Fritz Szoncso CERN TIS
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The wide dynamic range required for LHC frontend electronics demands a quasitotal elimination of noise. Even the effects of thermal noise must be limited using extensive signal processing. Handling of noise originating from signals outside the frontend electronics requires, above all, a clear understanding of its origin and nature. The noise paths also need to be followed and understood. Noise is firstly generated by induction coming from extra low frequency fields. Secondly, noise is transferred by conduction through galvanically coupled lines such as power supply lines, monitoring lines, test pulse system and improper earthing. Noise may, thirdly, also be provoked by radiation from nearby circuits leaking out radio frequency. The abundant presence of charged particles travelling at the speed of light also adds radio frequency background.
In order to assess the relevant EMC parameters of frontend electronics several well proven tests using standard instrumentation like pulse generators and oscilloscopes are described. 
Focus is then given on precise in situ measurements of EMC parameters using professional EMC equipment available at CERN and in specialized laboratories. Such measurements may ideally be performed during beam tests of prototypes. Radio frequency leakage and conducted noise both on low and radio frequency are the main concern. Standard aerials and current probes are used in combination with proper receiving equipment. The identification of the weaknesses of installed prototypes is the only way to improving on the harsh radio frequency near-field exposure of LHC-electronics. Much the same can be said about conducted noise and supply line feedthrough parameters. 
The test procedure for LHC frontend electronics ideally covers five measurements. A broadband radio frequency leakage measurement using a standard aerial in a distance of 1m, scanning of accessible electronics with H-field probes, measurement of conducted noise on the supply line using current probes, a short radio frequency irradiation test using ISM-frequencies (i.e. frequencies kept free for industrial, medical and scientific use) and an immunity test using an extra low frequency current probe. The duration of standardized measurements would be of the order of one hour. Setting up and transfer of the required apparatus is not included. 
Knowledge of frontend EMC parameters enables designers to avoid pitfalls in system design. The synchronous mode of operation may well prove very challenging on busbars and supply voltage feedthrough performance. In addition, knowledge on radiofrequency leakage values and locations clearly paves the way for system improvement prior to construction. Once the apparatus will run synchronously it will be virtually impossible to separate conducted from radiated noise. Even the identification of the source will be cumbersome. Profound appreciation of EMC effects will limit the requirements on screening and equipotentiality via long distances and metallic  structures.

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Characteristic EMC phenomena in high energy physics installations will be treated first. An assessment of EMC parameters using standard instruments and methods is given. The remedies of precise in-situ EMC measurements during prototype testing are evoked in detail. Finally a proposal is made on a test procedure for electronics during beam tests using standard EMC receiving equipment. Parameters found will enable designers to correct most problems prior to installation. Parameters will also be very useful for the layout of power supply and busbar systems. 
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