A key advantage to NI modular instruments 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. NI modular instruments are tested to ensure that they are delivering the best performance possible with extensive benchmark and performance testing.
NI performs several tests, such as thermal chamber evaluations, on modular instrument designs to ensure that they operate to full design specifications. For every new modular instrument, NI performs an infrared scan to determine what the critical components on the board are.
Once the critical components are determined, we place thermocouples on these components and load the instrument in a PXI chassis for testing. Every other slot in 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. 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. We then operate the product in a worse case scenario. For example, we turn everything on the board on so it is using the maximum amount of power. We place the PXI chassis in a thermal chamber and ramp the temperature until it reaches 55 degrees Celsius and hold it there until all of the components reach steady state.
In addition to stress testing modular instruments to validate operation to the stated specifications, NI goes one step further to improve the reliability of our products. The company performs a HALT evaluation on every modular instrument design. A combination of temperature stepping, rapid temperature transitions, vibration, and electrical variations is used expose latent design defects in the instrument. 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.
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 modular instruments. 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 instrument at operational extremes. After the instrument 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.
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 modular instrument 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 Vpk/60 Vdc) 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.
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 cannot occur.
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. NIs 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 modular instrument.
Figure 1. European Conformity, U.S. and Canada Safety, European Safety, Hazardous Locations, and Marine Approval Certification Markings