Detailed introduction to how to use an oscilloscope
fluorescent screen
The fluorescent screen is the display part of the oscilloscope tube. There are multiple scale lines in the horizontal and vertical directions on the screen, indicating the relationship between the voltage and time of the signal waveform. The horizontal direction indicates time, and the vertical direction indicates voltage. The horizontal direction is divided into 10 grids, the vertical direction is divided into 8 grids, and each grid is divided into 5 parts. The vertical direction is marked with 0%, 10%, 90%, 100% and other marks, and the horizontal direction is marked with 10% and 90% marks, which are used for measuring parameters such as DC level, AC signal amplitude, delay time, etc. According to the number of grids occupied by the measured signal on the screen multiplied by the appropriate proportional constant (V/DIV, TIME/DIV), the voltage value and time value can be obtained.
Oscilloscope tubes and power systems
1. Power
Oscilloscope main power switch. When this switch is pressed, the power indicator light lights up, indicating that the power is on.
2. Intensity
Turn this knob to change the brightness of the light spot and scan line. It can be smaller when observing low-frequency signals and larger when observing high-frequency signals. Generally it should not be too bright to protect the fluorescent screen.
3. Focus
The focus knob adjusts the cross-section size of the electron beam and focuses the scan line into the clearest state.
4. Illuminance
This knob adjusts the brightness of the light behind the fluorescent screen. Under normal indoor light, it is better to dim the lighting. In an environment with insufficient indoor light, the lighting can be appropriately brightened.
Vertical deflection factor and horizontal deflection factor
1. Vertical deflection factor selection (VOLTS/DIV) and fine adjustment
Under the action of a unit input signal, the distance the light point deflects on the screen is called offset sensitivity. This definition applies to both the X-axis and the Y-axis. The reciprocal of the sensitivity is called the deflection factor. The unit of vertical sensitivity is cm/V, cm/mV or DIV/mV, DIV/V. The unit of vertical deflection factor is V/cm, mV/cm or V/DIV, mV/DIV. In fact, due to common usage and the convenience of measuring voltage readings, the deflection factor is sometimes regarded as the sensitivity.
Each channel in the tracking oscilloscope has a vertical deflection factor selection band switch. Generally, it is divided into 10 levels from 5mV/DIV to 5V/DIV according to the 1, 2, and 5 methods. The value indicated by the band switch represents the voltage value of one grid in the vertical direction on the fluorescent screen. For example, when the band switch is placed in the 1V/DIV position, if the signal point on the screen moves one grid, it means that the input signal voltage changes by 1V.
There is often a small knob on each band switch to fine-tune the vertical deflection factor of each gear. Turn it clockwise all the way to the "calibration" position, where the vertical deflection factor value is consistent with the value indicated by the band switch. Turn this knob counterclockwise to fine-tune the vertical deflection factor. After fine-tuning the vertical deflection factor, it will cause inconsistency with the indicated value of the band switch, which should be noted. Many oscilloscopes have a vertical expansion function. When the trim knob is pulled out, the vertical sensitivity expands several times (the deflection factor decreases several times). For example, if the deflection factor indicated by the band switch is 1V/DIV, when using the ×5 extended state, the vertical deflection factor is 0.2V/DIV.
When doing digital circuit experiments, the ratio of the vertical movement distance of the measured signal on the screen to the vertical movement distance of the +5V signal is often used to determine the voltage value of the measured signal.
Time base selection (TIME/DIV) and fine-tuning
The use of time base selection and fine-tuning is similar to the vertical deflection factor selection and fine-tuning. The time base selection is also realized through a band switch, and the time base is divided into several levels according to the 1, 2, and 5 modes. The indicated value of the band switch represents the time value for the light spot to move one grid in the horizontal direction. For example, in the 1μS/DIV setting, the light point moving one grid on the screen represents a time value of 1μS.
The "Fine Adjustment" knob is used for time base calibration and fine adjustment. When it is fully rotated clockwise and is in the calibration position, the time base value displayed on the screen is consistent with the nominal value shown on the band switch. Turn the knob counterclockwise to fine-tune the time base. After the knob is pulled out, it is in the scan expansion state. Usually it is ×10 expansion, that is, the horizontal sensitivity is expanded by 10 times and the time base is reduced to 1/10. For example, in the 2μS/DIV file, the time value represented by one horizontal grid on the fluorescent screen in the scan expansion state is equal to 2μS × (1/10) = 0.2μS.
There are 10MHz, 1MHz, 500kHz, and 100kHz clock signals on the TDS experimental bench, which are generated by quartz crystal oscillators and frequency dividers. They are highly accurate and can be used to calibrate the time base of the oscilloscope.
The standard signal source CAL of the oscilloscope is specially used to calibrate the time base and vertical deflection factor of the oscilloscope. For example, the standard signal source of the COS5041 oscilloscope provides a square wave signal with VP-P=2V and f=1kHz.
The Position knob on the front panel of the oscilloscope adjusts the position of the signal waveform on the fluorescent screen. Rotate the horizontal displacement knob (marked with a horizontal bidirectional arrow) to move the signal waveform left and right, and rotate the vertical displacement knob (marked with a vertical bidirectional arrow) to move the signal waveform up and down.
