Report of the meeting of SC-05-05, Working Group on Grounding and EMC
Practices of the SC-05 Subcommittee on Interconnections, held in conjunction
with the 112th AES Convention in Munich, Germany on Friday 2002-05-10.
The meeting was convened by the chair, B Olson.
The agenda order was revised by the chair to have the AES-X13 item appear at the end of Current Projects. The revised agenda was approved. The report of the meeting in November 2001 in New York City was accepted as written.
Current Projects
AES-X27 Test Methods for Measuring Electromagnetic Interference
This document is intended to be an Engineering Report outlining useful procedures for measuring the electromagnetic interference created by real-world conditions.
A report called "Informal immunity testing of small mic pre-amps and mix consoles" was presented by J Brown. This showed the general direction that we will need to go to produce a set of guidelines allowing users to determine the susceptibility of equipment to electromagnetic interference.
R Caine pointed out that this testing could be much more stringent than the legal requirements and is intended to show the ability of equipment that is most suitable for the highest quality pro-audio systems.
It is hoped that manufacturers will be encouraged to produce a low-cost test generator that will allow suitable testing of equipment using a variety of test fixtures.
Alternatively, the document will describe procedures that can be used with radios transmitters or cell-phones as the interference source. These radios and cell-phones would need to be used in their normal operation by licensed operators as required by relevant statute.
The following observations were made from initial experience of testing with radios and cell-phones:
1) As frequency increased, the immunity improved.
2) As the distance from the device increased past a wavelength of the RF carrier, the cable attenuation reduced the level of the interference and therefore the immunity was also increased.
3) The headphone output stages of some mixers were often the most susceptible to interference.
This report on informal immunity testing was NOT directed only at AES-X27, but rather at demonstrating the general level of immunity of some typical low cost products to a real world interference source. Inclusion of such a test into AES-X27 was discussed and considered useful by those members present, but the need for cautions regarding the avoidance of interference to radio communications and conformance with national regulations was emphasized.
Caine points out that a coupling device would be useful for the radiated immunity tests.
J Woodgate pointed out that this project originally started as a set of tests for low-frequency interference. He also pointed out that it should reference IEC 61004 as the primary test method.
Olson proposed a foreword for AES-X27 that clearly presents why these tests are different from either EN 55103-2 or IEC 61004. AES-X27 should address testing for pin 1 problems at both audio and radio frequencies, testing of excessive input and output bandwidth, and general RF immunity testing.
Brown offered to lead the writing effort for AES-X27.
The expectation is for a PWD for the Standards Project Report by 2002-09.
AES-X35 Installation Wiring Practices
Olson proposed an outline to guide further development of the document.
I. Cable Grouping
II. Grounding
A. Mesh
B. Star
C. Hybrid
D. Wrong
III. Safety
A. Fire and Smoke
IV. Shielding
V. Cable Types
A. Conduit
B. Plenum requirements
VI. Wiring Practices
A. Permanent installations
B. Temporary installations
VII. Connectors
Woodgate pointed out the need for Normative References to the relevant safety standards and documents. This will be a substantial amount of work.
The chair will find help to merge the existing AES-X35 document into the new outline.
AES-X112 Insulating Cable-Mount XL Connectors
A new, clearer title was proposed: 'XLR free connectors with non-conducting shells'.
The intent is to create an Information Document on applications of connectors for facilities. This should include an explanation of stopgap measures using non-conductive covers to prevent inadvertent ground connections to the shielding contact. This work should appear as part of the X35 document. Woodgate offered to write a section for AES-X35 regarding this.
AES-X125 Input filtering for electromagnetic compatibility
Waldron indicated that K Armstrong would write an information document for this project.
Brown proposed that the scope be expanded to include output and control port filtering. This need not be specific, but should list the appropriate issues to consider. The WG decided that just input and output filtering would be included at this stage.
AES-X13 Guidelines for Grounding
The scope of the document has been greatly simplified. Specific wording was discussed to remove performance requirements, and clarify definitions. The meeting agreed on all the wording changes and decided that the PWD was ready to be progressed to a PCFC. The revised document will be posted to the reflector before being forwarded to the Secretariat to be formatted as a PCFC.
M Natter presented preliminary results of measurements made on a connector prototype that incorporates some ideas for coaxial connection thru a quasi-discoid capacitor to the shell of an XLR connector. The results look promising but need further investigation and testing.
Much discussion ensued about the need for protection from surges across the capacitor. More testing and measurement is required to show whether this is a problem. R Cabot pointed out that, for the value of capacitance under consideration, it did not appear that a damaging voltage would appear across the capacitor in any configuration.
New projects
There were no new projects.
New business
There was no new business.
The next meeting will take place in conjuntion with the 113th AES Convention in Los Angeles, CA, US.
