1. The main controls of the display part are:
(1) power switch.
(2) Power indicator light.
(3) The brightness of brightness level spot.
(4) Focus to adjust the light spot or waveform clarity.
(5) The auxiliary focus is matched with the "focus" knob to adjust the clarity.
(6) the brightness of the scale line on the scale brightness level coordinate table.
(7) Tracking the light spot deviating from the fluorescent screen back to the display area when the key is pressed, and finding the position of the light spot.
(8) The standard signal output is 1kHz, and the square wave calibration signal of 1V is derived from this. It is added to the Y-axis input terminal to calibrate the Y-axis input sensitivity and the X-axis scanning speed.
2.y-axis plug-in
(1) The display mode selector switch is used to switch the control components of the two Y-axis preamplifiers YA and YB, and there are five different display modes:
"Alternate": When the display mode switch is set to "alternate", the electronic switch is controlled by the scanning signal, and the YA or YB signal is turned on in turn for each scanning. When the frequency of the measurement signal is high, the frequency of the scanning signal is also high. electric current
The faster the switching rate of the sub-switch, there will be no flicker. This working state is suitable for observing two signals with higher working frequency.
"Intermittent": When the display mode switch is set to "Intermittent", the electronic switch is not controlled by the scanning signal, and generates a square wave signal with a fixed frequency of 200kHz, so that the electronic switch can quickly turn on YA and YB alternately. Because the switching frequency is higher than the frequency of the measurement signal, the waveforms of the two channels displayed on the screen are intermittent. When the frequency of the measured signal is high, the intermittence phenomenon is very obvious and even impossible to observe; When the frequency of the measurement signal is low, the intermittent phenomenon is masked. Therefore, this working state is suitable for observing two signals with lower working frequency.
"YA" and "YB": When the display mode switch is set to "YA" or "YB", it means that the oscilloscope works in a single channel. At this time, the working mode of the oscilloscope is equivalent to a mono oscilloscope, that is, only the signal waveform of "YA" or "YB" channel can be displayed separately.
"YA+YB": When the display mode switch is set to "YA+YB", the electronic switch does not work, and both signals of YA and YB pass through the amplifier and gate circuit, and the oscilloscope displays the waveform of the superposition of the two signals.
(2) The "DC-⊥-AC" Y-axis input selector switch is used to select the coupling mode of the measured signal to the input terminal. Set "DC" as direct coupling, which can input AC signal with DC component; Put it in the "AC" position to realize AC coupling and only input AC components; When placed in the "⊥" position, the Y-axis input terminal is grounded, and the displayed time baseline is generally used as the reference baseline for testing the zero level of DC voltage.
(3) "Fine-tuning V/div" sensitivity selector switch and fine-tuning device. The sensitivity adopts the open-relation sleeve shaft structure, and the black knob is the Y-axis sensitivity coarse adjustment device. From 100 mV/div to 20V/div, it is divided into 1 1 file. The red knob is a fine-tuning device, and it is a calibration position when it is increased to full scale clockwise. The amplitude of the measurement signal can be read according to the value indicated by the coarse adjustment knob. When the knob rotates counterclockwise to full scale, its change range should be greater than 2.5 times. Continuously adjusting the "fine-tuning" potentiometer can achieve sensitivity coverage between all steps. When making quantitative measurement, the knob should be placed in the "calibration" position with full scale clockwise.
(4) "Balance" When the input circuit of the Y-axis amplifier is unbalanced, the displayed light spot or waveform will shift to the Y-axis direction with the "fine adjustment" rotation of the "V/div" switch. Adjusting the "balance" potentiometer can minimize this offset.
(5) The Y-axis displacement potentiometer adjusts the vertical position of the waveform.
(6) Push-pull switch is used for the "polarity, pull ya" ya channel of polarity conversion. When pulling out, the YA channel signal is displayed in reverse phase, that is, when the display mode is (YA+ YB), the displayed image is YB-YA.
(7) "Internal trigger, YB pull" trigger source selection switch. In the pressed position (normal), the scanning trigger signal is taken from the input signals of YA and YB channels respectively, which is suitable for single-channel or dual-channel display, but the time of dual-channel waveform cannot be compared. When the switch is pulled out, the trigger signal of scanning is only taken from the input signal of YB channel, which is suitable for comparing the time and phase difference of two waveforms in dual trace display.
