Advanced application of SMT digital oscilloscope
1. Advanced applications of vertical systems
(1) Channel settings. The vertical menus of the CH1 and CH2 channels of the oscilloscope are independent. Each item must be set separately for a different channel, but the items and operation methods of the two channel function menus are completely the same. Now take the CH1 channel as an example.
Press the CH1 key, the function menu of the CH1 channel is displayed on the right side of the screen.
① Set the channel coupling mode. If the signal under test is a sinusoidal signal with a DC offset, the setting method is: press CH1-Coupling-AC/DC/Ground, respectively set to AC, DC and ground coupling modes, pay attention to the waveform display and the lower status bar channel Change of coupling mode symbol.
② Set the channel bandwidth limit. Suppose the signal under test is a pulse signal with high frequency oscillation. The setting method is:
Press CHI-bandwidth limit t off/on, and set the bandwidth limit to off/on respectively. The former allows the high-frequency components contained in the measured signal to pass through, while the latter prevents and isolates the high-frequency components greater than 20 MHz. Pay attention to the waveform display and the lower status bar, and the change of the bandwidth limit symbol after the vertical attenuation gear.
Adjust the probe ratio. In order to match the probe attenuation coefficient, you need to adjust the probe attenuation ratio in the channel function menu. For example, the probe attenuation coefficient is 1. :1. The ratio of the oscilloscope input channel probe should also be set to 10x to avoid errors in the displayed gear information and the measured data.
<b>PCBA processing 009</b>
① Vertical gear adjustment setting The vertical sensitivity adjustment range is 2 mV/div~5 V/divo gear adjustment is divided into two modes: coarse adjustment and fine adjustment. Coarse adjustment adjusts the vertical gear sensitivity in steps of 2 mV/div, 5 mV/div, 10 mV/div v 20 mV/div,…, 5 V/div. Fine-tuning refers to further fine-tuning in the current vertical gear. If the input waveform amplitude is slightly larger than the full scale in the current gear and the waveform display amplitude of the next gear is slightly lower, fine adjustment can be used to improve the waveform display amplitude to facilitate the observation of the details of the signal.
② Waveform inversion setting. When the waveform inversion is off, the normal measured signal waveform is displayed; when the waveform inversion is turned on, the displayed waveform of the measured signal is inverted by 180% with respect to the ground potential.
③ Digital filter setting. Press the “No. 4” function menu operation key corresponding to the digital filter to open the Filter (digital filter) sub-function menu, select the filter type, turn the multi-function knob to adjust the upper and lower limits of the frequency; set the bandwidth range of the filter, etc.
(2) MATH (mathematics operation) key function. The math operation (MATH) function menu and description are shown in Figure 1.4.15 and Table 1.4.3. It can display the results of addition, subtraction, multiplication and FFT (Fourier Transform) operations of the CHI and CH2 channel waveforms. Mathematical calculation results can also be measured by grid or cursor,
(3) REF (reference) key function. Under the condition of the reference waveform of the circuit operating point, the measured waveform can be compared with the reference waveform sample through the menu of the REF button to determine the cause of the fault.
