Page 10 - Enclosure Fall-Winter 2023-24

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Radio Frequency Interference (EMI/RFI) and potential power ENVIRONMENTAL COMPATIBILITY TEST
surges, because of the increased likelihood of extraneous When there is no available software code for verification
noise being misinterpreted as legitimate logic signals. As and validation of the firmware, the EDD of COS hardware
current draw increases and operating voltage decreases, is usually addressed by environmental compatibility test.
electromagnetic noise threatens high-performance This includes Electromagnetic Interference (EMI), Radio
processors. New digital items are moving to lower voltages Frequency Interference (RFI), operability testing, emission
which make them more susceptible to noise.
tests including power surges, temperature tests, and Seismic
EDD EVALUATION qualification testing. The verification shall address the item,
physical, performance, and dependability characteristics
A major cause of problems for software-based equipment of the “built-in” software, and the test procedures will
is inadequate requirement definitions for EDDs. Special verify the item's “must-do” and “must-not-do” functions.
consideration should be applied to the engineering Additionally, an evaluation of the manufacturer’s available
evaluation and qualification of digital technologies to commercial testing, error tracking, configuration control,
address these issues. These considerations are integrated and installation history shall be performed. All partial list of
into the commercial grade dedication process. Critical critical characteristics (CC) to be addressed:
Characteristics to be evaluated are Item, Physical, • Item critical characteristics (CC): Operating system,
Performance which is consistent with prior analog computer name & version number, operating
evaluations. EDDs have an additional requirement known as environment, etc.
dependability characteristics. Dependability characteristics
address: (1) the evaluation of digital items and suppliers; • Physical CC: interfaces, size, life cycle documentation, etc.
(2) the design documentation; (3) the design/development • Performance CC: abnormal behavior, accuracy, tolerance
process; (4) the QA and configuration control; (5) the vendor output, response time, critical input parameters and valid
testing; (6) the product's operating experience; and/or (7) ranges, respondent time, throughput, reliability, etc.
any failure analyses. In addition to the design requirements • 16 Dependability CC: 11 built-in Quality such as QA
for the intended functions and anticipated failure modes, program training, adherence to coding; 2 Failure
it is particularly important in software-based equipment to management CC, configuration control, problem
identify any requirements related to unused, unintended, or reporting, and supportability
prohibited functions.
Interfaces should address input signal, input impedance,
The evaluation of EDD should include the collection of power, signal, data communications, setpoint adjustment,
product data for the item under evaluation. This step of the contact output, pneumatic supply air connection, pneumatic
evaluation can be very challenging, especially since OEMs output, grounding and shield termination provisions,
are constantly upgrading EDDs to improve performance and response time, including time for signal conditioning and for
reduce costs. Screening for digital content includes supplier bistable units to produce bistable trip output in response to
information, such as: OEM webpages; third-party reseller valid input, time for logic units to produce actuation output
websites; brochures or product descriptions; technical in response to appropriate combination of bistable or other
manuals; installation, operation, and maintenance manuals; valid inputs, as appropriate.
configuration instructions; and data sheets. Generally, this
material makes the item easily recognized as a digital item Behavior under abnormal or faulted conditions must be
because the digital attributes become obvious. For example, addressed, including issues such as loss of signal, loss
a review of product literature terminologies may indicate of power, signal over or under range, loss and re-gain of
digital content that can be used in the technical evaluation, power, loss of one or more signal inputs, input signal over or
such as: microprocessor-controlled; microcontroller; under range, loss of supply air, loss of power to one or more
software or firmware version; configurable with a PC; modules, failure of an i/o module, and loss of one or more
configurable with test or manufacturing equipment; and signal inputs, as appropriate.
stating relevant government approvals such as FCC Class A Generally, EMI/RFI product qualification requires some
or B, etc. However, some items are not clearly identifiable form of modification, such as grounding the chassis and
or recognizable as digital items; this is because the digital internal electrical components as well as shielding and
content is embedded and may be evident only when the filtering for enclosures, wiring apertures, and internally
item is disassembled. Examples of these devices include protected components, to determine if a product meets
microprocessors, microcontrollers, field-programmable operability requirements as well as operates within the limits
gate arrays (FPGAs), complex programmable logic devices of the EMI/RFI. The final EMI/RFI configuration establishes
(CPLDs), and application-specific integrated circuits the suitability of the design prior to initiating procurement;
(ASICs). To identify these variables, disassembly and otherwise, the risk shall be accepted by the facility project
inspection of additional destructive testing sample items is team. The commercial grade dedication process should
required after receipt. align with the final design.

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