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It is important to understand the availability requirements of your applications when building test, measurement, and control systems.
Test, measurement, and control systems are critical in the design, prototyping, and deployment of today’s new products. Downtime caused by these systems often results in lost company revenue, especially in areas such as manufacturing where uptime is crucial. Because all electronic and automation devices have a finite lifetime, it is important to understand the availability (uptime) requirements of your applications. National Instruments can help with your high-availability needs, including those related to PXI systems.
PXI is a test, measurement, and control platform designed for demanding applications that require maximum uptime and a high level of reliability. The PXI specification ensures this with requirements such as rugged Eurocard design and forced-air cooling. Moreover, NI designs, manufactures, and tests its PXI products to deliver the highest quality for the most demanding applications. By following a few best practices, you can use NI PXI chassis, controllers, and modules to achieve maximum uptime for your applications.
Assembling Your PXI System
When assembling a PXI system, it is important to select the correct components. A PXI system includes three types of components – a chassis, a controller, and a set of modules. You must select these components not only based on measurement and control performance but also on the environment in which you are deploying the system in addition to extended operation and power requirements.
Environmental conditions are characterized by temperature, humidity, shock, vibration, and altitude. You should verify that the components you plan to use have specifications that meet or exceed the environmental conditions for your application. For example, if your PXI system is operating in an ambient temperature less than 5 °C or greater than 50 °C, you must select a chassis and embedded controller with an extended operating temperature range.
Additionally, all high-availability systems benefit from optimal cooling, which requires the installation of chassis filler panels in unused or empty slots. A PXI system is rated to operate up to its specified maximum operating temperature; if you desire improved cooling performance, you also should consider using PXI slot blockers, which improve air flow through modules. Finally, many NI chassis include a fan-speed selector switch on the rear panel of the chassis. For maximum cooling performance, select “HIGH.”
Figure 1. For maximum cooling performance, set the fan-speed selector to “HIGH” on
applicable PXI chassis, use chassis filler panels, and clean fan filters every six months.
Deploying Your PXI System
You can deploy PXI systems into a variety of rack-mount, benchtop, and embedded environments. When deploying a PXI system, consider the ambient temperature, cooling clearances, power quality and reliability, and ruggedness of the system.
The ambient temperature of a PXI system is defined as the temperature at the chassis fan inlet (air intake). If a PXI system consistently has an ambient temperature greater than its maximum specification, this may ultimately lead to measurement inaccuracy, system shutdown, or premature system failure.
In addition to ensuring that the ambient temperature of a PXI system is within the specifications for all of the system components, it is vital that you provide adequate cooling clearances for the chassis to achieve the required air flow. You must install your chassis such that the cooling clearances meet the specifications stated in the user manual. The cooling clearance for a National Instruments PXI-1045 chassis, for example, is 1.75 in. (1U) at the top of the chassis.
Additionally, the power you provide to your PXI system should be free of any spikes and noise that could degrade performance, reduce operating lifetime, or cause damage or failures to electronic equipment. You should consider using an uninterrupted power supply if your PXI system receives power from an unreliable source.
To overcome extreme temperature and humidity environments, you can install your PXI system in a sealed enclosure that includes a heater, air conditioner, or heat exchanger. Also, an enclosure with shock mounts can help overcome excessive shock and vibration.
Using and Maintaining Your PXI System
Once you have deployed your PXI system, it is important that you use and maintain it properly. If you are not the sole operator of the system, you should educate the other operators on the proper use and maintenance of the system. Failure to do so can lead to easily avoidable measurement errors or downtime.
NI provides a variety of tools and services to assist you in maintaining the maximum performance and availability of your PXI systems, including the following:
Software architecture guidelines
Software recovery and backup tools
System power-down procedures
Fan filter replacements and system cleaning
Integrated troubleshooting resources
Spare component recommendations
Worldwide technical support
– Richard McDonell
Richard McDonell is a product manager for PXI and instrument control. He holds a Bachelor of Science in electrical engineering from Texas A&M University.
Table 1. Following a few best practices can help you build and maintain your high-availability PXI systems.
This article first appeared in the Q2 2007 issue of Instrumentation Newsletter.
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