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.
(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.
Basic principle and measuring method of analytical oscilloscope
Oscilloscope is a widely used electronic measuring instrument.It can transform the invisible electric signal to the naked eye into the visible image, which is convenient for people to study the change process of various electric phenomena. A oscilloscope USES a narrow beam of high-speed electrons, struck on a surface coated with fluorescent material, to produce tiny points of light (this is how a traditional analog oscilloscope works). Under the action of the measured signal, the electron beam ACTS like the tip of a pen and can plot the instantaneous value of the measured signal on the screen. Use oscilloscope to be able to observe all sorts of different signal amplitude the waveform curve that changes with time, still can use it to test all sorts of different electric quantity, be like voltage, current, frequency, phase difference, amplitude modulation.
(1) Presetting: rotate the brightness knob counterclockwise to the bottom, move the vertical and horizontal position to the middle, and the attenuation is placed in the highest level, and the scanning is placed in the "outer X gear";
(2) Turn on the power again, and wait for one or two minutes after the light is on for preheating before carrying out relevant operations;
(3) First adjust the grayscale, then focus, and then adjust the horizontal and vertical displacement to make the highlights in the center of the appropriate area;
(4) Adjust scanning, scanning fine tuning and X gain, observe scanning;
(5) Unplug the outer X gear to the appropriate position in the scanning range file, and observe the voltage waveform in the vertical direction changing according to the law of sines and cosines provided by the machine;
(6) To study the external voltage from Y input and indirectly into the oscilloscope, adjust each gear to the appropriate position, you can observe the voltage waveform (and time changes of the image)(synchronous polarity switch can make the starting point of the image from the positive half cycle or negative half cycle start;
(7) If you want to observe the vertical offset of bright spot (such as when applied with a constant current voltage), you can adjust the scan to "outer X gear". (different oscilloscopes may operate in different ways), etc.
(1) Insert the oscilloscope probe into the socket of channel 1, and put the attenuation on the probe into "1" gear;
(2) Put channel selection in CH1 and coupling mode in DC file;
(3) Insert the probe into the pinhole 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 put the vertical fine-tuning and horizontal fine-tuning in the calibration position;
(5) The number of cells occupied by the waveform in the vertical direction is multiplied by the indicating value of the vertical attenuation knob to obtain the amplitude of the calibration signal.
(6) The number of bars occupied by each period of the waveform in the horizontal direction is multiplied by the indicating value of the horizontal scanning knob to obtain the period of the calibration signal (the inverse of the period is the frequency).
(7) 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.
How to use digital oscilloscope to distinguish analog bandwidth from digital real - time bandwidth？
Bandwidth is one vital index of oscilloscope. Bandwidth of analog oscilloscope is one certain value, however, bandwidth of digital oscilloscope has two kinds, analog bandwidth and digital real-time bandwidth. Digital oscilloscope to repeating the signal in a sequential sampling and random sampling technology can achieve the maximum bandwidth of the oscilloscope digital real-time bandwidth, real-time digital bandwidth and the highest frequency and digital waveform reconstruction technology related factor K = (digital real-time bandwidth digital highest rate/K), generally not directly given as an indicator. It can be seen from the definition of the two kinds of bandwidths that the analog bandwidths are only suitable for the measurement of repeated periodic signals, while the digital real-time bandwidths are suitable for the measurement of repeated signals and single signals at the same time.
The manufacturer Zhengzhou Defy claims the bandwidth of oscilloscope can achieve how many megabytes, it is analog bandwidth actually, digital real time bandwidth is below this value. For example, if the bandwidth of an oscilloscope is 500MHz, it actually means that its analog bandwidth is 500MHz, while the highest digital real-time bandwidth can only reach 400MHz, which is much lower than the analog bandwidth. Therefore, when measuring a single signal, it is necessary to refer to the digital real-time bandwidth of the digital oscilloscope, otherwise it will bring unexpected errors to the measurement.