VXIbus System Integration Integrating a test system requires a detailed study of the Unit Under Test (UUT). This study should define each signal and describe its functions and tolerances. When all the signals are identified and a compiled list is generated, design goals are set describing the test system objectives. The UUT test requirements and system design goals are an important first step, with the method of analysis being dependent on available data. This technical note serves as a tool to aid the user in designing and integrating a test system after the UUT analysis. The test station design activity itself can be broken down into several stages as follows: 1. Test Requirement Definition 2. Test Equipment Selection 3. System Host Controller Selection 4. System Software Selection 5. VXIbus Mainframe Selection 6. UUT Interfacing 7. Test Station Design and Documentation Test Requirement Definition Breaking the UUT requirement to smaller functions makes the integration task manageable. In addition to complete signal definitions and tolerances, trade-off studies and risk analyses are also performed to insure the integrator can solve all the potential problems and generate a test program to mitigate these issues. Test Equipment Selection Before test equipment can be selected, a test requirement matrix is generated which correlates every requirement with its respective stimulus or measurement functions. Test equipment can then be selected to satisfy these requirements. Practical systems may include both VXIbus and non- VXIbus instruments and the system integrator must decide what these instruments are as they suit each application. Table 1 shows an example of how a test requirement/selection matrix can be set up. Requirement Specification Comment Test Resource Pulse Width 1ns Single Shot Racal 2251 Timer/Counter Frequency 200MHz 9 digit Racal 2251 + opt Voltage 50ppm 6 1/2 digit Datron 1362 Resistance 150ppm - Datron 1362 Table 1 System Host Controller For every automatic test system, computer control is essential. Typical controllers are either embedded or stand alone. Computer choice may impact test execution speed and file transfer speed. If an external computer is selected, the interface to the VXIbus chassis must be selected. Possible configurations include IEEE-STD-488, MXI or Ethernet. The selection of a host controller depends largely on the software platform selected, the operating system and the development software. System Software Selection There are a number of software issues an integrator needs to consider. The key parameters are the station's operating system, the program language and any software programming tools or program generators. For further information on software selection, refer to Racal Instruments, "Instrumentation Software, The Key to the System" technical application note. VXIbus Mainframe Selection The VXIbus specification requires each manufacturer of modules and chassis to define both power and cooling capabilities of their products. These specifications are then used by the integrator to conduct power and cooling analysis. This analysis is performed at two levels; VXIbus level and system level. A more detailed analysis of power and cooling is discussed further in this paper. UUT Interfacing A critical part of designing a test system is to define the interface between the system resources and the Unit Under Test (UUT). Typically, two approaches are used: the Application Specific Front Panel (ASFP) or a patch panel. ASFP interfaces are used for dedicated systems testing a single product type or for testing a family of products that share the same interface. Figure 1 illustrates an ASFP with a VXIbus chassis. The patch panel method allows the user to test multiple UUTs by creating an interface adapter for every UUT, or a group of UUTs. System resources are mapped to the specific patch panel and test adapters use this to route signals as required by the UUT. Figure 1: VXIbus chassis with Application Specific Front Panel (ASFP) Interface. System Design and Documentation Designing and building a test system requires detailed system engineering efforts in order to design and supply a system that is supportable, maintainable and reproducible. There are a number of tasks that have to take place to achieve this goal. A system that is not properly designed and documented will result in both maintenance and support problems. Accurate and fully-documented designs allow identical systems to be built and supported by different personnel or facilities. The following breaks down the tasks needed to provide a fully documented system: A. Electrical design B. Mechanical design C. Software design and coding D. Documentation and drafting The following provides an example of the process of designing and documenting a typical system. This example system contains the following instruments: VXIbus Chassis, RI 1261B DC Power Supply, Elgar AT8000 Desk Top PC, DELL MXI/VXIbus Interface Waveform Generator, Racal, 3151 Timer/Counter, Racal 2251 DMM, Datron 1362 High Freq. Switch, Racal 1260-50A w/ option 01 DMM, MUX, Racal 1260-35A Power Switch, Racal 1260-20 System Power Control Unit, Marway Power Control System, UPC3000 Rack System and Hardware System Software, National Instruments LabVIEW Virginia Panel Series 90 Interface A. Electrical Design Tasks 1. Indented List This document describes the structure of the system. This approach allows the integrated system to use subassemblies as part of its overall function. Figure 2 shows a sample of an indented list. 123456 Test System 12345 RI, VXIbus Chassis Assembly 1234 RI, VXIbus Chassis 1261B 1234 NI, VXIbus MXI-2 Interface 1234 RI, Waveform Generator 3151 1234 RI, Timer/Counter 2251 1234 .Datron, DMM 1362 1234 RI, HF Switching 1260-50A 123 RI, Switching Controller 1260 Option 01 1234 .RI, MUX 1260-35A 1234 RI, Power Switch 1260-20 12345 Elgar, DC Pwr Supply AT8000 12345 Marway, Power Controller UPC3000 12345 Knurr, Rack Equipment 12345 . VP, RCVR VP-90 Figure 2: Example of a portion of an indented list used to document a test system. 