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

EMC Test Plans compliance tricks

8. November 2021 10:49 by Christian in EMC/EMI, EMC TEST PLAN, OEM Specs, Test Methods
How to cheat EMC requirements

FMC1278R3 specification mention that CI 280 (ESD Test Methods) must be carried out prior to any other test methods. If CI 280 fails, continuing the rest of EMC validation must be decided by FORD. The same 2 samples must theoretically withstand all FMC1278R3 test methods selected by EMC Test Plan.

The order of the test methods is critical, and the test results listed by laboratory report applies only to the two samples provided (Part Number, Serial Number, HW/SW revision). Some Europeans & Japanes automotive makers allow the use of multiple groups of samples to be used for simultaneously running test methods, probably to to speed up the completion of validation. This means that no sample is exposed to the full validation test list leaving room for insufficient EMC compliance evaluations.

Example of potentially destructive test methods:

  1. ESD on the first group of samples.
  2. Transients on supply lines on a second group of samples.
  3. Reverse Polarity on a third grtoup of samples

To compensate somehow such selective test methods allocation, the EMC Test Plan authors would require 3 samples per group instead of 2 samples per full validation. 

A parametric test is required following each immunity test method, and this may reveal some tolerances being pushed to one extreme if not outside the acceptable range. In a real scenario, following ESD powered one unit out of three was measured with 12 KΩ impedance on B+ line versus 16 KΩ prior to test. Other than that everything was functional, the DUT current consumption was the same before and after ESD. Theoretically this unit survived ESD and based on EMC Test Plan was not supposed to be tested for Transients on Supply Lines. By mistake this unit was tested for JASO Pulse B-2 (-260V) and the outcome was "sample damged on the second pulse". This EMC test plan trick was used to hide a poor DUT design performance for Honda that otherwise would have never pass FMC1278R3 spec.

  

 

Christian Rosu, Nov 8, 2021.

ISO 7637-2 Pulse #1 & Droputs monitoring tricks

5. November 2021 20:04 by Christian in EMC/EMI, EMC TEST PLAN, OEM Specs, Test Methods
EMC Test Plan tricks

ISO 7637-2 Pulse 1

Conducted Immunity to Transients on battery lines.

Pulse 1 (Us = -150V, Ri = 10Ω, td = 2 ms, tr = 1µs, t1 = ≥ 0.5s (repetition rate), t2 = 200 ms, t3 < 100µs) can upset functionality of electronic modules. Most automotive OEM specs are accepting Class B response (DUT self-recoverable deviations), others are asking Class A response (no deviations) during Pulse 1.

In this particular case the pass/fail criteria was Charging Voltage remains 5V ±0.5V for 12V Battery dropouts ≤ 500µs. The EMC test plan asked the use of DMM to monitor the USB charging function for a Class A expected response:

  • This was a simulation of a mobile phone charging event.
  • DMM can only detect 5V Charging Voltage dips/drops ≥ 250 µs. A FLUKE can be set to count MAX and MIN voltage peaks, otherwise to monitor 5V fast voltage fluctuations is not practically possible.
  • The EMC test plan allowed the use of oscilloscope only for information.

Download this movie to see how the charging function was monitored simultaneously on both oscilloscope and DMM:

 

5V_Charging_during_P1.mp4 (127.57 mb)  

 

A similar monitoring equipment limitation was imposed the EMC Test Plan for dropouts test. Download this movie to see how the charging function was monitored simultaneously on both oscilloscope and DMM:

 

5V_Charging_during_500_microSec_dropout.mp4 (30.91 mb) 

 

 Christian Rosu, Nov 8, 2021

EMC Test Plan - Pass/Fail Criteria

20. April 2021 22:08 by Christian in EMC/EMI, EMC TEST PLAN
One common mistake in EMC Test Plans is to associate Pass/Fail criteria with DUT Operating Modes. Fo

One common mistake in EMC Test Plans is to associate Pass/Fail criteria with DUT Operating Modes.

For Operating Modes it is critical to define how DUT's:
1) Load Simulator & Support Equipment is configured.
2) Functions are activated.
3) Behavior is monitored.
4) data is collected and reported.

Defining Pass/Fail Criteria for a particular Operating Mode maybe in conflict with requirements listed by automotive OEM EMC spec or standard. The DUT performance and response behavior will always vary depending on the Test Method.

Based on Functional Status Classification the Pass/Fail Criteria must be specified for each Test Method while the DUT is activated in a particular Operating Mode.

For example, ISO 7637-2 Pulse #1 (t2 is 0V for 200 ms). I doubt that an E-Net port won’t miss data packets generating bit errors under such circumstances. Depending on the Test Method and required immunity severity level the EMC spec/standard would allow certain self-recoverable DUT anomalies. Since the EMC Test Plan can override the EMC spec requirement would be a mistake to mention something like "no loss of E-Net data packets" as pass criteria for "DUT Operating Mode #1". This would imply that loosing one packet of data during Pulse #1 the DUT "fails" when in fact the EMC spec would allow it:

"One or more functions of the DUT can go beyond specified tolerance provided that all functions return within normal limits after the exposure is removed (e.g., after UA power is re-applied after the 200 ms defined by t2 as defined in ISO 7637-2). No damage or degradation of memory functions is permitted."

 

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) &amp;lt; 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

NOTE:
 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