. This results for the third harmonic 42.441 and for the fifth: 25.4646 etc. Conclusion. The results of the program are in very good agreement  ith the analytical results

For the program FOURIER.8xp , FOURIERL.8xp and FUNCGEN send a request to or chat and the program will be sent. 

Don't forget to provide your email address!!

bottom of page