EMC Product Focus: Keeping EMI in its place

1608-emc187

A statement from a Murata news release1 succinctly describes the need for EMI suppression in cars, but also applies to many other application areas with a significant complement of electronics. The release states, “As automobiles incorporate an ever-increasing amount of electrical parts and as more and more electrically powered automobiles are being developed, more noise suppression products are being used in the powertrain and safety circuits that require high levels of reliability.”

EMI from internal as well as external sources can interfere with the correct operation of sensitive circuits. This product focus highlights devices that minimize the generation and effects of EMI. Also included are a magnetic field test system and a magnetically shielded enclosure suitable for scientific research.

Reference

  1. “Automotive 150°C class ferrite bead, solder mountable,” Murata Manufacturing, News Release, May 10, 2016.

 

Pulse test system

The AXOS 8 includes an integrated single-phase coupling/decoupling network (CDN) and can be configured to provide 7-kV surge combination wave, 7-kV ring wave, 7-kV telecom wave, 5-kV EFT/burst or dips and interrupts, and magnetic field test to IEC/EN 61000-4-9. The Compact Test System Model 2490800 has all these capabilities except telecom wave.

Operation is via the front-panel graphic interface or remotely from a PC. Predefined routines for different standards make testing easy and reliable. Customer-specific test environments are supported by additional functions such as external start/stop. The capability to vary parameters allows performance issues to be thoroughly investigated during the design phase as well as in precompliance testing.

A range of options and accessories complements the basic AXOS 8 unit. The MSURGE-A is a 1 m x 1 m antenna plus cables for use with the AXOS 8 to perform a pulse magnetic field test. Several types of CDNs, a capacitive coupling clamp, and data- and control-line decouplers also are available. Haefely Hipotronics


1608 Emc187 300x244Automotive common-mode choke

The RA6870-AL common-mode choke is intended for use in receiver and transmitter sections of MOST 150 coaxial applications. This 0805-size component is RoHS compliant with matte tin over nickel over silver-palladium-glass frit contacts. For each winding, the inductance at 100 MHz and the DC resistance are 700 nH and 0.69 Ω, respectively.

Common-mode chokes increase impedance to common-mode signals because the currents have the same phase in both coils, causing the magnetic flux to add. In a 50-Ω system, the typical attenuation of the RA6870-AL is about 27 dB at 700 MHz. Conversely, a well-designed common-mode choke causes minimal disturbance to a differential signal because the currents have opposite phases and the magnetic flux cancels. In the MOST 150 application, a common-mode choke restores the balanced differential signal by substantially removing common-mode interference that may have been introduced in a wiring harness.

Operating temperatures from -40°C to +125°C are supported with three 40-s reflows at +260°C allowed during soldering. Two sizes of 8-mm reels are available: 7-inch with 2,000 parts and 13-inch with 7,500. Coilcraft


1608 Emc192 300x210High-temperature ferrite bead

Automotive applications can be particularly demanding because of the high temperatures that are encountered. Three new series of 0603-size ferrite beads feature solder mounting and guaranteed operation at +150°C.

The BLM18AG_BH1 Series is optimized for noise suppression over a wide frequency range and comprises seven values from 120 Ω to 1,000 Ω. The BLM18BD_BH1 Series is similar but has a steeper impedance characteristic with values up to 2,500 Ω. The BLM18KG_JH1 and BLM18KG_BH1 Series handle noise suppression in power supply lines and have values from 26 Ω to 600 Ω with current capacity up to 6 A. As an indication of the very low DC resistance that these beads exhibit, a 100-Ω model in the BLM18KG_JH1 Series has a maximum 30-mΩ DC resistance. Murata Manufacturing


1608 Emc188 300x200Low-frequency ferrite cores

The type 75 material featured both in solid cores and the manufacturer’s Snap-it form of easily assembled split cores provides relatively high impedance at frequencies from 150 kHz to 10 MHz. The Snap-it form is especially useful for cable assemblies and suppresses noise caused by conducted common-mode EMI from sources such as switching power supplies.

With five turns of wire through a solid core, impedances from 310 Ω to 800 Ω at 200 kHz can be achieved. For split Snap-it cores at the same frequency, impedance ranges from 330 Ω to 760 Ω.

