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EMI/RFI Filters
In addition to blocking electromagnetic energy in radiated form, a shielded enclosure must also be capable of blocking electromagnetic energy - alternatively referred to as "electromagnetic interference" (EMI) or "radio frequency interference" (RFI) - that travels along the conductors entering and leaving the enclosure. Left unhindered, electromagnetic energy can be picked up and conducted by the electrical wiring, telephone and data lines, fire alarm systems and control cables that enter or exit a shielded enclosure thereby destroying the shielding effectiveness. In order to keep this electromagnetic interference from being conducted into or out of the enclosure, it is necessary to use EMI/RFI filters on all conductors that penetrate the enclosure (the only exception being RF cables).
DJM Electronics can provide filters for all types of shielding requirements:
- Shielded Rooms and Screen Rooms
- Desktop Enclosures and Shielded Cabinets
- TEMPEST and Sensitive Compartmented Information Facilities (commonly called SCIFs)
- Commercial Product Enclosures
- Military Product Enclosures
And for all applications:
- Facility Power Line Filters
Facility filters are used to filter electrical power entering shielded rooms, screen rooms, desktop enclosures, shielded cabinets, TEMPEST facilities, SCIFs and anechoic chambers. They come in varying sizes dependent on current requirements, source voltage, number of conductors/phases, performance requirements and whether or not an electrical panel is required.
- Signal Line Filters
Signal line filters are used to filter signal lines entering shielded rooms, screen rooms, desktop enclosures, shielded cabinets, TEMPEST facilities, SCIFs and anechoic chambers. Signal filters tend to be more complicated than power filters because of the vast number of permutations of passband, impedance and load requirements. DJM Electronics offers a wide selection of signal line filters and a generous exchange program to insure that our customers find the filter that meets their requirements.
Today's digital signals (like Ethernet and digital phone filters) present additional challenges because common electrical filters destroy the signal integrity of digital signals by filtering out the high frequencies necessary for the sharp corners of the digital square wave. DJM offers a number of signal line filters designed specifically for digital signals. Take a look at our Ethernet EMI filters or our USB 2.0 EMI filters.
- Component Single Line and Tubular Feed-through Filters
(aka Feed-thru Filters, Feedthrough Filters)
Single line and tubular feedthrough filters are commonly used as components to suppress electromagnetic emissions or increase electromagnetic immunity. They come with threaded or terminal style inputs/outputs for ease of installation. We use the highest grade capacitors to achieve excellent high frequency performance.
- Component Power Line Filters
Component Power Line Filters are commonly used as components to suppress a product's electromagnetic emissions or increase electromagnetic immunity. They are typically used to bring electrical and electronic products into compliance with National (FCC) and International EMC standards like the European norms and VDE regulations. The filters can also protect sensitive electronic circuits from extraneous surges, spikes, ESD, and interference in the environment.
- Custom Commercial, Aerospace and Military Filters
We offer a complete range of Commercial/Military/Aerospace EMI Filters. These include standard off-the-shelf as well as custom designed and build-to-print EMI suppression filters. Filters are also available with optional EMP, surge and spike suppression networks.
Testing
All of our filter products are designed to meet MIL-F-15733, which is the general US Military standard for RF filters. A subset is tested for UL1283, which is an Underwriter's Laboratories requirement for features which are primarily related to safety considerations.
The individual heavy power filters or inserts for both UL and MIL-STD applications are all equipped with oil-filled hermetically sealed bypass and feed-through capacitors. UL1283 listed models use capacitors which are designed to withstand mandatory high potential factory tests of up to 2,200 volts.
Filters are tested for:
- Visual inspection
- Mechanical inspection
- Dielectric withstanding voltage
- Insulation resistance
- Capacitance measurement
- Inductance measurement
- Insertion loss
Applicable Specifications:
- MIL-F-15733 - General specification for filters, military
- MIL-STD-202 - Test methods for component parts, military
- MIL-STD-220A - Test method of insertion loss, military
- CISPR17 - Test method of insertion loss
- MIL-STD-285 - Test method of shielding effectiveness
- NFPA 70-1987 - National Electrical Code, standards
- UL1283 - Underwriters Lab filter requirements
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Facility Power Line Filters
Facility filters are used to filter electrical power entering shielded rooms, screen rooms, desktop enclosures, shielded cabinets, TEMPEST facilities, SCIFs and anechoic chambers. They come in varying sizes dependent on current requirements, source voltage, number of conductors/phases, performance requirements and whether or not an electrical panel is required.
