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

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

CISPR-25 RE per CS.00054:2018

15. October 2019 10:00 by Christian in EMC/EMI, OEM Specs, Test Equipment, Test Methods
CISPR-25 Generic Test Setup for compliance to CS.00054:2018.

CISPR-25 Generic Test Setup for compliance to CS.00054:2018

CS.00054 Radiated Emissions Block Diagram
 
The vertical monopole element is centered at 1m from the center of the 1.7m test harness. Note that 1.5m of the harness is running at 10 cm parallel with ground plane edge. The antenna counterpoise is placed +10/-20 mm vs GP. 
 
CISPR-25 Generic DUT Setup. The DUT is placed @ 20 cm from the edge of GP. The 1.7 m Test Harness is routed 90 degrees towards DUT.
 
The ground plane is connected to chamber's floor to a dedicated Earth Grounding Rod.
 
LISN (700 V DC / 500 A) & Load Simulator side of the test setup. 
DUT's B+ & GND lines are connected to LISN's outputs.
 
THE BICONICAL ANTENNA IN VERTICAL POLARIZATION. 
The antenna is centered on the 1.5m harness running at 10 cm parallel with GP edge.
 
THE BICONICAL ANTENNA IN HORIZONTAL POLARIZATION. 
The antenna is centered on the 1.5m harness running at 10 cm parallel with GP edge.
 
THE LOG PERIODIC ANTENNA IN VERTICAL POLARIZATION. 
The tip of antenna is 1 m away from the center of the test harness.
 
THE LOG PERIODIC ANTENNA IN HORIZONTAL POLARIZATION. 
The tip of antenna is 1 m away from the center of the test harness.
 
Octave Antenna Vertical Polarization with its aperture centered on DUT at 1 m distance from test harness.
 
Octave Antenna Horizontal Polarization with its aperture centered on DUT at 1 m distance from test harness.
 
Horn Antenna Horizontal Polarization with its aperture centered on DUT at 1 m distance from test harness.
 
Horn Antenna Vertical Polarization with its aperture centered on DUT at 1 m distance from test harness.

 

 
3-METER ALSE CHAMBER & Equipment Control Shielded Room.
 

ALSE CHAMBER EARTH GROUNDING ROD.

RI 115 "ALSE chamber open door" test configuration

5. June 2017 09:22 by Christian in
A few months ago I was surprised that UL lab (Novi, MI) runs RI 115 (Immunity to Hand Port

A few months ago I was surprised that UL lab (Novi, MI) runs RI 115 (Immunity to Hand Portable Transmitters) leaving the ALSE chamber door fully open. I have requested the test engineer to confirm that he follows correctly UL lab internal test procedure. The response was that this is practically near field RF immunity, therefore there is no concern to interfere with other lab test equipment.


This is completely false, the reason for closing ALSE chamber door during RF immunity is to evaluate the DUT performance in a noise free environment with minimum of reflections from the chamber's walls. By opening ALSE chamber door RF emissions from nearby test equipment, broadcast and mobile services may be reflected from walls affecting DUT performance simultaneously with the intended RF near field.

I would be very curious to understand how was possible for A2LA to certify such test setup. Is this "open door" RI 115 configuration acceptable for Ford?



CISPR-25 RF emissions ambient test pitfalls

25. April 2017 15:48 by Christian in EMC/EMI, EMC TEST PLAN, Standards
CISPR-25 is not very specific in regards to chamber ambient test setup configuration in regards to d

CISPR-25 is not very specific about device under test and support equipment configuration during chamber ambient test. The automotive OEM require the ambient for RE, CE-V, CE-I with support equipment energized. The test laboratories will typically disconnect VBATT line from LISN output. The GND line remains connected to LISN. By doing so is assumed that DUT is not energized. The support equipment remains connected to the input of the LISNs being turned on (energized). The CAN bus is powered but w/o traffic. It is unclear if the load simulator energized it means powered but inactive (standby). By activating PWM pulses as inputs for DUT it may yield unwanted CE-I and RE ambient noise. All these aspects must be clarified in the EMC test plan.

In the sample presented the CE-V ambient noise is well below the 6 dB requirement. However, this type of noise is being captured while DUT's integrated buttons are being pressed and released via a pneumatic system with no electrical connection to DUT or test ground plane. Specifying that DUT must be unpowered may not be enough, the DUT's buttons should not be mechanically activated, nor its inputs subjected to electrical signals.

 
Christian Rosu

RI 115 copy and paste fake report

22. April 2017 02:28 by Christian in
The automotive OEM that certifies EMC laboratories to carry out validation testing invested a lot of

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). 

Page #6 vs Page #18

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.

The issue with the above result is that the same severity level threshold result was copied from one sample to another (7002 to 7000). It is impossible to have identical 3-digit accuracy readings between two test samples for the same antenna position and orientation. In fact, considering the uncertainty of test equipment combined with HW/SW tolerances of DUT it is impossible if scanning the same sample twice. The test result data file is generated automatically by the software running the test equipment. Chances to be a copy and paste mistake are zero.
Page #7 vs Page #24

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.

Page #9 vs Page #21
The test operator was in rush missing to change the test sample number from 7002 to 7000. Page #9 was supposed to show results from sample #7000. For the failed frequency step (850 MHz) the test operator slightly changed the Level 1 threshold value on the second tested sample (from 6.058 to 6.15 Watts) leaving unchanged the level 2 threshold values for all other  frequencies. Looking closely to date/time stamps they also are identical on both pages. Is this a honest mistake? 

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

Page #11 vs Page #23

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?

Page #12 vs Page #19

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.

Page #13 vs Page #25

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