How to Improve the Sensitivity of an Oscilloscope Current Probe

Oscilloscope current probes are widely used. 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. By cooperating with an oscilloscope, the corresponding current waveform can be observed. It is widely used in switching power supply, motor driver, electronic rectifier, LED lighting, new energy and other fields.

For many engineers who can use oscilloscopes, how to use current probes is very simple for them. So what is the sensitivity of current probes? Today PRBTEK will briefly share with you:

There are many types of current probes on the market. One of them is the clamp-on AC/DC type, which can be used to clamp a current-carrying conductor to measure AC or DC current.

There are two useful techniques for using this type of current probe:

1. Eliminate magnetism (degaussing/degaussing) and DC bias

To reliably measure low-level currents, you need to demagnetize the core to eliminate residual magnetism. Just like eliminating the redundant magnetic field of a CRT monitor can improve image quality, you can eliminate any residual magnetism by degaussing or degaussing the current probe. If the probe core is magnetized, a bias voltage proportional to the residual magnetization will be generated, causing measurement errors.

Whenever you turn the probe's power switch on/off or feed excessive current to it, it is important to eliminate the magnetism of the probe core. To degauss a probe, disconnect the probe from all wires, ensure the probe is locked, and press the probe degauss button. In addition, a zero control button on the probe can be used to correct for excessive voltage offset or temperature drift of the probe.

2. Improve probe sensitivity

Current probes measure the magnetic field produced by the current flowing through the probe's clamp. It produces a voltage output proportional to the input current. If you are measuring a DC signal or a low-frequency AC signal with small amplitude, you can increase the measurement sensitivity by wrapping multiple turns of the conductor under test around the probe. At this point, the signal strength will increase based on the number of turns of the conductor under test wrapped around the probe. For example, if a wire is wound around the probe 5 times and the oscilloscope reads 25mA, the actual current is 25mA divided by 5, which is 5mA. The sensitivity of the current probe can be increased by 5 times.

Current can be measured very easily using a clamp-on current probe and an oscilloscope without damaging the circuit. However, when you introduce the oscilloscope's broadband noise into your measurements, the oscilloscope's vertical noise can hinder your low-level current measurements. By applying one or more of the measurement techniques described in this article, you can significantly improve measurement accuracy by eliminating the random noise of the oscilloscope and the redundant magnetic offset or DC offset of the current probe.