Oscilloscope method of testing current waveforms
Oscilloscopes are most electronic engineers use the most of an instrument, mention oscilloscopes we immediately think of is the test voltage, of course, many oscilloscopes can also be done to do a relatively rough spectrum analysis, etc., but many oscilloscopes are very concerned about an indicator of electronic engineers - current can not be tested in some analysis and verification of not only need to test the voltage, and sometimes more need to test the current; some of the more high-end oscilloscopes can test current, but you need to purchase another active current probe. Oscilloscopes can test current, but you need to purchase another active current probe, mentioned the word active, it means that the price is not expensive, good, to buy an active current probe cost almost can buy some brands of mid-range oscilloscopes, so this is not a general small company to play with the "tycoon" equipment ah.
When it comes to current testing, some people may say that a multimeter can measure it, right? Of course, the multimeter can measure the current at a certain moment, but there are several problems: 1, due to the slow reaction speed of the multimeter (generally 100mS level); 2, the multimeter can not be recorded for a long time the results of the test, some of the good table can be recorded as the maximum, minimum value, etc.; 3, the most critical is that the multimeter can not see the process of the current changes, many times we want to see the changes in the process and not just the results! For example, we would like to know the transistor overcurrent damage is most likely to occur at what time rather than just want to see the transistor in the smoke.
No No expensive current probe can not use an oscilloscope to see the process of current changes? In fact, we change the idea or can find a solution, the method is actually very simple, is our secondary school physics over the I = V / R, tears, right? Note that this V is not a point of voltage, but the potential difference between the two points, this is a key, but also some beginners are prone to fall into the wrong place, if the voltage change to speculate on the change in current at a certain point that many times have to make a mistake, the back of the test from the examples we can see this point.
Specific method:
The specific approach of this method is: with two probes were measured out of a resistor (or even a section of the line, of course, provided that the resistance of this section of the line is large enough to produce the appropriate potential difference between its ends) voltage V1, V2, and then use the oscilloscope's calculator function can be real-time calculations of △ V = V1-V2, and I = △ V / R, as long as the environment does not undergo a drastic change, etc., we can assume that the R is unchanged, so I is with the △ V = V1-V2, and I = △ V / R. As long as the environment does not change drastically, etc., we can assume that R is unchanged, so I changes linearly with △V, so the change of △V reflects the change of current. We will verify whether this method is feasible by an example below.
