NI PXI Design Validation

National Instruments validates the designs of NI PXI chassis and controllers by performing an exhaustive series of rigorous tests. From guaranteeing reliable performance over the specified temperature range of the product to ensuring that inappropriate installation conditions do not create unsafe conditions that could destroy the equipment or harm operators, NI spends a great deal of time and resources to ensure its PXI systems can meet the toughest specifications and your application demands. Much of this testing and evaluation is done in-house by full-time dedicated test engineers, many of whom are industry experts in their disciplines, such as electromagnetic compatibility, safety, and mechanical engineering. In addition, National Instruments performs most of the tests on the company’s designs using NI PXI systems and NI LabVIEW and NI TestStand.

Cross-Product Integration Evaluation 

A key advantage to an NI PXI system is the assurance that all products have undergone extensive testing for integration with other National Instruments hardware and software products. The NI Cross-Product Integration Services team verifies that modules will operate properly together in different configurations. NI does not test every possible configuration, but it does test the most common and the most demanding configurations. For example, NI validates high-channel configurations as well as those for maximizing bus bandwidth and streaming data to disk.

National Instruments chassis and controller products are tested to ensure that they are delivering the best performance possible with extensive benchmark and performance testing.

Environmental Evaluation 

NI performs several tests, such as thermal chamber evaluations, on chassis and controller designs to ensure that they operate to full design specifications. The chassis is populated with “thermal load cards,” which have passive loads to pull the maximum specified power for a PXI or PXI Express module. Each slot of the chassis is filled, creating a system pulling full power. The load cards not only pull enough power for a fully loaded chassis, but each load card also dissipates the amount of heat that a spec-compliant module would create. The system is then powered on and monitored to verify that it operates throughout the following tests. The controller is also configured to run a series of tests to constantly exercise the hard drive, memory, CPU, graphics card, and other system components.

The temperature is then raised from a room temperature of about 25 °C to just above the highest temperature specified for the chassis and controller, 55 °C for many NI systems, and remains there for 18 hours. Then, the temperature is rapidly changed to just below the lowest temperature specified, 0 °C for many NI systems, and remains there for 18 hours. This four-day test ends with a 48-hour humidity test. The temperature is brought to 40 °C and the humidity is controlled at 93 percent R.H. During this test, the chassis and controller must operate reliably within specifications without any failures to pass satisfactorily and for NI to begin shipping them to customers.

In addition to the operational test, NI also packages the product and tests it for 18 hours at each of the specified storage temperature extremes.

Highly Accelerated Life Testing (HALT) Evaluation 

In addition to stress testing its chassis and controllers to validate operation to the stated specifications, NI goes one step further to improve the reliability of NI PXI chassis and controllers. The company performs a HALT evaluation on every chassis and controller design. A combination of temperature stepping, rapid temperature transitions, vibration, and electrical variations is used expose latent design defects in the chassis or controller.  Random vibration levels up to 30 grms and temperature ranges from 60 to 100 °C within minutes stress the components and the finished design to find  possible latent design defects. Oftentimes the detection of these latent defects is used to improve the mechanical or electrical design so that the product  meets or exceeds NI expectations.

Electromagnetic Compatibility Evaluation 

As device speed and operational frequency have increased, electromagnetic compatibility (EMC) has become more important to ensure proper operation of test and measurement products. National Instruments has invested heavily in the EMC performance evaluation of NI PXI chassis and controllers. The multimillion-dollar NI EMC test facility and complete full-time staff work proactively to ensure each product not only meets the applicable EMC standards but also works appropriately in the intended environment.

Similar to other tests, EMC evaluations analyze the PXI chassis and controllers at operational extremes. The controllers undergo operational tests that involve continually writing to memory/disk and operating the CPU and graphics chipsets at the highest performance settings. The chassis are configured for testing at the lowest and highest voltage inputs while data is continuously sent across the backplane. After the system is exercised properly, it goes through more than a week of EMC testing in the NI lab. This evaluation includes radiated and conducted emissions, radiated and conducted immunity on power and applicable signal lines, power surge tests, harmonic and flicker emissions, electrostatic discharge tests, and magnetic field immunity, to name a few. NI does not release a product until it passes all of the applicable worldwide EMC requirements.

Safety 

Employee safety is critical in today’s offices, laboratories, manufacturing facilities, and industrial settings. The NI safety evaluation is performed by the company’s internal UL-accredited safety laboratory. NI has a full-time staff of certified safety engineers and technicians who evaluate each product NI makes to ensure it meets the highest worldwide safety standards. Some of the most common tests/requirements applied to each NI PXI chassis and controller are featured here. To view full standards, articles, and video demonstrations, visit ni.com/certification.

