EMC FLEX BLOG A site dedicated to Automotive EMC Testing for Electronic Modules

Automotive EMC Load Simulators

28. September 2020 11:20 by Christian in EMC/EMI, EMC TEST PLAN, Load Simulator
During EMC compliance validations we monitor DUT (Device Under Test) errors visible for the occupant

The Load Simulator is defined in ISO 11452-1:2015 as: “physical device including real and/or simulated peripheral loads which are necessary to ensure DUT nominal and/or representative operation mode.”

 

During EMC compliance validations we monitor DUT (Device Under Test) errors visible for the occupant in vehicle in parallel with stored or not stored yet DTC (Diagnostic Trouble Codes). Disruptions in data bus or communication bus that do not set a DTC are not visible for the end user, since many of them are controlled safely by Vehicle Software & BCM.

 

 The driver can be distracted by vehicle cluster signs/indicators turning red, like an imminent hazard. 

  • If the incident self-recovers, it may not be a problem but it depends on DUT's Classification and Required Immunity Level.
  • If the DUT does not self-recover and require driver's intervention, then the LS support software must mimic the user response to resume operation (automation). Such anomaly is marked in a data log but should not be a reason to stop on-going testing.
  • If the DUT does not self-recover requiring Hard Reset (VBATT on-off-on), then it's really bad. This is like a stop show but make sure it is always driven by DUT, never the LS.
  • The pass/fail criteria mentioned in EMC test plan must guide your LS design effort, especially to decide on what type of FO monitoring equipment is needed.
  • Ideally is to use production intent DUT's I/O loading and Vehicle Software reducing the entire effort to monitoring the communication bus & FO equipment (e.g. FO Voltage Probes, FO Signal/Data Probe).
  • The moment you’re forced to use excessive HW/SW simulation, you practically spend more time validating the Load Simulator instead of focusing on DUT's EMC performance.
  • If possible, avoid using active electronic components for the LS placed inside ALSE chamber.
  • Use production intent loads, ideally EMC validated by OEM.
  • Use FO devices that are certified for 200 V/m, CISPR 25, 30KV ESD.
  • The support software should not stop the show if errors occur, only the DUT should be able to stop the show.
  • Pay attention how is the shielding of I/O lines terminated/grounded in vehicle and use if possible production intent cables and proper wire gauge.
  • For remote grounded module, make sure the only possible connection to battery negative pole is via supply return line. 
  • The LS metallic enclosure is bonded to GP (ground plane) being used as shield. 
  • The LS metallic enclosure is not being used as grounding point for DUT or LS electronics.
  • All signal return lines are closed to their source, never to GP.

 

Grounding Requirements

If DUT and LS grounding requirements are not defined by the automotive OEM EMC spec or Test Plan, then using automotive industry standards is acceptable (ISO 11452-2:2004-11-01, ISO 11452-4:2011-12-15, ISO 7637-2:2011-03-01, CISPR 25:2016-10-27):

"The DUT shall be placed on a non-conductive, low relative permittivity (dielectric-constant) material (εr ≤ 1,4), at (50 ± 5) mm above the ground plane. The case of the DUT shall not be grounded to the ground plane unless it is intended to simulate the actual vehicle configuration.”  

 

Preferably, the load simulator shall be placed directly on the ground plane. If the load simulator has a metallic case, this case shall be bonded to the ground plane. Alternatively, the load simulator may be located adjacent to the ground plane (with the case of the load simulator bonded to the ground plane) or outside of the test chamber, provided the test harness from the DUT passes through an RF boundary bonded to the ground plane.” 

 

“Bonded – grounded connection providing the lowest possible impedance (resistance and inductance) connection between two metallic parts with a d.c. resistance which shall not exceed 2,5 mΩ. Note 1 to entry: A low current (≤100 mA) 4-wire milliohm metre is recommended for this measurement" . This resistance needs to be verified with a milliohm meter. (ISO 11452-1:2015-06-01, MIL-STD-461G:2015-12-11).

