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

CISPR 25 Conducted Emissions Current (CEI) Grounding Scheme

An incorrect DUT grounding scheme can easily make the difference between compliance and non-complian

An incorrect DUT grounding scheme can easily make the difference between compliance and non-compliance to CISPR 25 CEI limits. Sometimes we have to evaluate CEI from two modules, one used as DUT and the other one used as DUT's load (e.g. Module #1 is a PWM maker while Module #2 is an LEDs Lamp).


Christian Rosu, 2021-06-09

Common Test Requirements in EMC Validations

19. April 2021 09:30 by Christian in EMC/EMI, EMC TEST PLAN, Load Simulator
Based on FMC1278R3 and CS.00054:2018 Production Representative Hardware and Software should be used

Based on FMC1278R3 and CS.00054:2018 Production Representative Hardware and Software should be used for all verification testing unless approved differently by OEM via EMC Test Plan. 

The Production Representative Test Sample is built using production representative hardware and software constructed using production representative processes, tooling, etc.

Following Software Changes in addition to PCB Changes re-validation for test methods like ESD, CISPR 25 RE, BCI, RI ALSE , Hand Portable Transmitters, Transients, Voltage Dips and Dropouts may be required. 

FMC require DV testing to be performed using production representative components but not necessarily components constructed from production tooling.

EMC DV1 Testing for PCM (Powertrain Control Module) is normally performed with test software mutually agreed to by FMC D&R, EMC and the supplier.
EMC DV2 Testing for PCM must be completed using Production Intent Hardware and the latest available Application Software.

FCA require DUT Validation Testing done on Production Intent Samples using Production Intent Hardware and Software.
Production Intent Components must be used for the inputs and loads including switches, sensors, pulse width modulated loads, solenoids and motors.

Using DC Power Supply to simulate Automotive Battery for EMC testing

19. April 2021 08:23 by Christian in EMC/EMI, EMC TEST PLAN, Load Simulator
The DC Power Supply should be selected as follows:Rs (Internal Resistance) < 0.01 OHM DCZs (Inter

The DC Power Supply should be selected as follows:
Rs (Internal Resistance) < 0.01 OHM DC
Zs (Internal Impedance) = Rs for frequencies < 400 Hz.
Output Voltage:
▶ does not deviate more than 1 V from 0 to maximum load (including inrush current)
▶ recovers 63% of its maximum excursion within 100 ms
Vr (Superimposed Ripple Voltage):
▶ does not exceed 0.2 V peak-to-peak
▶ maximum frequency of 400 Hz

 When a battery is used for EMC testing, a charging source is needed to achieve the specified voltage reference levels.

It is important to ensure that the charging source does not affect the test.

 Linear Power Supplies are preferable vs Switching Power Supplies.

 Prior to CISPR 25 test methods ensure that the RF noise produced by the power supply is at least 6 dB lower than the limits specified in EMC Test Plan.

 If the Power Supply is located outside of the EMC test chamber, ensure thzt a bulkhead RF filter is used to prevent RF noise from entering or leaving the shielded enclosure.

 If using a HV battery, then it must be contained in a shielded enclosure.

 12V Power Supply Volatge = 13.5 (+0.5/-1.0)V

 24V Power Supply Voltage = 26 (+1.0/-2.0 V

CISPR25 Conduct Emissions Current Grounding Scheme

A few remarks on correct Load Simulator configuration for CISPR 25 Conducted Emissions Current test

A few remarks on correct Load Simulator configuration for CISPR 25 Conducted Emissions Current test method.

First of all you have to show the LISN in your EMC Test Plan block diagrams. The way the LS is connected is not identical for each CISPR 25 test method. I will never use a Load Simulator unless is no other way around or I would want to turn it into a RF filter box. Examples of CEI good and bad setups are shown below:




To clarify how a PWM maker is connected:

From EMC compliance perspective the goal is to avoid as much as possible common line impedances:


Christian Rosu


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.