Basic principle and measuring method of oscilloscope
Oscilloscope is one kind of electrical measurement equipment with wide application. It could transfer invisible electrical signal to visible image to facilitate people research change processes of all kinds of electricity phenomenon. Oscilloscope use narrow electron beam which consists high-speed electronics and project onto screen coated with fluorescent substance to produce small spot (this is original working principle of analog oscilloscopes. Under the function of measured signal, electronics like the point of a pen which could on screen describe change curve of measured signal during instantaneous value. An oscilloscope can be used to observe the waveform curves of various signal amplitudes varying with time. It could also be used to measure various electricity, such as voltage, current, frequency, phase, amplitude modulation and etc.
(1) pre-adjusting: counterclockwise rotate the brightness button to the bottom, shift vertical and horizontal positions to the middle, set the attenuation gear at the highest level, place scan “outside X gear”
(2) turn on the power, do following steps waiting for one or two minutes after the indicator light is on
(3) adjust luminance first, then adjust the focus, adjust vertical and horizontal displacement to make the light point in center of suitable area.
(4) adjust scan, scan fine tuning and X gain, observe scan.
(5) adjust outside X gear to suitable scan range, observe the voltage waveform according to sine and cosines law on vertical direction inside the device.
(6) Connect the applied voltage to be studied to oscilloscope through Y input and earth. Adjust all gears to suitable position and observe waveform (the picture changes with time) (the synchronous polarity switch can make the starting point of the image start from positive half cycle or negative half cycle.)
(7) If you want to observe the vertical migration of light spot (with one added DC voltage), could adjust scan to “outside X gear”.
In general, the frequency of the calibration signal is 1kHz and the amplitude is 0.5v, which is used to calibrate the internal scanning oscillator frequency of the oscilloscope. If it is abnormal, the corresponding potentiometer of the oscilloscope (internal) should be adjusted until it is consistent.
Digital oscilloscope generally provides online display of root mean square value, its accuracy is generally what?
For oscilloscope amplitude measurement accuracy, many people use A/D digit to measure. In fact, it varies depending on the oscilloscope bandwidth you use, the actual sampling rate Settings, and so on. If the bandwidth is insufficient, the amplitude measurement error itself will be very large; if the bandwidth is sufficient, the sampling setting is very high, and the actual amplitude measurement precision is not as good as that of the sampling rate when the sampling rate is low (you may refer to the user's manual of the oscilloscope, which may give the actual effective digits of an oscilloscope at different sampling rates). In general, oscilloscope measurement amplitude, including root mean square value accuracy is often less than the multimeter, similarly, measuring frequency it is less than the frequency counter.
What are the different voltage measurements for different oscilloscope probes?
It is recommended to use the original probe for better impedance matching. If different voltage probes are used, the measurement value will sometimes be larger and sometimes smaller, because the bandwidth of the probe will be very different, the bandwidth itself and flatness will be different, and the length of the ground wire will also have some small differences. Assuming, of course, that the decay is the same.