Dual-trace oscilloscope usage and precautions

The dual-trace oscilloscope can directly check the waveform of the electrical signal, analyze and study the change rules of the electrical signal, and can also test a variety of electrical quantities, such as amplitude, frequency, phase difference and time. If equipped with a sensor, it can also measure some non-electrical quantities. This article takes the SR-8 dual-trace oscilloscope as an example to introduce its panel knobs, dual-trace oscilloscope usage methods and usage precautions.

SR-8 Dual-Trace Oscilloscope Application
The SR-8 dual-trace oscilloscope is a fully transistorized portable general-purpose oscilloscope. Its bandwidth is DC15MHz, and it can simultaneously observe and measure the instantaneous process of two different electrical signals, and display their waveforms on the screen together for analysis and comparison. The dual-trace oscilloscope can superimpose two electrical signals and then display them, and can also be used as a single-trace oscilloscope.

①Y-axis system
The front expander of the Y-axis system is composed of two circuits with similar structures. It can observe and measure two time signals at the same time by electronic switches. Therefore, the functions and accuracy of the front channels YA and YB of the dual-trace oscilloscope are the same.
a. Input sensitivity: 10mV/div～20V/div, divided into 11 levels according to 1-2-5. When in the calibration position, the error is ≤5%, and the fine-tuning gain ratio is ≥2.5:1.
b. Bandwidth. "AC" (AC coupling): 10Hz～15MHz, ≤3dB; "DC" (DC coupling): 0～15MHz, ≤3dB.
c. Input impedance. Direct input, 1MΩ/35pF. Probe coupling (10:1), 10MΩ/15pF.
d. Maximum input voltage. DC coupling: 250V[DC+(ACP-P)]. AC coupling: 500V(ACP-P).
②X-axis system
a. Scanning speed: 0.2μs/div～ls/div, divided into 21 levels according to 1-2-5, error ≤5%. Fine adjustment ratio＞2.5:1. When expanding × ten, its fastest scanning speed can reach 20ns/div. Except for the 0.2μs/div level ≤15%, the error of other levels is ≤ten%.
b. Bandwidth. OHz～500kHz, ≤3dB.
c. Input impedance. 1MΩ/35pF.
d. X external sensitivity ≤3V/div.
③ Dual-trace oscilloscope host calibration signal
a. Waveform, rectangular wave.
b. Frequency: 1kHz, error ≤2%
Rising: 1V, error ≤3%.
Working environment: temperature is (-ten to +40)℃; relative humidity is 85%. Power supply: voltage is 220V±ten%, frequency is 50Hz±4%. Power consumption: about 55V.A. Continuous working time: 8h.

SR-8 dual-trace oscilloscope panel knobs and instructions
Before using the dual-trace oscilloscope, a novice must carefully read the oscilloscope manual to understand the operation and use of each button on the dual-trace oscilloscope panel, so that he can use the dual-trace oscilloscope accurately and skillfully during the measurement process. The SR-8 dual-trace oscilloscope panel diagram is shown in the figure.

