I now do it myself, but I have been engaged in software development work for many years. When I come back to think about myself, I feel particularly desperate to begin with Java/DOT. NET technology friends say something, I hope you can inspire us from our experience.
First, in China, you must not learn stable technology for a stable life and high salary. You must not think that those who are engaged in market development and run errands have no future.
We have a large number of software companies in China. Their software development teams are very poor, not even a project team, and such teams have to undertake all the software development tasks of a software company. Day and night work overtime, closed development, you usually eat and sleep besides coding.
Maybe you got the salary of the so-called white-collar workers, but you have lost the freedom to enjoy life. If you want to be a technical person, especially a developer, I think you will soon understand how much you want to look forward to in a place for some time. , Meet some friends and have more time to live.
Second, when learning technology, do not think that if you achieve the strongest technology, you can become a 100% respected person.
There is such a paragraph: I only use the most obedient person, according to my requirements as long as it is obedient, if you do not listen to him regardless of his technology is no better. The person was then given a trial opportunity. If nothing else, he would be the successor to the next project manager.
If you are fortunate to be able to hear the conversations of marketers or leaders, you will vaguely think that they are all looking at the technicians as coding machines. Your value is not as important as you think. Inside your team, you may be engaged in internal friction with your colleagues for a discussion of a technical issue. Because he doesn't accept you, you don't accept him. You all think you're right. In fact, both of you are right and they are arguing. The purpose is to prove that they are better than the other party's technology and stronger than the other party in key situations.
Allows you to easily select the probe
Since we can't rely on technology alone, we can rely on technology and engineering tools. For example, we will continue to give everyone Amway's dry goods. How do we choose probes?
Let's learn the probe selection guide program together. All of them are dry goods.
Signal Source Requirements and Purpose
Choosing the Right Probe Because of the wide range of oscilloscope measurement applications and requirements, there are many oscilloscope probes available on the market, so the probe selection process can easily be confusing. To reduce the amount of confusion and narrow the selection process, always observe the oscilloscope manufacturer's probe recommendations.
In addition, the probe selection process should consider the measurement requirements. Which items do you want to measure? Is it voltage? Current? Or light signal? By selecting the probe for the signal type, direct measurements can be obtained more quickly.
Make sure the bandwidth or rise time on the probe exceeds the signal frequency or rise time that you plan to measure. Keep in mind that non-sinusoidal signals have important frequency components or harmonics that can largely exceed the fundamental frequency of the signal. For example, to measure the fifth harmonic that includes a 100 MHz square wave, you need a 500 MHz bandwidth measurement system on the probe. Similarly, the rise time of the oscilloscope system should be 3-5 times faster than the signal rise time of the planned measurement.
On the other hand, always consider the signal load that the probe may cause. Use high-resistance, low-capacitance probes whenever possible. For most applications, a 10MΩ probe with 20pF or lower capacitance should provide adequate signal source loading. However, for some high-speed digital circuits, you may need to switch to active probes to provide lower capacitance.
Finally, remember that you must be able to connect the probe to the circuit before taking measurements. This may require selective consideration of probe head specifications and probe adapters to simply and conveniently connect the circuit.
Understand the source
There are four basic signal source issues to consider when choosing a probe: signal type, signal frequency content, signal source impedance, and the physical properties of the test point.
1 signal type
Signal Type The first step in probe selection is to evaluate the type of signal to probe. For this purpose, the signals can be divided into: Voltage Signals Current Signals Logic Signals Other signal voltage signals are the most common signal types encountered in electronic device measurements, and because of this, voltage sensing probes are the most commonly used oscilloscope probe types.
The logic signal is actually a special type of voltage signal. Standard voltage probes can be used to view logic signals, but more often it is necessary to view specific logic events. A logic probe is set up to provide a trigger signal to the oscilloscope that allows the specified logic event to be viewed on the oscilloscope display when the specified logic combination trigger condition is met. In addition to voltage, current, and logic signals, there may be many other signal types of interest to the user, such as light sources, mechanical sources, heat sources, sound sources, and other sources.
Various converters can be used to convert these signals into corresponding voltage signals for display and measurement on an oscilloscope. When this conversion is completed, the converted signal is selected to select the probe and the converted signal is transmitted to the oscilloscope.
2 signal frequency components
Regardless of the type of signal frequency component, all signals have a frequency component. The frequency of the DC signal is 0 Hz and the pure sine curve has a single frequency, which is the reciprocal of the sine curve period.
All other signals contain multiple frequencies, and the frequency value depends on the signal waveform. For example, the fundamental frequency (fo) of a symmetrical square wave is the reciprocal of a square wave cycle, and there are other harmonic frequencies that are odd multiples of the fundamental frequency (3fo, 5fo, 7fo, ...). The fundamental frequency is the basis of the waveform, and the harmonic frequency is combined with the fundamental frequency, adding structural details such as waveform transitions and corners.
In order for the probe to transmit signals to the oscilloscope while maintaining sufficient signal fidelity, the probe must have sufficient bandwidth to transmit the main frequency components of the signal with minimal interference. In square wave and other periodic signals, this generally means that the probe bandwidth must be 3-5 times higher than the fundamental frequency of the signal. This can transmit the fundamental frequency and the first few harmonics without attenuating their relative amplitude. Higher harmonics will also be transmitted, but the attenuation will increase because these are more
High harmonics exceed the 3dB bandwidth point of the probe.
However, because there are still higher harmonics at least to some extent, they still affect the structure of the waveform to some extent. The main effect of limiting bandwidth is to reduce the signal amplitude. The closer the base frequency of the signal is to the probe's 3dB bandwidth, the lower the overall signal amplitude seen at the probe output. At the 3dB point, the amplitude drops by 30%.
In addition, due to bandwidth roll-off, signal harmonics or other frequency components that extend above the probe bandwidth experience a higher degree of attenuation. The degree of attenuation is higher at higher frequency components, as can be seen by the change in corners and the slower edge of the fast waveform transitions.
3 source impedance
The probe capacitance also limits the rise time of the signal conversion. However, this is related to signal source impedance and source loading, which we will discuss later.
Discussing the source impedance impedance can be refined into the following points:
The combination of the impedance of the probe and the signal source impedance creates a new signal load impedance that will affect the signal amplitude and signal rise time to some extent.
When the probe impedance is significantly higher than the signal source impedance, the influence of the probe on the signal amplitude is negligible.
The probe capacitance, also known as input capacitance, affects the rise time of the signal. This is due to the time required to increase the input power to the probe from 10% to 90%. The formula is as follows: tr = 2.2 x Rsource x Cprobe.
In addition, the influence of the probe load can be further reduced by selecting a low impedance signal test point where possible. Physical Connection Considerations The location and shape of the signal test points are also major considerations for probe selection. Is it enough to just touch the probe to the test point and observe the signal on the oscilloscope? Is it still necessary to connect the probe to the test point to monitor the signal and perform various circuit adjustments at the same time? In the former case, needle probes are suitable; in the latter case, certain types of retractable hook probes are required.
Tips:
Always observe the probe's maximum specified voltage function. Connecting the probe to a voltage exceeding its function may result in personal injury and equipment damage.
Plan focus:
Differential probe systems often contain sensitive devices and overvoltage can damage these devices, including electrostatic discharge. To avoid damaging the probe system, always follow the manufacturer's recommendations and observe all precautions.
Finally, keep in mind that for any given application, there is actually no "proper" probe selection, but only the "suitable" oscilloscope probe combination options, which first depend on the defined signal measurement requirements.
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