Teseq Conducted RF Test System
Contents
Overview IEC 61000-4-6 TestingApplication NotesCDNsEM ClampsCurrent Clamp/BCITest Systems

Conducted RF & Immunity Testing

What is Conducted RF?

Conducted RF are radio frequency spectrum signals and energy transmitted though capacitive and inductive coupling onto different lines and cabling including power and data.
RF conducting along cables towards TV and light

Unlike radiated RF, conducted RF is focused on coupling and exposure via connected lines or cables. Both capacitive and inductive coupling methods have the potential to provide transmissions of noise onto associated cables providing a path towards the electronic or electrical devices.[1]

The levels of interference traveling down these conducted cabling paths will vary in strength in relation to the field that they are exposed to. The greater the electric or magnetic (E and H) fields [2], the higher the level of RF noise that can be expected traveling along the associated cabling. 

Conducted RF Immunity Testing

Immunity testing to conducted RF noise or interface attempts to replicate the same environmental stress by using different injection and testing methods. The below image illustrates the concepts of the test using the substitution method with a coupling decoupling network (CDN) commonly done to IEC 61000-4-6.

Conducted RF Immunity test using CDN

What is Conducted RF Immunity Testing?

Conducted RF Immunity testing is an EMC test where the EUT is subjected to verifying levels of radio frequency EMI stress through exposure through cabling to determine any impact on the function.

Conducted RF Testing requirements and frequency ranges

Conducted RF immunity testing is a continuous EMC test commonly required for commercial, automotive, and military equipment or products. Testing requirements, frequency range, setup, as well as the required test equipment will vary by standard and test level.

The image to the left provides a reference for some of the most common requirements including their associated frequency ranges. While some automotive and military testing can span a much larger frequency range, 150 kHz to 230 MHz is the most common.

Our focus will be on IEC 61000-4-6 methods focusing heavily on the requirements and calibration process.

IEC 61000-4-6 Testing

The test methods and procedures discussed will be based around IEC 61000-4-6, which has been harmonized with the European EN 61000-4-6. The below image provided by the Teseq CDN selection guide, provides the rules for selecting the injection method. The injection method will determine what equipment is required as well as EUT/DUT considerations.

IEC/EN 61000-4-6: Rules for selecting the injection methon

Test Levels - Substitution Method

The test level requirements for this standard, regardless of injection method are :

  • Test Level 1 - 1V r.m.s.
  • Test Level 2 - 3V r.m.s.
  • Test Level 3 - 10V r.m.s.
  • Test Level X - Special (unspecified)[1]

IEC 61000-4-6 uses the substitution method for testing (with all injection devices) where the voltage level of the calibration data over the given frequency is applied to the EUT. The calibration setup for this standard specifies an 150Ohm source impedance and uses the associated levels to conduct testing. Given the large impact that the calibration has on testing, we will spend a considerable amount of time on it.

RF Signal Modulation

The two signal modulations used for conducted RF testing are amplitude modulation (AM) and amplitude modulation peak conservation  (AM PC). IEC 61000-4-6 uses the more common AM of 80% which can be seen below.

Conducted RF signal types and modulation methods

Calibration

Regardless of the injection method used, the calibration of setup is the first step. During this process the associated test levels and corresponding power levels are saved to be used later while conducting the test.

Conducted RF test setups for calibration and testing using CDN

Application Notes/Guides

The below applications notes provide excellent information on how to conducted RF immunity testing to a variety of standards using different injection methods.

CDN Injection Method

What are Coupling Decoupling Network (CDNs)?

CDNs are devices that allow for injection RF disturbances on cables towards the EUT and subsequently removing them prior to auxiliary equipment while providing 150 Ohm impedance.

Coupling Decoupling Networks (CDNs) are the preferred injection method of IEC 61000-4-6 as seen above from the selection rules. They provide repeatable, accurate results while ensuring auxiliary equipment is protected. CDNs also have the benefit of being the most efficient method for injection allowing lower power RF amplifiers to be used.

    Types of CDNs

    These networks are designed specifically for a particular port or cable type (power, communication, etc.). This has the potential to lead to multiple CDNs required for testing depending upon the test plan and ports tested. The most common CDN types include:

    Conducted RF CDN Method common Types

    The vast number of coupling decoupling networks available relate to the variety of different cables and ports tested. Teseq, a manufacturer of EMC equipment, provides an excellent guide that goes into great detail on the variety of CDNs available. The guide can be accessed by clicking here.

    CDN Setup & Calibration

    Common CDN Calibration setup

    The calibration setup for IEC 61000-4-6 using the CDN injection method can be seen to the left.

    • 1) Conducted RF Test System (NSG 4070)
    • 2) 100Ω Adapters
    • 3) 6 dB Attenuator
    • 4) Coupling Decoupling Network (CDN)
    • 5) 50 Ω Termination Load

    Direct Injection

    This method requires a physical connection from the RF generator to the cabling of the device or equipment under test. This can involve some work as it is required to make manual connections including splitting the EUT cabling. This method when used for IEC 61000-4-6 also requires capacitors and resistors put in place between the connection.