Standard Features:
- Manufactured and tested to applicable portions of MIL-F-15733
- Hermetically sealed with welded an soldered seams for ≥ 100dB shielding effectiveness
- Bleeder resistors incorporated to eliminate potential shock hazard
- Typically 1% voltage drop at full rated unity power factor load
- 4% max harmonic distortion at full rated unity power factor load
- Temperature Rating -10C to +85C Per MIL-F-15733 and UL1283
- Survives 150% maximum current rating for 15 minutes
- Dielectric withstanding voltage of 2,200 VDC per UL1283
Specifying A Facility Power Line Filter
When specifying a facility power line filter, use the following structure:
Performance Level; Conductors x Current; Voltage;
[Cycles]; [UL Listed]; [Options]
Example: Standard; 2x30; 120/208VAC
Performance
- Standard (100dB Insertion Loss 1MHz - 10GHz)
Standard performance is used in the majority of applications (especially wireless applications) and allows for the least expensive and smallest filters.
- Industrial (100dB I.L. 150kHz - 10GHz)
Industrial performance filters are used almost exclusively for regulatory chambers and enclosures. The increased performance at lower frequencies requires a larger filter.
- High Performance (100dB I.L. 14kHz - 10GHz)
Extended High Performance (100dB I.L. 10kHz - 10GHz)
High performance and extended high performance filters are used almost exclusively by the military. They are the largest and most expensive filters we carry.
Source/Output Power
- Conductors
The number of conductors or lines required in the power filter. Three phase power requires 4 conductors if using a neutral or 3 conductors in a Wye configuration. Three phase power normally requires a panel style filter (see below). However, 3 conductor filters are available in a standalone style filter if the current requirement is 30 amperes or less. Single phase power requires 2 conductors. DC applications need only 1 conductor. Remember that hot and neutral lines are filtered, but it is not necessary to filter ground.
- Current Rating
Current rating expressed in amperes. Always round up to the next level available, but do not over specify too much or performance will degrade (a filter not used to its rated amount will not function as well as one that is).
Filters are available in the following current ratings:
5A, 10A, 15A, 20A, 30A, 50A, 60A, 100A, 150A, 200A, 225A, Contact us for higher current requirements
- Voltage
The source voltage of the power usually falls within one of three ranges: 100VDC (used for all DC applications less than 100V), 120/208VAC, or 277/480VAC.
- Cycles
The cycles are normally only important if you require 400Hz. When using 400Hz power, it is usually necessary to have power factor correction coils (see below).
UL Listing
If it is necessary for you to have UL Listed filters, please make that known when you place an order. We offer various filters that are not UL Listed at a lower price. These filters undergo the same in-house testing, but have not undergone testing by Underwriters Laboratories.
Options
FILTER ENCLOSURES
Standalone filters offer the identical levels of filter performance as panel models, but are available with self-enclosed terminals for individual and dual line applications (and occasionally three line applications). Penetrations for installation are provided for this type of unit directly from the factory.
Standalone Case Assembly
- Enclosed terminations, input end
- Pigtail terminations, output end
- Multi-circuit configurations
- Welded and soldered seams for shielding effectiveness
- Discharge circuits (bleeder resistors) to reduce shock hazard
- Electroplated cold rolled steel (not less than 16 gauge) filter case
- RF tight removable covers
- Prewired standoffs and lugs
Panel style filters consist of removable filter inserts mounted in a radio frequency secure cabinet (the panel). Panel filters allow multiple filtered lines to enter a shielded enclosure with a simplified, single penetration, providing greater RF integrity and simpler filter maintenance. Panel style filters are necessary for the majority of three phase power applications.
Panel Assembly
- UL Listed filter panel assembly
- Enclosed terminations, both ends
- Multi-circuit configurations
- Welded and soldered seams for shielding effectiveness
- Discharge circuits (bleeder resistors) to reduce shock hazard
- Powder coated cold rolled steel (not less than 14 gauge) filter case
- Weather tight outer panel cover
- RF tight removable covers
- Prewired standoffs and lugs
- Optional Legs (12" standard)
LOW LEAKAGE
All power line filters have capacitance from the live and neutral lines to ground in order to achieve a high level of insertion loss. Depending on the performance required, this current to ground can be quite substantial. This is why it is essential that filters are adequately and permanently grounded to safely carry these "leakage currents" away.
In applications where high levels of leakage current are unacceptable (typically medical applications or where Ground Fault Current Interruption systems are in use) it is necessary to use Low Leakage filters. These filters are designed without capacitance from the live wire to ground. This significantly reduces leakage current.
POWER FACTOR CORRECTION COILS
Power factor correction coils are recommended for 400Hz applications where power levels exceed 25 amps per phase. All 400Hz power filters draw high level of reactive current when compared with equivalent 50/60Hz systems. To counteract this effect, external-mounted inductors can be placed in parallel with the filter's capacitors to provide more efficient operation.
