What is the working principle of the RF Current Probe?

I. Introduction
With the increasing popularity of electronic devices, electromagnetic disturbance has become a critical factor affecting the operational stability and safety of equipment. Among them, disturbance voltages generated by wired network interfaces (such as Ethernet interfaces, USB interfaces) and ELV (Extra Low Voltage) lamp interfaces (such as LED strip control interfaces) are directly related to signal transmission and device interconnection. Their compliance testing is incorporated into core standards including CISPR15, IEC/EN55015, and GB/T17743. Traditional testing methods suffer from issues such as interfering with the tested circuit and insufficient measurement accuracy. However, the LISUN VOL-CP RF Current Probe, leveraging the advantage of non-contact measurement, has emerged as a key device to address such testing needs.
This raises a core question: What is the working principle of the RF current probe? This question directly determines the probe’s measurement accuracy, applicable scenarios, and standard compliance. Taking the LISUN VOL-CP RF Current Probe as the research object (product details:https://www.lisungroup.com/products/emi-and-emc-test-system/radio-frequency-current-probe.html), this article systematically analyzes its working principle and verifies its application effects across multiple fields through testing practices, providing practical references for enterprises to conduct compliance testing.

II. Analysis of the Working Principle of RF Current Probe
(I) Core Principle: Electromagnetic Induction and Rogowski Coil Technology
The working principle of the RF current probe is essentially the practical application of Faraday’s Law of Electromagnetic Induction. The LISUN VOL-CP Probe adopts a high-precision Rogowski Coil as the induction core to achieve non-contact measurement of RF current. The specific mechanism is as follows:
Magnetic Field Induction: When a wired interface or ELV lamp interface of the tested device generates disturbance voltage, it is accompanied by RF current flowing through the conductor. According to Faraday’s Law of Electromagnetic Induction, a changing current creates an alternating magnetic field around the conductor, with the magnetic field strength proportional to the current magnitude.
Coil Coupling: The Rogowski Coil of the VOL-CP Probe is wrapped around the exterior of the tested conductor (no need to disconnect the circuit). The number of coil turns and magnetic field coupling area are precisely designed to efficiently capture changes in magnetic flux of the alternating magnetic field, inducing an induced voltage signal across the coil that is proportional to the rate of change of magnetic flux.
Signal Conversion: The induced voltage signal is a differential signal. The probe is equipped with a built-in integrated operational amplifier and integrating circuit, which convert the differential signal into a voltage signal consistent with the waveform of the tested RF current. It also amplifies weak signals (especially low-frequency disturbance signals) to ensure measurement accuracy.
Data Output: The converted voltage signal is transmitted to an EMC test receiver (such as the LISUN EMC Test Receiver) via a coaxial cable. After data analysis, the disturbance voltage value is directly output to determine compliance with standard limits.
(II) Key Technical Advantages: Performance Optimization Based on Principles
The working principle of the LISUN VOL-CP Probe determines its core advantages:
Non-contact Measurement: No need to disconnect the tested circuit, avoiding interference with the normal working state of the equipment. It is particularly suitable for online testing scenarios where power cannot be cut off.
Wide Frequency Band Adaptability: The structural design of the Rogowski Coil enables it to cover a frequency range of 10kHz~30MHz, fully matching the frequency requirements for disturbance voltage testing specified in standards such as CISPR15.
High Sensitivity: The collaborative design of the integrating circuit and amplifier can capture RF currents as low as microampere level, accurately identifying weak disturbance signals.
Strong Anti-interference Capability: The coil adopts a shielding design to effectively resist external electromagnetic interference, ensuring the purity of the measured signal.

III. Core Parameters and Adapted Standards of LISUN VOL-CP RF Current Probe
(I) Core Technical Parameters Table
The LISUN VOL-CP series RF current probes include multiple models to adapt to different interface types and testing needs. Their core parameters are shown in the following table:

