Innov-X Systems's Portable X-Ray System Aids Scientific, Forensic Research with Blackfin®
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When asked for the definition of an X-ray, most people would say it is a photograph of the body taken for medical purposes. Actually, an X-ray is more than just a photograph. It is a stream of high-energy, short-wavelength photons used in radiography, radiology, radiotherapy, and scientific research. X-rays can be used to authenticate art objects such as paintings, to investigate ancient metallic objects, or to analyze crime scenes, among other uses.

Massachusetts-based Innov-X, a company that specializes in elemental analysis solutions, manufactures portable X-ray systems that can be used for on-the-spot analysis. Innov-X portable X-ray systems have been used in situations ranging from the examination of the hull of the sunken S.S. Hunley (the first combat submarine of the American Civil War period) to the recent search for weapons of mass destruction in Iraq.

The theory behind the Innov-X portable X-ray system has to do with the interaction of electromagnetic radiation (the energy inherent in light) with matter. This interaction helps determine the identity of compounds and their concentration in mixtures. In the past, Innov-X used a proprietary field programmable gate array (FPGA) system to conduct pulse analysis a low-energy X-ray that analyzes materials by exciting electrons in target material to identify the composition of the material. While effective, the solution was quite costly.

"I don't think another processor could offer the combination of signal processing/embedded controller features and performance at this price point."
Alan Peevers                              
Innov-X Consultant                     
Designer of the portable X-ray unit

Analyzing the Elements
The Innov-X product is a highly portable handheld XRF element analyzer, featuring a miniature, rugged X-ray tube. It performs rapid on-the-spot analysis by analyzing the whole suite of elements from atomic No. 22 to 90 (P to U) on the periodic table, so there is no chance of missing important information. By calculating only the most important elements for each application, the Innov-X instrument operates very quickly and accurately.

Innov-X employs an X-ray method called X-ray fluorescence (XRF) to determine the atomic composition of solid materials. First, it bombards atoms, which starts a process whereby interior electrons are ejected from the atom. Remaining electrons then fill the vacancy. The "electron transitions" emit X-rays of their own that give off energies or wavelengths that are specific to the compositional elements of a substance. XRF is excellent for screening for the presence of metals to determine if lead is present in a painted wall, and other uses. It is unsurpassed for its ease of use and the fact that it can be used to analyze a solid without dissolving or extracting it.

The Innov-X system itself gathers "pulse" data using a PIC microprocessor, and then transfers it to the Blackfin for processing via general-purpose I/O (GPIO) pins. A "fast filter" is placed on the raw data stream to locate peaks. Peaks that exceed a certain energy threshold are time stamped and recorded in a separate array. A secondary process then runs a more accurate and more expensive filter on just those peaks. This stage of processing gives a good estimate of the energy of the individual X-ray events that were detected. Innov-X accumulates the results of the materials under test in a histogram, which is sometimes called a "multi-channel analyzer," maintaining detailed descriptions of the composition of the materials. A detachable HP iPAQ handheld holds instrument calibrations in flashcard memory, enabling the instrument itself to concentrate entirely on analysis.

Today, an ADSP-BF533 Blackfin® processor from Analog Devices, Inc. (ADI) is behind the scenes enabling the Innov-X portable X-ray system to analyze the whole spectrum of elements on the periodic table, calculating the important elements for each application quickly, accurately, and cost effectively.

More Than Enough Cycles
Innov-X had a lengthy list of requirements for the portable X-ray unit, which included: a high-speed parallel peripheral interface (PPI); a direct memory access (DMA) controller to transfer high-speed data to on-chip memory; general-purpose I/O (GPIO) pins to communicate with its I2C bus (a control bus that provides the communications link between integrated circuits); a universal asynchronous receiver/transmitter (UART) port to interface with peripherals; and several timers (including a watchdog timer). Innov-X also required fast interrupt servicing, extremely high-speed processing, and low cost.

Blackfin included all of the features Innov-X was looking for, and at just the right price point. The processor provides one PPI that can connect directly to parallel A/D and D/A converters and other general-purpose peripherals. The Blackfin has multiple, independent DMA controllers that support automated data transfers with minimal overhead for the processor core. Blackfin's full-duplex UART port is fully compatible with PC-standard UARTs and supports full duplex, DMA, or asynchronous transfers of serial data. The UART has two dedicated DMA channels, one for transmit and one for receive.

Blackfin includes 14 programmable timer units, 12 of which are general-purpose timer units that can be independently programmed as pulse width modulators (PWMs), internally or externally clocked timers, or pulse width counters. The general-purpose timer units can be used in conjunction with the UART to measure the width of the pulses in the data stream to provide an auto baud detect function for a serial channel.

Alan Peevers, the Innov-X consultant who designed the portable X-ray unit, said, "The Blackfin processor was fast enough that we were able to replace the dedicated external pulse-discriminator circuit we were using with optimized filter code, running on the full-speed (20 MHz) X-ray data to identify X-ray events. We also implemented UART communications with other parts of our system to transfer X-ray measurements to the HP iPAQ. There were still cycles left over to perform preliminary pulse detection, pulse processing, statistics extraction, an I2C bus interface protocol, and DMA transfers! Plus, Blackfin's signal processing/control processing is an excellent combination."

The Blackfin processor's unique combination of processing attributes eliminates the need for separate digital signal and control processors, which reduces bill of material (BOM) costs and greatly simplifies hardware and software design tasks. "Blackfin simplified the board design, made the pulse analysis algorithm more extensible, and reduced our parts count and our system cost," said Peevers. "Other processors offered similar performance but Blackfin offered much more flexibility. I don't think another processor could offer the combination of signal processing/embedded controller features and performance at this price point."

Great Tools
Innov-X said ADI's tools were exceptional. "I found VisualDSP++ to be a breeze to work with," said Peevers. "It was very stable and easy to use, and included excellent programming features." VisualDSP++, an easy-to-install and easy-to-use integrated software development and debugging environment (IDDE), enables efficient management of projects from start to finish from within a single interface. The project development and debugging environments are integrated, allowing movement quickly and easily between editing, building, and debugging activities.

"The all-important edit/compile/download cycle was quite fast with ADI's EZ-KIT," said Peevers. The EZ-KIT Lite Evaluation Kit is a standalone evaluation board and an evaluation suite of VisualDSP++ that facilitates architecture evaluations via PC-hosted toolsets. Users can evaluate ADI's processors, learn about DSP applications, simulate, debug, and prototype applications.

Peevers said that because of ADI's excellent tools, and because so many of the features that Innov-X required were standard fare with Blackfin, development time for the portable X-Ray system port to Blackfin was just three weeks.

For more information about Innov-X, visit the company Web site at www.innovxsys.com.

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