How to use an electronic oscilloscope

　　① Check whether the power supply voltage is within the range of 220V±10%.

　　②The operating ambient temperature should be 0～＋40℃.

　　③ Excessive high voltage should not be fed into the input terminal.

　　④ The brightness of the displayed light spot should not be too bright to avoid damaging the screen.

　　⑤ Do not use excessive force when switching the control devices.

　　(2) Operation steps after power on After placing all control components in the positions listed in Table 1, turn on the power and look for the light spot. If you see the light spot, adjust the brightness to make the light spot or time base line of appropriate brightness; if you cannot find the light spot, press the "tracking" button to find the location of the light spot.

　　Table 1 Oscilloscope control locations

　　Adjust the Y-axis and X-axis shifts to move the light spot (or time base line) to the center of the screen, and then use the "Focus" and "Auxiliary Focus" knobs to make the waveform clearest.

　　(3) Connection of input signal Take the display calibration signal as an example. Use a coaxial cable with a BNC connector to connect the calibration signal output end to the input end of the YA channel. The input coupling selection switch of the YA channel is in the "AC" position, the sensitivity selection switch "fine adjustment V/div" is set to the "0.2" gear, and the "fine adjustment" knob is turned clockwise to the full "calibration" position. The trigger mode is in the "automatic" position.

　　At this time, a rectangular wave of about 5div is displayed on the screen, but this is a self-excitation scanning method, and the waveform may not be very stable. If the trigger scanning method is used, the above-mentioned instability can be reduced.

　　When using this machine, you should pay attention to the connection of the input signal, especially when observing the waveform of a low-level signal containing higher or lower frequency components, you must use a shielded cable, and the core wire and shield ground wire of the cable must be directly connected near the measured signal source, otherwise it will cause measurement errors. Even when measuring and observing general waveforms, it is advisable to use a shorter connection at the input end of the oscilloscope. The oscilloscope is sufficient to distort the input waveform under the following conditions.

　　① Under AC coupling working state, observe lower frequency signals.

　　② The impedance of the high-frequency signal source being measured does not match the impedance of the oscilloscope input terminal.

　　③The frequency of the input signal exceeds the bandwidth of the oscilloscope. When using an oscilloscope to measure the input signal, the impact of the oscilloscope on the input signal load must be considered. However, it is often ignored when used for general observation. In order to improve the measurement accuracy, a probe can be used to work, so that the impact caused by the load can be ignored or reduced.

　　(4) Use of probe When using an oscilloscope to observe the signal waveform, since the signal source is affected by the test load, a certain error will be generated during measurement. To reduce this error, a probe can be used to isolate the two from each other during measurement. The voltage divider of the probe can be attenuated to adapt to the measurement of signals with large amplitudes. The measured reading should be 10 times the scale indication value of the "fine adjustment V/div" switch. The maximum amplitude of the probe input signal should be less than the maximum input voltage of the instrument.

　　When using a probe to measure a fast-changing waveform, the grounding point should be connected near the measured point.

　　(5) Selection of trigger control components

　　①Selection of trigger source (select internal trigger "Normal", "YB" or external trigger).

　　a. Internal trigger. When the trigger source is set to the "internal" position, the trigger signal is taken from the Y-axis amplifier and fed back to the trigger circuit after being properly amplified. This trigger mode is relatively simple to operate.

　　The internal trigger has two trigger signals: "normal" and "YB", which are selected by a push-pull switch.

　　"Normal" - The trigger signals are taken from the amplified signals of the YA and YB channels respectively. The trigger scan is synchronized with its own signal alone. There is no time relationship between the two trigger signals. Therefore, in this trigger state, the dual-trace display is only used for general waveform observation and cannot be used for time comparison.

　　"Pull YB" - use the input signal of channel YB as the trigger source to start the scan, which is suitable for occasions where the time of two signals is compared and analyzed.

　　b. External trigger. The external trigger mode can be used to start scanning with a specific signal. This trigger mode is not affected by the Y-axis deflection operating system and can also be taken from a part of the measured signal.

　　② Selection of the coupling mode between the trigger signal and the trigger circuit. The panel of this machine is equipped with three coupling mode selection switches marked with "AC", "AC (H)", and "DC". Whether the trigger source selection switch is placed in the "inside" or "outside" position, it can play the same role.

　　"AC" - The trigger signal is coupled via a capacitor, thus isolating the DC component in the trigger signal. The triggering function is completed by the AC component, and stable scanning can be performed. This is a commonly used coupling method, but it is not suitable when the trigger signal frequency is low.

　　"AC (H)" - The trigger signal is coupled with the trigger circuit after passing through the high-pass filter. Therefore, the low-frequency signal or low-frequency noise superimposed on the trigger signal is suppressed by the high-pass filter and cannot pass through. Only the high-frequency component can be coupled with the trigger circuit to obtain a more stable scan.

