(1) Understand the working principle of oscilloscope.
(2) Learn to observe various signal waveforms with an oscilloscope.
(3) Measure the voltage, frequency and phase difference of the signal with an oscilloscope.
Main instruments and equipment:
YB4320G double trace oscilloscope, EE 164 1B function signal generator YB4320G double trace oscilloscope, EE 164 1B function signal generator.
appliance
Experimental principle and content:
1. Basic structure of oscilloscope
Oscilloscope is mainly composed of oscilloscope tube, amplification and attenuation system, trigger scanning system and power supply, in which oscilloscope tube is the core part.
The basic structure of the oscilloscope tube is shown in the following figure, which is mainly composed of an electron gun, a deflection system and a fluorescent screen, and is sealed in a vacuum environment by an external glass shell.
The function of the electron gun is to release and accelerate the electron beam. The first anode is called focusing anode and the second anode is called accelerating anode. By adjusting the * * * interaction between them, the electron beam can hit the screen to produce bright and clear points.
The deflection system consists of two pairs of deflection plates x and y. By applying a voltage to the deflection plate, the electron beam is deflected, thereby changing the position of the bright spot on the screen accordingly.
The fluorescent screen is coated with fluorescent powder, and electrons can shine on it to form light spots. Different phosphors have different luminescent colors and afterglow time.
The amplification and attenuation system is used to appropriately scale input signals of different sizes to make their amplitudes suitable for observation.
The function of the scanning system is to generate sawtooth scanning voltage (as shown in the upper left picture), so that the electron beam moves periodically and uniformly from left to right on the screen. This process is called scanning. The start time of scanning is controlled by the trigger system.
2. The principle of oscilloscope display waveform.
If only AC voltage is applied to the vertical deflection plate and five points are applied to the X deflection plate at the same time, the electron beam moves back and forth in the vertical direction to form a bright line, as shown in the left figure:
If sine voltage and sawtooth voltage are applied to the Y deflection plate and the X deflection plate at the same time, the electrons will make a synthetic motion of sine oscillation and horizontal scanning under the reasonable action of horizontal and vertical directions. When two voltage periods are equal, a full-cycle sinusoidal voltage waveform can be displayed on the screen. The development principle is shown on the right:
3. Scan synchronization
In order to display the periodic waveform of the external input signal completely, it is necessary to adjust the scanning period to make it the same as or have an appropriate relationship with the external signal period. When the period changes due to some factors, the scanning synchronization function can make the scanning starting point automatically track the changes of external signals, thus displaying the waveform stably.
Steps and operation methods:
1. The oscilloscope measures the voltage and frequency of the signal.
For a stable sinusoidal voltage waveform, the voltage and frequency can be read by the following methods.
,
Where a is the vertical deflection coefficient (voltage deflection coefficient) (which can be read directly from the attenuator switch on the oscilloscope panel), and the unit is V/div or mV/div；; ; H is the peak-to-peak height of the input signal in div；; B is the scanning time coefficient, which can be read directly from the main scanning time coefficient selector switch, and the unit is s/div, ms/div or μ s/div; L is the width of a single period of the input signal in div.
(1) Turn on the power switch, switch to DC gear, toggle the vertical working mode switch, and select the channel where the unknown signal is located.
(2) By adjusting the "scanning time coefficient selection switch" and "vertical deflection coefficient switch" and their corresponding fine-tuning switches, the height and waveform number of unknown signal patterns can be measured conveniently. At the same time, the values of A and B required for calculation are read out on the switch.
(3) Adjust the "vertical displacement" and "horizontal displacement" knobs, and read and record the L and H values with the scales on the fluorescent screen.
2. Observe the half-wave and full-wave rectified waveforms directly with an oscilloscope.
(1) Connect the unknown signals provided by the laboratory to the AB terminal of the rectifier circuit respectively, and send the CD terminal to the CH 1 or CH2 terminal of the oscilloscope.
By adjusting the "scanning time coefficient selection switch" and "vertical deflection coefficient switch", the signal is displayed on the screen, and the rectified waveform is observed respectively.