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Abstract

The LISUN RFCI61000-6 series RF Conducted Immunity Test System is a fully integrated solution designed for precise and repeatable RF conducted immunity testing. This article provides a comprehensive guide on calibrating this system, ensuring compliance with international standards. The system, available in 35W and 85W power variants, combines a signal source, power amplifier, and power meter into a single chassis, simplifying test setups for EMC laboratories. By detailing calibration procedures, injection methods, and performance verification against IEC 61000-4-6 clauses, this guide empowers engineers to maintain test validity and measurement accuracy for applications in LED lighting, medical devices, and industrial control systems.

1.1 Integrated Signal Source and Amplification Module

The core of the RF conducted immunity test system is its self-contained, synthesized signal generator and broadband power amplifier. Unlike modular systems requiring external instruments, the RFCI61000-6 series integrates these functions, minimizing cable losses and impedance discontinuities. The internal signal source provides calibrated amplitude modulation (AM) at 1 kHz with 80% depth, as required by IEC 61000-4-6 clause 6.2.3. This architecture reduces complex interconnections, ensuring a low voltage standing wave ratio (VSWR) and stable output power across the 150 kHz to 230 MHz frequency range.

1.2 Power Amplifier Variants: 35W vs. 85W

The system is offered in two distinct output power levels to address varying EUT immunity thresholds. The RFCI61000-6-35W delivers 35 watts of continuous wave (CW) power, suitable for most consumer electronics and lighting products. The RFCI61000-6-85W provides 85 watts, necessary for testing high-power industrial drives and new energy charging stations with high injection currents. Both variants maintain a flat frequency response, with output power deviation typically within ±1.5 dB across the band, as defined in the product specification sheet.

1.3 Integrated Coupling Network Management

The system features a dedicated port for controlling external coupling-decoupling networks (CDNs). It automatically recognizes LISUN CDN models, loading the correct calibration factors (K-factor) for each network. This capability is critical for maintaining test repeatability across different injection points, such as M2 (Mains) or M3 (Signal) ports. The integrated control logic reduces operator error and ensures the injected disturbance level is accurately defined at the EUT port.

2.1 Pre-Calibration System Verification

Before commencing formal calibration, a visual inspection and basic functional test must be performed. Check all RF connectors (N-type and BNC) for damage and ensure CDN impedance matches 50 Ω. The system provides a self-test routine that verifies the internal power meter’s linearity and the signal source’s frequency accuracy. This step is essential to confirm that the RF conducted immunity test setup meets the performance requirements of GB/T 17626.6 clause 7.1.

2.2 Setting the Forward Power Level

The calibration process begins with defining the test level, usually 1 V, 3 V, or 10 V (open circuit voltage). The operator must calculate the required forward power (Pforward) using the calibration factor (K) of the specific CDN. The formula is simple: (P{forward} = V_{test}^2 / (4 imes 50 imes K)). The system’s touchscreen interface allows direct input of the target test voltage, and the software automatically computes the setpoint, adjusting the amplifier output.

2.3 Closed-Loop Leveling and Power Meter Integration

A critical element of the calibration is the use of the internal power meter to establish a closed-loop control system. The system compares the measured forward power against the calculated setpoint and adjusts the signal source level in real-time. This compensates for minor frequency response variations in the amplifier and cabling. The calibration procedure requires the operator to verify this leveling mechanism at a minimum of 16 points per octave, as recommended by IEC 61000-4-6 clause 5.4.

3.1 Selecting the Correct Injection Method (EM, EM/J, CDN)

IEC 61000-4-6 defines three primary injection methods: Coupling/Decoupling Network (EM), Direct Injection (EM/J), and Bulk Current Injection (EM/J with clamp). The LISUN system supports all methods. For calibration, the CDN method (EM) is most common. The user must select the correct injection method in the system software, which then applies the appropriate calibration curve. For example, method EM/J (Direct Injection) requires a 6 dB attenuator at the EUT port for impedance matching, while the CDN method does not.

