Specification for radio disturbance and immunity measuring apparatus and methods—Part 1-3:Radio disturbance and immunity measuring apparatus—Ancillary equipment—Disturbances power
1 Scope
This document specifies the characteristics and calibration method of the absorption clamp for radio disturbance power measurements in the frequency range 30 MHz to 1 GHz.
2 Normative references
The contents of the following documents constitute essential provisions of this document by means of normative references in the text. Where a reference is dated, only the version corresponding to that date applies to this document; where a reference is not dated, the latest version (including all amendment sheets) applies to this document.
3 Terms and definitions, abbreviations
3.1 Terms and definitions
The terms and definitions defined in GB/T 4365-2003 apply to this document.
4 Absorption clamp equipment
4.1 Overview
Nuisance power measurement using an absorber clamp is a method for determining radiated disturbances in the frequency band above 30 MHz. The measurement method is used as an alternative method for measuring nuisance field strength on an open test site (OATS). The Absorption Clamp Measurement Method (ACMM) is described in Chapter 7 of CISPR 16-2-2:2003.
4.2 Absorption clamp device
4.2.1 Description of the Absorption Clamp Device
Appendix A describes the construction of the absorbing clamp and gives a typical example.
The absorber clamp unit consists of the following five components:
--- Broadband RF current transformer;
--- Impedance stabiliser for the broadband RF power absorber and the line under test (LUT);
--- Absorption sleeves and accessories for ferrite rings to reduce the RF current on the surface of the coaxial cable from the current transformer to the measurement receiver
current;
--- 6 dB attenuator between the output of the absorber clamp and the coaxial cable connected to the measurement receiver;
--- Coaxial cable to the measurement receiver.
the absorber clamp reference point (CRP), i.e. the longitudinal position of the front of the current transformer in the absorber clamp (see Figure A.2). This reference point is used to determine the measurement
The CRP should be marked on the housing of the absorber.
4.2.2 Absorption clamp factor and site attenuation at the absorption clamp test site
A diagram of the actual measurement using the ACMM is shown in Figure 2. More detailed provisions on ACMM are given in CISPR 16-2-2:
2003 in Chapter 7.
The nuisance power measurement is based on the measurement of the asymmetric current generated by the EUT by using a current probe at the input of the absorber clamp. The ferrite of the absorber clamp around the LUT isolates the disturbance from the supply power from the current transformer. The absorber is moved along the elongated LUT (as a transmission line) to find the maximum current. The input impedance of the clamp is converted to the output of the EUT via this transmission line. After optimal adjustment, the maximum disturbance current is measured at the current probe, i.e. the maximum disturbance voltage measured at the input of the measurement receiver.
4.2.3 Decoupling function of the absorber clamp
When the current transformer of the absorber clamp measures the disturbance power, the decoupling attenuation of the ferrite ring around the LUT generates an asymmetric impedance and isolates the current transformer from the remote end of the LUT, which reduces the disturbance effect of the connected power supply and the disturbance effect of the remote impedance as well as the effect on the measured current. This decoupling attenuation is called the decoupling factor (DF).
Secondary decoupling is required for the absorber clamp. Secondary decoupling is the decoupling of the asymmetric (common mode) impedance of the current transformer from the receiver cable. It is achieved by placing a ferrite ring on the cable between the current transformer and the measurement receiver. This decoupling attenuation is called the decoupling factor (DR) to the measurement receiver.
4.2.4 Requirements for the absorber clamp unit
Absorber clamps for nuisance power measurements shall meet the following requirements:
a) The actual clamp factor CFact (see definition in 4.2.2) of the absorber clamp device shall be determined according to the method specified in Appendix B. The uncertainty of the actual clamp factor shall be determined in accordance with the requirements of Appendix B.
b) The decoupling factor DF of impedance stabilisers for broadband RF absorbers and LUTs shall be verified in accordance with the measurement procedure described in Appendix B. The decoupling factor shall be at least 21 dB over the entire frequency band.
c) The decoupling performance of the measurement output from the current transformer to the absorber clamp shall be determined according to the measurement procedure described in Appendix B.
The decoupling factor DR to the measurement receiver should be at least 30 dB over the entire frequency band. 30 dB includes 20.5 dB of absorber clamp
30dB includes 20.5dB of absorber clamp attenuation and 9.5dB of coupling/decoupling network (CDN) attenuation.
d) The length of the absorber clamp housing should be 600mm ± 40mm.
e) A 50Ω RF attenuator of at least 6dB in size should be connected to the output of the absorber clamp.
4.3 Calibration methods of the absorber clamp and their interrelationships
The purpose of calibrating the absorber clamp is to determine the absorber clamp factor CF as close as possible to the actual measurement of the EUT. however, in
4.2.2 it has been shown that the absorption clamp factor is a function of the EUT, the characteristics of the absorbing clamp and the performance of the site. In order to achieve standardised (reproducible) measurements, the calibration method should use a well-defined and reproducible test site, together with a reproducible signal generator and measurement receiver. In this case, the only remaining variable is the calibrated absorber.
Two methods of calibrating the absorber clamp are described below with their respective advantages, disadvantages and areas of application (see Table 1). A diagram of the two available methods is given in Figure 3.
In general, each calibration method consists of the following two steps.
