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.
Window technology in frequency domain of oscilloscope
The FFT function of oscilloscope USES window technology to reduce the influence of spectrum leakage.Before executing the DFT, the DFT frame is multiplied by a window function of the same length for each sample.Window functions are usually bell-shaped and reduce or eliminate discontinuities at both ends of the DFT frame.
The four most commonly used window functions are listed below for recommended purposes:
(1) Rectangle - measures a sudden transient signal in which the signal level before and after the event is almost equal
(2) Hamming – measurement of sinusoidal, periodic, or narrow-band random noise, where the signal level before and after the event is significantly different
(3) Hanning - measuring amplitude accuracy (low at analytical frequency) with significantly different levels of transient or burst signals before and after an event
(4) Blackman/Harris - measure frequency amplitude, measure waveform with single frequency, search for higher harmonics
Causes of damage to oscilloscope current probe
The reasons for the damage of the current probe, the methods for preventing the damage and the instructions for using the current probe can be summarized as follows:
Circuit board damage caused by plugging current probe after current amplifier is turned on.
Protection against damage: - do not plug or unplug the current probe while it is still active.
Magnetic ring is fragile material, drop or use too hard when it is easy to damage. Damaged/damaged magnetic rings will result in inaccurate or no longer detectable current.
How to prevent damage and use: - avoid dropping or using too hard.
Magnetic ring coil is thin, over current will cause coil burn out.
Prevent damage method: - avoid the load flow when using.
The current clamp is not aligned, and cracks will make the test inaccurate or unable to measure the current. Be careful how you push the clip.
Method to prevent damage: - when using the current clamp to align. Be careful and be careful when pushing the clip.
The cable can be easily damaged if it is pulled too hard or twisted.
Prevention of damage: - do not use the cable too hard to pull, twist, etc.