Customer SolutionsPXI-Based Oscilloscope Breaks New Ground in Real-Time Monitoring
Author(s):V. Arunachalam, SOliton Automation Private Limited
Industry:Life Science
Product:LabVIEW, Modular Instruments, Oscilloscopes/Digitizers, PXI/CompactPCI
The Challenge:Automating the real-time monitoring of "spits," or arcing, inside X-ray tubes -- a high-speed phenomenon not possible using our previous method of a traditional oscilloscope and a PC with GPIB.
The Solution:Developing a PXI-based oscilloscope solution combining the superior data transfer capabilities of the PCI bus with the flexibility of National Instruments software drivers to configure data acquisition.Monitoring and Recording Spits During manufacturing, we "season" a new tube by subjecting it to different voltages for various exposure durations. We typically define spits in terms of a drop in the voltage of more than 20 percent for 40 microseconds or longer. A leading manufacturer of medical imaging equipment in India wanted an automated system to monitor and record the spits, and the ability to raise an alarm if the number of spits exceeded a user specified limit during the hour runs. A major oscilloscope vendor, who had supplied the scopes for the manual monitoring of spits, was called to automate the process using GPIB. After substantial study and trials, the company determined that the triggering capabilities offered by a traditional scope could not reliably capture the spits. Subsequently, the company contracted Soliton Automation Pvt. Ltd. because we have an established record of delivering solutions to challenging measurement and automation problems using National Instruments products. We needed this mode for noisy signals. The noise triggers the scopes, which was not a problem since our spit detection algorithm would filter out these events. But when the frequency of false triggers is high, the system partly or fully misses genuine spits during the "rearm" time - the time taken by the scopes to arm themselves for the next trigger after an acquisition completes. In this case, continuous acquisition with the spit detection done in software proved to be a better solution. We found an effective way to perform continuous acquisition with the two 5102 scope cards. We connected each scope’s PFI1 line, on which we can access the end-of-acquisition signal, to the other scope’s TRIG line via the RTSI bus. Scope 1 would acquire 125,000 samples, and at the end of acquisition would trigger Scope 2 and rearm itself while Scope 2 acquired 125,000 samples, which in turn would trigger Scope 1 at the end of its acquisition, and so on. We could not get the scopes to reliably stream data to memory at 250 KS/s/channel, which was the maximum limit for the spit detection algorithm in software. In this application, the virtual instrumentation solution clearly stands out because a traditional scope-based system could not meet the requirement. We delivered a very cost-effective and high-performance solution using National Instruments products and custom-developed software. The customer was delighted that we developed and validated the solution in 12 weeks, despite the fact that spits rarely occur and validating the system was time consuming. We believe that the PXI-based scope breaks new ground for oscilloscope applications requiring high-data throughput combined with unconventional software and hardware triggering. V. Arunachalam Senior Project Engineer Classic Towers 1547 Trichy Road Coimbatore - 641018, India Phone: +91 (422) 302374, 302371 Fax: +91 (422) 302375
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