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.
Oscilloscope chooses appropriate storage depth, also called record length
Storage depth is a measure of how many sampling points an oscilloscope can store. If you need to capture a pulse string continuously, you need the oscilloscope to have enough memory to capture the entire event. The required storage depth can be calculated by dividing the length of time to be captured by the sampling rate needed to accurately reproduce the signal.
Storage depth is closely related to sampling rate.The depth of storage you need depends on the total time span to be measured and the required time resolution.
Modern oscilloscopes allow users to select record lengths to optimize the details of some operations. Analysis of a very stable sinusoidal signal requires only 500 points of record length;But to parse a complex stream of digital data, you need a million points or more of record length.
Capturing the effective trigger of the signal in the right position can usually reduce the storage capacity of the oscilloscope.
What are the different voltage measurements for different oscilloscope probes?
It is recommended to use the original probe for better impedance matching. If different voltage probes are used, the measurement value will sometimes be larger and sometimes smaller, because the bandwidth of the probe will be very different, the bandwidth itself and flatness will be different, and the length of the ground wire will also have some small differences. Assuming, of course, that the decay is the same.