ELECTROMAGNETIC PULSE (EMP) and
HIGH ALTITUDE EMP (HEMP) PROTECTION
We can provide power line filters with differing levels of EMP and HEMP protection depending upon installation requirements. These filters come with an inductive input design for greater surge protection, and factory installed surge arrestors. All of our filters may be ordered with transient suppressors for improved protection against voltage transients.
Signal Line Filters
All communication lines entering or leaving a shielded enclosure must be filtered for the same reasons that all power lines must be filtered. Because of the many varieties of communication methods and protocols, signal line filters come in a staggering number of designs, specifications and configurations. To simplify the decision process, we have identified common requirements and uses. However, if you fail to see a filter that meets your needs, be sure to check our complete filter listing below. Also, it is important to choose the right filter for the application because the wrong filter may seriously degrade performance or disrupt communications completely. If you have questions, please feel free to contact us.
- Telephone Filters
- PA System Filters
- Fire Alarm Filters
- Relay/Thermostat Filters
- Ethernet Filters
- Digital Data Filters
Signal Line Filter Enclosures
Signal line filters are available in two different case configurations:
Standalone Assembly
Standalone cases are supplied with a threaded conduit pipe for penetration into the shielded enclosure.
Features:
- Manufactured and tested to the applicable portions of MIL-F-15733
- Hermetically sealed for high reliability
- Single, Dual, or Multi-circuit arrangements to 5.0 Amps available
- 100 dB up to 10 GHz per MIL-STD-220A
Panel Assembly
Panel-style filters may be packaged in a common shielded panel housing any number of circuits. Panels are NEMA type with two compartments to provide the necessary isolation for secure applications. Filters mounted in panels are wired to both line and load side DIN type connectors on a DIN rail. Panels may be supplied with optional threaded conduit pipe penetrations which provide for a single point penetration to accommodate multiple lines.
Standard communication and control line filter panels are available in sizes that can accommodate from 1 to 900 filters. We recommend that each panel contain spare or empty positions for future additions. Individual filters in panels are readily replaceable. Filters with the same mounting provisions may be used to replace, upgrade, change impedances or change passbands as necessary.
Features:
- 20 standard enclosures holding from 1 to 900 signal line filters
- Different filter types are interchangeable in the same enclosure
- Modified NEMA type enclosures with wall of floor mounting
- Prewired push pin terminal blocks or 8-32 screw terminations
- EMI gasketing to insure 100 dB shielding effectiveness per MIL-STD-285, NSA and TEMPEST Requirements
- Lifting ears included on heavier enclosures
Options
- Various Impedances
- Standard Baud Rates
- Special Response Curves
- Legs (12.0 Inch Standard)
- EMP, MOV and Surge Arrestors Available
- Hub or Penetration Installation
Applicable Specifications
- MIL-F-15733 - EMI/RFI Filter Specification, Military
- MIL-F-18327 - General EMI/RFI Filter Specification, Military
- MIL-STD-220A - Test methods for insertion loss, military
- MIL-STD-285 - Test method for shielding effectiveness
Single Line Feed-through Filters
(aka Feed-thru Filters, Feedthrough Filters)
These high performance RFI filters are ideal for cellular base stations, telephone racks, high current power supplies, amplifiers and server stations.
Features:
- Threaded feedthrough filters with threaded or terminal style inputs/outputs.
- Currents ranging from 0.5 to 75Amps
- AC voltages 30 - 250V, DC voltages 100-600V
- Tested Per MIL-F-15733
Commercial Power Line Filters
These commercial power line filters are ideal solutions for products that must conform to US and international susceptibility and emissions standards. We use only metal cases which provide the highest performance.
Features:
- Excellent attenuation of high voltage impulses.
- Excellent filtering for both common and normal mode.
- Current: 5-50amps
- Voltage: 100VDC, 125VAC 0-60/400Hz, 250VAC 0-60/400Hz
- 1,2,3, or 4 circuits per case.
Custom Commercial, Aerospace and Military Filters
DJM Electronics recognizes that standard products do not work for every situation. We are ready to work with you to develop a custom filter or filter package that will help your products comply with MIL-STD-461/2/3, FCC, VDE, CE, CSA or other specifications.
We can:
- Provide standard filter designs in custom-sized cases or panels to meet specific installation requirements.
- Design filters to meet nearly any requirement
- Provide filter designs with transient protection, circuit breakers, voltage cut-off, EMP protection, and a host of other options.
- Incorporate filtering and custom circuitry in to one design package
- Build filters using customer designs
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