Experiment collection of University "Fundamentals of circuit analysis". Experiment 6 - observation and measurement of typical signals

    

Experiment six    Observation and measurement of typical signals

Catalog

Experiment six    Observation and measurement of typical signals

1 The experiment purpose

2 Experimental instruments and equipment

3 Preview the experiment

4 Experimental principle

5 Experiment content and steps

6 Experimental requirements and precautions

7 Experimental report and thinking questions

​ edit

---

1 The experiment purpose

1. Learn function signal generator 、 How to use AC voltmeter and dual trace oscilloscope .

2. Learn to observe the waveform of several typical signals .

3. Master the signal amplitude 、 cycle （ frequency ） And the measurement method of phase difference between two sinusoidal signals with the same frequency .

2 Experimental instruments and equipment

A multimeter                                               a

Integrated circuit test box                                       a

Dual trace oscilloscope                                           One

3 Preview the experiment

1. Review several common communication signals .

2. Understand the content and principle of the experiment .

3. Familiar with function signal generator 、 How to use AC voltmeter and dual trace oscilloscope .

4 Experimental principle

4.1  Several typical signals

（1） Periodic sinusoidal signal

The main parameters that describe the characteristics of sinusoidal signals are ： Peak value （UP）、 peak – Peak value （Up—p）、 Valid values （U）; cycle （T）、

frequency （f）; First phase （θ）、 Phase difference （φ） etc. , Pictured 9-1（a） Shown . The parameters satisfy a certain relationship

          

（2） Periodic rectangular signal

The main parameters describing rectangular signals are ： Range （Up—p）、 Pulse repetition period （T） And pulse width （τ）, It is usually called duty cycle , Pictured 1-1（b） Shown .

（3） Periodic sawtooth signal

The main parameters that describe sawtooth signals are ： Range （Up—p）、 Pulse repetition period （T） etc. , Pictured 1-1（c） Shown .

The above three signals can be generated by the function signal generator .

   

chart 1-1   Several common signal waveforms

4.2 Basic measurement method

（1） Measurement of amplitude

The amplitude of sinusoidal signal can be measured by AC voltmeter and oscilloscope , The measured value of AC voltmeter is only its effective value , The oscilloscope can

Directly measure its peak value or peak – Peak value . We should convert the measured data according to the experimental requirements .

The amplitude of rectangular signal and sawtooth signal can be measured by oscilloscope .

（2） Measurement of period and frequency

The period and frequency of the three signals can be measured by oscilloscope and frequency meter respectively , You can also measure a certain parameter of the signal , According to the requirements

Make a conversion .

（3） Measurement of phase difference between two sinusoidal signals with the same frequency

When the dual trace oscilloscope display shows figure 1-2 When two signal waveforms of the same frequency are shown , Calculate the phase difference according to the following formula ：

chart 1-2   The phase of two sinusoidal signals with the same frequency

 A Represents the number of cells occupied by two waveforms in a period in the horizontal direction ,B It represents the lattice occupied by the difference between the corresponding points of the two waveforms in the horizontal direction

Count .

4.3 Dual trace oscilloscope CH2(Y2) Use of polarity controls

When two channels of dual trace oscilloscope display a sinusoidal signal waveform at the same time ,

（1）CH2(Y2) Polarity selection is “＋” when , The two waveforms displayed on the display screen are in phase , That is, the phase difference is 0°, Pictured

1-3（a） Shown .

（2） Such as the CH2(Y2) Polarity selection is “－”, Then the two waveforms displayed on the display screen are reversed , That is, the phase difference is 180°, Such as

chart 1-3（b） Shown .

   

chart 1-3   Dual trace oscilloscope CH2(Y2) Use of polarity controls

 

5 Experiment content and steps

5.1 Observe sinusoidal signal

（1） According to the figure 1-4 Connecting circuits , The function signal generator generates a frequency of 500HZ（ The value displayed by the function signal generator is

accurate ）、 The effective value of the voltage is 2V（ The measured value of AC voltmeter shall prevail ） The sine signal of , Use an oscilloscope to display the sinusoidal signal wave

shape , Measure its voltage peak – Peak value Up—p And period T, At the same time, the voltage is read out by the voltage indication window of the function signal generator UP value , End

Tabulation 1-1.

chart 1-4 Observe the sinusoidal signal circuit

（2） Change the frequency of the above sinusoidal signal to 10kHZ, The effective value of voltage is changed to 4V, Finish the table 1-1.

