Gluing hardware and software together to make a customized test system is an evolving science. Small companies of specialists have mastered the techniques of system design to integrate system building blocks in unique ways.
Large manufacturers prefer to deal with systems integrators. For the big companies, the bottom line is cost. They look for ways to reduce their dependence on inventory and cut labor expenses. Purchase of a test system fits this paradigm shift because a user can buy a custom system at an attractive price from a systems integrator.
The integrator develops a turnkey system that, wherever possible, includes equipment, connectors, power supplies, and cables to meet specific requirements. The test software also is based on industry-standard products such as National Instruments’ LabVIEW and LabWindows/CVI or Microsoft’s Visual C++ and Visual Basic.
About 80% to 90% of all test systems are unique. There are exceptions but those are very rare. However, the successful systems house serves the customer best and minimizes costs by standardizing to the highest degree possible. Each of 100 one-of-a-kind systems is likely to incorporate much of the same hardware and software as the other 99.
System Examples
Systems integrators are doing exciting things using standard hardware and software to build custom test stations. Some examples of this work unfolded during interviews with several companies.
Rear-End Crash Avoidance System Test
Rear-end automotive crashes are avoidable, yet in 1996 at least 1.8 million such accidents occurred in the United States, resulting in approximately 2,000 fatalities and 800,000 injuries. Driven in part by these grim statistics, forward-collision warning (FCW) systems now are offered to help drivers avoid these collisions by providing timely alerts.
“The test system,” as defined by Dean Streck, vice president of operations at VI Engineering, “has two visual displays, one mounted on the vehicle dashboard and the other projected into the driver’s line of sight to provide visual warnings. Audio alarms are generated and amplified through the vehicle radio. An analog output controls a vehicle brake booster to generate a haptic (touch) brake pulse.”
Accelerometer signals, vehicle speed, brake switch, steering-wheel position, brake-pedal load sensors, and the distance to the front vehicle are collected. With the test system, researchers can evaluate the effectiveness of various visual, auditory, and haptic methods used to alert drivers to collision conditions.
CAMP testing requires a flexible in-vehicle data acquisition, analysis, and control system to acquire live vehicle parametric, video, and collision avoidance-alert data for both real-time and post-test analysis. It also needs network communications between two test vehicles and serial communications with a range sensor, a VCR, and a global positioning system (GPS) receiver. Communications hardware also is needed to transfer data between moving vehicles. The program uses high-speed SCXI products for analog input and output, frequency-to-voltage conversion, signal filtering, and digital input and output.
Because of its graphical display of local, remote, or analysis channels, LabVIEW software was selected. The test system controls the VCR and reads video time code, permitting the user to view test data and video synchronously by choosing a time cursor position.
RF-based data acquisition is used between a control vehicle and the remote vehicle containing the Driver Warning System. A sophisticated, interactive data acquisition and control system collects data on a laptop in each vehicle and performs real-time alert evaluation based on locally and remotely acquired data. Four video cameras are positioned in the control vehicle, and video data is recorded and time-stamped for playback and analysis. Acquisition on all systems is synchronized to begin on receipt of a digital hardware trigger.
Production Test System for Instrument Transformers
ABB Power is a leading producer of instrument transformers, also called metering transformers, used by electric utility companies to measure bulk electricity consumption. The products consist of current and voltage transformers with ratings up to 4,000 A and 90 kV. Production tests have been automated to expand the functionality, improve the reliability and repeatability of results, and log information to databases to increase throughput rates.
“Transformer tests for ABB Power,” according to Stan Craft, vice president of MicroCraft, “are run on a 20´ dia turntable divided into six stations, one for each unit under test. Each station performs a series of tests, including polarity, coil turns, resistance, hipot, excitation, and phase-ratio.”
The automated system incorporates more than a dozen instruments with GPIB or RS-232 interfaces. These include power supplies, comparators, transformers, and voltage dividers. An embedded computer with Windows NT is housed in a PXI/Compact PCI chassis with SCXI signal conditioning.
A programmable logic controller (PLC) was designed into the system for monitoring the shutdown, indexing the turntable, and maintaining the correct position of the high-current and high-voltage probes. A LabVIEW RT card provides the necessary real-time control. Also, its shared-memory communications with the controller are fast and reliable.
NI’s I/O card was chosen to interface with the digital and analog signals from each test station. SCXI cards work seamlessly with LabVIEW’s data acquisition virtual instruments (VIs).
