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

The automotive OEM that certifies EMC laboratories to carry out validation testing invested a lot of trust in accuracy and correctness of so called "sign-off" reports. This "sign-off test results"  or "not for sign-off test results" statement maybe an excuse for skipping a full review if the summary looks clean.

The automotive electronic device supplier must always verify in detail the report to clarify each reported non-conformance. Otherwise it may adversely affect the entire validation process through endless testing to fix potential false issues.

The sample of bad report shown below may easily go undetected by those searching for easy resolutions (pass / fail). 

In tis particular case two samples (7000 & 7002) are being evaluated for near filed interferences from portable transmitters.

The requirement for DUT in question is to pass Level 1 in band#9 (no deviation allowed under 7 Watts). The testing is carried out at 14 Watts, which is the Level 2 Severity. Whenever a deviation occurs the test operator must threshold the lowest severity level where the problem goes away.

Looking over page's date/time the scan below was generated before the scan above. However the order of pages is as was listed in the full report.

This kind of precision in measurements would humiliate any theory so far.

The perfect DUT type ever, perfect RI 115 equipment, perfect test operator, perfect identical hand portable transmitters immunity!

Going over pages's date/time they both have the same stamp. Theb why inserting them such that they apear to belong to separate test samples?

Surprisingly, but there is an antenna position where the result was either correctly tested or correctly represented.

This was the only instance where the RI 115 result from one sample was not copied over the for the other sample.

The RI 115 make up report saga continues. As long as the customer is preoccupied by the deviation in Level 1 it will never pay attention that only one sample was fully tested. The really bad part is that the designer will believe there is some sort of stability in DUT's behavior when in fact it was a huge instability.

Again same date/time stamp but different test sample numbers. How was this possible?

Christian Rosu

Trialon EMC Laboratory, Burton, MI

Igor Klivak

ES-XW7T-1A278-AC Immunity from Continuous Disturbances: CI 210

This test refers to continuous disturbances produced by vehicle’s charging system that can affect DUT functions.

• Level 2 requirements, as delineated in ES-XW7T-1A278-AC was removed in EMC-CS-2009.1, then added back in FMC1278.
• The frequency range allocated for severity levels was changed subsequently in all three Ford EMC specifications.
• The most significant differences for Us Vp-p requirements occurred between  ES-XW7T-1A278-AC & EMC-CS-2009.1.

• The test harness connecting the DUT to the Test Fixture and transient pulse generator shall be < 2000 mm in length.
• The DUT and wire harness shall be placed on an insulated support 50 mm above the ground plane. If the outer case of the DUT is metal and can be grounded when installed in the vehicle, the DUT shall be mounted and electrically connected to the ground plane.
  

1. Adjust DC offset of the signal generator/audio amplifier to 13.5 volts with the DUT disconnected (open circuit)
2. At each test frequency set and record the signal generator output to the specified voltage level with the DUT disconnected (open circuit).
3. Without the test signal present, connect the DUT and verify that it is functioning correctly.
4. Apply the test signal to the DUT and the Test Fixture such that all power and control circuits are exposed to the disturbance. All power and control circuits are tested simultaneously.
   

• The test harness connecting the DUT to the Load Simulator and modulated DC supply shall be < 2000 mm in length.
• All DUT power/power return circuits shall be connected together at the modulated power supply.
• Per previous versions of this requirement, a ground plane may be placed under the DUT and Load Simulator, but if used, the DUT and wire harness shall be placed on an insulated support 50mm above the ground  plane. Additionally, the negative connection of the modulated DC supply and case of the Load Simulator shall be referenced to the ground plane.
  

1. Without the DUT connected, adjust the DC voltage offset "Up" of the modulated power supply to 13.5 volts. Initially set the AC voltage amplitude "Us" to zero volts.
2. Connect and activate the DUT and verify it is functioning correctly. Verify that Up remains at 13.5 VDC. Adjust the supply as required to achieve this voltage level.
3. At each test frequency increase Us to the corresponding stress level while the DUT is operating. The dwell time shall be at least 2 seconds. A longer dwell time may be necessary if DUT function response times are expected to be longer. This information shall be documented in the EMC test plan.
   