（3） Compare function signal generator 、 The relationship between the voltage displayed or measured values of the three instruments of AC voltmeter and oscilloscope .

surface 1-1   Measure sinusoidal signal

Using instruments	Function signal generator		AC voltmeter	Dual trace oscilloscope
Measurement items	voltage UP	frequency	Voltage RMS	Up—p =H·V∕div	T=D·s∕div
Measured value		500HZ	2V
Measured value		10kHZ	4V

explain ： H Representative peak - The number of cells occupied by the peak , V∕div Is the vertical deflection sensitivity gear ;D Represents the lattice occupied by a cycle

Count ,s∕div Is the scanning speed gear .

5.2 Observe rectangular signal

（1） According to the figure 1-5 Connecting circuits , The function signal generator generates a frequency of 1.2kHZ、 The range is 4V Rectangular signal ,

（2） According to the table 1-2 The requirements of , The oscilloscope shall select different vertical deflection sensitivity gears to display waveforms , Measure the amplitude ; Different choices

Scanning speed gear display waveform of , Measure cycle and pulse width , Finish the table 1-2.

Compare the measured data in the table , Analyze whether the vertical deflection sensitivity and the shift of scanning speed have an impact on the measured data .

chart 1-5   Observe the rectangular signal and sawtooth signal circuit

surface 1-2   Measure rectangular signal

Y   Axis   Ministry   branch			X   Axis   Ministry   branch
Vertical deflection Sensitivity knob (V/div)	Number of cells occupied by amplitude （div）	Amplitude value （V）	Scanning speed knob （ms /div）	The number of cells occupied by time （div）		Time ( s ) （V）
				cycle	Pulse width	cycle	Pulse width
1			0.1
2			0.2

5.3 Observe sawtooth wave and triangular wave signals

According to the figure 1-5 Connecting circuits , The modulation function signal generator generates a sawtooth signal , The frequency is 1.2kHZ、 The range is 4V Sawtooth wave signal and triangle wave signal , Observe with an oscilloscope . Finish the table 1-3.

surface 1-3   Measure sawtooth signal

	Range	cycle
Sawtooth signal
Triangular wave signal

5.4 Observe the phase difference of sinusoidal signal in two channels of dual trace oscilloscope

（1） According to the figure 1-6 Connecting circuits , The function signal generator generates a sinusoidal signal , The frequency is displayed as 8kHZ、 Amplitude shows peak – Peak value

by 2V about , Use a dual trace oscilloscope CH1(Y1) and CH2(Y2) At the same time, the signal waveform is displayed .

（2） Adjust the waveform displayed by two channels , take CH2 Polarity selection “＋”. Finish the table 1-4,

（3） take CH2(Y2) Polarity selection “－”, Finish the table 9-4

 

chart 1-6   Observe the phase difference circuit

 

surface 1-4   Measure the phase difference of sinusoidal signal in two channels

Phase difference		CH2 Polarity “＋”	CH2 Polarity “－”
Theoretical value
Dual trace oscilloscope Measured value	B
	A
	Phase difference

explain ： In order to reduce the measurement error , The number of cells occupied by the cycle should be adjusted A For approaching 10 The integer of , Read the difference between the two waveforms again B Of

size .

6 Experimental requirements and precautions

1. In order to improve the accuracy of experimental measurement , When connecting the circuit and measuring, try to use the function signal generator 、 AC voltmeter and dual

The grounding terminals of the oscilloscope are connected together , To reduce the interaction between instruments .

2. AC voltmeter is a highly sensitive instrument , Pay attention to correctly connect and disconnect the input terminal wiring during measurement , And choose the right amount

cheng , In case of playing the watch .

7 Experimental report and thinking questions

1. Write the experimental data table .