2. Parts List Parts list enables buyers to purchase material for the system. This includes all items large and small from sophisticated test instruments to screws which hold it in the rack. Absolute detail is critical since any device or component not on this list will not be provided. The parts list should also be kept under revision control to keep track of any changes. This provides the ability to build identical testers in the future. Figure 3 shows a portion of a parts list taken from an actual VXIbus test system. 3. Wire List The wire list provides point to point wiring information of the system. This list describes the wiring of instruments, interface pins, switching and power distribution. The wiring list is detailed to the level of the wire gauge, length, and color. Figure 4 shows an example of a typical wire list. This level of detail is needed to allow the assembly of identical test systems by different people. Additionally, this level of detail ensures system support and maintenance. The Wire List should be under revision control allowing modifications, upgrades, etc., to take place while maintaining system integrity. 4. Power and Cooling Analysis System designers must perform power and cooling analysis at two levels - the VXIbus chassis and the system. At the VXIbus chassis level, individual components are plotted on the chassis cooling curve to verify the ability to cool each module. In addition, power analysis determines the chassis' ability to provide power for each instrument. At the system level the system's overall power consumption is determined and the cooling capacity is analyzed. For the VXIbus subsystem, each module must provide its requirements in terms of power and the amount of cooling it needs to operate with an acceptable temperature rise. Traditionally, this temperature rise is expected to be 10¯C above ambient. While commercial instruments will operate at higher temperatures, their performance and life expectancy suffer as a result. VXIbus chassis power analysis can be accomplished by compiling the specific data as shown in Figure 5, and adding up all of the peak (IMP) and dynamic (IMD) currents needed by each module. This number is then compared with the chassis rating for each voltage supplied by the chassis. A chassis rating higher than the sum of the currents for each supply insures that the chassis is capable of providing adequate power. Please refer to the technical paper, "Understanding Power Supplies in a VXIbus Mainframe", for an explanation of peak and dynamic current. Dynamic current capability is important to insure that the selected VXIbus chassis can meet the system's requirements. Dynamic current affects the ripple and noise performance of the power supply. If the power supply is not rated adequately, the VXIbus noise and ripple specifications may be violated. Cooling verification is accomplished by plotting the cooling required by each module against the chassis cooling curve. This is usually expressed in liters per second of airflow for a specified pressure drop in mm of H20. Figure 6 shows this analysis conducted for our example system. Figure 6: A 1261A VXIbus chassis cooling curve with VXI modules cooling needs plotted against it. On a system level, the VXIbus chassis is considered as a unit. In our example, and from data sheets, the chassis power consumption is 800 watts. The Elgar DC power supply requires 900 watts maximum. This totals 1700 watts. By using a safety factor of 25%, our rack needs to provide 1700 x 1.25 = 2125 watts of cooling. Figure 3: A page of an actual systems parts list Figure 4: A part of an actual system wire list Figure 5: Power & Cooling Analysis of a Typical Test System Figure 7: shows the cooling capacity of fans. If we consider a 10°C rise, and a total power of 2125 watts, we would require a fan with 500 CFM capacity. Figure 7: Cooling fan capacity as a function of CFM and water static pressure. 5. System Configuration At the rack level this task provides each instrument location and its address in the system. Within the VXIbus chassis each VXIbus instrument is assigned a logical address. The outcome of this task is a configuration sheet as illustrated in Figure 8. 1261A Chassis Modules Slot Device Logical Address Interrupt Level ID Byte (SW1 5-6) Module Address (SW1 1-4) 0 NI/MXI 0 N/A N/A N/A 1 3151 8 1 3 1 2 2251 9 1 0 2 3 1260-50A-01 10 1 2 3 4 1260-20 N/A N/A 0 4 5 1260-35 N/A N/A 0 5 6 1362 11 1 0 6 Elgar, DCPS AT8000, GPIB Address=5 Figure 8: A Typical System Configuration Sheet B. Mechanical Design Tasks Assembly and elevation drawings need to be developed. These drawings document the rack location occupied by every instrument and its size. In addition, the mechanical engineer qualifies the system's ergonomics. For example, verifying that system monitors and instruments with displays are located at the operator's eye level. Typically the test interfaces are placed within the operator's reach and at waist level, while heavy instruments such as power supplies are placed at the bottom of the rack to insure a low center of gravity. Figure 9 illustrates the elevation drawing of the example system. C. Software Tasks Software engineers select the software platform that is consistent with the design goals of the station and the application at hand. The software platform and language directly impact the time it takes to implement and document the actual test programs. Each instrument requires a software driver. The example system uses