27. April 2016 01:39 by Christian
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.
3. April 2016 13:31 by Christian
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:
BCI Probe Insertion Loss per MIL STD 416F CS114:
RF Immunity Ratio mA versus V/m per MIL STD 416F:
Ford RI 112 (BCI) Calibration Limits requirements per FMC1278:
28. March 2016 01:35 by Christian
CAN Bus Off is an error state of the CAN controller and it can be set only by the Transmitter Node when Transmit Error Counter is above 255. Such critical error is usually the result of a critical hardware issue (e.g. high level of electromagnetic field, bus wiring short-circuit, defective transceiver).
Methods to self-recover from a Node CAN Bus Off state:
1) Automatically after the CAN controller generates an interrupt.
2) Manually upon User request (ISO11898-1 §6.15).
In both the above instances the bus turns back on after 128 occurrences of 11 consecutive Recessive Bits (BOSCH CAN 2.0B §8.12).
Auto-Bus-ON is not required by ISO 11989, therefore the CAN controller makers let the application to decide on its implementation. The automotive industry does not encourage the auto-bus-on feature.
If application's driver reports repeatedly the CAN Bus Off state the application should stop using the CAN.
27. March 2016 09:49 by Christian
The data is carried on the CAN bus as a voltage difference between the
two signal lines. If both lines are at the same voltage, the signal is a
recessive bit. If the CAN_H line is higher than the CAN_L line by 0.9V,
the signal line is a dominant bit.
Immunity to Ground Noise
The CAN bus does not use the ground as
reference point for these two signal lines. Therefore the CAN bus transmissions lines are immune to any
ground noise typically present in automotive applications.
Immunity to Electromagnetic Filed
The signals on the two CAN lines will both be subject to the same
electromagnetic filed level. Therefore no differences in voltages between
the two lines should become relevant under
Using Twisted Pair Wires for Differential Signal Lines
Bad connectors are almost guaranteed to present an impedance discontinuity,
and hence will cause reflections. Transmission line stubs of any length are also a source of
reflections, longer the stub, the worse the impact of the reflections on lower data rate signals. Reflections are bad because they can cause destructive interference that can corrupt any transmitted data.