SR-8 dual-trace oscilloscope panel diagram
① Dual-trace oscilloscope display parts
a. "Power on". Control the main power switch of the SR-8 dual-trace oscilloscope. When this switch is turned on, the indicator light will light up immediately, indicating that the dual-trace oscilloscope is powered on.
b. "Indicator light". It is an indicator of power on.
c. "*-Brightness". It is used to adjust the brightness of the waveform or light spot of the dual-trace oscilloscope. When rotating clockwise, the brightness increases; when rotating counterclockwise, the brightness decreases until the brightness disappears.
d. "⊙-Set". It is used to adjust the clarity of the waveform or light spot of the dual-trace oscilloscope.
e. "○-Auxiliary Set". It cooperates with the "Set" control knob to adjust the clarity of the waveform or light spot in the effective working surface of the dual-trace oscilloscope display.
f. "⊕-Scale brightness". It is a control knob used to adjust the brightness of the scale lines on the oscilloscope coordinate axis. When rotating clockwise, the scale line brightness will increase; otherwise, it will decrease.
g. "Trace search". When the key is pressed down, the light spot on the screen returns to the display area, and then the address position of the light spot is found. In practice, its effect is to reduce the magnification of the Y-axis and X-axis expanders, and at the same time put the time base generator in a self-excitation state.
h. "Calibration signal output". This socket is a BNC type. The calibration signal is output from this socket during the use of the dual-trace oscilloscope.
②Dual-trace oscilloscope Y-axis plug-in
a. Display mode switch. It is used as a control part to change the working status of the two Y-axis front expanders YA and YB. It has five effect positions.
"Alternate", YA and YB channels are in alternate working state. Its alternate working change is controlled by the scanning repetition frequency to display the dual-trace signal.
"YA", YA channel expander works alone. The oscilloscope is used as a single-trace oscilloscope.
"YA+YB", YA and YB channels work together. Through the "polarity" effect switch of the YA channel, the sum or difference of the input signals of the two channels can be displayed.
"YB", YB channel expander works alone, "intermittent" is controlled by the self-excited vibration frequency of the electronic switch (about 200kHz), so that the two channels work in parallel, and then the dual-trace signal is displayed.
"Intermittent", the electronic switch turns on the YA and YB channels at a fixed frequency of 250kHz, and then the dual-trace display is completed. When the signal frequency is low during the use of the dual-trace oscilloscope.
b. "D-┻-AC" - Y-axis input selection switch. It is used to select the coupling method of the measured signal to the input end of the oscilloscope. When it is set to the "DC" position, the input signal rich in DC power can be queried. When it is set to the "AC" position, only the AC power is coupled, and the DC power rich in the input signal is cut off. When the switch is set to the "┻" position, the input end of the Y-axis expander is cut off from the measured input signal, and the input end of the expander in the dual-trace oscilloscope is grounded. At this time, it is very easy to check the display position of the ground potential. It has the advantage of simple operation and is usually used as a reference in testing DC power.
C. "Fine Adjustment Y/div" - Sensitivity selection switch and its fine adjustment device. The sensitivity selection switch is connected to the shaft device. The black knob is the coarse adjustment device for the Y-axis sensitivity. There are 11 levels from 10 mV/div to 20V/div. The most appropriate level can be selected according to the fluctuation of the measured signal for observation.
When the red knob of the "fine adjustment" device is turned clockwise to the full scale, that is, the "calibration" position, the fluctuation value of the measured signal can be read according to the nominal value on the panel indicated by the black knob.
The red knob of "fine adjustment" is a fine adjustment device used to continuously adjust the input signal gain. When this knob is turned counterclockwise to the full scale (non-calibration position), its change range should be greater than 2.5 times. Therefore, the "fine adjustment" device can be continuously adjusted to obtain the sensitivity coverage between each level. Only when doing quantitative testing, this knob should be in the "calibration" position of the full clockwise scale.
d. "Balance". When the input stage circuit of the Y-axis expander is unbalanced, the flashing light spot or waveform will make an axial displacement of the Y-axis with the "fine adjustment" of the "V/div" switch. The "balance" controller can adjust this change to the minimum.
e. "↓↑-Y-axis shift". It is used to adjust the vertical position of the waveform or light spot in the use of the dual-trace oscilloscope. When the flashing position is higher than the required position, it can be adjusted in the counterclockwise direction to move the waveform downward. If the position is too low, it can be adjusted in the clockwise direction to move the flashing measured waveform upward to the required position.
f. "Polarity pull-YA". In the YA channel system, there is a polarity change push-pull switch. When this switch is pulled out during the use of the dual-trace oscilloscope, the YA channel flashes in reverse phase.
g. "Internal trigger pull-YB". This push-pull switch is used to select the internal trigger source. In the "press" position (normal), the trigger signal of the scan is taken from the input signal of the YA and YB channels after expansion. In the "pull" position, the trigger signal of the scan is only taken from the input signal of the YB channel, which is usually suitable for the display of two tracking signals with time connection.
