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The use of digital oscilloscope
- Apr 23, 2018 -

Digital oscilloscope

Although the number, model and variety of the oscilloscope are various, its basic composition and function are much the same. This paper introduces the use of general oscilloscope.

1. Panel introduction.

1. Brightness and focus knob.

The brightness adjustment knob is used to adjust the brightness of the light trace (some oscilloscopes are called "luminance "). When used, the brightness should be appropriate, and if it is too bright, it can damage the oscilloscope. The focus adjustment knob is used to adjust the focus (thickness) of the light trace.

2. Signal input channel.

Oscilloscope is commonly used for double trace oscilloscope, two input channel, channel 1 (CH1) and 2, respectively (CH2), can be connected to an oscilloscope probe, respectively, then the oscilloscope enclosure grounding, probe to measure parts under test.

3. Channel selection key (vertical mode selection)

The commonly used oscilloscope has five channel selection keys:

(1)CH1: channel 1 is displayed separately;

(2)CH2: channel 2 is displayed separately;

(3)ALT: alternate display of two channels;

(4)CHOP: intermittent display of the two channels, which is used for the double trace display when the scanning speed is slower;

(5)ADD: signal superposition of two channels. In maintenance, select channel 1 or channel 2 for more.

4. Vertical sensitivity adjustment knob.

Adjust the vertical deflection sensitivity, should be based on the location of the input signal amplitude adjustment knob, the knob indicator values (such as 0.5 V/div, per said vertical amplitude of 0.5 V) multiplied by the measured signal in the vertical direction is the number of the screen, it is concluded that the extent of the measured signal.

5. Vertical adjustment knob.

Used to adjust the position of the measured signal light in the vertical direction of the screen.

6. Horizontal scan adjustment knob.

Horizontal velocity regulation, should be based on the frequency of the input signal is the position of the adjusting knob, the knob indicating numerical (such as 0.5 ms/div, horizontal direction per time of 0.5 ms), the number multiplied by the measured signal a cycle of, namely it is concluded that the signal cycle, can also be converted to frequency.

7. Horizontal position adjustment knob.

Used to adjust the position of the measured signal light in the horizontal direction of the screen.

8. Trigger mode selection.

Oscilloscopes usually have four modes of triggering:

(1) NORM: when there is no signal, there is no display on the screen; When there is a signal, the stable waveform is displayed with the level control.

(2) AUTO (AUTO) : when there is no signal, the light trace is displayed on the screen; The stable waveform is displayed with the level control with the signal;

(3) TV field (TV) : used to display TV signal;

(4) peak automatic (p-p AUTO) : when there is no signal, the light trace is displayed on the screen; When there is a signal, there is no need to adjust the level to obtain a stable waveform display. This method is only used in some oscilloscopes (such as CALTEK kartek CA8000 series oscilloscope).

9. Trigger source selection.

The oscilloscope trigger source has both internal and external trigger sources. If the external trigger source is selected, the trigger signal should be input from the external trigger source, which is rarely used in home appliance maintenance. If you select the trigger source, generally choose the channel 1 (CH1) or 2 (CH2), should choose according to the input signal channel, if the input signal channel selection of channel 1, trigger source also should choose to channel 1.

2. Measurement method.

1. Measurement method of amplitude and frequency (taking the calibration signal of the oscilloscope as an example)

(1) insert the oscilloscope probe into the channel 1 socket and place the attenuation on the probe into "1";

(2) place the channel selection in CH1, and the coupling mode is placed in DC;

(3) insert the probe probe into the hole of the calibration signal source, and the light trace appears on the oscilloscope screen;

(4) adjust the vertical knob and horizontal knob to stabilize the waveform displayed on the screen, and place the vertical and horizontal fine tuning in the calibration position;

(5) read the number of the waveform in the vertical direction, multiply by the indicator value of the vertical attenuation knob, and get the amplitude of the calibration signal;

(6) read the number of each cycle in the horizontal direction, multiply by the indicator value of the horizontal scan knob, and get the period of the calibration signal (the inverse of the period is the frequency);

(7) general calibration signal frequency of 1 KHZ, the range of 0.5 V, used to calibrate oscilloscope internal oscillator frequency, if abnormal, the oscilloscope should be adjusted (internal) corresponding potentiometer, until is consistent.

2. Example of oscilloscope application (taking measurement of 788 mobile phone 13MHz clock pulse as an example)

The 13MHz clock signal in the mobile phone is a necessary condition for starting up, so it is necessary to constantly measure the 13MHz clock signal in maintenance. The steps are as follows:

(1) open the oscilloscope, adjust the brightness and focus knob, and make the screen display a horizontal bright line with moderate brightness and good focus;

(2) calibrate the oscilloscope according to the above method, and then place the coupling mode in AC;

(3) connect the earthing clip of the oscilloscope probe to the location of the mobile circuit board, and the probe is inserted into the CPU of 788 mobile phone;

(4) turn on the power of the mobile phone, press the power button, adjust the vertical scan water and sweep the knob, and observe whether there is a stable waveform on the screen. If not, it generally indicates that there is no 13MHz.