Automated Calculations and Extensive Component Database Streamline Analysis

Switching from manual analysis to reliability analysis software helped the NexWatch group of Honeywell, Fremont, California, reduce the time needed to perform a mean time between failure (MTBF) analysis on its integrated access control systems from 30 days to 1 day. Computing MTBF was in the past a difficult task that involved determining individual failure rates for perhaps 1500 components, many of which involved multiple calculations, and then performing a failure analysis on the entire assembly. Lottie Smink, quality consultant for NexWatch, came up with the idea of using commercial reliability analysis software to make the job easier. The software can import the bill of materials from the company's product data management system, search through its database of components for liability parameters to determine individual failure rates, and automatically perform the system-level calculations. "The calculations come out perfectly," Smink said, "saving huge amounts of time, reducing the chances for error, and improving the reports we provide to our customers."

More than 50,000 locations around the world rely on NexWatch systems to handle their access control needs. NexWatch is the only single-source manufacturer of complete analog and digital proximity access control systems. Its product line includes all the necessary components for integrating everything from a simple security system to highly-customized, large systems with hundreds of closed circuit television cameras and sophisticated alarm monitoring devices. From powerful host software to advanced controllers, readers, and cards, all essential elements of NexWatch systems are designed, tested, and built to work as synergistic components of a single system. With proximity, magnetic stripe, bar code, keypad, photo ID, smart card, and biometric capabilities from which to choose, users of NexWatch systems can now select the specific technology combination that best suits the needs of different applications, or they can add yet another level of security by using multiple technologies at each door.

Reliability Critical in Security Business

Because the security of their customers' facilities depends on their access systems, NexWatch has long calculated the reliability of its systems and provided the information to customers. These calculations are complicated by the large numbers of components involved and the fact that these components, can be arranged in many different configurations. Performing these calculations has been Smink's responsibility. "The first step was performing the paperwork needed to determine failure rates for the individual components," she said. "For many components this involved a number of different subcalculations, such as determining the alpha and lambda factors that relate to the performance of the build of the component. These calculations by themselves involved mountains of paperwork that made it very difficult to provide presentable documentation to the customer. Then I tabulated all of the results in a spreadsheet in order to develop a failure and the time rate for the entire assembly."

"I have been performing this process by hand for the past 10 years or so," Smink said. "As we increased the pace of new product development, I found that more and more of my time was occupied with this task. I decided to find a commercial software package that was capable of automating it. I investigated a number of different packages and selected the Reliability Prediction module from Relex Software Corporation, Greensburg, Pennsylvania, primarily because I felt that its huge component database would go the farthest towards automating the process. You see, it takes just as much time in reliability analysis to collect the information on the individual components as it does to perform the calculations. A key advantage of Relex is that it includes a huge component database that, after the bill of materials is imported into the program, automatically identifies the failure rate for all of the components that it can identify. Relex also has implemented the Telcordia TR-332 standard, which is the one that we use for reliability calculations."

Automating MTBF Calculations

Using the Relex software, Smink has virtually completely automated the reliability analysis process. She now begins by exporting the bill of materials for the system in question from the company's Agile product data management system into an Excel spreadsheet. Then she imports the spreadsheet into the Relex Reliability Prediction software one assembly at a time, which maintains as much as possible of the hierarchical structure of the system. Recently, she has simplified this process by adding codes to the bill of materials that indicate the position of each item in the hierarchy. For example, a 92 code indicates a complete system and a 62 indicates a first level assembly. She uses the graphical interface provided by Relex to define the product hierarchy.

The next step is determining the reliability levels for the individual components. She encourages the company's design engineers to list products in the bill of materials by industry standard nomenclature, as opposed to the company's own product numbers. When the standard names are entered, the Relex software will in most cases find the items from its database, eliminating the need to calculate failure for individual components. In cases where standard nomenclature is not available or doesn't exist, Smink enters specifications for the components so that the software can determine their reliability. The information requested varies for each component but may include items such as power dissipation, rated voltage, resistance value, number of pins, and operating temperature. The software prompts for the entry of the individual parameters, providing a list of choices when applicable, and validating all entries. Once she has entered the information for a new component, Smink adds it to a custom library that she has created so it will be automatically determined from that point on.

Use of Telcordia Method

Smink uses the Telcordia method, created by the company that was previously known as Bell Communications Research, to calculate system reliability. This method provides reliability models for commercial grade electronic components. It also makes it possible to incorporate device burn-in data, unit burn-in data, data obtained from laboratory testing, in addition to information from actual field testing. Relex software provides the base failure rate for each component and also provides factors that adjust for specific operating conditions. For example, if you are running a resistor at 50% of rated wattage, its multiples the failure rate by one; at 25% of rated wattage, it multiplies the failure rate by the applicable Telcordia factor.

Relex also provides access to several other reliability models. MIL-HDBK-217 is the original worldwide standard for electronic reliability analysis and supports both commercial and military grade components. Both the part stress calculation method, which allows taking actual temperature and stress information into account, and the simpler parts count method, used for quick estimates and early design analyses, are supported. Relex extends these calculations by supporting the mathematical models from the Telcordia specification, allowing incorporation of burn-in as well as laboratory and field data. In addition, Relex supports the "Handbook of Reliability Prediction Procedures for Mechanical Equipment," which contains reliability models for devices such as seals, springs, solenoids, bearings, gears, splines, valves, actuators, pumps, brakes, clutches, and more.

Producing Customer Reports

The last step is simply pushing a button and letting Relex calculate the MTBF. It performs calculations up to 100 parts per second, providing failure rates for each component, subassembly, assembly, and the complete system. Overstressed components are highlighted, providing useful feedback for design engineers. "One of the things that I like most about the software is that once I have created the reliability analysis, the information is available for reporting in any format that I want," Smink said. Relex includes many standard reports and a powerful Visual Report Designer that provides graphic tools to generate customized reports. The user can create line, bar, pie, area, and doughnut graphics, and select fonts, colors and incorporate bitmaps and product logos. The reports can include 3D effects, line styles, and as many curves as desired on a particular graph. Spotlights can be inserted to emphasize important areas.

"I could easily produce a reliability analysis of a security system in only one day, a huge savings over the 30 days that it used to take," Smink said. "I compared the first few calculations that I did to the manual method and found that they were every bit as accurate. In addition, having the reliability information on the computer makes it much easier to generate reports and presentations for customers and management. All in all, it's hard to imagine why anyone is still performing reliability analysis by hand on complex assemblies when Relex software can reduce the time required to perform this otherwise tedious task by more than 90%."

About Relex Software Corporation

Relex Software Corporation is a world leader in reliability analysis software. Its products are used by thousands of engineers in a variety of businesses around the globe. In business since 1986, Relex Software Corporation asserts that its mission is to produce a superior line of high-quality software tools for reliability analysis. Long-recognized for their user-friendly, state-of-the-art features, the modular tools in the Relex Reliability Software Suite include an intuitive graphical user interface, support for scientific graphical charts, an enhanced CAD interface, visual system modeling with redundancy support, completely customizable output reports, extensive parts libraries, and a comprehensive online help system. For more information on Relex Software Corporation, call 724.836.8800 or visit www.relex.com.