Safety evaluation includes more than electrical safety − it also includes thermal, mechanical, and fault tolerance scenarios. Basically, NI safety evaluations verify that operator use or misuse does not lead to a condition where someone could get injured.

Safety awareness among test and measurement equipment users is increasing because of new hazardous voltage (>42 V_pk/60 V_dc) measurement categories and extra precautions required for safe operation. For example, some test and measurement products measure voltages up to and greater than 1000 V. These hazardous voltage levels can be reached during measurement procedures via sensors and probes, but NI requires that users not be able to readily access hazardous voltages during normal operating conditions as well as some of the fault conditions described below.

To ensure that the user cannot access these voltages, NI begins with design and follows UL and IEC spacing requirements. Manufacturers do not always follow these because of today’s highly dense design requirements. Expensive board real estate must be allocated to ensure that a hazardous condition is not created by a faulty component or air pollutant. For hazardous voltage input products, 100-240 V AC input, NI uses the spacing requirements under Pollution Degree 2 and overvoltage category II. This basically requires a spacing of 3mm minimum on PCBs from high (hazardous) to low (user touchable) voltage. Some vendors skirt this rule by incorrectly classifying their equipment to Pollution Degree 1 and/or category I, Pollution Degree I only require 1.5mm spacing. This simple difference may allow another vendor to populate more relays on a board, or make an instrument smaller, but ultimately may create a liability for you and your company since this may subject users, products and surrounding to electrical and fire hazards.

NI spacing requirements are validated by high-potential (hipot) testing. After preconditioning the product for 48 hours at 92.5% relative humidity and 40 degree C, a 2,300 V AC high potential voltage is applied across the high-voltage I/O circuit and any touchable metal surface of the chassis. There can be no electrical breakdown (arc-over).

Several tests are performed to verify that the thermal performance of the system does not create an unsafe condition. This begins by populating a chassis with a full maximum load, that is, each module is drawing the maximum current specified and dissipating the maximum power specified. The system is then taken to the highest-rated temperature specified on the data sheet. Then each touchable surface is verified to be less than 80 °C for any plastic surfaces and less than 70 °C for any metal surfaces. During this test, NI also monitors critical components such as transformers, ICs and PCBs with thermocouples to make sure their temperature specifications are not exceeded during these normal conditions.

In addition to this normal operation evaluation, NI tests for fault conditions. First, NI blocks the fan inlets and verifies that no surface reaches 105 °C. Users are directed to reserve at least 3 in. of space available for the fans, but what if they do not? This test simulates this scenario and verifies that no one would get injured if the installation requirements were not followed.

Also, consider if one of several fans was damaged. To simulate this, NI engineers lock up a fan by placing a screwdriver into one of the fan blade’s paths, which stops it from operating. Then they measure the surface temperatures to ensure no surface reaches 105 °C.

Other fault test conditions include performing opens and shorts on critical components such as power capacitors to make sure a fire or other unsafe condition can not occur.

A heavy metal ball (500g) is used to simulate other items falling on the PXI system. If the ball creates an aperture or breaks a fan blade, this situation would develop into an unsafe condition.

Certifications 

These tests are also required for the well-known CE (European Conformity) marking, the European marking that manufacturers must apply to their products to ship them to Europe. Many users misunderstand this marking as a certification when it is not. Any manufacturer can apply the CE marking as a self-declaration, meaning that the manufacturer self-declares that the product meets all of the applicable requirements for safety and EMC (and any other applicable standards). Manufacturers are not required to do any validation testing, and some may elect to simply self-declare. NI does not. NI dedicated full-time EMC and safety engineers not only perform the evaluations for safety and EMC in-house but also certify most PXI systems with at least two other third-party safety markings including UL and Demko when applicable. NI also requires manufacturers of any critical components used in NI designs to obtain third-party certification. Oftentimes, components are marketed as “designed to meet” and are not actually certified or marked by independent third parties, also known as certification bodies. “Designed to meet”, without a certification mark, is similar to a manufacturer self-declaring compliance. Refer to Figure 1 for the certification markings used on NI products and visit ni.com/certification to view markings for a particular PXI chassis or controller.

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Figure 1. European Conformity, U.S. and Canada Safety, European Safety, Hazardous Locations, and Marine Approval Certification Markings

Other NI PXI Design Advantages 

For more information about how National Instruments chassis and controller design advantages, what verification tests each manufactured unit undergo, and what software and services are available, please view the other sections of this series:

NI PXI Chassis and Controllers Design Advantages

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