This post based on last time out, introduce a tuning capacitor, adjust the oscilloscope probe and will affect the oscilloscope waveform acquisition, we have to analyze the basic principle:
Above a is directly connected mode, the equivalent of with two wire directly connect to test signal and the oscilloscope probe,
Above b the most commonly used for us to the oscilloscope probe, namely passive probe, probe the internal attenuation resistance and the equivalent input capacitance, there is a common bandwidth is below 500 MHZ, oscilloscope OSC482M model is equipped with P2060 oscilloscope probe, detailed specifications are as follows:
The third column: 60 MHZ gear (10 x), on the surface of the probe effective bandwidth to 60 MHZ, beyond the scope of the use of lead to measurement deviation is more, another rise time is 5.8 ns, input capacitance: 1 x gear in 70-120 pf, 10 x gear at 14 to 18 pf, compensation capacitance range is: 15-45 pf, input resistance to 1 mhe 10 m ohm,
And active probe, active difference is the need of power supply, internal operational amplifier circuit, and the differential probe, current probe, such as
Take a look at the below type of oscilloscope hardware parameters:
Vertical resolution: 8 to 13
The ADC device within the oscilloscope digit 8 bits, oscilloscope is generally hardware device determines the resolution, or 8, 10, 12 or 14, here the factory wrote a range value, likely USES a 14 bit ADC device, practical use can be removed, low transformation to a low number,
Such as the oscilloscope measurement range is + 5 V, fengfeng value 10 V, said the oscilloscope to voltage of 10 V/256=39.06 mV, so choose the measurement range as small as possible, in order to obtain more accurate measurement results, the measurement range +/- 1 V, 8-bit resolution to distinguish the minimum voltage of 7.813 mV, but pay attention to the need to consider the signal peaks,
The highest sampling rate: 50 m
Unit is MS/s sampling rate (Megasamples per second) or GS/s (Gigasamples per second), such as a two channel used at the same time, the highest sampling rate by half,
The Nyquist specific law, cooked not familiar with? Simply think that the sampling rate is only 2 times the bandwidth of signal under test can,
But it is not enough, the distortion is serious, general need 3 to 5 times of sampling rate and to minimize distortion,
The diagram below: we try a 8 MHZ crystal oscillation waveform sampling:
As you can see, the top right corner has marked the current sampling rate is 50 m, has reached the oscilloscope nominal limit, 8 bit each,
Can see the oscilloscope can be a good reduction is XuanBo, under the automatic measurement of frequency is measured is also very accurate, also no longer need to manually adjust the cursor,
Bandwidth (3 db) : 20 MHZ
Bandwidth is a sine wave input, the amplitude unchanged, increasing signal frequency, as shown on the oscilloscope signal is 70.7% of the actual signal amplitude (i.e., 3 db attenuation), the corresponding frequency is equal to the oscilloscope bandwidth, but we are often measured by the square wave or digital signal, the principle of the most commonly used 5 times is to choose the high signal frequency oscilloscope,
So we here of the oscilloscope can be accurately measured about 4 MHZ signal, and the higher the signal frequency distortion,
Input sensitivity: - 2 v/10 mv/frames, namely the oscilloscope the smallest unit of each grid,
Input range (1 x) : + - 100 mv - + - 5 v 7 fixed range, such as
Time base: 50 ns - 25 s/case, namely the smallest unit inverse time,
Storage depth: 512 b - 62 MB, storage depth=sampling rate * sampling time, that is, how much can store samples,
Or actual next to the PC interface under test:
Dual channel test 1 KHZ square wave:
Here the test head adjustments capacitance, found that the waveform changes (on the way A signal compensation is insufficient, B signal overcompensation), be careful to use plastic screwdriver, metal affect itself very small capacitance, capacitance value is not allowed to adjust,
Then adjust the PWM signal frequency to 10 KHZ, found the probe compensation effect is reduced, this is just said to the problem of sampling rate,
We will signal amplification and see:
To see the triangle wave, in fact, this is what the ADC sampling value fluctuations, a bit up and down which will see that there are a few changes in the mv, but this does not affect our regular observation and measurement of basic signal because conventional we measure is low speed signal, and the signal to rise along the speed is not attention, generally need to pay attention to the tendency of the waveform and logic functions,
Then tell me the difference of the AC and DC coupling, actually the most important is to DC, AC across the capacitor, which we are measuring AC AC signal, DC signal is filtered, so is the most commonly used AC measurement power supply ripple,
But the oscilloscope probe is not equipped with communication in spring, there is no analysis of the measured signal, because the earth clamp will introduce more noise signal, lead to inaccurate measurement, does not have significance test,
Why is this? Here involves the field of high frequency signal, high frequency electronic knowledge that we can know, the higher the frequency of the signal, the more prone to EMC, and the longer the signal flow path, can also cause noise increases, this is why high frequency circuit requirements of multipoint earthing, and the power supply ripple contains high frequency components, so we don't do the test and analysis,
Common signal capture: we actually use the oscilloscope as the most commonly used is to pick up the waveform, ah, signal have boosted, have lower, how many V? How to change?
But if good with a departure function, can let the waveform capture get twice the result with half the effort, here is mainly aimed at the oscilloscope to see how to trigger the fetching waveform,
Pictured above, set up the trigger, select A channel, click on A single trigger, drag threshold T there to set the trigger level, as long as there is signal to meet from low to high beyond the threshold will trigger the grab, so don't watched waveform,
Here again on a FFT figure:
Fast algorithm of FFT is the discrete Fourier transform, can be a signal transformation to the frequency domain, some characteristics of signal in time domain is hard to see what, but if after transformation to the frequency domain, it is easy to see the features, that is the reason why many signal analysis by FFT transform, on the other hand, FFT can be extracted from the frequency spectrum of a signal, it is also often used in spectrum analysis,
So the picture above you can see below the signal frequency domain on the performance of the again, transverse frequency, the range value of the vertical axis is one of the first circle show the strongest local energy of the signal in 8 MHZ, and here you can see how much energy peak in the frequency offset, frequency deviation,? Whether the feeling is very strong, the lower the circle, it shows that there is 2 times the frequency of energy, but is very weak, but can also be measured,
Conclusion:
1, oscilloscope interface basic function is rich, bandwidth and sampling rate to satisfy common signal measurement requirements,
2, contains an adjustable signal source output, easy to test,
3, AC/DC function also can meet the conventional test, especially FFT function, can do further analysis of the measured signal,
Next will be further practice of oscilloscope: measurement based on can communication and protocol analysis,