(8) The Y-axis input socket adopts BNC socket, and the measurement signal is directly input or input through the probe.
3.x-axis plug-in
(1) "t/div" scanning speed selector switch and fine-tuning knob. The moving speed of the X-axis light spot is determined by it, ranging from 0.2μ s to 1s * * * to 2 1. When the switch "fine-tunes" the potentiometer clockwise to the end, when the switch is turned on, it is the "calibration" position. At this time, the indicated value of "t/div" is the actual value of the scanning speed.
(2) "expanding×10" scanning speed-increasing device. It is a cable switch, which can be used normally when pressed, and the scanning speed of cable position is increased by 10 times. The indicated value of "t/div" should also be calculated accordingly. Using "extended pull×10" is suitable for observing waveform details.
(3)X-axis position adjustment knob. It is a horizontal position adjustment potentiometer for X-axis light trace, and it is a sleeve shaft structure. The outer ring knob is a coarse adjustment device. When rotating clockwise, the baseline moves to the right, and when rotating counterclockwise, the baseline moves to the left. The small knob on the sleeve shaft is a fine-tuning device, which is suitable for adjusting the extended signal.
(4) "External trigger and external X connection" socket adopts BNC socket. When an external trigger is used, it is used as a socket for connecting external trigger signals. When an X-axis amplifier is externally connected, it can also be used as a signal input socket. Its input impedance is about 1mω. For external use, the peak value of the input signal should be less than 12V.
(5) The "trigger level" knob triggers the level adjustment potentiometer knob. Used to select the trigger point of the input signal waveform. Specifically, it is to adjust the start time of scanning and decide at which point of the trigger signal waveform to trigger scanning. When rotating clockwise, the trigger point tends to the positive part of the signal waveform, and when rotating counterclockwise, the trigger point tends to the negative part of the signal waveform.
(6) "Stability" triggers the stability fine-tuning knob. Used to change the working state of the scanning circuit, which should be in the state to be triggered. The adjustment method is to set the Y-axis input coupling mode selection (AC-grounding -DC) switch as the grounding gear, and set the V/div switch as the gear with the highest sensitivity. When the horizontal knob is out of the self-excited state, use a small screwdriver to turn the stable potentiometer clockwise to the end, and the scanning circuit will generate self-excited scanning, at which time a scanning line will appear on the screen. Then slowly turn counterclockwise, so that the scanning line just disappears. At this time, the scanning circuit is in a triggered state. In this state, when measuring with an oscilloscope, a stable waveform can be obtained on the screen by adjusting the level knob, and the starting point position of the waveform on the screen can be adjusted and selected at will. In a few oscilloscopes, when the stable potentiometer rotates counterclockwise to the end, scanning lines appear on the screen; Then slowly rotate clockwise, so that the scanning line on the screen just disappears, and the scanning circuit is in a triggered state at this time.
(7) "Inside and outside" trigger source selection switch. When placed in the "internal" position, the scanning trigger signal is taken from the measurement signal of the Y-axis channel; When placed in the "external" position, the trigger signal is taken from the external trigger signal introduced by the "external trigger x external" input terminal.
(8) AC, AC (H) and DC trigger the coupled mode switch. "DC" gear is in DC coupling state, which is suitable for trigger signals with slow change or low frequency (such as 100Hz or below). The "AC" file is in AC coupling state, and the performance of the trigger is not affected by the DC component, because it cuts off the DC component in the trigger. "AC(H)" gear is in the state of AC coupling with low frequency suppression. When a high-frequency complex wave containing low-frequency components is observed, the trigger signal is coupled through a high-pass filter, which suppresses low-frequency noise and low-frequency trigger signal (low-frequency components below 2MHz) and avoids waveform flicker caused by false trigger.
