Set E1 - Immunity Development System
Exhibitor
Langer EMV-Technik GmbH
Field Sources: Essential Tools for EMC Immunity Testing During Development
Field sources are essential tools for EMC immunity testing during the development phase. They enable developers to selectively apply electric or magnetic fields to various surface areas of electronic assemblies.
Initial Low-Resolution Field Application
Typically, this process begins with low-resolution field sources to influence larger areas of the assembly with broad field bundles. This helps to narrow down the fault areas but does not determine the exact causes of the disturbances. Therefore, higher-resolution field sources are subsequently used. These emit narrow and concentrated field bundles, allowing clear identification of weak points within the fault areas. It is essential that the assembly is subjected to a standard generator (ESD or Burst) according to the norm. The resulting fault patterns are precisely recorded and must be replicated during localization with field sources.
Note: During analysis with field sources, new fault patterns may be discovered. These often occur below the disturbance threshold of the standard test and are therefore less critical. These additional fault patterns can be eliminated afterward, contributing to the hardening of the assembly.
Practical Example
Figures 1 to 3 show an electronic circuit where a processor controls a screen via HDMI. The processor is connected to a memory circuit (RAM) via bus lines (Figures 1-3) and continuously retrieves its program from it.
Subjecting the assembly to a standard generator results in the fault pattern where the screen content on the HDMI monitor freezes. The processor can only be reset by interrupting its power supply.
The first task is to reproduce the screen-freezing fault when the assembly is subjected to field sources. The HDMI system (connectors, HDMI cable, monitor) is initially considered a potential fault source. The troubleshooting begins with the BS 02 magnetic field source, the largest magnetic field source in the E1 set development system. Alternatively, the BS 02-h from the H2/3 field source set in combination with a burst generator or the BS 02-h from the TroubleStar ESD/Burst TS 23 set can be used. The BS 02 is guided over the assembly at a maximum distance of two centimeters (Figure 1). The possible localization of the weak point corresponds approximately to the size of the field source head.
When the HDMI system is subjected to the field source, image disturbances or a black screen occur, which do not match the sought fault pattern. Subsequently, the entire assembly is subjected to the BS 02 field source step by step. The sought fault can indeed be reproduced in the area of the processor and RAM.
Using the higher-resolution BS 04 DB field source (E1 set), the fault can be further localized (Figure 2). Alternatively, the BS 04DB-h from the H2 and H3 field source sets in combination with a burst generator can be used.
Initially, it is unclear whether the cause lies in the RAM, the traces, or the processor. Subjecting the surface of the memory circuit to the field source generates new fault patterns on the monitor (similar to a checkerboard pattern), which are initially not relevant (see above).
For further analysis, the BS 05 DU field source is used to examine the area of the bus traces between the two ICs (Figure 3). The fault pattern can be directly reproduced on the traces. With this knowledge, appropriate countermeasures can now be tested.
To eliminate the interference on the bus lines, they need to be shielded. For testing, the bus lines are covered with copper foil, and the assembly is subjected to the standard generator again. The result is that the shielding prevents the previous fault pattern. The successful shielding can now be implemented in practice through appropriate layout measures. For example, the bus lines could be placed in an inner layer and shielded with a ground plane.
Note: This immunity test should be conducted at the earliest development stage (first prototype) to avoid unnecessary layout changes. Through the targeted, strategic use of field sources, developers gain effective tools to identify weak points in the design and take targeted countermeasures.
Immunity trouble Shooting - Testing with E1 Set - Subject assemblies with Burst and replicate fault patterns with field sources,to harden your device.
1. Analysis of disturbance current paths Disturbance currents flow through the modules of an EUT during burst tests. The corresponding magnetic fields generate voltage differences in the GND system and/or induce voltages in signal loops. When a functional fault is produced in the EUT, the first step of the subsequent fault localization is to examine individual parts of the EUT such as individual modules, individual cable connections, small areas of a large module.
2. Fault localization with field sources The functional fault is often caused by magnetic fields of the disturbance current or by electric fields (inductive coupling). In order to pinpoint the place of interference, these fields are now injected with field sources which generate a magnetic or electric field in a small space. If a functional fault occurs when conducted disturbance current flows into and out of the EUT, magnetic field sources are used for fault localization. E field sources are used in the event that the fault occurs during inductive coupling.
3. Monitoring of EUT logic signals Signals are monitored when disturbances are coupled in so as to recognize disturbed logic signals and test the efficiency of EMC measures. These measurements allow statements with regard to the instantaneous operating state of EUTs if an interference is not immediately recognizable or not at all from outside. A sensor S21 is installed in the EUT for signal monitoring. This sensor transmits a signal which is significant for the EUT function without interacting with the EUT to the SGZ 21 via optical fibre.
4. Measuring burst magnetic fields The E1 allows measurements of burst magnetic fields in the EUT with hardly any interaction with the EUT, thus indicating the run of burst currents. Each measurement of burst magnetic fields provides two results: the amount of the magnetic field and the direction of the magnetic field. The direction of the magnetic field lines - the current involved flows at an angle of 90° to them - can be easily determined by turning the probe. It is thus possible to obtain a precise idea of the magnetic field in the EUT and to assess which structures are particularly at risk.
The surface of the E field source head allows the extensive coupling into housing surfaces and interior areas, connection technology and assemblies with conducting path structures and ICs ( e.g. bus systems, LCD displays). Furthermore its tip can be used for the localization of small E- field sensitive weak spots (conducting paths, quartz crystal, pull-up resistance, ICs).
The SGZ 21 burst generator generates floating, pulse shaped disturbance. Its outputs are seperated symmetrically and galvanically. SGZ 21 can be partially coupled to constructional parts, cables, shieldings, ground connections; directly in assemblies or indirectly via field sources of a device under test. A pulse rate counter with an optical input which detects signals from assemblies is integrated into SGZ 21. During burst testing with the S21 sensor which is installed on the assembly, electical signals from the assembly are transformed into optical signals. The pulse rate counter of SGZ 21 detects these optical signals. Futhermore, the MS 02 magnetic field probe can measure burst magnetic fields on the assembly and can transform them into optical signals during the test. This measuring procedure is suitable for signal monitoring during the burst tests or before and after measurements for controlling the EMC steps. The SGZ 21 conforms to following standards: EN 50 081-1/-2 and EN 50 082-1/-2.