System for Production Test of Photodiode Arrays
While most test systems can be built from commercial off-the-shelf (COTS) instruments, some must be fabricated with little or no COTS hardware. The latter was the case when the Cottonwood Technology Group developed a photodiode array production tester in support of a new medical product. A system solution based solely on COTS instrumentation was unacceptable due to cost, factory floor-space limitations, and throughput constraints.
The customized test system provides more than 1,000 channels of capacitance, current, and resistance measurement in 100-plus operating states. Current measurements have a resolution of <1 pA, and the system provides ±0.1°C control over a range of elevated temperatures. Finally, the system optimizes test-cycle timing.Since it was necessary to develop a special per-channel signal-conditioning assembly, multiplexing, measurement, and control were incorporated into this assembly. Each of these 64-channel subsystems features an embedded controller. The total system has 20 modules for core stimulus and measurement.
With this approach, time-consuming measurement and processing occur in parallel across all measurement assemblies, and the user has a significant degree of fault tolerance. Also, the logistics of support are simplified since all these parts are identical.
System complexity and numerous technical challenges imposed some schedule risks. These were compounded by the decision to pursue a custom solution.
Recognizing this, a team was formed to develop the measurement assembly. It addressed the custom development, including hardware and firmware design, material procurement, fabrication, and testing. This ensured that the modules would be ready for integration.
Concurrently, development proceeded on the balance of the hardware and application software. Parallel development ensured that the bulk of the requirements could be verified prior to integration.
The design team was in continual contact with the customer to ensure that the system would meet expectations. Despite the technical challenges and unpredictable difficulties with tools, components, and subcontractors, the company deployed three systems at widely separated customer sites, and all installations were brought to operational status quickly. Development of the next-generation system is underway.
System to Test Building Health and Efficiency
When the environmental conditions and use of utilities in large buildings are automatically monitored and analyzed, it is not uncommon to realize energy savings of up to 30%. Supersymmetry has developed a system to collect, process, and display vital statistics for commercial and industrial facilities.
The highly regarded Leadership in Energy & Environmental Design (LEED™) green-building rating system defines a certain quality of building operation and requires users to take accurate data continuously. The critical part of data acquisition is to start with good, stable, and accurate sensors. Thermistors are used for temperature measurements, and full-bore magnetic flow meters monitor cooling and heating water.
Data is taken on a continuous basis and compiles a story of the building—a building signature. After analysis, incremental changes can be made to optimize environmental control.
“The monitor system at Supersymmetry,” said Dan Purvis, general manager of Quantum Controls, “uses the IEEE 488 bus for an instrumentation interface. This multidrop capability allows additional data acquisition devices to be appended to the array as the needs change in a given building. In addition, the basic system can be repeated in a host of additional applications, with the only change being the amount and type of hardware.
“With LabVIEW, the basic software code is customized to each application. The building-block architecture allows modules to be removed if they are not necessary. Also, new functionality can be developed and tested independently of the overall system before it is incorporated into the design,” he concluded.
Brake Testing System
Inertia Dynamics manufactures a range of electromagnetically operated mechanical brakes. One requires 100% functional testing of its dynamic characteristics, starting with braking torque and the time to brake. Then they measure drag torque with the brake engaged, evaluate the integral proximity sensors, and record the pickup and dropout activation voltages.
“The Inertia Dynamics test rig,” said Robert Hamburger, principal engineer at Bloomy Controls, “has a large AC drive motor to spin the brake for dynamic measurements, a programmable DC power supply for actuating the brake, and speed, torque, and temperature sensors. For data collection and control, the test stand uses a PC and SCXI chassis from NI plus relay-switching modules with inputs from thermocouples, analog voltage sources, and strain gauges.
“In a test,” Mr. Hamburger continued, “the user spins the drive motor until the desired bearing temperature is reached, then shuts it down. The brake is engaged to verify correct operation of the proximity sensors. Next, the drive motor is accelerated again and shut off. The brake is engaged, and the speed and torque are recorded during deceleration. From this, the maximum braking torque is calculated along with the time required to stop.”
The data acquisition and control system was developed by Bloomy Controls using LabVIEW. The user interface displays the pertinent items of interest. A test status indicator shows which step the test sequence is executing and the status of the current step. It also prompts the operator for all actions that are necessary before proceeding to the next step. A real-time Butterworth filter cleans up the noise caused by vibration.
Upon completion of a test sequence, the system automatically reports the results of the test as shown in Figure 2. Data collected during the dynamic transient test is logged for further analysis, archiving, and reporting.