National Instruments LabVIEW for Windows. This choice eliminates the need for the integrator to develop device drivers since Racal Instruments provides LabVIEW and LabWindows/CVI drivers for all its instruments. Finally, the software engineer designs and implements the station's self-test routines to allow for station maintenance and performance verification. The self test can take one of two formats: a) a confidence test by which instruments are checked by the station's controller issuing each instrument its own self test command; or b) a loop-back self test with test adapter to route stimulus outputs back to measurement ports. While the loop-back test is recommended for most test systems, some smaller testers may require only simple confidence testing. D. System Documentation and Drafting Engineering designs, such as the test system described above, need to be documented and quality controlled with a revision control system. Ideally, the document control system should exist outside of the engineering environment. In general, the revision control system allows minor design changes and modifications to occur while generating a working document for the system. The intent is to generate complete system documentation, allowing the system to be put together without relying on engineering resources. A test system documentation package typically includes: 1) Assembly drawings 2) System block diagrams 3) Signal flow diagrams 4) Schematics The systems maintenance and operating manuals usually hold this information. Additionally, individual instrument manuals are also included in the station documentation package. Easing the Burden of System Integration Many companies help their customers ease the burden of integrating test systems. Methods of doing this include providing: 1) Standard systems for specific applications. 2) Standard "core" systems that are customized for specific applications. 3) "Show-off" systems that are intended to make customers feel comfortable with a companies ability to integrate systems. 4) The service of delivering custom systems that meet specific test requirements. Standard systems for specific applications can be used in large industries where all the companies make the same products such as Telecommunications. These systems are usually limited in there ability to be converted for use in testing new generations of products within a particular industry or new products in similar industries. Since these systems are designed, including both hardware and software, and manufactured for testing particular UUTs, they fail to take full advantage of VXIbus technology. Standardized "base" or "core" systems are very similar to "show-off" systems in that they provide samples that system users can visualize. They are great for trade shows and taking pictures of but do little good in meeting specific user requirements. They do instill confidence as to the competency of the integrator. This is critical for any system integrator but, by itself, does little to provide real solutions to test system users. Once test equipment users decide that they need a new system and obtain the required funding there is a race to get the system into use. Traditional system integrators require several months to analyze the mechanics of the system, design interface cabling, develop user manuals, and document the entire system with all of its unique parts. This process cannot be changed as long as systems are designed one at a time. Even small modifications to "standard", "base", or "core" system require significant effort to provide accurate documentation. The service of delivering custom systems that meet specific test requirements is by far the most difficult method but is the most rewarding to the test system user. This task has been made significantly easier by the development of the Racal Instruments Freedom Series Computer-Aided-Design (CAD) tools for test systems. The benefits from using a CAD tool for test systems are the same as using a CAD tool for other design work. A few of these include simplifying the test equipment selection process, shortening acquisition time, easing future modification of the system, and lowering total system cost. The acquisition time can be dramatically shortened if the standardization and documentation of products is moved from the system level to the piece level. This is the approach used by the Freedom Series CAD tool. This tool allows customers to choose the products they want while at the same time fully documenting the entire system. Freedom Series parts are designed and documented so that they can be assembled together to create a test system that meets a customer's specific needs. Once the system has been configured using the CAD tool, all the documentation necessary to build and maintain the system is automatically produced. This technique drastically reduces test system prices while also dramatically decreasing delivery time. An additional benefit of using the Freedom CAD tool is that it allows the user to reconfigure the system with out having to manually modify the documentation. When a change is needed, the CAD file can be modified and a new set of documentation produced, all without using engineering resources. Conclusion Designing a VXIbus test system requires the same level of engineering as any other system. Typically, customers pay for this engineering in terms of engineering labor charges. These charges pay for the electrical, mechanical, software and documentation tasks required to insure that the system is supported, easily maintained and reproducible. The use of sophisticated CAD tools like Racal Instruments Freedom Series software reduces the cost of designing, building and owning automatic test systems. TOC 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13