The order of measurements modeling and analysis of its results

LC-GENERATOR OF HARMONIOUS OSCILLATIONS

Purpose of work: To learn the fundamental principals of harmonic signal generation, explore the modes of harmonic signal LC-generator work, built according "inductive three-point” using the modeling in software Electronics Workbench.

The order of measurements modeling and analysis of its results

1. Build scheme of RC-generator, based on the principle of the inductive three-point (Fig. 6.4).

Fig. 6.4

Switch on the scheme of generator in a working condition using key [Q]. Draw oscillograms of oscillations on the output of the generator and on gate of field-effect transistor in a mode of oscillation exciting and in the steady mode. Evaluate the degree of harmonic oscillations on the output of the LC-generator. Evaluate the time of oscillation set up.

2. Investigate the influence of parameters in oscillatory circuit on frequency and amplitude of the generated oscillations.

To study the influence of parameters of oscillatory circuit on the frequency and amplitude of oscillations, that generate, set a parameters of loop according to table. 6.1.

Measure the frequency and amplitude of the generated oscillations and add the measured values to the table. 6.1. Calculate the theoretical values of frequency oscillations according to formula (6.6) and add calculations to the table. 6.1.

Table 6.1

L1, µHn
L2, µHn
C1, mФ	0,03	0,03	0,03	0,03	0,04	0,04	0,02	0,015
Uam, V	28,05	21.56	17,03	18.07	22.71	21.57	-	-
Fm, kHz	0,125	0,125	0,125	0,12	0,12	0,108	-	-
Ftheor., kHz	4,811	4,811	4,811	4,623	4,623	3,608	7,217	-
Uamp.m,V	19,25	8,75	5,25	5,833	9,625	8,75	8,75	8,75

Compare measured values, make conclusions.

3. Investigate influence of field-effect work mode on frequency and amplitude of oscillations, that generate.

For this, set up voltage sources, that define work mode, according to table 6.2. Parameters of loop elements set according to Fig. 6.4. Measure frequency and amplitude of generated oscillations, and add their values to the table 6.2.

Make conclusions.

Table 6.2

Ec, V
Eal, mV
Fmes, kHz	10,25	10,25	10,25	10,25	-	-	-
Uam, V	27,6	30.5	10,37	27.94	-	-	-
Uamp. m, V	0,125	0,126	0,125	0,126	-	-	-

4. Investigate conditions of oscillations exciting (according to formula 6.5) in the scheme of induction generator with inductive three-point, investigate separately the impact of values: resistance on the loop, the ratio of inductances in left and right branches of loop, slope of characteristic of field-effect transistor.

4.1. For studying of the impact of resistance in the loop R_c on conditions of exciting of oscillations in the scheme of induction generator with three-point scheme, set parameters of scheme according to Fig. 6.4, except of R_c, value of which set according to Table. 6.3.

Measure the frequency and amplitude of the generated oscillations and add the measured values to the table. 6.3.

Table 6.3

Rc, kOhm				3,75	3,6	3,5
Fmeas, kHz	0,125	0,125	0,128	0,128	0,128	0,125	-
Uamp, V	22,6	16,67	13,38	13.04	12.6	11,8	-
Fres.meas.circuit, kHz	117,5		110,6	107,5		114,4
Kmeas.circuit		13,1		10,3	10,1	8,5	9,93
φmeas.circuit	-188,4	-183,5	-178,8	-175,4	-180	-174,5	-183
Uamp.meas, V	10,25	10,25	10,25	10,25	10,25	10,25	10,25

4.2. To investigate the influence of the ratio of inductances in left and right circuit branches (L₁ /L₂) in conditions of excitation of oscillations in the scheme of induction generator with three-point, set parameters according to Fig. 6.4, except L₁ and I₂, the values of which set according to Table. 6.4.

Measure the frequency and amplitude of oscillations and add values to Table. 6.4. Identify the value L₁ /L₂, according to which the disruption of generation occurs.

4.3. To investigate the influence of slope characteristics of field-effect transistor S₁, in conditions of the excitation of oscillations in the scheme according to Fig.6.4, except E_s.i, which value is set according to the table. 6.5.