• The test harness connecting the DUT to the Load Simulator and modulated DC supply shall be < 2000 mm in length.
• All DUT power/power return circuits shall be connected together at the modulated power supply.

1. Without the DUT connected, adjust the DC voltage offset "Up" of the modulated power supply to DUT’s system voltage (13.5, 27 volts). “Us” is initially set to zero volts.
2. At each test frequency adjust and record the signal generator output required to achieve the specified modulation voltage level “Us” with the DUT disconnected (open circuit). Use the frequency steps listed.
3. Without the modulation signal present (i.e. Us = 0 volts), connect the DUT and verify it is functioning correctly.
4. At each test frequency, apply the signal generator levels recorded in step (2) to the DUT and the Load Simulator such that all power and control circuits are exposed to the disturbance. The dwell time shall be at least 2 seconds. A longer dwell time may be necessary if DUT function response times are expected to be longer. This information shall be documented in the EMC test plan and test report.
   

Types of load dump transient generators

The high energy content of load dump pulse require specialized pulse generators like classic LCR or DC amplifier based pulse generators.

E.1 Determination and verification of pulse generator minimum energy capability
E.1.1 Calculation method
This method is used to calculate the energy of the pulse as delivered by the generator to the matching resistor (resistive load RL ), utilizing the measured pulse parameters td and Us.
The transient generator used shall generate double exponential transients, which are a result of capacitive discharges into a pulse shaping network. This type of generator is applicable to pulses 1 (12 V), 1 (24 V), 2a, 3a/3b and 5.

SAE J1113-11 (2007)
The Load Dump Pulse Suppressed or Unsuppressed  is defined regardless to specification used by (Us) Peak Voltage in Volts, (Ri) Internal Resistance in ohms, and (td) Duration in ms.



The precise characteristics of suppressed load dump pulse varies based on automotive OEM type of centralized LD suppressor used. The testing methodology is periodically adjusted to accommodate new type of electronic devices. As of today most OEM specifications tend to relay on ISO 16750 for Load Dump.

GM9105P Pulse#6 (LD)

• DUT that operate in a vehicle using avalanche/zener diodes in the alternator for LD protection
• suppressed LD must be clamped to the avalanche diode clamp level.
• DUT that provide vehicle LD protection must be tested to verify
• the peak current sinking capability
• the clamping voltage under load
• DUT expected to sink greater than 40 amps peak current (e.g., engine controller)
• tested with an additional 1 ohm of resistance in series with the simulator.
• DUT expected to sink greater than 25 amps peak current (e.g.,airbag control module)
• tested with an additional 2 ohms of resistance in series with the simulator.
• For both cases
• the clamping voltage under load, across the DUT, must be less than 40 volts
• For all other DUT
• open circuit pulse is clamped to an equivalent vehicle system level (40 V maximum, ramping to 35 V max at 100 ms and 25 V max at 200 ms) by connecting a vehicle suppression model in parallel across the load dump output

Case #2

• LD protection in a (single) centralized location
• The engine controller, airbag control module or other modules are not expected to sink load dump current.
• DUT that provide a centralized load dump clamp (e.g. zener protected power distribution center or PDC)
•  tested with the full simulator output with no additional series resistance.
• For all other DUT
• this open circuit pulse is to be clamped to an equivalent vehicle with simulated avalanche/zener diode suppression in the alternator system level (36 V maximum) by connecting an alternator simulator suppression model in parallel across the load dump output.

Case #3

• Alternator avalanche/zenner diode load dump protection
• LD test pulse applied to the DUT must be clamped to the avalanche/zener diode clamp level (32 V maximum) by an alternator equivalent suppression model.

Test Pulse #5B as delineated in LP-388C-36

• The suppression network shall be connected to the load dump simulator with a wire length of 20cm and in parallel with the DUT.
  
• Test all DUT supply terminals together.
• Leads to be load dumped include the following: battery, ignition and any other input and/or output sourced from battery or ignition voltage as configured in a DUT's complete vehicle system.
• Isolate any exerciser circuits, which are meant to simulate other electronic module peripherals to the DUT.
  
• Do not apply the transient to support equipment.
  
• The DUT supply voltage shall be provided through the load dump simulator, while the DUT exerciser shall be powered from a separate supply. The negative terminal for the two power supplies shall be connected together.