3.2 Calibrating with LISUN CDN Models

When calibrating with a specific LISUN CDN, such as the CDN-M2 series, the system loads pre-stored S-parameter data. This data defines the coupling factor, isolation, and impedance over frequency. The operator must connect the CDN’s EUT port to a calibrated 50 Ω termination and the RF input port to the system. The calibration procedure then sweeps the test frequency range, recording the actual forward power required to achieve the programmed test level at the EUT port.

3.3 Verification of CDN Isolation and Impedance

A key step in calibration is verifying the decoupling networks. The system can measure the isolation between the AE (Auxiliary Equipment) port and the EUT port. According to EN 61000-4-6 clause 6.2.1, isolation must exceed 40 dB at frequencies above 150 kHz. The RFCI61000-6’s internal power meter performs this measurement, generating a pass/fail result. This ensures that the disturbance is directed toward the EUT and does not affect auxiliary equipment, preserving test validity.

4.1 Amplitude Modulation (AM) Depth Verification

The system applies a 1 kHz sinusoidal amplitude modulation with a modulation depth of 80% as the standard disturbance signal. Calibration must verify that the modulation envelope is accurate. The internal power meter is capable of sampling the envelope, allowing the system to measure the sideband power levels. The ratio of sideband power to carrier power must be precisely 4:1 for an 80% depth. This ensures the effective test voltage is correct, as per clause 5.3 of the standard.

4.2 Pulse Modulation for Immunity Testing

For specific product standards, such as those for medical devices, pulse modulation may be used. The RFCI61000-6 series can generate pulse bursts. During calibration, the operator must verify the pulse width, rise time, and period using an oscilloscope connected to the system’s monitor port. The system’s accuracy in generating these pulses must be within ±5% of the set value, ensuring repeatable immunity testing for EUTs with digital circuits sensitive to specific pulse durations.

4.3 Disturbance Voltage and Current Confirmation

After the RF path is calibrated, the final step involves confirming the disturbance voltage at the EUT port under load. Using a high-impedance probe or a calibrated CDN, the operator measures the voltage at the output. The system software provides a comparative plot showing the target voltage versus the measured voltage. Any deviation greater than ±2 dB requires adjustment of the system’s calibration table. This closed-loop verification ensures the RF conducted immunity test is applied correctly to the EUT.

5.1 Defining the Frequency Range and Step Size

IEC 61000-4-6 requires testing from 150 kHz to 80 MHz (and optionally up to 230 MHz). The calibration setup must define a frequency step size. A logarithmic step of 1% of the current frequency is typical, resulting in approximately 500 points. The RFCI61000-6 allows the user to define this step size. A smaller step size (e.g., 0.5%) may be required when testing EUTs with narrowband resonances, while a larger step bandwidth is sufficient for broadband EUTs.

5.2 Dwell Time Configuration and Calibration

The dwell time, or the time the system remains at each frequency point, must be set during calibration. The standard recommends a minimum dwell time of 1 second, but faster sweeps (e.g., 0.1 seconds) can be used for pre-scanning. The calibration procedure must verify that the power amplification stage does not oscillate or sag during the dwell period. The system logs the output power stability over the dwell time, providing a quality metric for the calibration run.

6.1 Calibration Data Storage and Traceability

The RFCI61000-6 series incorporates a non-volatile memory for storing calibration data. Each calibration run, including date, operator ID, and environmental conditions, is saved. This creates a traceable record essential for ISO 17025 compliance. The data includes forward power, reverse power, and calculated VSWR at each frequency point. This historical data allows engineers to track amplifier aging and schedule preventative maintenance before a failure occurs.

6.2 Generating Calibration Certificates

After completing the calibration procedure, the system can automatically generate a formal calibration certificate. This report includes a summary of the calibration methods used (e.g., “CDN Method per IEC 61000-4-6 Clause 6.2”), the measurement uncertainty budget, and a graph of the injected level versus frequency. This feature significantly reduces the administrative burden on EMC laboratory personnel and ensures reports are standardized.

7.1 High VSWR and Power Reflection Alarms

A common issue during calibration is a high VSWR at the CDN or EUT port. This triggers a power limit alarm from the amplifier. The primary cause is often a damaged CDN or a missing 50 Ω load. The system displays the VSWR value in real-time. A VSWR reading above 2.0:1 requires immediate investigation. The calibration must be aborted, and the CDN’s internal components checked for damage.