(9) "High frequency, normal and automatic" trigger mode switch. Used to select different trigger modes to adapt to different test signals and test purposes. "High frequency" range, which is selected when the frequency is high (such as higher than 5MHz) and there is not enough amplitude to stabilize the trigger. At this time, the scanning is in high-frequency trigger state, and the measured signal is synchronized by the high-frequency signal (200kHz signal) generated by the oscilloscope itself. Without frequently adjusting the level knob, the stable waveform can be displayed on the screen, which is convenient to operate and conducive to observing the waveform of high-frequency signals. "Normal" files are scanned by using the input signal of Y-axis or external contact source, which is a common way to trigger scanning. "Automatic" file, the scanning is in an automatic state (similar to high-frequency trigger mode), but a stable waveform can be observed without adjusting the level knob, which is convenient to operate and beneficial to observing signals with low frequency.
(10) "+,-"triggers polarity switching. In the "+"position, select the rising part of the trigger signal, and in the "-"position, select the falling part of the trigger signal to trigger the scanning circuit.
(2) Inspection, adjustment and calibration before use
Before the oscilloscope is used for the first time or reused for a long time, it is necessary to check whether it can work, and adjust the stability of the scanning circuit and the DC balance of the vertical amplifier circuit. When measuring voltage and time quantitatively, the oscilloscope must also calibrate the gain and horizontal scanning speed of the vertical amplifier circuit. Because of the different parameters such as amplitude and frequency of calibration signals of various types of oscilloscopes, the methods of checking whether the oscilloscopes can work normally and calibrating the gain of vertical amplifier circuit and horizontal scanning speed are slightly different.
(3) Use steps
Oscilloscope can be used to observe the waveform curves of different electric signal amplitudes changing with time. On this basis, the oscilloscope can be used to measure electrical parameters such as voltage, time, frequency, phase difference and amplitude modulation. The following introduces the use steps of observing the waveform of electric signal with oscilloscope.
1. Select Y axis coupling mode.
According to the frequency of the signal to be measured, set the "AC-ground -DC" switch of Y-axis input coupling mode to AC or DC.
2. Select Y-axis sensitivity
According to the approximate peak-to-peak value of the measured signal (if an attenuation probe is used, it should be divided by the attenuation multiple; When the coupling mode adopts DC gear, the superimposed DC voltage value should also be considered), and the Y-axis sensitivity selection V/div switch (or Y-axis attenuation switch) should be placed in a suitable gear. In practical use, if it is not necessary to read the voltage value, you can adjust the Y-axis sensitivity fine-tuning (or Y-axis gain) knob appropriately, so that the waveform with the required height appears on the screen.
3. Select the source and polarity of the trigger (or synchronization) signal.
Usually, the trigger (or synchronization) signal polarity switch is set at the "+"or "-"position.
4. Select the scanning speed
According to the approximate value of the period (or frequency) of the measured signal, set the X-axis scanning speed t/div (or scanning range) switch at an appropriate level. In practical use, if it is not necessary to read the time value, you can adjust the scanning speed t/div fine-tuning (or scanning fine-tuning) knob appropriately, so that the waveform of the number of cycles required for the test can be displayed on the screen. If you need to observe the edge of the signal, you should set the scanning speed t/div switch to the fastest scanning speed.
5. Input measurement signal
After the measured signal is attenuated by the probe (or directly input by coaxial cable, it is not attenuated, but at this time the input impedance decreases and the input capacitance increases), it is input into the oscilloscope through the Y-axis input terminal.
Current phenomenon
Primitive cause
First, there are no light spots or waveforms.
The power supply is not connected.
The brightness knob is not adjusted properly.
Position adjustment of shift knob on X and Y axes.
Improper adjustment of Y-axis balance potentiometer leads to serious imbalance of DC amplifier circuit.
Second, it does not open horizontally.
When the trigger source selection switch is placed in the external gear and there is no external trigger signal input, sawtooth wave will not be generated.
Improper adjustment of horizontal knob.
Without adjusting the stable potentiometer, the scanning circuit is in the critical state of being triggered.
The X-axis is wrongly placed in the X external position, and there is no signal input on the external socket.
If the dual-trace oscilloscope only uses channel A (channel B has no input signal) and the internal trigger switch is placed in YB position, there will be no sawtooth wave.
Third, the vertical direction is not displayed.
The input coupling mode DC- ground-AC switch is wrongly placed in the ground position.
