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.
Are the different oscilloscope probes interchangeable?
It's interchangeable as long as it's the same interface
Note, however, that the matching capacitance of the probe matches that of the oscilloscope
So maybe it needs to be adjusted
The other is impedance matching of the probe.The impedance matching part of the probe should be adjusted prior to use.Usually there is an adjustable capacitance at one end of the probe near the oscilloscope, and some probes are near
The probe also has an adjustable capacitance at one end.They are used to adjust the impedance matching of the oscilloscope probe.If the impedance does not match, the measured waveform will be distorted. The method of adjusting the impedance matching of oscilloscope probe is as follows: firstly, the input selection of oscilloscope is played on GND, and then the Y-axis displacement knob is adjusted to make the scan line appear in the middle of the oscilloscope. Check if the scan line is horizontal (i.e., if it coincides with the horizontal center line of the oscilloscope), if not, adjust the horizontal balance knob (usually the analog oscilloscope has this adjustment terminal, in the hole, need to use a screwdriver into the adjustment.Digital oscilloscope need not be adjusted).
Then, the input selection of the oscilloscope is connected to the dc coupling, and the oscilloscope probe is connected to the test signal output end of the oscilloscope (generally, the oscilloscope has this output terminal, usually the square wave signal of 1KHz), and then the scanning time knob is adjusted to make the waveform display for about 2 cycles. Adjust the Y-axis gain knob so that the peak - peak of the waveform is about 1/2 screen width.Then look at the top and bottom sides of the square wave to see if they are horizontal.If the phenomenon of overshoot and tilt occurs, it means that the matching capacitance on the probe needs to be adjusted.Adjust it with a small screwdriver until the waveform on both sides is level and there is no overshot.Of course, due to the quality of the oscilloscope probe, may not be adjusted completely without distortion effect, then can only be adjusted to the best effect.
Twelve tips of oscilloscope you must know
(1). The most valuable index of oscilloscope: Bandwidth, class parameter
(2). How high is the sampling rate?
Generally speaking, the sampling rate is 5 times the bandwidth, such as 200M oscilloscope, with 1G sampling rate is ok.
The pursuit of higher sampling rate is nothing more than to catch small burrs, but these high frequency burrs have been filtered out in the bandwidth layer, and higher sampling rate cannot bring good benefits.
(3) What is the difference between normal trigger and automatic trigger?
Normal trigger, it will sample the waveform only with trigger event satisfies the condition.
Automatic trigger, after wait for a moment, if there is no eligible trigger events occur, the oscilloscope will force the trigger function and start sampling. As random trigger position, the waveform will show unsteady. If above sequence occurs, please adopt normal mode.
(4) How to catch abnormal signal under uncertain condition?
You could catch the signal with template trigger.
When the template trigger is turned on, the template actually comes as a layer. It will constantly detect whether there is waveform that will touch the area of the template. When there is waveform that touches the template, a signal will be detected and it will be filtered and displayed.
(5) Are those channels isolated of oscilloscope?
No. Bottom of oscilloscope is connected with the earth, it could not be connected directly with the zero line.
To isolation, transformer could directly measure 220V city power, however, this is not recommended, and the safest and correct method it to use difference probes.
(6) Which is more accurate between oscilloscope and multimeter when measure voltage?
The vertical resolution ratio of general oscilloscopes is 8 bits. The measure accuracy is related to vertical resolution ratio and vertical gear.
The accuracy of multimeter is much higher. ADC of six and a half meter is up to 24 bits. That of handheld meter is far more than 8 bits. The voltage measured by the multimeter is more reliable.
(7) Differences between probe X1 and gear X10?
Two important points
Different attenuate bandwidth, signal x1 gear amplitude does not decay. X10 gear signal decay to 1/10 of original signal.
Different bandwidth, bandwidth of X1 gear is almost 10M, and 250M for X10 gear.
(8) Does the general oscilloscope probe need to be calibrated periodically?
The standard does not have a specific metering specification for the probe, but for passive probes, at least the probe compensation must be adjusted when the probe is replaced and the probe switches channels.
(9) What is main factor determines the price of oscilloscope probe ?
The main determinants of price are, of course, bandwidth and functionality.
There are many types of oscilloscope probe, different performance, such as high voltage, difference, active high-speed probe and so on, the price also from a few hundred yuan to nearly ten thousand dollars.
The probe is part of the oscilloscope contact circuit. A good probe can provide the fidelity required for testing.To do this, even passive probes must have a very large number of passive device compensation circuits (RC networks) inside.
(10) Is there any way to measure the working condition of high frequency transformer or inductor core by oscilloscope?
Can rely on the oscilloscope's own power analysis software to do, there is a function - B-H curve analysis, it can reflect the working state of the magnetic core, but also can measure the dynamic inductance value, and get the core loss.
(11) Can an oscilloscope perform Fourier decomposition?
Modern digital oscilloscope mostly has FFT function, but need to pay attention to FFT can analyze the number of points, which directly determines the accuracy of FFT analysis results, avoid spectrum leakage.ZDS2000 series oscilloscope is equipped with 4M point FFT analysis.
(12) Can oscilloscope filter? Such as low pass filtering of PWM wave?
Oscilloscopes typically have a 20MHz bandwidth limit, and this is a hardware filter.Some oscilloscopes also support software filters with adjustable cutoff frequencies.The ZDS2024Plus is adjustable from 100Hz to 100MHz.