Table 6.4

L1,µHn					0,4635	0,465	0,4675
L2, µHn					0,0165	0,015	0,0125
L1 /L2							37,4
Fmeas, kHz	0,126	0,125	0,125	0,125	-	-	-
Uamp,V	11,85	24,32			-	-	-
Fres.meas.circuit, kHz	97,5	116,8	132,5	162,5
Kmeas.circuit	21,4	21,4	21,5	21,5	31,8	37,2
Φmeas.circuit	-185,4	-181,1	-182,1	-184,3	-264	-256	-254,4
Uamp.meas,V	10,25	10,25	10,25	10,25	10,25	10,25	10,25

Table 6.5

Eal,mV
S1,mA/V	0,009	0,015	0,01	0,011	0,0125	0,0125	0,0125
Fmeas,kHz	0,126	0,125	0,126	-	-	-	-
Uamp,V	28,007	27.9	27,3	-	-	-	-
Fres.meas.circuit,kHz	99,5	120,5	116,5	117,5	123,5	117,6	117,6
Kmeas.circuit	17,2	15,9	10,9	9,6	8,08	8,5	5,2
Φmeas.circuit	-148	-187	-180	-105,6	-211,1	-107,5	-208,5

According the drain gate characteristic of field-effect transistor, measured during the laboratory work 1, calculate the value S₁, which corresponds to the working point of the transistor, which is specified by the source E_al.i. Determine the value S₁, in which the generation failure occurs and add it to the table. 6.6.

4.4. Check the implementation of condition of self-exciting oscillations (6.5), in condition that R =R_c, S_dif = S₁.

Calculate the parameter R_cS₁L₂/L₁, its value add to Table. 6.6. Make conclusions.

Table 6.6

Rc,kOhm
L1/L2			37,4
S1,mA/V	0,011	0,0115	0,012
RcS1L2/L1	0,924	1,0695	1,34
Kres.circ	31,8	27,2
Φres.circ	-264	-256	-254,4

5. Explore the conditions of amplitudes balance and phase balance formula (6.3) and (6.4) in breaking of the oscillations in the generator scheme with inductance three-point. For this study separately the impact of variables:

- resistance of loop,

- ratio of inductances in left and right branches of the loop,

- slope of field-effect transistor characteristics.

In the scheme according to Fig. 6.4 Unlock the feedback circuit using Key [Q].

5.1. Set parameters of the scheme according to paragraph 4.1. Measure the amplitude K_{unlock.circuit} and the phase φ_{unclock.circuit} transfer coefficient of open circuit, and each frequency F_{res.unlock.circuit}, on which the amplitude of the transfer coefficient of unlocked circuit is maximum.

The results add to your table. 6.3 and 6.6. £ asses = P

5.2 Set parameters of the scheme according to paragraph 4.2. Measure the amplitude K_{unlock.circuit} and the phase φ_{unclock.circuit} transfer coefficient of open circuit, and each frequency F_{res.unlock.circuit}, on which the amplitude of the transfer coefficient of unlocked circuit is maximum.

The results add to your table. 6.4 and 6.6.

5.3. Set parameters of the scheme according to paragraph 4.3. Measure the amplitude K_{unlock.circuit} and the phase φ_{unclock.circuit} transfer coefficient of open circuit, and each frequency F_{res.unlock.circuit}, on which the amplitude of the transfer coefficient of unlocked circuit is maximum.

The results add to your table. 6.5 and 6.6.

5.4. Compare the results of measurements according to 4 and 5 paragraphs. Compare the conditions (6.5) and (6.3) - (6.4). Make conclusions.

6. Explore the stationary conditions of amplitude and balance of phases at a disruption of oscillations in a generator scheme with inductance three-point using formulas (6.7), (6.8). For this study separately the impact of variables: resistance of loop, inductance ratio values ​​in left and right branches of the contour, slope characteristics in field-effect transistor in operating point.

6.1. Approximate the drain-gate characteristics of field-effect transistor, measured the at a performance of the laboratory work1, by polynomial according to formula (6.9) for all variants of work points, used in the circuits with parameters according to

Table. 6.1-6.4. For all cases calculate S_aver by the formula (6.9). Plot the graphs S_av=f(U_1alt.c).

Fig. 6.5

6.2. Graphically calculate the amplitude of output oscillation of LC-generator of harmonic signal, whose parameters are given in the table. 6.1-6.4. The results of calculations add to your table 6.1-6.4 correspondingly. Make conclusions. (Example of graphical measurement is shown in Fig. 6.5).

7. Explore the hard excitation regimes and the breakdown of oscillations in the scheme of induction generator with a three-point.

7.1. To study the hard excitation use key [W]. Switch on modeling at the left key position [W] and the meaning of E_v.i = 0.75 V. Draw, scillogram. Switch on modeling at a right position of key [W] and the meaning of E_v.i = 1.75 V. Draw oscillogram.

Turn on the modeling at a left position of key [W] and the meaning of E_v.i = 0.75 V, get the established mode, and then switch the key in a right position (E_v.i = 1.75 V). Draw the oscillogram. Make conclusions.

7.2. Explore the breaking of oscillations. For this, set the voltage source value according to table 6.7. Measure the frequency and amplitude of oscillations and add their value to the table. 6.7. Make conclusions.

Table 6.7

Ec.i,V
Ev.i, mV
Fs, kHz	0,125	0,125	0,126	0,126	0,126	0,126	0,126
Uamp	27,33	27,1	27,02	27,01	26,84		26,7

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