Current probe measurement examples and tips

- May 24, 2018 -

Current probe measurement examples and tips


The application of current probe is extensive. The basic principle is that the current flowing through the wire will generate a magnetic field around it. The current probe converts the magnetic field into a corresponding voltage signal. Through the cooperation with the oscilloscope, observe the corresponding current waveform. Widely used in switching power supply, motor driver, electronic rectifier, LED lighting, new energy and other fields. This article will describe the classification, principle, and important technical indicators of common current probes. Through examples, we will understand the differences between probes so that everyone can have a basic understanding of the probes.


1. A current probe is divided into AC current probe and AC/DC current probe.

Current probes on oscilloscopes are basically divided into two types: AC current probes and AC/DC current probes. AC current probes are usually passive probes. They have low cost but cannot handle DC components. AC/DC current probes are usually active. Probes are divided into low-frequency probes and high-frequency probes. The common bandwidth of low-frequency probes is below several hundred KHZ, and the bandwidth of high-frequency probes is generally more than a few MHZ.


2. the important indicators of current probe 

2.1 Accuracy

Accuracy: Refers to the accuracy of current-to-voltage conversion. Taking the AC/DC current embedding as an example, the accuracy of the open-loop system is generally poor, with a typical value of about 3%. The accuracy of the closed-loop system is relatively high, and the typical value is about 1%. The accuracy of our high frequency current probe is 1%.


2.2 Bandwidth

Bandwidth: All probes have bandwidth. The bandwidth of the probe is the frequency at which the probe response causes the output amplitude to drop to 70.7% (-3 DB), as shown in Figure 5. When selecting oscilloscopes and oscilloscope probes, be aware that bandwidth affects measurement accuracy in many ways. In amplitude measurements, the sine wave's amplitude becomes increasingly attenuated as the sine wave frequency approaches the bandwidth limit. At the bandwidth limit, the amplitude of the sine wave is measured as 70.7% of the actual amplitude. Therefore, to achieve maximum amplitude measurement accuracy, you must select an oscilloscope and probe with a bandwidth several times higher than the highest frequency waveform you plan to measure. The same applies to measuring the waveform rise time and fall time.

Waveform transition edges (such as pulses and square wave edges) consist of high frequency components. The bandwidth limit causes these high-frequency components to attenuate, causing the display to switch slower than the actual conversion speed. To accurately measure the rise and fall times, the measurement system used must have sufficient bandwidth to maintain the high frequency components that make up the waveform's rise and fall times. In the most common case, when using the rise time of the measurement system, the rise time of the system should generally be 4-5 times faster than the rise time to be measured. In the field of switching power supplies, a bandwidth of several tens of MHZ is generally sufficient. Our high-frequency current probes have a bandwidth of 5 MHz to 100 MHz.

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