　　"DC" - The trigger signal is directly coupled to the trigger circuit, so the scan can be started even when the signal changes slowly. The DC level in the internal trigger signal fed back to the trigger circuit in this coupling mode will change with the Y-axis shift. If the Y-axis signal moves within the effective working surface of the oscilloscope screen, the trigger "level" knob can be adjusted to trigger the scan. [page]

　　(6) Application of oscilloscope

　　① Voltage measurement: When measuring, turn the "fine adjustment" knob of the sensitivity selection switch "fine adjustment V/div" clockwise to the full-scale "calibration" position, so that the voltage value of the measured signal can be directly calculated according to the indicated value of "fine adjustment V/div".

　　When measuring AC voltage, set the Y-axis input coupling switch to the "AC" position to display the AC component of the waveform being measured. If the AC frequency is very low, set the Y-axis input coupling switch to the "DC" position.

　　Use the "fine-tuning V/div" switch to control the measured waveform within the effective working area of ​​the screen to read its peak-to-peak distance H, as shown in Figure 1, and calculate the peak value Up-p of the measured AC voltage value according to formula (8-5).

　　Figure 1 AC voltage measurement diagram

　　Up－p=H·u （8－5）

　　If using a probe,

　　Up－p＝10H·u

　　When measuring DC voltage, set the Y-axis input coupling switch to the "⊥" position, and the trigger mode switch to the "auto" position, so that a horizontal scan line is displayed on the screen, and the scan line is moved to a position that is easy to observe, and this scan line is set as the zero level line. After inputting the measured signal, set the input signal coupling switch to the "AC" position. At this time, the scan line generates a jump displacement along the Y-axis direction, as shown in Figure 2.

　　Figure 2 DC voltage measurement diagram

　　The measured signal DC voltage U can be calculated by formula (8-6):

　　U=H·U (8-6)

　　If using a 10:1 probe

　　U＝10H·u（8－7）

　　② Current measurement. When using an oscilloscope to observe current signals, a non-inductive resistor R with high precision and much smaller resistance than the original circuit should be connected in series in the current loop to be measured. A voltage signal proportional to the current to be measured is taken from both ends of R and sent to the Y-axis input of the oscilloscope. The waveform displayed on the oscilloscope screen is the changing waveform of the current to be measured. The peak-to-peak value of the voltage signal is measured and converted into an effective value, and then the current value of the circuit to be measured is calculated using Ohm's law.

　　③ Time measurement. The scanning signal of the oscilloscope is linearly related to time, so the horizontal scale on the screen can be used to measure the time parameters of the waveform, such as the repetition period of a periodic signal, the time difference between two signals, the time interval and the width, rise time, and fall time of a pulse signal.

　　When the "fine adjustment" knob of the oscilloscope's scanning speed switch "fine adjustment t/div" is placed in the calibration position, the time represented by each grid scale of the displayed waveform in the horizontal direction is determined by the "fine adjustment t/div" indication value r, which can be directly read and calculated, thereby more accurately calculating the time parameters of the measured signal. [page]

　　a. Measure the time interval. The waveform displayed is easy to observe, as shown in Figure 3. The time interval T between any two points of the waveform is equal to the product of the "fine adjustment t/div" indication value Sha and the distance D between the two points of the time base measured value, that is,

　　T＝Dt（8－8）

　　If the "Extended × 10" device is used, it is equivalent to speeding up the scanning speed by (8-9) calculation time interval

　　T＝10Dt（8－9）

　　b. Measure the time difference. Use the "alternating" or "intermittent" display mode to measure the time difference between two signals. When measuring, the Y-axis trigger source switch should be set to the "YB" position. After the phase-leading signal is input into the YB trigger scan, the waveforms of the two signals are displayed on the screen. As shown in Figure 4, read the horizontal reading D of the two time differences, and calculate the time difference T of the two signals according to formula (8-10)

　　D·t (8-10)

　　Figure 3 Time interval measurement diagram

　　Figure 4 Measurement of the time difference between two signals

　　④ Phase measurement. Dual-trace display can be used to compare and measure the phase relationship between two signals of the same frequency.

　　When measuring, connect the phase-advanced signal to the YB channel, the phase-lag signal to the YA channel, and select the YB trigger. Adjust the "fine-tuning t/div" switch so that one cycle of the waveform to be measured

　　The period accurately occupies 8 div on the horizontal scale. At this time, the phase angle of one cycle, 360°, is divided into 8 equal parts, and each div is equivalent to 45°. The distance D between the two corresponding points of the two signal waveforms is read out, as shown in Figure 5. The phase difference is calculated according to formula (8-11):

　　Φ＝45（°／div）×D（div） (8-11)

　　but

　　Φ＝45（°／div）×1.5（div）＝65°

　　⑤Frequency measurement. For any periodic signal, its period T can be measured by the above method of measuring time intervals, and then its frequency can be calculated according to f=1/T.

　　Figure 5 Phase measurement diagram