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NI Single-Board RIO OEM devices are designed to be integrated into larger systems deployed to meet a variety of monitoring and control application needs. Because of this, these devices are not required to undergo EMC or safety testing. Instead, the OEMs that purchase the devices are required to validate their overall products for compliance with the requirements of the countries or regions where they intend to sell their products. For example, OEMs must ensure that their end products meet European Union requirements to affix CE marks to the final products.
To facilitate this task, NI designed NI Single-Board RIO devices while keeping in mind that the end product needs to meet international/global EMC standards. The information in this white paper provides guidelines on how to integrate these devices as components in your overall OEM product or application. Following these guidelines minimizes the impact NI Single-Board RIO devices have on the overall OEM product’s ability to meet international/global EMC requirements.
This white paper addresses this topic by focusing on three areas: chassis, ports, and cabling.
Table of Contents
Chassis
The NI Single-Board RIO OEM printed circuit board (PCB) is designed to be installed in a metallic enclosure to control emissions radiated from the PCB and all internal cabling. The ideal chassis design should minimize seams, slots, or holes that could allow emissions to radiate out of or into the chassis. Extruded or cast metal chassis work best, while plastic or “folded” metal chassis are not recommended because they do not provide adequate protection from emissions radiating into or out of the chassis. You need to attach the different metallic components of the chassis with screws sufficient to ensure the shielding effectiveness of the overall enclosure as required by the end application. Areas where metallic components are making contact should be free of paint or other nonconductive coatings to ensure a low-impedance connection.
Once you have chosen an appropriate chassis, you need to ensure that all mounting holes (see No. 18 in the figure for mounting hole locations) connecting to digital or chassis ground are connected to the chassis with a conductive, low-impedance connection. You can best accomplish this by using metal standoffs or cast/milled and threaded mounting supports. In addition, instead of relying on the screw threads, you should use a pan head screw for the low-impedance connection to ensure even contact between the PCB mounting holes and the chassis mounting supports. This is because you need a conductive, metal-to-metal contact between the chassis and the PCB mounting holes. Furthermore, you need to mask off the location of all the connections between the chassis and mounting holes on the PCB before painting to ensure that they are not covered with paint or other nonconductive coatings.
Ports
When you have finished properly mounting the NI Single-Board RIO PCB in the metal chassis, you need to consider all the connections you can make to and from the ports on the product. Connect the power port (No. 16 in the figure), as specified in the user manual, to a power supply that provides an adequate level of power line filtering. Power ports may require you to place a ferrite bead (Fair-Rite Type 43 or 44 materials or equivalent) around the power cable close to the chassis to control emissions that could be radiated from an unshielded power cable.
You do not need to connect the protective earth port or ground lug (No. 14 in the figure) on the NI Single-Board RIO for proper operation of the device. However, depending on the application, you may need to connect the protective earth port to the protective earth grounding system of the facility in which you install the product to enhance EMC performance. In addition, connecting this lug to earth ground usually results in less noise on the analog input measurements.
NI Single-Board RIO Parts Diagram
All NI Single-Board RIO devices come with three 15-pin high-density D-Sub connectors (Nos. 3 and 5 in the figure) to connect up to three supported NI C Series modules in addition to any I/O that is integrated into the NI Single-Board RIO devices. Because of this, you should connect these ports only to C Series modules. When integrating these modules into the overall system, you should follow the same installation recommendations discussed above for the chassis.
You should connect header I/O ports, such as the digital or analog I/O connectors (Nos. 2, 4, 7, 9, 17, and 19 in the figure) on the NI Single-Board RIO devices, only to other PCBs within the same chassis because no EMI protection or filtering is included on these ports. The chassis can help prevent any undesired emissions from leaving or entering the system through these ports. If, however, you need to connect one or more of these connectors outside of the chassis, be careful to connect these ports first to a connector that supports an overall shield and that is mounted on the chassis. Then use a shielded cable from the chassis connector to the outside connection.
With all remaining connectors that must be wired outside of the chassis such as the Ethernet or RS232 connectors (Nos. 10 and 12, respectively, in the figure), you need to use high-quality, shielded cables to minimize any undesirable interference.
Finally, any custom I/O you add externally to the NI Single-Board RIO device should incorporate connectors that include termination for an integral cable shield (for example, coaxial, twinaxial, D-Sub, Ethernet, USB, IEEE 1394, and so on).
Cabling
In general, you need to use high-quality, shielded cables for any connections that leave the metal chassis that houses NI Single-Board RIO devices. The use of discrete wires or unshielded cables for external connectivity through connector blocks and screw terminals is not recommended unless the shielding of the connected cabling is not necessary for the product’s required EMC performance.
As far as specific connector and cabling types, the following applies:
- Use coaxial connectors and cables only for chassis-referenced signals such as nonisolated or single-ended signals including audio, TTL, CMOS, and most RF applications (RS232 is a single-ended interface, but it uses shielded, untwisted cable).
- Use connectors and cabling that support shielded, twisted pairs for isolated or differential signals such as RS422, RS485, most Ethernet, USB, IEEE 1394, and low-voltage differential signaling (LVDS).
EMC Testing Requirements
When you have integrated your NI Single-Board RIO devices and have met all of these requirements, you should evaluate your overall product for EMC performance by conducting the necessary EMC testing for the markets in which you are selling the product. For test and measurement products, the primary requirements are those of the European Union. National Instruments tests similar products according to IEC/EN 61326-1 to meet Class A emissions and industrial immunity requirements.
Additional NI Single-Board RIO Resources
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