1 May 2005

Traceability goes out front

By Elizabeth Zybczynski

Good traceability can sometimes mean the difference between a recall and no action at all.

"Traceability" requirements of the Bioterrorism Act of 2002 have thrust that term into the spotlight in the food and beverage or life sciences industries.

Safety-critical, medical, and other regulated products require traceability. It is a fundamental requirement for any comprehensive product or process test strategy.

Traceability in the world of testing is, in its simplest sense, knowing when, how, and on what equipment a particular device was tested. This information is imperative in order to provide ongoing confidence that if anyone ever questions calibration, test process, or system integrity, you can quickly and accurately quantify and address the impact and scope of the question.

Good traceability can sometimes mean the difference between a recall and no action at all.

While there are several components for achieving total test traceability, let's take a look at the identification and tracking of device identity.

2D data matrix

The simplest method for discretely identifying a device under test (DUT) is using 2D data matrix. This "bar code on steroids" has numerous advantages over its more familiar ancestor, the 1D bar code, known to us from the UPC labels at our local grocery store. 2D data matrix can print in a much smaller area and contains redundancy within its structure, which provides better reliability for automated reading, virtual elimination of erroneous reads, and even some resilience to damaged, scratched, or otherwise obstructed labels. 2D data matrix readers are widely available and very cost effective. Commonly used serial, USB, and Ethernet protocols, along with substantial availability of software drivers for this device, make integration simple and the total cost of ownership for the addition of an automated 2D data matrix to your existing test scenario low.

Machine vision

Should the addition of an additional identification form be incompatible with your process, machine vision provides an alternative. You can also add on an optical character recognition (OCR) package with a vision toolkit. This again allows for easy integration and lower cost of ownership of a traceability system.

Tracking DUT

In the event you are performing one to four-up test (or some similar small number), the 2D Matrix Scanner or Machine Vision System can often mount directly above the test system, and the identity of the DUT can be acquired at the same time that test is run. However, this is not possible for high-capacity test systems used during processes such as burn-in. In these systems, we must find a way to utilize DUTs prior to the test process and have this information available and cross-referenced once the DUT loads into the test system.

The most cost-effective and reliable way for achieving this is placing several DUTs into a removable fixture. The fixture tray identity and the identity of its DUTs come in at a separate station. The information can then write to a networked location accessible by the test system. The information referenced is according to fixture ID. You can then identify the fixture by the test system via four through 16 digital lines (depending on the number of fixtures in your process) and that binary fixture ID used to reference the identity and position of each DUT.

Alternatively, a more robust process is available. For the addition of an inexpensive component, information about the DUTs can write directly to the fixture. Non-volatile RAM (NVRAM) can provide a simple way for traceability and other test information to literally follow your devices through your process.

Maximizing throughput

In-line or end-of-line test can often represent a bottleneck in your process. Auto-mated traceability can maximize the utilization of your test assets by minimizing time between test runs. Instead of having an operator enter what can sometimes be substantial amounts of information into the system before the next test can begin, you read all of this information directly off the test fixture. This practically eliminates downtime between test runs and data entry errors.

The addition of a vision traceability system can at once increase the quantity, quality, and usefulness of data produced by your existing test system ... and often for roughly 10% of the cost of system itself.

Behind the byline

Elizabeth Zybczynski is an engineering team leader at the Minneapolis office of VI Engineering, Inc., headquartered in Detroit. VI Engineering is a registered member of the Control and Information System Integrators Association (CSIA). Her e-mail is ezybczynski@viengineering.com.