The high potential end and the low potential end of the input terminal are connected with the high potential end and the low potential end of the tested circuit.
The input signal is small, and the V/div is wrongly placed in the low sensitivity file.
Fourth, the waveform is unstable.
Excessive clockwise rotation of the stabilized potentiometer causes the scanning circuit to be in a self-excited scanning state (non-critical state is triggered).
The trigger coupling mode AC, AC(H) and DC switches failed to correctly select the corresponding gears according to different trigger signal frequencies.
When selecting the high-frequency trigger state, the trigger source selection switch is mistakenly placed in the outer gear (it should be placed in the inner gear. )
When some oscilloscopes scan in automatic mode (continuous scanning), the waveform is unstable.
5. Vertical lines are dense or rectangular.
Improper selection of t/div switch leads to F scanning < < F signal.
Six, the horizontal line is dense or inclined.
Improper selection of t/div switch leads to f scan > > f signal.
Seven, vertical voltage reading is not allowed.
The deflection sensitivity (v/div) in the vertical direction is not calibrated.
When calibrating v/div, the v/div fine-tuning knob is not placed in the calibration position (that is, it is not rotated clockwise).
During the test, the v/div fine-tuning knob is not in the calibration position (that is, it is not in the clockwise position).
Using l0: 1 attenuation probe, the voltage is not multiplied by 10 times.
The frequency of the measured signal exceeds the maximum frequency of the oscilloscope, and the oscilloscope reading is less than the actual value.
The measured value is peak-to-peak, and the sine rms needs to be converted.
Eight, no horizontal reading.
Horizontal deflection sensitivity (t/div) calibration is not performed.
When calibrating the t/div, the fine-tuning knob of the t/div is not placed in the calibration position (that is, it is not rotated clockwise).
During the test, the t/div fine-tuning knob is not in the calibration position (that is, it is not in the clockwise position).
When the scanning speed expansion switch is placed in the pull (× 10) position, the test fails to increase the sensitivity by 10 times according to the indicated value of the t/div switch.
Nine, the DC voltage value of AC /DC superimposed signal is unclear.
Y-axis input coupling selection DC- ground-AC switch is misplaced in AC gear (it should be placed in DC gear).
Before the test, the DC- grounding-AC switch was not placed on the grounding device for DC horizontal reference point correction.
Improper adjustment of Y-axis balance potentiometer.
Ten, can't measure the phase difference between two signals (waveform display method)
Double-trace oscilloscope mistakenly put the internal trigger (pull YB) switch in the pressed (normal) position, and should put it in the YB position.
Dual-trace oscilloscope did not correctly select alternating and intermittent files for display mode switching.
The trigger selection switch of the single-wire oscilloscope is misplaced in the internal file.
Although the trigger selection switch of the single-wire oscilloscope is placed in the external gear position, the two external contacts do not use the same signal.
Eleven, amplitude modulation waveform disorder
Improper selection of t/div switch and wrong selection of scanning frequency by carrier frequency of AM wave (it should be the frequency selection of audio AM signal).
12. The waveform cannot be adjusted to the required start time and position.
The stability potentiometer is not adjusted to the critical trigger point to be triggered.
Trigger polarity (+,-) and trigger level (+,-) do not match.
The trigger mode switch is mistakenly placed in the automatic gear (it should be placed in the normal gear).
6. Trigger (or synchronize) scanning
Slowly adjust the trigger level (or synchronization) knob, and a stable waveform will appear on the screen. Adjust the level knob appropriately according to the observation needs, and display the waveform at the corresponding starting position.
If the waveform is observed with a dual trace oscilloscope, when the single trace is displayed, the display mode switch is set to YA or YB. The measured signal is input into the oscilloscope through the YA or YB input terminal. The trigger source of Y axis selects the "internal trigger-pull YB" switch and puts it in the pressed (normal) position. If the oscilloscope performs double trace display, the display mode switch is set to alternate gear (suitable for signals with not too low observation frequency) or intermittent gear (suitable for signals with not too high observation frequency). At this time, the trigger source of Y axis selects the "internal trigger-YB pull" switch to set the "YB pull" gear.