7.2 Frequency Flatness Anomalies

If the measured output power shows a drop of more than ±3 dB at specific frequencies, the calibration process identifies a system anomaly. This may be caused by a bad RF cable or a failing amplifier stage. The system’s calibration software provides a diagnostic mode that isolates the issue to either the signal source or the power stage. Replacing the RF cable is the most common corrective action.

The LISUN RFCI61000-6 series RF Conducted Immunity Test System provides a robust, integrated platform for performing compliant immunity tests. The calibration procedures outlined, from forward power leveling to CDN verification, are critical for achieving repeatable and accurate results. By adhering to the structured calibration protocols referenced in IEC 61000-4-6 and GB/T 17626.6, testing professionals can ensure their EUTs meet global electromagnetic compatibility requirements across diverse industries. The system’s ability to handle multiple injection methods and its integrated data logging make it an indispensable tool for any modern EMC laboratory.

Q1: What is the recommended frequency step size for calibrating the RFCI61000-6 system according to IEC 61000-4-6?
A: The standard suggests testing at 1% of the current frequency on a logarithmic scale, which translates to approximately 500 steps across the 150 kHz to 80 MHz range. During calibration, you may choose a finer step (e.g., 0.5%) for EUTs with known narrowband resonances, such as power supply filters. However, for a general pre-compliance calibration, the 1% step is sufficient. The system’s software allows you to save these settings as a calibration profile, ensuring consistency across all tests. Using too large a step (e.g., 5%) may miss critical immunity frequencies and invalidate the calibration.

Q2: How does the system verify the accuracy of the 80% amplitude modulation (AM) depth during calibration?
A: The RFCI61000-6 uses its internal, high-speed power meter to sample the RF envelope at each calibration point. The software calculates the ratio of the carrier power (Pc) to the sideband power (Ps). For an 80% AM depth, the theoretical ratio is Ps/Pc = 0.16. The system compares this measured ratio against the target value with an accuracy tolerance of ±2%. If the measured modulation depth falls outside this range, a system alert prompts the operator to check the modulation settings in the signal source module. This verification is crucial because an incorrect modulation depth changes the RMS voltage level applied to the EUT.

Q3: What specific steps must be taken when calibrating the system for testing medical devices per EN 61000-4-6?
A: For medical device testing, the calibration must also verify the pulse modulation function if required by the product standard. First, select the pulse modulation mode (e.g., 1 Hz, 50% duty cycle). Use an external oscilloscope at the system’s monitor port to confirm the pulse shape and timing. Second, ensure that the calibration includes a check of the CDN’s common-mode impedance. For medical applications, the impedance tolerance is often stricter (±10% versus the standard ±20%) to avoid influencing sensitive patient-connected circuits. Finally, the calibration record must explicitly state that the system was verified for pulse and continuous wave modes.

Q4: Can the calibration factors for third-party CDNs be manually entered into the LISUN RFCI61000-6 system?
A: Yes, the system provides a manual calibration factor entry mode. You will need the S-parameter data or the K-factor table for the specific third-party CDN. Navigate to the ‘CDN Management’ section on the touchscreen, select ‘User Defined,’ and input the correction factors (in dB or linear ratio) for each frequency point. The system will then apply these factors during the closed-loop leveling procedure. It is highly recommended to perform a validation check at three spot frequencies (e.g., 1 MHz, 10 MHz, 80 MHz) using a calibrated measurement receiver to confirm the manual entry was accurate.

Q5: How often should the RFCI61000-6 series undergo a full system calibration?
A: The manufacturer’s recommendation is an annual full system calibration. However, the interval should be adjusted based on usage intensity and laboratory quality standards (e.g., ISO 17025). A daily or weekly functional check (e.g., a quick 6-point sweep at 3 V) is advisable to catch drift early. The internal power meter reference should be calibrated externally every 12 months. The system records the number of operating hours for the power amplifier, which is a key metric for scheduling preventative maintenance. Long-term data from the calibration log will indicate if a more frequent interval, such as every 6 months, is necessary for high-volume test environments.