How to Measure Oscilloscope Current Probe Delay
The standard probe of the oscilloscope can only measure voltage, in fact, the oscilloscope itself can only measure voltage. If you want to measure current, you have to choose a current probe, which actually converts the current signal into a voltage signal and transmits it to the oscilloscope, equivalent to a sensor.
The following points should be noted when choosing a current probe. Some current probes can only measure alternating current, not direct current. These probes are usually passive and do not require an external power supply. If you need to measure DC, you need to find a current probe that supports AC/DC measurements; secondly, you need to consider whether the maximum and minimum values of the current to be measured are within the current probe's measurement range and whether its accuracy is acceptable; the current probe's bandwidth is also a consideration, and a current probe with a bandwidth that is too small may distort when testing signals with higher signal frequencies; and the dimensions of the current probe's jaws determine the The size of the current probe's clamp determines the maximum diameter of the wire under test. Finally, measurements with current probes are likely to generate very high temperatures, so the temperature range of the probe is also a big consideration.
One of the major uses of current probes is for power measurements. Since power is equal to voltage times current, we tend to take one channel of an oscilloscope and measure the voltage, the other channel measures the current, and then the product of the two channels is its power. Previously we have shared with you the delay measurement of differential probes, the same current probe also has its own delay, and is often different from the voltage probe. This leads to the oscilloscope in the measurement and calculation of power, its voltage channel and the current channel measured value, the actual is not in the same point in time, so that the calculation of real-time power will have an error.
First of all, we prepare a special current signal board to convert the signal from the source into a current signal. In order to reduce the influence of parasitic inductance and capacitance on the signal, the test area of the current signal board is a straight line in series with several sampling resistors. During testing, a current probe is clamped to the edge of the straight line in the test area, and the current direction is the direction indicated by the current probe. The ends of the sampling resistors are then soldered by the feeder, since it is a purely resistive load, the voltage and current are equal in phase. Finally the signal source outputs a 100Hz square wave signal, and the rising edge delay of the oscilloscope current probe and feeder sampling waveform is observed.
We reduce the time base of the oscilloscope and extend the waveform. Since the bandwidth of the current probe under test is 800K (CP2100X), and then the sampling resistor ends of the soldered feeder can be regarded as the bandwidth of 20M, so the two channels capture the rising edge of the rising time is not the same. We can take the starting point of the rising edge of the two signals as the difference calculation point. Open the oscilloscope X cursor, X1 moved to the starting point of the rising edge of channel 2, X2 moved to the starting point of the rising edge of channel 1, you can see the difference between X1 and X2, the resulting difference is basically the delay time of this current probe.
