How to choose digital oscilloscope?
How to choose oscilloscope reasonably as the price difference of oscilloscope nearly 50 times between low-grade with high-grade.
The relationship between the bandwidth selection and the highest signal frequency to be measured is needed if accurate measurements are required. Let’s check below example, there is one pulse signal with 50 MHZ, to ensure scope of signal and accuracy of rising delay, the bandwidth of oscilloscope should be 3-5 times of measured signal’s frequency and the accurate measurement should be 8-10 times or more.
Sine wave: as usual, need more than 5 sampling sites during one period as the waveform will be more close to the actual one with more sampling sites.
Pulse wave: rising delay should be more than 5 sampling sites.
Accurate measurement rising delay should be more than 10 sampling sites.
3. Record length: record length=sample*scanning speed*10, it could also be called waveform observation time.
4. Trigger function: ensure that the measured signal can be captured and synchronized to facilitate the observation and analysis of the measured waveform
Trigger methods: automatic trigger, normal trigger and single trigger
Two kinds of trigger function
1) Edge trigger: all digital oscilloscopes have this function, It refers to positive edge, negative edge trigger, window trigger, before trigger and after trigger.
2）Smart trigger：This is considered perfectly in high-grade oscilloscopes. currently there are: delay trigger, sequence trigger, burr trigger, interval trigger, leakage logic surface trigger, TV trigger, this trigger......
5. Analysis function: Should have very strong automatic processing, computation, test and analysis ability of signal
1）Shape and parameters pass/fail automatic test function
2) Advanced function processing: average, differential, polar, exponential, logarithm, power, square root, envelope, high score system, etc.
3）FFT spectrum operation function from 10k-4m point, with power spectrum, power density, phase vector, imaginary part, real part and other measurements;
4）The direct square analysis can be used for the stability calculation of the direct square test signal from 500 points to 8M points according to various parameters
5）Waveform parameter Trend analysis function, Jitter and time analysis;
6) Could open 2-8 windows to observe original waveform and processed waveform simultaneously.
X-Y display and X-Y+X-T and Y-T display are provided, can also carry on the vernier measurement makes it specially suitable for vector diagram analysis of digital communication signals.
6. Record and print signal
1) Can be stored in a test line on a floppy and hard disk, and can be read on a PC. Some digital oscilloscopes are equipped with built-in, convenient to print and analyze long time signal;
2) Some oscilloscopes also provide VGA interface.
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
Principle of handheld oscilloscope
A hand-held oscilloscope USES a narrow beam of high-speed electrons to produce tiny points of light on a screen coated with fluorescent material. Under the action of the measured signal, the electron beam ACTS like the tip of a pen and can draw the curve of the instantaneous value of the measured signal on the screen.The use of oscilloscope can observe various different signal amplitude changes with time waveform curve, but also can use it to test a variety of different electricity, such as voltage, current, frequency, phase difference, adjustment amplitude and so on.
How to choose handheld oscilloscope?
Select handheld oscilloscope mainly pay attention to several indicators, bandwidth, storage depth, sampling rate, waveform update rate, isolation channel, display, language, easy operation, and some other kinetic energy (waveform recording, 232/422/485/CAN/I2C/SPI bus decoding) bandwidth: bandwidth is 100M, 200M commonly now, since buy at least buy 100M, each manufacturer is about the same; Storage depth: this various manufacturers vary from 10K to dozens of M have, in general, a few hundred K is enough, too small waveform expansion can not see, square wave are changed into triangular wave. Sampling rate: as long as this index reaches more than 5 times of the bandwidth, all manufacturers have basically reached; Waveform update rate: this index is also a very important index, waveform update rate is too low will lead to some abnormal signals can not be seen; Isolation channel: in the handheld oscilloscope, this is very important, can reduce the risk of accidental short circuit, electric shock, etc., can also reduce the parasitic capacitance during testing, etc., but fortunately, most manufacturers are isolated.