    Electromagnetic (EM) Clamp Injection Method

    What are Electromagnetic (EM) Clamps?

    EM clamps are hinged enclosures that use split-core ferrites to inject disturbance signals through a combination of inductive and capacitive coupling towards the EUT.
     EM101 EM Clamp close up with split ferrite visible

    EM Clamps are typically used when CDNs aren't applicable as a more suitable option. The clamps themselves are made of ferrite as well as conductor and insulating plates providing a combination of inductive and capacitive coupling. The ferrite used in construction of the clamp must be in good condition, both on the top and bottom, for the equipment to be functional.

    The EM Clamps provide an excellent option when longer EUT cable lengths are available as they're more efficient allowing for less power to be used.

    It is important to consider the cable length available and thickness of the cables or bundles when using EM clamps. Most clamps have a length between 58 inchs and 70 inchs and can handle a max diameter cable or bundle of 20mm.

    Typical EM Clamp Method Calibration Setup

    Common EM Clamp test setup with EM101 and NSG 4070
    • 1) Conducted RF Test System (NSG 4070)
    • 2) CAL 801A 100Ω Adapters
    • 3) 6 dB Attenuator
    • 4) EM Test EM101 Clamp
    • 5) 50 Ω Termination Load
    • 6) Calibration Cable

    Current Clamp Injection Method

     Common Bulk Current Injection (BCI) probes including frequency range & power

    The bulk current injection method is commonly required for many military and automotive applications and can use the substitution method for injection. The component that induces the associated RF onto the cable(s) is the current injection probe (CIP). These probes use split ferrite pieces with a clamping mechanism as way of injecting required current levels onto cables and associated connected devices.

    A major benefit of using this method is having a sizable window or opening on the injection probe, typically 43 mm and a clamping feature. This is ideal for situations where RF testing is required on bundles of cables, where otherwise testing would be substantially more difficult. This is also an easier solution when cabling cannot be cut, because the clamp can be opened and closed around the wires/cables.

    This method is measured in either mA or dBµA with a current monitoring probe during calibration processes. Typical frequency ranges start at around 4 kHz to 400 MHz with some automotive requirements going into the Gigahertz range. This test typically requires the most power to drive enough RF though the injection probe, often requiring external power amplifiers mentioned above.  

    The video shows the current clamp calibration setup according to IEC 61000-4-6 using the Teseq NSG 4070 conducted RF test system. While setups may very, it does provide a introduction to:

    • Setup of RF Injection Equipment
    • Calibration Process to Test Levels
    • Using Front Panel Software

    Conducted RF Test Systems

    Conducted RF Equipment Rental Categories

    Conducted RF Test Systems

    Conducted RF systems provide many of the commonly required equipment in a single, easy to use system that allows for effective testing. These systems can be configured with different capabilities, it is important to ensure that system is capable of meeting associated testing requirements. The block diagram of the Teseq NSG 4070 shows the different components inside of the RF test equipment.  These systems typically include:

    Common EM Clamp test setup with EM101 and NSG 4070

    RF Power Amplifier

     Teseq CBA 400M-110 Amplifier

    The RF power amplifier, along with the other associated equipment, determines the test level and frequency limitations. The amplifiers used for BCI testing can go as high as 260 watts, with 110 Watts often needed for higher test levels in automotive and commercial requirements. The most common RF amplifiers include:

    At lower power levels amplifiers are often built into the test systems and at higher levels tend to be external. When using an external amplifier a dual directional coupler is needed for forward and reverse power measurements typically run through the RF system. When testing at higher levels it is crucial that proper attenuation is used to help protect the power meters or analyzer.

    The use of a dual directional coupler with an external amplifier provides additional setup connections and considerations. The video to the left provides a guide for adding an external amplifier to an RF system and includes:

    • Connecting External RF Power Amplifier
    • Using Dual Directional Coupler & Importing Data
    • Running System Calibration to Verify
    BCI Injection Probes with cables

    Conducted RF Immunity FAQ

    What is conducted RF test?
    The conducted RF test is an EMC immunity test where equipment is subjected to radio frequency disturbances through injection on power or data lines. 
    What is conducted RF immunity?
    Conducted RF immunity is when EUT/DUT are able to withstand when radio frequency EMI is injected at set levels on associated cabling going to the equipment or device. 

    References/Additional Information

    [1]https://www.emcstandards.co.uk/files/61000-4-6_immunity_to_conducted_rfi_2_1.pdf

    [2]https://atlasce.com/services/immunity-testing/conducted-rf-testing/

    [3]https://www.fuseco.com.au/articles/what-is-rfi-emi-emc

    http://www.unitest.com/pdf/RF_immunity_testing_e_3.pdf

    https://www.rfvenue.com/blog/2014/12/14/common-sources-of-interference

    https://www.teseq.com/applications/induced-rf-i.php

     

    1 comment

    marya ahuja

    Your blog gives very vast information about conductor transmitting devices operating today. This type of testing is required for both compliance and product reliability. This information helps us a lot. But the performance of such electronic devices depends upon the quality of the product. Because these products are costly, For the long durability of such products, we should purchase them from the authorized dealers.

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