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

Compliance to CISPR-25 Conducted Emissions Voltage

8. February 2020 07:30 by Christian in
When comes to achieving EMC compliance for automotive specs a 2-layer PCB works only for very simple

When comes to achieving EMC compliance for automotive specs a 2-layer PCB works only for very simple designs. Modules having CAN/LIN, USB, E-Net, LVDS are normally using 4-layer PCBs. If adding CPU and memory a 4-layer PCB may not be good enough.

Ford (FMC) mentioned 20 years ago in their EMC design guide for 2-layer PCB to use the “Ground Grid Technique” for top and bottom side of PCB. They also recommended the use of "Faraday Cage" by installing ground vias around the perimeter of the PCB every say 15mm that are connected together on both PCB sides by 0.4 mm thick traces.

The problem with CE-V is that even using a “ground grid” or “faraday cage” won’t prevent DUT’s noise to be coupled into Supply Lines. Assuming that in your case CE-V are higher on GND line I would:

  1. determine potential sources of noise with harmonics in FM band
  2. determine the noise coupling method (e.g. common mode current, common return path, ground loops)
  3. Clamp ferrite corres on the entire test harness to lower CE-V noise below limit. Clamp the same ferrite separately on VBATT or GND line to determine which one is more affected. 

RF filters are effective for emissions exceeding the limit with 2-3 dB. For conducted emissions exceeding the limit with 10 dB you better try to fix the layout first.


Christian Rosu Feb 8, 2020.

CAN Bus Hardware Verification

4. February 2020 04:46 by Christian in
CAN Bus TerminationThe termination is used to match impedance of a node to the impedance of the tran

CAN Bus Termination

The termination is used to match impedance of a node to the impedance of the transmission line being used. When impedance is mismatched, the transmitted signal is not completely absorbed by the load and a portion is reflected back into the  transmission line. If the source, transmission line and load impedance are equal these reflections are eliminated. This test measures the series resistance of the CAN data pair conductors and the attached terminating resistors.

1. Turn off all power supplies of the attached CAN nodes.

2. Measure the DC resistance between CAN_H and CAN_L at the middle and ends of the network.

The measured value should be between 50 and 70 Ω. The measured value should be nearly the same at each point of the network. If the value is below 50 Ω, please make sure that:

- there is no short circuit between CAN_H and CAN_L wiring

- there are not more than two terminating resistors

- the nodes do not have faulty transceivers.

If the value is higher than 70 Ω, please make sure that:

- there are no open circuits in CAN_H or CAN_L wiring

- your bus system has two terminating resistors (one at each end) and that they are 120 Ω each.

 

CAN_H/CAN_L Voltage Verification

Each node contains a CAN transceiver that outputs differential signals. When the network communication is idle the CAN_H and CAN_L voltages are approximately 2.5 volts. Faulty transceivers can cause the idle voltages to vary and disrupt network communication. To test for faulty transceivers, please

1. Turn on all supplies.

2. Stop all network communication.

3. Measure the DC voltage between CAN_H and GND

4. Measure the DC voltage between CAN_L and GND

Normally the voltage should be between 2.0 V and 4.0 V. If it is lower than 2.0 V or higher than 4.0 V, it is possible that one or more nodes have faulty transceivers. For a voltage lower than 2.0 V please check CAN_H and CAN_L conductors for continuity. For a voltage higher than 4.0 V, please check for excessive voltage.

 

CAN Bus Ground Verification

The shield of the CAN network has to be grounded at only one location. This test will indicate if the shielding is grounded in several places: 

1. Disconnect the shield wire (Shield) from the ground.

2. Measure the DC resistance between Shield and ground.

3. Connect Shield wire to ground.

 The resistance should be higher than 1 M Ω. If it is lower, please search for additional grounding of the shield wires.

 

CAN Transceiver Resistance Test

CAN transceivers have one circuit that controls CAN_H and another circuit that controls CAN_L. Experience has shown that electrical damage to one or both of the circuits may increase the leakage current in these circuits. To measure the current leakage through the CAN circuits, please use an resistance measuring device and:

1. Disconnect the node from the network. Leave the node unpowered.

2. Measure the DC resistance between CAN_H and CAN_GND.

3. Measure the DC resistance between CAN_L and CAN_GND.

Normally the resistance should be between 1 M Ω and 4 M Ω or higher. If it is lower than this range, the CAN transceiver is probably faulty.

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.

VISIT OUR NEW EMC LAB BLOG

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?