(4) Abnormal phenomena caused by improper use
When the oscilloscope is used, it is often because the operator does not understand the principle of oscillography and the function of the control device of the oscilloscope panel, and improper adjustment will lead to abnormal phenomena. Table 5- 1 lists the common abnormal phenomena caused by improper use of oscilloscope and their causes, for the reference of oscilloscope users.
Third, the test application of oscilloscope
Measurement of voltage
Any measurement made by an oscilloscope can be attributed to the measurement of voltage. Oscilloscope can measure the voltage amplitude of various waveforms, not only DC voltage and sinusoidal voltage, but also pulse or non-sinusoidal voltage amplitude. More useful, it can measure the voltage amplitude of each part of the pulse voltage waveform, such as overshoot or top drop. This is unmatched by any other voltage measuring instrument.
1. Direct measurement method
The so-called direct measurement method is to measure the height of the measured voltage waveform directly from the screen and then convert it into a voltage value. When quantitatively testing voltage, generally turn the fine-tuning knob of the Y-axis sensitivity switch to the "calibration" position, so that the measured voltage value can be directly calculated from the indicated value of "V/div" and the ordinate value of the measured signal. Therefore, direct measurement method is also called ruler method.
Measurement of (1) AC voltage
Put the Y-axis input coupling switch in the "AC" position to display the AC component of the input waveform. If the frequency of AC signal is very low, the Y-axis input coupling switch should be placed in the "DC" position.
Move the measured waveform to the center of the oscilloscope screen, control the measured waveform in the effective working area of the screen with the "V/div" switch, and read the degree H of the whole waveform in the Y axis direction according to the division of coordinate scale, then the peak-to-peak value VP-P of the measured voltage can be equal to the product of the indicated value of the "V/div" switch and H. If the probe is used for measurement, the attenuation of the probe should be taken into account, that is, the value calculated above should be multiplied by/kloc.
For example, the Y-axis sensitivity switch "V/div" of the oscilloscope is located at step 0.2, and the coordinate amplitude H of the measured waveform on the Y-axis is 5div, then the peak-to-peak value of this signal voltage is1v. If the probe still shows the above values after measurement, the peak-to-peak value of the measured signal voltage is 10V.
(2) Measurement of 2)DC voltage
Set the Y-axis input coupling switch to the "ground" position and the trigger mode switch to the "automatic" position, so that a horizontal scanning line will be displayed on the screen, which is a zero-level line.
Set the Y-axis input coupling switch to the "DC" position, and add the measuring voltage. At this time, the scanning line produces a jump displacement h in the Y-axis direction, and the measured voltage is the product of the indicated value of "V/div" switch and h.
The direct measurement method is simple and easy, but the error is large. The factors causing errors include reading error, parallax and system error of oscilloscope (attenuator, deflection system, oscilloscope tube edge effect) and so on.
2. Compare measurement methods
Comparative measurement method is to compare a known standard voltage waveform with the measured voltage waveform to get the measured voltage value.
Input the measured voltage Vx into the Y-axis channel of the oscilloscope, adjust the Y-axis sensitivity selection switch "V/div" and its fine-tuning knob, so that the height Hx convenient for measurement can be displayed on the fluorescent screen and recorded, and the positions of the "V/div" switch and the fine-tuning knob remain unchanged. Remove the measured voltage, input a known adjustable standard voltage Vs on the Y axis, and adjust the output amplitude of the standard voltage to display the same amplitude as the measured voltage. At this time, the output amplitude of the standard voltage is equal to the amplitude of the measured voltage. The comparison method can avoid the sum error caused by vertical system, thus improving the measurement accuracy.
(2) Measurement of time
The time base of an oscilloscope can produce a scanning line with a linear relationship with time, so the horizontal scale of the fluorescent screen can be used to measure the time parameters of the waveform, such as the repetition period of the periodic signal, the width of the pulse signal, the time interval, the rising time (rising edge) and falling time (falling edge), the time difference between the two signals, and so on.
When the "fine adjustment" device of the scanning speed switch "t/div" of the oscilloscope is turned to the calibration position, the time represented by the scale of the horizontal display waveform can be directly read out and calculated according to the indicated value of the "t/div" switch, so that the time parameters of the measured signal can be calculated more accurately.