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 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.
Digital oscilloscope automatic verification system
With the development of electronic technology, digital oscilloscope with the digital technology and software greatly expanded the ability to work, the early products of low sampling rate, there is a big dead zone time, less than be improved screen refresh rate low, difficult to observe before modulation signal, communication eye diagram, such as composite video signal is more and more easy to observe. Digital oscilloscope can calculate and analyze data, which is especially suitable for capturing all details and abnormal phenomena in complex dynamic signal.In order to make the oscilloscope work in a qualified state, it is an urgent task for the test engineer to verify the oscilloscope regularly, quickly and comprehensively and to ensure the traceability of its value.
Manual verification is inefficient and prone to errors. The verification of each oscilloscope requires the test engineer to read a lot of data.The automatic test system has the characteristics of accurately and quickly measuring parameters, intuitively displaying test results, automatically storing test data and so on.It will be the trend of instrument verification to realize program control verification of oscilloscope with automatic test system.
GPIB, VXI and PXI are the standard buses of automatic test system. GPIB has won the recognition of users for its stable performance, convenient operation and low price.Here, GPIB is selected as the bus of the test system.
The hardware of automatic verification system of digital oscilloscope based on GPIB is composed of GPIB controller, FLUKE5500A, verified digital oscilloscope, PC and printer