(II) Standard Adaptation Logic
Standards such as CISPR15, IEC/EN55015, and GB/T17743 clearly require that in addition to power interfaces, the disturbance voltage of external connection interfaces (such as wired network interfaces and ELV lamp interfaces) of electrical equipment must be controlled within specific limits (for example, CISPR15 specifies that the disturbance voltage limit in the 3MHz~30MHz band is ≤40dBμV).
The working principle and parameter design of the LISUN VOL-CP Probe are fully compatible with standard requirements:
The frequency range covers the core band of 10kHz~30MHz specified by the standards, with no testing blind spots.
The sensitivity index ensures accurate measurement of disturbance signals near the standard limits, avoiding misjudgment.
The non-contact measurement method complies with the standard requirement that the testing process shall not interfere with equipment operation, ensuring the authenticity of test results.
IV. Testing Scenarios and Practical Application Cases of VOL-CP Probe
(I) Typical Testing Scenarios
Wired Network Interface Testing of Consumer Electronics: For example, the Ethernet interface of smart refrigerators and the USB-C data interface of tablets. The VOL-CP100/200 Probe is used to test disturbance voltage to ensure compliance with CISPR15.
ELV Lamp Interface Testing: For example, the control interface of smart light strips and the signal interface of LED spotlights. The VOL-CP300 Probe is adopted for testing to meet the special requirements of GB/T17743 for ELV equipment.
Communication Interface Testing of Industrial Equipment: For example, the RS485 interface of PLC controllers and the Ethernet interface of industrial computers. The VOL-CP200/400 Probe is used for testing, adapting to the industrial-grade requirements of IEC/EN55015.
(II) Analysis of Practical Application Cases
Case 1: Disturbance Voltage Testing of Smart Home Appliance Ethernet Interface
A home appliance enterprise’s smart refrigerators need to pass CISPR15 certification, requiring testing of the disturbance voltage of their Ethernet interfaces (non-power interfaces). The LISUN VOL-CP200 Probe was used for testing:
Test Procedure: Wrap the VOL-CP200 Probe around the exterior of the refrigerator’s Ethernet cable, connect it to a LISUN EMC Receiver, set the test frequency to 10kHz~30MHz, and simulate the refrigerator’s normal networked working state.
Principle Application: The RF current generated by the refrigerator’s interface forms an alternating magnetic field. After induction by the probe coil, it is converted into a voltage signal. Analysis by the receiver shows that the disturbance voltage in the 20MHz band is 38dBμV, which is lower than the CISPR15 standard limit of 40dBμV, so it is determined to be compliant.
Core Value: Non-contact measurement did not affect the refrigerator’s network communication function. The high sensitivity captured weak disturbance signals (12dBμV) in the low-frequency band of 15kHz, verifying the stability of the product’s electromagnetic compatibility.
Case 2: Disturbance Voltage Testing of ELV Smart Light Strip Control Interface
An LED smart light strip from a lighting enterprise needs to comply with GB/T17743, requiring testing of the disturbance voltage of its control interface (non-power interface). The LISUN VOL-CP300 Probe was selected:
Test Procedure: Sleeve the probe coil on the connecting wire of the light strip’s control interface, apply the working voltage required by the standard, and record the disturbance voltage value through the receiver.
Test Result: The disturbance voltage measured in the 10MHz band is 35dBμV, which meets the standard limit. The probe’s anti-interference design effectively eliminates external interference from the light strip’s driver circuit, with a repeatability error of test data ≤±2%.
Principle Advantage: Due to the small current (microampere level) of the ELV lamp interface, the high sensitivity (1.2mV/mA) of the VOL-CP300 ensures accurate capture of weak disturbance signals, avoiding misjudgment caused by signal attenuation.

V. Conclusion
Returning to the core question “What is the working principle of the RF current probe?”, the answer can be summarized as follows: Based on Faraday’s Law of Electromagnetic Induction, it couples the alternating magnetic field of the tested conductor through a Rogowski Coil, converts changes in magnetic flux into induced voltage signals, and after processing such as integration and amplification, outputs measurable signals proportional to the RF current, realizing indirect non-contact measurement of disturbance voltage.
Based on this principle, the LISUN VOL-CP RF Current Probe, combined with precise structural design and circuit optimization, has become a core testing device adapted to standards such as CISPR15, IEC/EN55015, and GB/T17743. Its advantages such as non-contact measurement, wide frequency band coverage, and high sensitivity perfectly solve the pain points of disturbance voltage testing for wired network interfaces and ELV lamp interfaces, providing reliable support for compliance certification of products in multiple fields including home appliances, lighting, and industrial electronics.
In the future, with the continuous upgrading of electromagnetic compatibility standards, the requirements for the accuracy and anti-interference capability of disturbance voltage testing will further increase. The LISUN VOL-CP series probes will also continue to iterate based on the core working principle, by optimizing the coil structure and improving signal processing efficiency, to better meet industry testing needs and help enterprises achieve continuous improvement in product electromagnetic compatibility.
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