h. Y-axis input socket. It is a BNC type socket. When the oscilloscope is used, the measured signal is input directly or through the probe.
③ Oscilloscope X-axis plug-in
a. "Fine adjustment t/div" - scanning speed switch. When the voltage and time relationship curve is displayed with a dual-trace oscilloscope, the Y axis usually indicates voltage and the X axis indicates time. The
moving speed of the light spot along the X axis on the oscilloscope screen is determined by the scanning speed switch "t/div". When the "fine adjustment" potentiometer on the switch is turned clockwise to full scale and the switch is connected, it is the "calibration" position. At this time, the nominal value indicated on the panel is the scanning speed value.
b. "Fine adjustment". The red knob placed on the scanning speed selection sleeve shaft switch is a fine adjustment device used to continuously change the scanning speed of the dual-trace oscilloscope. When this knob is turned counterclockwise to full scale, it is in the non-calibration position, and the sweep speed change plan should be greater than 2.5 times. When it is turned clockwise to full scale and the switch is turned on, it is the "calibration" position.
C. "Calibration". This is a sweep speed calibration device. When the oscilloscope is used, the sweep speed can be calibrated with a high-precision time-scale signal.
d. "Expand pull × ten". The expansion device of the dual-trace oscilloscope is a push-pull switch. In the "press" position, the instrument is used normally. In the "pull" position, the X-axis expansion appears, which can be expanded ten times. At this time, the nominal value of the sweep speed on the panel should be calculated ten times, and the allowable error value after expansion should be increased accordingly.
e. "→-X axis shift". It is a sleeve shaft knob used to adjust the position of the oscilloscope's time base or spot. When rotated clockwise, the time base moves to the right; when rotated counterclockwise, the time base moves to the left. The small knob on its sleeve shaft is a fine-tuning device.
f. "External trigger X external connection" socket. It is a BNC type socket. When the oscilloscope is in use, this socket can be used as a socket for connecting an external trigger signal. It can also be used as an external signal input socket for the X-axis expander.
g. "Level". It is used to select the trigger point of the input signal waveform so that the scan is initiated at a certain required level. When the position of the trigger level jumps over the trigger area, the scan will not be initiated and no waveform will appear on the screen.
h. "Stability". It is a semi-adjustment device. When the dual-trace oscilloscope is used, this device is used to adjust the working state of the scan circuit to achieve a stable trigger scan. After adjustment, it does not need to be adjusted frequently.
i. "Inside and outside" - trigger source selection switch. In the "inside" position, the scan trigger signal is taken from the measured signal of the Y-axis channel; in the "outside" position, the trigger signal is taken from the external signal source, that is, the external trigger signal from the "external trigger × external connection" input terminal.
j. "ACAC (H) DC" - trigger coupling method selection switch. There are three coupling methods. When the external trigger input method is selected, the coupling method of the input signal can also be selected at the same time.
The "AC" trigger method is an AC coupling method. Since the DC power of the trigger signal has been cut off, its trigger function is not affected by the DC power.
The "AC(H)" trigger mode is a low-frequency suppression state. It is coupled through a high-pass filter, and the high-pass filter suppresses low-frequency noise or low-frequency signals. The
"DC" trigger mode is a DC coupling method, which can be used to trigger and scan slowly changing signals.
k. "High-frequency trigger active" - ​​trigger mode switch. Its function is to change the trigger mode according to different purposes or uses. When it is set to "high frequency", the scan is in the "high frequency" synchronization state, and a self-excitation signal of about 50kHz is generated in the machine to perform synchronous scanning on the measured signal. This method is usually used to query the waveform of higher frequency signals. When the switch is set to "trigger", it is a commonly used trigger scanning method for querying pulse signals. The scan is triggered by the input signal from the Y axis or external touch source. When the switch is set to "active", the scan is in the self-excitation state. There is no need to adjust the "level" knob, and the scan line can be automatically displayed. It is suitable for observing lower frequency signals.
"+ -" - trigger polarity switch. It is used to select the rising edge or falling edge of the trigger signal to trigger the scan.
The "+" scan is triggered by the rising edge of the input trigger signal waveform and initiates the scan.
"-" scanning is triggered by the falling edge of the input trigger signal waveform and initiates the scanning.
④
The power socket on the rear panel is used for the main power input of the dual-trace oscilloscope. Use the power plug provided by this machine to plug the fuse holder and use a 1A fuse tube.
⑤
"YA gain calibration" and "YB gain calibration" on the bottom cover plate adjust the sensitivity of the YA and YB channels respectively. When
using the oscilloscope,
adjust the baseline and place each control element in the position shown in the table. If you can't see the light trace, identify the direction of the light trace, then release the button to move the light trace to the appropriate position on the fluorescent screen.