First, the measurement receiver obtains an output power Pgen as a reference value directly from the RF signal generator (50 Ω output impedance) via a 10 dB attenuator [Fig. 3a)]. Next, the nuisance power is measured by using one of the two available calibration methods below, with both the RF signal generator and the 10 dB attenuator unchanged, by using an absorption clamp.
a) Raw calibration method
The calibration arrangement for the raw calibration method is shown in Figure 3b), with a large vertical reference plane on the reference field. By definition, this gives a direct CF value and is used as a reference since the original calibration method is used for the determination of the limit values. The LUT is connected to the centre of the feedthrough connector on the vertical reference plane and the feedthrough connector is connected to the signal generator on the other side of the vertical reference plane. In this calibration configuration, the absorber clamp is moved along the LUT to find the maximum Porig value at each frequency point, according to the measurement procedure specified in Appendix B.
b) Fixture calibration method The fixture calibration method is achieved by means of a calibration fixture, the length of which is capable of accommodating the absorber calibrated and the auxiliary absorption device (SAD). The fixture provides a reference structure for the absorber clamp [see Figure 3c)]. In this calibration configuration, the Pjig is a function of frequency when the absorber clamp is held in one of the fixture positions.
4.4 Auxiliary Absorption Device
In addition to the absorbing part of the absorber clamp, a secondary absorbing device (SAD) should be placed directly behind the absorber clamp to reduce the measurement uncertainty. the SAD serves to provide additional decoupling attenuation on top of that provided by the absorber clamp. During calibration and measurement, the SAD should be moved in the same way as the absorber clamp. To enable the SAD to be easily moved, wheels are required and the SAD should be sized so that the height of the LUT in it corresponds to its height in the absorber clamp.
The decoupling factor of the SAD should be verified according to the measurement procedure described in Appendix B. The decoupling factor of the SAD should be measured together with the absorber clamp.
The decoupling factor of the SAD should be measured together with the absorber clamp.
Note: New technology has made it possible to integrate the additional decoupling function of the SAD into the absorber clamp. Therefore, it is not necessary to use the SAD if the decoupling factor requirement is already met by the absorber clamp itself.
4.5 Absorbing Clamp Test Site (ACTS)
4.5.1 Description of ACTS
The ACTS is suitable for use with the ACMM, either outdoors or indoors, and consists of the following components (as per Figure C.1 in Appendix C)
Figure C.1):
--- Test table to hold the EUT;
--- Clamp slides to support the connection cable (i.e. LUT) between the absorbent clamp and the EUT;
--- rails for the connection cable between the Absorbing Tongs and the Measuring Receiver;
--- Auxiliary means, such as a rope to assist the movement of the absorber clamp.
All ACTS components mentioned above (excluding the EUT test table) should be measured in accordance with the ACTS validation procedure.
The end of the clamp slide closer to the EUT side is used as the reference point for the slide (SRP, as per Figure C.1). This reference point is used to determine the horizontal distance between this point and the CRP of the absorber clamp.
4.5.2 Performance of the ACTS
The ACTS has the following properties:
a) Physical: It provides a specific means of support for the EUT and LUT.
b) Electrical: It provides an ideal (from an RF point of view) site for the absorber clamp and the EUT, providing a good measurement environment for the use of the absorber clamp [without
good measurement environment [no distortion of the emission due to walls or support elements (e.g. EUT test tables, clamp slides, rail fixings and cords)].
4.5.3 ACTS]
4.5.3 ACTS requirements
4.5.4 Method of ACTS validation
The characteristics of the ACTS are confirmed as follows.
4.6 Quality assurance procedures for absorption clamp systems
4.6.1 Overview
The performance of absorbent tongs and SADs is subject to change over time due to use, ageing or defects. Similarly, the performance of ACTS can change due to changes in their construction or the onset of ageing.
If the initial fixture clamp factor is known, then the fixture calibration method can be easily used for quality assurance procedures.
4.6.2 ACTS quality assurance verification
Data from the site attenuation Aref identified at the site after ACTS has been verified can be used as reference data.
After an interval of time or after a change of site, the site attenuation measurements should be repeated and the results compared with the reference data.
The advantage of this method is that all components of the ACMM can be evaluated in one go.
4.6.3 Quality assurance verification of the absorber clamp
The decoupling factor and the clamp factor determined for a validated absorber clamp can be used as reference data.
These two performance parameters should be revalidated after a period of time or after a change of site by measuring the decoupling factor and by measuring the clamp factor using the fixture calibration method (as per Appendix B).
4.6.4 Pass/fail quality assurance guidelines
The pass/fail criteria for quality assurance tests relate to the measurement uncertainty of these measurement parameters. This means that if the variation in these parameters is less than the measurement uncertainty, the variation in the parameters is acceptable.
Appendix A (informative) Structure of the absorption clamp (see 4.2)
Appendix B (normative) Calibration and validation methods for absorbing tongs and auxiliary absorbing devices (Chapter 4)
Appendix C (prescriptive) Confirmation of the absorption clamp test site (Chapter 4)
Bibliography
1 Scope
2 Normative references
3 Terms and definitions, abbreviations
4 Absorption clamp equipment
Appendix A (informative) Structure of the absorption clamp (see 4.2)
Appendix B (normative) Calibration and validation methods for absorbing tongs and auxiliary absorbing devices (Chapter 4)
Appendix C (prescriptive) Confirmation of the absorption clamp test site (Chapter 4)
Bibliography