 

 

Grounding Solutions:

  • Copper Tape (colored) with conductive adhesive.
  • Silver Tape with pressure sensitive adhesive (better contact), and tin-plating allowing soldering the tape directly to the ground plane, overall better resistance to corrosion.
  • Bonding Strap made from a semi-rigid flat metallic braid/weave that is copper tinned/untinned. Bonding straps are better than wires since their length to width ratio has lower inductance per unit length. The EMC test plan ahould specify that any ground straps used maintain a “5:1 length to width ratio or less” per MIL-STD-464C:2010-12-01. The impedance of ground straps at high frequencies varies with their width, length and addition of connectors (e.g. banana plugs). Since the ends of the braid may fray, ideally is to solder the ends of the braid. If adding a hole for a fastener (e.g. screw), the edges of the hole should be soldered to prevent fraying. The best grounding solution is to solder the braid to the ground plane.

Before using any of the above grounding solutions, the ground plane should be cleaned from oxidazation to achive better conductivity.

 

Grounding Point:

The EMC Test Plan should specify the DUT's case grounding point to ensure repeatsble results. The same for Load Simulator. 

 

Christian Rosu, Sep 28, 2020.

 

 

Validation Testing for Compliance to Automotive EMC Specs/Standards - EMC Test Plan

29. March 2020 05:35 by Christian in EMC/EMI, Load Simulator
A successful electronic module validation testing depends on:DUT Design Performance (60%).Load Simul

A successful electronic module validation testing depends on:

 

  1. DUT Design Performance (60%).
  2. Load Simulator & Support Equipment EMC compliance (20%). 
  3. EMC Test Plan (20%).

The Load Simulator must be CISPR-25, ISO 11452-2, and ISO 11452-4 compliant.

EMC Test Plan:

  • Select representative samples covering multiple vehicle platforms having design differences.
  • Select all applicable test methods except those that:
    • are not required for certain module category as outlined by OEM spec selection matrix.
    • are in conflict with design requirements imposed by Component Technical Specification (CTS).
  • Define for each DUT Type/Model:
    • Known sources of RF noise.
    • Functions Performance Classification.
    • Operating Modes per Test Method:
      • DUT Configuration:
        • Block Diagram including grounding scheme.
        • Connectors Pinout.
        • Test Harness Type & Mate Connectors:
          • standard 1.7 to maximum 2 m.
          • customized (inserted banana jacks & plugs @ 20cm from DUT  connectors).
          • ESD mate connectors with 2.5 solid core wire.
      • Activation Method:
        • Load Simulator HW/SW Configuration - Operating Manual.
        • Other DUT Support Equipment (e.g pneumatic activation).
        • Other DUT Support Software.
      • Monitoring Method:
        • DUT Test Points.
        • Load Simulator Test Points.
        • LS Configuration (e.g. switches, I/O lines). More details in LS Operating Manual.
      • How to evaluate a HW/SW Reset condition.
      • How to evaluate successful Self-Recovery.
      • Measurable Parameters & Tolerances:
        • Support Equipment:
          • Resolution (e.g. use oscilloscope vs DMM during voltage transients/dips/drops).
          • Fiber Optic (CAN, USB, E-Net, LVDS, etc). Must be 200 V/m compliant.
        • Support Software:
          • Configuration, data files format.
      • Differences between DUT Reset and Support Equipment Reset.
      • Pass/Fail Criteria per Test Point and DUT Function.
    • Reporting Data type and format (e.g. tables, plots, pics).
  • Negotiate EMC compliance deviations based on known DUT design limitations driven by cost/delivery.

 

Ground Return & Common Impedance Coupling

27. January 2020 09:26 by Christian in EMC/EMI, Load Simulator
Understanding the role of return ground is essential in EMC testing.Christian Rosu, Flexautomotive.n

Understanding the role of return ground is essential in EMC testing.

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See Differential Mode vs Common Mode Current

 

 
 

 
 

 
 

 

 

 
 
 
Christian Rosu, Flexautomotive.net,  2020-01-27