Suppression Module Verification

• Before the test, the Suppression Module must be verified with 13.5 dc volts offset.
  
• The output waveform is evaluated using the specifications defined in PF-9326.
  
• The results of both open and loaded measurements must be documented.

Load Dump Simulator Impedance Verification
The load dump waveform shall be verified with the output open-circuited and shall be evaluated using the specifications defined in PF-9326. Verify that the effect is not caused by the transient interfering with the DUT support equipment. If there is suspicion that the load dump is interfering directly with components of the DUT exerciser, measure the pulse amplitude appearing at the input to the exerciser component which is not meant to be tested. If a substantial amplitude is present, investigate by removing such components.



ES-XW7T-1A278-AB CI 240
A load dump typically occurs during a vehicle-to-vehicle jump start when the jumping vehicle can experience a significant load dump or due to a loose battery terminal. It represents sudden disconnection of load from alternator. Max voltage ESC is exposed to is about 45 V.

• Open Circuit: Vbat+ 60V, 300 ms
• Loaded Circuit: (R = 0.7W): Vbat+30 V, 150 ms

EMC-CS-2009.1 CI 220 Pulse G2 (Centralized Load Dump)
Practically the same CLDS suggested by SAE J1113-11.


FMC1278 Rev 2 CI 222 (Suppressed Load Dump Pulse 5b )



DUT Load Dump Protection using TVS Diodes
1. Darlington LD Suppression Circuit for low current consumption devices



2. P-FET LD Suppression Circuit



3. P-FET LD Suppression with Isolation Switch Circuit



Summary
1) TVS Diodes are used to protect DUT from various supply line transients


2) For vehicle having centralized load dump protection the test pulse used is ISO 7637-2:2004 (ISO 16750) 5b.
3) Avalanche diodes or Zener diodes are used in alternators to suppress the load dump to a voltage defined by automotive OEM.

The generic shielding effectiveness requirement is 40 dB for magnetic field, electric field, and plane waves. Depending on the application the frequency range can start from 10 Hz going up to GHz.

To predict shielding effectiveness (SE) of a metal sheet the following factors are summed:  Absorption Loss (A), Reflection Loss (R), re-Reflection Correction Factor (C).  SE = A + R – C (see MIL-HDBK-419A).

Absorption loss depends on material thickness, permeability, electrical conductivity, and the frequency of the incident wave.  It is the same for all electromagnetic waves.

Reflection loss depends on the distance of the EMI source to the material (different for electric, magnetic, and plane waves), material electrical conductivity, and the frequency of the incident wave.

• Materials_for_electromagnetic_interference_shielding.pdf (388.20 kb)
• Engineering_Aspects_of_Electromagnetic_Shielding.pdf (9.47 mb)
• IEEE-299-1997.pdf (502.42 kb)
• MF_SE_of_thin_conductive_coatings.pdf (282.80 kb)
• Predicted_and_measured_EMI_shielding.pdf (668.60 kb)
• Properties_of_metals_used_for_RF_shielding.pdf (4.80 mb)
• Shielding_Effectiveness_Superalloy_Aluminum_Mumetal_Shielding_Tapes .pdf (443.55 kb)

The Bulk Current Injection (BCI) test method simulates a field-to-wire coupling from nearby low frequencies radiated fields induced onto a test harness small relative to wavelength.
The coupling from BCI probe will increase with test frequency when the cable is electrically short, and then flatten out when the cable approaches and exceeds a half-wavelength in length.

The transducers (RF current transformers) inject current into both sides of the test harness, therefore both DUT and Load Simulator are subject to test. RF radiation from load simulator cables is possible, but it can be reduced placing 20cm of clip-on split-ferrite RF suppressers close to the transducer.

The BCI common-mode current injected in the test harness simulates an illuminating RF field.
To simulate conducted differential-mode disturbances the BCI induced current is injected in individul conductors.

Using the Substitution Method the actual current injected in test cables can vary from what was initially  calibrated, being less likely to over-test but more real-life representative.

To ensure the repeatability of test results, the cable under test must be centered within BCI current probe, the test set-up must be consistent, especially cable routing, placement of the clamp, and proximity to metal structures.

BCI Calibration Levels per MIL STD 416F CS114: