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

LISN (Line Impedance Stabilization Network) or AN (Artificial Network)

14. September 2015 14:29 by Christian in EMC/EMI, Standards, Test Equipment
Purpose of the LISN:1. Provide well defined RF impedance to the DUT.2. The 1μF & 50μH filt

Purpose of the LISN:
1. Provide well defined RF impedance to the DUT.
2. The 1μF & 50μH filter isolates the noise that is put on the supply lines by DUT from feeding back to the power supply / battery.
3. Provide a low impedance path for the noise to be measured at the output port of the LISN coupling the interference voltage generated by DUT via 0.1μF to the analyzer or receiver.

The role of the LISN is to isolate the DM current and CM current from the power supply, and to minimize the impact of the CM current by returning it to its sources.

The wire harness inductance for large systems (aircraft) is 50μH whereas for small systems (automotive) is 5μH. However, the LISN selection criteria should be based on the frequencies of the measurements required.

     

Types of LISN

  1. V-LISN: Unsymmetrical emissions (line-to-ground)
  2. Delta-LISN: Symmetric emissions (line-to-line)
  3. T-LISN: Asymmetric emissions (mid point line-to-line)

 

There are two types of V-LISN with different impedances.

  • 5 µH inductance (CISPR 16-1-2, CISPR 25, ISO 7637, SAE J1113-41, DO160) are normally used to measure equipment for vehicles, boats and aircrafts connected to on-boards mains with DC or 400 Hz.
  • 50 µH according to CISPR 16-1-2, MIL STD 461 and ANSI C63.4 is intended to operate at mains frequencies of 50 Hz or 60 Hz.

The T-LISN measures the asymmetric disturbance voltage (common mode voltage) and provides it to an EMI Receiver. It is normally used for measuring telecommunication and data transmission equipment connected to symmetrical lines as e.g. twisted pairs.

CISPR-25 (Ed 3.0)
A network inserted in the supply lead or signal/load lead of apparatus to be tested which provides, in a given frequency range, a specified load impedance for the measurement of disturbance voltages and which may isolate the apparatus from the supply or signal sources/loads in that frequency range.
CISPR-25 (Ed 3.0) & ISO-11452-2:2004 & ISO-11452-4
The AN impedance ZPB (tolerance ± 20 %) in the measurement frequency range of 0.1 MHz to 100 MHz it is measured between the terminals P and B with a 50 Ω load on the measurement port and with terminals A and B short-circuited.

  

The 1μF capacitor is populated in CISPR-25 LISN; R=1Kohm.

 

ISO 7637-2:2011 & ISO-11452-2:2004 & ISO 7637-2:2004
The artificial network is used as a reference standard in the laboratory in place of the impedance of the vehicle wiring harness in order to determine the behavior of electrical/electronic devices.
ISO 7637-2:2011 & ISO 7637-2:2004
The resulting values of impedance ZPB, measured between the terminals P and B while terminals A and B are short-circuited, are given in figure below as a function of frequency assuming ideal electric components. In reality, the impedance of an artificial network shall not deviate more than 10 % from the given curve.

  

No 1μF populated in ISO 7637-2 LISN; R =50 ohm, C is function of voltage.

 

Sample setup: CISPR-25 require separate LISN for B+ and GND lines.

Christian Rosu

Electromagnetic Spectrum

13. September 2015 15:32 by Christian in Standards
Spectrum is a continuum of all electromagnetic waves (EM) traveling at constant speed (300,000 km/s)

Spectrum is a continuum of all electromagnetic waves (EM) traveling at constant speed (300,000 km/s). An electromagnetic wave consists of electric and magnetic fields which vibrates thus making waves. EM wave wavelength decreases as its frequency increases. Shorter the wavelength, higher is the EM wave energy. Waves with higher frequency can carry a higher energy. The energy is measured in Joules or Electron-Volt (1 J = 6.241509 *10^18 eV).

Wave speed is independent of frequency. Frequency has an inverse relationship to the wavelength, λ (lambda). Lambda * Frequency = Speed

 

 

 

 

Frequency Allocation Charts:

US: 2011_US_rf_spectrum_chart.pdf (334.3KB)

CANADA: 2014_Canadian_Radio_Spectrum_Chart.pdf (279.1KB)

UK: uk_frequency_allocations_chart.pdf (325.8KB)

AUSTRALIA: aust_rf_spectrum_allocations_chart.pdf (296.7KB)

IEC 61000-4-4 (Electric Fast Transients / Burst)

13. September 2015 14:28 by Christian in Test Methods
A burst arc occurs when a mechanical contact is open during the switching process.Burst sources:• Ci

A burst arc occurs when a mechanical contact is open during the switching process. Burst sources:
• Circuit Breakers in electrical circuits
• High Voltage switchgear
• 110/230V Power Supply systems
• 24V Control Lines

A burst has a single pulse rise time/duration of 5 ns / 50 ns from a 50 Ohm source impedance.
Bursts of 15 ms duration with a repetition rate of 5 kHz (or 100 kHz) are applied every 300 ms.

Voltage test levels:
• Power ports: 0.5 KV, 1 KV, 2 KV, 4 kV
• Signal and Control ports: 0.25 KV, 0.5 KV, 1 KV, 2 kV

• Coupling method is used to transfer the transient to the DUT.
• Decoupling method is used to block the transient from entering the mains and damaging other equipment connected in the network.

• Power line coupling is done with direct CDNs (Coupling/Decoupling Networks).
• Signal line coupling is done with a CCC (Capacitive Coupling Clamp): two metal plates which sandwich the line under test (cable) to provide a distributed coupling capacitance.

Test waveform verification is mandatory prior to each test.
For equipment connected to power ports all lines are coupled simultaneously.

Christian Rosu

Plug-in Electrical Vehicle - Residential Charging Time

13. September 2015 13:09 by Christian in
Installing residential EVSE (Electrical Vehicle Supply Equipment) in a garage for Level 2 charging m

Installing residential EVSE (Electrical Vehicle Supply Equipment) in a garage for Level 2 charging may require changes to the home’s electrical wiring and a permit from the local jurisdiction.

CAN bus (Controller Area Network)

8. September 2015 16:37 by Christian in
CAN bus (for controller area network) is a vehicle bus standard designed to allow microcontrollers a

CAN bus (for controller area network) is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer. CAN bus is a message-based protocol, designed specifically for automotive applications but now also used in other areas such as aerospace, maritime, industrial automation and medical equipment. 

CAN bus is one of five protocols used in the OBD-II vehicle diagnostics standard. The OBD-II standard has been mandatory for all cars and light trucks sold in the United States since 1996, and the EOBD standard has been mandatory for all petrol vehicles sold in the European Union since 2001 and all diesel vehicles since 2004. 


Automotive Applications


A modern automobile may have as many as 70 electronic control units (ECU) for various subsystems. Typically the biggest processor is the engine control unit (also engine control module/ECM or Powertrain Control Module/PCM in automobiles); others are used for transmission, airbags, antilock braking/ABS, cruise control, electric power steering/EPS, audio systems, windows, doors, mirror adjustment, battery and recharging systems for hybrid/electric cars, etc. Some of these form independent subsystems, but communications among others are essential. A subsystem may need to control actuators or receive feedback from sensors. The CAN standard was devised to fill this need.

The CAN bus may be used in vehicles to connect the engine control unit and transmission, or (on a different bus) to connect the door locks, climate control, seat control, etc.

Today the CAN bus is also used as a fieldbus in general automation environments, primarily due to the low cost of some CAN controllers and processors.

Bosch holds patents on the technology, and manufacturers of CAN-compatible microprocessors pay license fees to Bosch, which are normally passed on to the customer in the price of the chip. Manufacturers of products with custom ASICs or FPGAs containing CAN-compatible modules may need to pay a fee for the CAN Protocol License.

Technology

CAN is a multi-master broadcast serial bus standard for connecting electronic control units (ECUs). Each node is able to send and receive messages, but not simultaneously. A message consists primarily of an ID (identifier), which represents the priority of the message, and up to eight data bytes. The improved CAN (CAN FD) extends the length of the data section to up to 64 bytes per frame. It is transmitted serially onto the bus. This signal pattern is encoded in non-return-to-zero (NRZ) and is sensed by all nodes.  

The devices that are connected by a CAN network are typically sensors, actuators, and other control devices. These devices are not connected directly to the bus, but through a host processor and a CAN controller. If the bus is idle which is represented by recessive level (TTL=5V), any node may begin to transmit. If two or more nodes begin sending messages at the same time, the message with the more dominant ID (which has more dominant bits, i.e., zeroes) will overwrite other nodes' less dominant IDs, so that eventually (after this arbitration on the ID) only the dominant message remains and is received by all nodes. This mechanism is referred to as priority based bus arbitration. Messages with numerically smaller values of IDs have higher priority and are transmitted first.


Each node requires:

Host processor

• The host processor decides what received messages mean and which messages it wants to transmit itself.

• Sensors, actuators and control devices can be connected to the host processor.

CAN controller (hardware with a synchronous clock).

Receiving: the CAN controller stores received bits serially from the bus until an entire message is available, which can then be fetched by the host processor (usually after the CAN controller has triggered an interrupt).

Sending: the host processor stores it’s transmit messages to a CAN controller, which transmits the bits serially onto the bus.


Transceiver

Receiving: it adapts signal levels from the bus to levels that the CAN controller expects and has protective circuitry that protects the CAN controller.

Transmitting: it converts the transmit-bit signal received from the CAN controller into a signal that is sent onto the bus.


Bit rates up to 1 Mbit/s are possible at network lengths below 40 m. Decreasing the bit rate allows longer network distances (e.g., 500 m at 125 kbit/s). The improved CAN (CAN FD) extends the speed of the data section by a factor of up to 8 of the arbitration bit rate.

The CAN data link layer protocol is standardized in ISO 11898-1. This standard describes mainly the data link layer (composed of the logical link control (LLC) sublayer and the media access control (MAC) sublayer) and some aspects of the physical layer of the OSI reference model.  All the other protocol layers are the network designer's choice.

Sources: Bosch

Christian Rosu