Commercial-Testing Equipment
A systems job involved the integration of data acquisition, motion control, GPIB, and a special database on a large tester. The customer needed to upgrade some older controls that were no longer supportable and wanted to include additional functionality as well.
“The PC, PC-based data acquisition equipment, and custom application software include user interface screens, configuration files, database design, and report layout,” noted Jim Campbell, president of Viewpoint Systems. “Third-party vendors were used for the motion-control part, programmable logic controller (PLC) setup, panel manufacture, and field wiring fabrication.
“Data collection and control were tricky,” Mr. Campbell continued, “because many subsystems were involved, and we needed to synchronize data collection. As a result, the system design called for a combination of smart remote controllers and hardware-sequenced data collection. This could not be done with software because that would cause too much jitter in data collection and control.”
Many of the data collection and control devices are networked. Smart PLCs and motion controllers reduce the burden on the PC by monitoring safety interlocks, controlling subsystems, and making measurements for processing and archival.
Robust fault tolerance helps to prevent product and machine damage. Further, the database provides values for test setup and stores results. The system analyzes information and presents results in graphical format. Finally, the documentation package includes hardware schematics, software architecture, and operator manuals.
The system is designed around NI data acquisition hardware and LabVIEW software. It includes the SQL Server and MS Access programming for the database.
This job had a short schedule because the work had to be completed during an annual shutdown. Timing and integration of various subsystems were critical.
Further, software subsystems with their unique installation and integration issues had to be glued together and interfaced with two databases. Also, the several product types, each with several permutations, required unique testing and tweaking.
Reducing a Test System to Its Lowest Common Denominator
Costs of a test system tend to escalate when greater labor content is needed, such as nonrecurring engineering labor for hardware and software designs. When common elements of a test system can be identified, these can be designed once and the implementation repeated to save time and money while improving quality.
A multifaceted system solution described by Jason Gilligan, national sales manager at VI Technology, reduces the wide variety of test systems to its lowest common denominator. This is possible because automated test systems using PC-based technologies have several items in common. Each has a PC with high-performance processors, RAM, CD R/W drives, and color displays. You can add a keyboard, a mouse, special test cards, a network card, and high-performance software. Other common components include multivoltage DC power supplies, AC power distribution units, power controls, emergency cutoff circuits, safety interlocks, and forced-air cooling. Possibly everything else is unique, but at least there is a common starting point.
“The first step on any system,” according to Mr. Gilligan, “is to learn the customer requirements. It is rare that a detailed specification for a test system is prepared by the procuring agency. Even a detailed specification generally needs clarification because the customer has implicit assumptions that are not on paper. This situation invites engineer-to-engineer discussion and documentation of mutual understandings. In many cases, the systems house even writes a draft specification for customer editing and approval.
“Even with the uniqueness of an application,” Mr. Gilligan continued, “certain common hardware and software can be used to save development time and expense. This starts with the PC. With its related data acquisition and digital/analog conversion, the system designer has an arsenal of existing tools. Leading-edge technology companies such as NI offer a large variety of PC-based hardware and software to support the test equipment designer. These de facto standards of the industry allow commonality of elements in new designs.”
The de facto standard concept is expanded by VI Technology to include a standardized test rack that can be defined in a similar manner for circuit-board and software building blocks. Since each customer has a unique need, this standard is available in several versions to meet specialized requirements.
Documentation includes technical manuals of all the hardware and software as well as system-level functional diagrams, cable wiring lists, and operating instructions. Generally, the customer wants and needs a hands-on training session, and the systems supplier is the ideal source.
Since the standardized system shares components with many other systems from the same supplier, this reduces sparing requirements at the user location and minimizes downtime. Test engineers have an easy way to select additional equipment, spares, boards, components, and cables to keep the production line running. This enhances the reputations of systems engineers as miracle workers.
For more information:
Bloomy Controls
www.rsleads.com/207ee-225
Cottonwood Technology Group
www.rsleads.com/207ee-226
MicroCraft
www.rsleads.com/207ee-227
Quantum Controls
www.rsleads.com/207ee-228
Viewpoint Systems
www.rsleads.com/207ee-229
VI Engineering
www.rsleads.com/207ee-230
VI Technology
www.rsleads.com/207ee-231
Return to EE Home Page
Published by EE-Evaluation Engineering
All contents © 2002 Nelson Publishing Inc.
No reprint, distribution, or reuse in any medium is permitted
without the express written consent of the publisher.
July 2002