Applications include automotive inverter assemblies and inductive motors, power supplies and peripheral cables in consumer electronics, and control units and motors in white goods. Sample kit No. 0199000041 is available with a total of 17 type-75 Snap-it parts in six sizes.
Fair-Rite Products


1608 Emc193 270x300Power entry module

The KMF entry module is intended for protection class II applications that typically require double-insulated modules without an external metal case and ground connection. The module is designed to IEC 60320-1, style C18 and meets IEC 60601-1-11, which outlines additional safety measures specific to medical equipment intended for use in the home. In addition to a two-pole line switch, the module is available with a choice of a one- or two-pole fuse holder. For medical applications, further choices include an “extra-safe” fuse holder that requires a tool to open and an M5 low-leakage EMC filter.

The standard models have current ratings from 1-A to 10-A at 250 VAC, and connections are via 0.187-inch quick-connect terminals. The module’s insulation system is guaranteed to withstand >2.7 kVDC between the mounting panel and the line (L) or neutral (N) conductors and >1.7 kVDC between L and N. Schurter


1608 Emc191Magnetic-shielded enclosure

A series of Zero-Gauss Chambers provides the low magnetic field required for sensitive scientific experiments or when developing devices based on magnetic field sensors such as fluxgate compasses. Fabricated from MuMETAL alloy, the chamber reduces ambient magnetic fields and the earth’s geomagnetic field (0.25 to 0.65 Gauss) to the milliGauss level.

The chambers are effective from DC to 100 kHz because of layering. When two or more concentrically spaced magnetic shields are used in series (one inside the other) and magnetically isolated, the attenuation of the external field is multiplied, yielding an overall factor of about 1,500 for three layers. This multiplying effect of successive shields provides substantially greater attenuation of magnetic fields than a single shield of equivalent total wall thickness. For strong external fields, the outer layer may be manufactured from a high-saturation NETIC alloy. Standard chambers are available in four sizes ranging from the smallest with an internal 6-inch dia and 15-inch length to the largest with 18-inch internal dia and 54-inch length. Magnetic Shield


Display screen shielding

WINAL 75-080 transparent conductive shielding is based on a 75-µm layer of PET polyester film. An indium tin oxide (ITO) layer provides conductivity, and a clear top layer adds protection. Surface resistance is specified to be 80 Ω/square, achieving shielding >20 dB at 100 MHz. The combination of PET film and ITO and protective coatings has 76% light transmittance.

WINAL 75-080 film can be grounded by an optional layer of conductive fabric tape, and both custom die cutting and hole punching are available. The standard size sheet is 420 mm x 600 mm, and custom-length rolls also can be provided. In addition to EMI shielding and transparency, the film is flame retardant to UL94 VTM-2. Rather than the more common UL94 V-0 standard used for testing self-supporting materials, UL94 VTM-0, -1, and -2 specify flammability limits for thin materials that are tested after being formed into a self-supporting cone. VTM-2 is the least stringent of the three classifications but still requires less than 30 s of flaming combustion after application of a test flame. Kitagawa Industries America


1608 Emc194Dual-stage power line filter

The EMC series of dual-stage RFI filters provides high attenuation in a compact design. Current ratings at 250-VAC range from 3 A (0.21-mA leakage) to 30 A (1.52-mA leakage) at temperatures up to +40°C. Above 40°C, derating is necessary.

Differential-mode (line-to-line) and common-mode (line-to-ground) insertion loss at 1 MHz measured in a closed 50-Ω system are >60 dB for most filter models and >47 dB for the 30-A device.

The metal-cased units vary in size from the 3-A 3EMC1 at 3.35 x 1.81 x 1.16 inches to the 30-A EMC6 that is 6.05 x 3.12 x 2.18 inches. Wires and two types of terminals are available: ¼-inch Fast-on and 8-32 threaded studs. The overall length dimensions include the terminals. TE Connectivity


1608 Emc211PCB-mounted shielding

Standard and custom board-mounted shielding is manufactured using a photo chemical etching process that makes it possible to offer custom single-piece and standard two-piece designs with no tooling charges. For multicavity applications, internal dividers can be added, and through-holes and slots also are available for heat dissipation.

Shields typically are etched from 0.007-inch to 0.020-inch thick brass, nickel silver, copper, or cold-rolled steel. If spring qualities are needed, beryllium copper can be used. The standard finish is tin plate although other finishes are available.

Standard tooling exists for spring finger and dimple designs. Soldered or resistance-welded seams are optional as are custom fences and removable covers. Tech-Etch

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